HV dc/dc...

[Bill Sloman]

On Saturday, July 18, 2020 at 2:49:22 AM UTC+10, jla...@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?k=&pkeyword=&sv=0&pv183=354808&pv183=354809&pv2211=i1&pv1525=100671&pv1525=114705&pv1525=140848&pv1525=157291&pv1525=182727&sf=1&FV=-8%7C922&quantity=&ColumnSort=0&page=1&pageSize=25

I guess I\'ll have to design it. Coilcraft has some nice little flyback
transformers.

I think I can use one flyback driver circuit and put all eight
primaries in parallel. Maybe regulate a little on the high sides.

The application is eight isolated high-voltage pulse outputs. My first
idea was to use grounded drivers and final pulse transformers, but the
volt-seconds get huge so the pulse transformer would be awful. Better
to float the entire output circuit.

http://www.farnell.com/datasheets/1872308.pdf

The coil former has 24 pins, which is enough to accommodate your 16 isolated outputs and the five or six pins you\'d need to drive a centre-tapped primary and pull off the base/gate drives.

It\'s a fairly big core, but coil formers with lots of pins are thin on the ground.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Saturday, July 18, 2020 at 2:49:22 AM UTC+10, jla...@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?k=&pkeyword=&sv=0&pv183=354808&pv183=354809&pv2211=i1&pv1525=100671&pv1525=114705&pv1525=140848&pv1525=157291&pv1525=182727&sf=1&FV=-8%7C922&quantity=&ColumnSort=0&page=1&pageSize=25

I guess I\'ll have to design it. Coilcraft has some nice little flyback
transformers.

I think I can use one flyback driver circuit and put all eight
primaries in parallel. Maybe regulate a little on the high sides.

The application is eight isolated high-voltage pulse outputs. My first
idea was to use grounded drivers and final pulse transformers, but the
volt-seconds get huge so the pulse transformer would be awful. Better
to float the entire output circuit.

http://www.farnell.com/datasheets/1872308.pdf

The coil former has 24 pins, which is enough to accommodate your 16 isolated outputs and the five or six pins you\'d need to drive a centre-tapped primary and pull off the base/gate drives.

It\'s a fairly big core, but coil formers with lots of pins are thin on the ground.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Saturday, July 18, 2020 at 2:49:22 AM UTC+10, jla...@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?k=&pkeyword=&sv=0&pv183=354808&pv183=354809&pv2211=i1&pv1525=100671&pv1525=114705&pv1525=140848&pv1525=157291&pv1525=182727&sf=1&FV=-8%7C922&quantity=&ColumnSort=0&page=1&pageSize=25

I guess I\'ll have to design it. Coilcraft has some nice little flyback
transformers.

I think I can use one flyback driver circuit and put all eight
primaries in parallel. Maybe regulate a little on the high sides.

The application is eight isolated high-voltage pulse outputs. My first
idea was to use grounded drivers and final pulse transformers, but the
volt-seconds get huge so the pulse transformer would be awful. Better
to float the entire output circuit.

http://www.farnell.com/datasheets/1872308.pdf

The coil former has 24 pins, which is enough to accommodate your 16 isolated outputs and the five or six pins you\'d need to drive a centre-tapped primary and pull off the base/gate drives.

It\'s a fairly big core, but coil formers with lots of pins are thin on the ground.

--
Bill Sloman, Sydney

 

[server]

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[legg]

On Fri, 17 Jul 2020 19:11:16 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.

It will depend a bit on whether your circuit is
continuous-incomplete energy transfer, or not.

Pretty simple to spice it out for a first order
approximation. A bit of copying/pasting, but don\'t
expect much speed in the sim. Multiple parallel
inductors give spice the heartburn.

RL

 

[legg]

On Fri, 17 Jul 2020 19:11:16 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.

It will depend a bit on whether your circuit is
continuous-incomplete energy transfer, or not.

Pretty simple to spice it out for a first order
approximation. A bit of copying/pasting, but don\'t
expect much speed in the sim. Multiple parallel
inductors give spice the heartburn.

RL

 

[legg]

On Fri, 17 Jul 2020 19:11:16 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.

It will depend a bit on whether your circuit is
continuous-incomplete energy transfer, or not.

Pretty simple to spice it out for a first order
approximation. A bit of copying/pasting, but don\'t
expect much speed in the sim. Multiple parallel
inductors give spice the heartburn.

RL

 

[server]

On Sat, 18 Jul 2020 01:40:56 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 19:11:16 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.

It will depend a bit on whether your circuit is
continuous-incomplete energy transfer, or not.

Pretty simple to spice it out for a first order
approximation. A bit of copying/pasting, but don\'t
expect much speed in the sim. Multiple parallel
inductors give spice the heartburn.

RL

This is pretty close:

https://www.dropbox.com/s/gnyjq9ufo34pvao/8-chan_Flyback_1.asc?dl=0

I essentially paralleled all 8 isolated channels. I don\'t think
leakage inductance will matter much. Spice runs better without it.

Loop dynamics depends on a lot of things, so might be tweaked a little
more. Or left alone.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sat, 18 Jul 2020 01:40:56 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 19:11:16 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 21:45:59 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 21:41, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 21:22:44 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-07-17 20:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 17:32:44 -0700 (PDT), sea moss
danluster81@gmail.com> wrote:

On Friday, July 17, 2020 at 5:00:09 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Fri, 17 Jul 2020 19:22:37 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 17 Jul 2020 14:31:26 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 17 Jul 2020 22:42:44 +0200, Piotr Wyderski
peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

If each channel needs some degree of control, the ultimate low-cost
solution looks like this thing:

https://www.ti.com/lit/ds/symlink/tpic6c595.pdf

Strobe G, load whatever you want to SER IN. One of my faves; works like
a charm.

If no control is needed, use 8 MOSFETs fed with the same 50% waveform,
then use each of them as the switch driving a forward/flyback
transformer, whatever you like, and burn excessive power in a zener.

Best regards, Piotr

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything. It\'s refreshing to design an all-analog box
once in a while.

I think one big fet can drive all 8 flyback transformers.

With independent flyback transformers, you\'ll get lousy
cross-regulation, and poor output voltage tolerance, due
to Lp differences (that determine energy transfer).

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.


You\'d be better off going for preregulated voltage inverters,
which are (at least) voltage regulated, to begin with.

Or fit all the flyback secondaries on the same core. ($)

RL

I was planning to regulate in each isolated channel

https://www.dropbox.com/s/5lkbvlwz7b4rb2h/Isol_Pulser_1.jpg?raw=1

so the primary-side flyback regulation doesn\'t need to be very good.
Just good enough to make about 200 volts in each channel.

It doesn\'t need to be flyback. Some h-bridge forward converter would
work, if I can get the right transformer ratios. But the flyback looks
easy and versatile.








--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

A single flyback with multiple secondaries seems like the cleanest solution. Since you would need 18 pins on a bobbin, it might be more practical to use two independent flyback converters, each with 4 outputs. There might actually be an off-the-shelf transformer that works for this.

I\'ve never considered driving multiple flyback primaries from one switching FET, but it seems like the outputs could vary by a lot. ... ok you piqued my curiosity, I scribbled out the equations, using V = L dI/dt , and E = 1/2 L I^2, if you vary L by say 20% it looks like the transferred energy will also vary by 20% (if I did that right). So for your idea it might just work. It might be a good idea to add a DC load at the outputs to soak up any energy from the transformers\' leakage inductance.


If the transformers primaries are in parallel, and the turns ratios
are identical, the secondary voltages will be the same.

Hmm, interesting. ISTM that only works with sufficiently tight
coupling--in the limit of loose coupling the secondary voltages can be
anything depending on the loading on each one. Might work fine for this
purpose though.


Leakage inductances won\'t affect rectified voltage much, and are a
fraction of magnetizing inductance, and the transformers are
identical.



Yeah, but flyback transformers have pretty loose coupling, 0.8 or
thereabouts IIRC. Probably still fine at the +-15% level.

Cheers

Phil Hobbs

For the Coilcraft Q4436-BL, leakage inductance is spec\'d as about 2%
of the primary inductance. And I wouldn\'t expect that to vary much
between units.

It will depend a bit on whether your circuit is
continuous-incomplete energy transfer, or not.

Pretty simple to spice it out for a first order
approximation. A bit of copying/pasting, but don\'t
expect much speed in the sim. Multiple parallel
inductors give spice the heartburn.

RL

This is pretty close:

https://www.dropbox.com/s/gnyjq9ufo34pvao/8-chan_Flyback_1.asc?dl=0

I essentially paralleled all 8 isolated channels. I don\'t think
leakage inductance will matter much. Spice runs better without it.

Loop dynamics depends on a lot of things, so might be tweaked a little
more. Or left alone.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Piotr Wyderski]

jlarkin@highlandsniptechnology.com wrote:

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything.

You don\'t need an MCU. Just connect SER IN to VDD, SER CLK to G and have
fun.

> I think one big fet can drive all 8 flyback transformers.

8*150V*1e-3A=1.2W
*Big* fet?

Use both channels of IR21531 to drive two out of phase flybacks.

Best regards, Piotr

 

[Piotr Wyderski]

jlarkin@highlandsniptechnology.com wrote:

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything.

You don\'t need an MCU. Just connect SER IN to VDD, SER CLK to G and have
fun.

> I think one big fet can drive all 8 flyback transformers.

8*150V*1e-3A=1.2W
*Big* fet?

Use both channels of IR21531 to drive two out of phase flybacks.

Best regards, Piotr

 

[Piotr Wyderski]

jlarkin@highlandsniptechnology.com wrote:

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.

The inductor used in a flyback is not a transformer. Ideally, both
cycles don\'t overlap. In reality, they do --it is due to the rectifier\'s
finite reverse recovery time and this effect contributes to the losses.

> I was planning to regulate in each isolated channel

Regulate a 150mW channel? Why would you want to do that? Make it 300mW
and burn the surplus power.

Best regards, Piotr

 

[Piotr Wyderski]

jlarkin@highlandsniptechnology.com wrote:

All 8 transformers will have the same turns ratio. I was thinking
their primaries would be in parallel. Same input, same output.

The inductor used in a flyback is not a transformer. Ideally, both
cycles don\'t overlap. In reality, they do --it is due to the rectifier\'s
finite reverse recovery time and this effect contributes to the losses.

> I was planning to regulate in each isolated channel

Regulate a 150mW channel? Why would you want to do that? Make it 300mW
and burn the surplus power.

Best regards, Piotr

 

[Joerg]

On 2020-07-17 09:49, jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?k=&pkeyword=&sv=0&pv183=354808&pv183=354809&pv2211=i1&pv1525=100671&pv1525=114705&pv1525=140848&pv1525=157291&pv1525=182727&sf=1&FV=-8%7C922&quantity=&ColumnSort=0&page=1&pageSize=25

I guess I\'ll have to design it. Coilcraft has some nice little flyback
transformers.

I think I can use one flyback driver circuit and put all eight
primaries in parallel. Maybe regulate a little on the high sides.

The application is eight isolated high-voltage pulse outputs. My first
idea was to use grounded drivers and final pulse transformers, but the
volt-seconds get huge so the pulse transformer would be awful. Better
to float the entire output circuit.

Mostly I used CCFL inverter transformers for that. Cheap, fairly small.
Even complete modules can be had for a few dollars:

https://www.ebay.com/itm/1Pc-CCFL-inverter-board-for-LCD-screen-with-1CCFL-backlight-LCD-JN/392849295194

Or course, with everything going LED and OLED these days it\'s only a
matter of years until the available selection starts to thin out.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 2020-07-17 09:49, jlarkin@highlandsniptechnology.com wrote:

I need eight isolated 150 volt DC supplies, low current, under 1 mA
average. Commercial dc/dc converters are crazy expensive:

https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?k=&pkeyword=&sv=0&pv183=354808&pv183=354809&pv2211=i1&pv1525=100671&pv1525=114705&pv1525=140848&pv1525=157291&pv1525=182727&sf=1&FV=-8%7C922&quantity=&ColumnSort=0&page=1&pageSize=25

I guess I\'ll have to design it. Coilcraft has some nice little flyback
transformers.

I think I can use one flyback driver circuit and put all eight
primaries in parallel. Maybe regulate a little on the high sides.

The application is eight isolated high-voltage pulse outputs. My first
idea was to use grounded drivers and final pulse transformers, but the
volt-seconds get huge so the pulse transformer would be awful. Better
to float the entire output circuit.

Mostly I used CCFL inverter transformers for that. Cheap, fairly small.
Even complete modules can be had for a few dollars:

https://www.ebay.com/itm/1Pc-CCFL-inverter-board-for-LCD-screen-with-1CCFL-backlight-LCD-JN/392849295194

Or course, with everything going LED and OLED these days it\'s only a
matter of years until the available selection starts to thin out.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Piotr Wyderski]

jlarkin@highlandsniptechnology.com wrote:

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything.

You don\'t need an MCU. Just connect SER IN to VDD, SER CLK to G and have
fun.

> I think one big fet can drive all 8 flyback transformers.

8*150V*1e-3A=1.2W
*Big* fet?

Use both channels of IR21531 to drive two out of phase flybacks.

Best regards, Piotr

 

[server]

On Sat, 18 Jul 2020 20:10:45 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything.

You don\'t need an MCU. Just connect SER IN to VDD, SER CLK to G and have
fun.

I think one big fet can drive all 8 flyback transformers.

8*150V*1e-3A=1.2W
*Big* fet?

Bigger than SOT-23.

Use both channels of IR21531 to drive two out of phase flybacks.

We have LTC3803 in stock and they work great.

Here\'s my circuit so far:

https://www.dropbox.com/s/gnyjq9ufo34pvao/8-chan_Flyback_1.asc?dl=0

It has ground-side flyback voltage feedback (D3 etc) to make the
isolated voltages about 200, so I can regulate them to 150.

Since the Coilcraft transformer has dual secondaries, I guess I could
have one transformer power two channels, with a voltage doubler in
each. That would be fun. The caps in the doubler could be current
limiters, so I could shunt regulate.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sat, 18 Jul 2020 20:10:45 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

We use a ton of TPIC6595, a simlar part, as our universal relay and
LED driver. But I don\'t need independent control, and there will be no
uP or FPGA or anything.

You don\'t need an MCU. Just connect SER IN to VDD, SER CLK to G and have
fun.

I think one big fet can drive all 8 flyback transformers.

8*150V*1e-3A=1.2W
*Big* fet?

Bigger than SOT-23.

Use both channels of IR21531 to drive two out of phase flybacks.

We have LTC3803 in stock and they work great.

Here\'s my circuit so far:

https://www.dropbox.com/s/gnyjq9ufo34pvao/8-chan_Flyback_1.asc?dl=0

It has ground-side flyback voltage feedback (D3 etc) to make the
isolated voltages about 200, so I can regulate them to 150.

Since the Coilcraft transformer has dual secondaries, I guess I could
have one transformer power two channels, with a voltage doubler in
each. That would be fun. The caps in the doubler could be current
limiters, so I could shunt regulate.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard