Clever ways to get +/- volts from MC34063

On Jan 25, 12:44 pm, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12, +5, -5, and +3.3).  The +/- 5V supplies are for a bit of analog
circuitry on a largely digital board, so they have low current
requirements.  My plan for the +5V supply is to just hang a 78xx05 off
the +12V.  +12V and +3.3V are going to come from switchers off of +24V.

Anyone have any suggestions for a clever way to get -(something) from
one of the positive supplies?  I'm thinking that if I can get some
negative voltage for cheap from one of the existing switchers that I
can then regulate it to -5V with a 79xx05.  I expect I'll end up using
a charge pump -- but suggestions are welcome.

--
My liberal friends think I'm a conservative kook. My conservative
friends think I'm a liberal kook. Why am I not happy that they have
found common ground?

Tim Wescott, Communications, Control, Circuits &
Softwarehttp://www.wescottdesign.com

The 34063 is false economy with its low frequency operation, internal
heat dissipation, and primitive PWM architecture.

On Thu, 26 Jan 2012 12:42:53 -0800, Fred Bloggs wrote:

On Jan 25, 12:44 pm, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12, +5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry on a largely digital board, so they have low current
requirements. My plan for the +5V supply is to just hang a 78xx05 off
the +12V. +12V and +3.3V are going to come from switchers off of +24V.

Anyone have any suggestions for a clever way to get -(something) from
one of the positive supplies? I'm thinking that if I can get some
negative voltage for cheap from one of the existing switchers that I
can then regulate it to -5V with a 79xx05. I expect I'll end up using
a charge pump -- but suggestions are welcome.

--
My liberal friends think I'm a conservative kook. My conservative
friends think I'm a liberal kook. Why am I not happy that they have
found common ground?

Tim Wescott, Communications, Control, Circuits &
Softwarehttp://www.wescottdesign.com
The 34063 is false economy with its low frequency operation, internal
heat dissipation, and primitive PWM architecture.

I hadn't realized just how primitive its PWM architecture is until I
looked closely. Now I know...

Tim Wescott wrote:
On Thu, 26 Jan 2012 12:42:53 -0800, Fred Bloggs wrote:

On Jan 25, 12:44 pm, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12, +5, -5, and +3.3).  The +/- 5V supplies are for a bit of analog
circuitry on a largely digital board, so they have low current
requirements.  My plan for the +5V supply is to just hang a 78xx05 off
the +12V.  +12V and +3.3V are going to come from switchers off of +24V.

Anyone have any suggestions for a clever way to get -(something) from
one of the positive supplies?  I'm thinking that if I can get some
negative voltage for cheap from one of the existing switchers that I
can then regulate it to -5V with a 79xx05.  I expect I'll end up using
a charge pump -- but suggestions are welcome.

--
My liberal friends think I'm a conservative kook. My conservative
friends think I'm a liberal kook. Why am I not happy that they have
found common ground?

Tim Wescott, Communications, Control, Circuits &
Softwarehttp://www.wescottdesign.com
The 34063 is false economy with its low frequency operation, internal
heat dissipation, and primitive PWM architecture.

I hadn't realized just how primitive its PWM architecture is until I
looked closely.  Now I know...

Yeah, it's ghastly. However ... it is one of very few chips that is
truly multi-sourced. And that counts for a lot. 15c a pop is also very
hard to beat but in my cases the multi-source argument usually matters more.

--
Regards, Joerg

http://www.analogconsultants.com/- Hide quoted text -

- Show quoted text -

MarkK wrote:
"Joerg" <invalid_at_invalid.invalid> wrote in message
news:9obcq6Fh32U1_at_mid.individual.net...
snip
If the - (something) is low current and you are going to post regulate it,
and you have a switcher already operating, you can pretty simply AC couple
the switching off of the switcher and use 2 diodes to rectify it to a
negative voltage = to the P-P of the switching waveform (less the diode
drops). Its basically a charge pump put you already have the waveform.

Check the full range of loads and line though.


I've done that when I needed a voltage above the input voltage. The idea
was implemented but was met with disgust, grunting and scoffing at the
design review

On Jan 26, 7:06 pm, Joerg <inva...@invalid.invalid> wrote:
Tim Wescott wrote:
On Thu, 26 Jan 2012 12:42:53 -0800, Fred Bloggs wrote:
On Jan 25, 12:44 pm, Tim Wescott <t...@seemywebsite.com> wrote:
I've got a 24V incoming supply, and a need for a number of supplies
(+12, +5, -5, and +3.3). The +/- 5V supplies are for a bit of analog
circuitry on a largely digital board, so they have low current
requirements. My plan for the +5V supply is to just hang a 78xx05 off
the +12V. +12V and +3.3V are going to come from switchers off of +24V.
Anyone have any suggestions for a clever way to get -(something) from
one of the positive supplies? I'm thinking that if I can get some
negative voltage for cheap from one of the existing switchers that I
can then regulate it to -5V with a 79xx05. I expect I'll end up using
a charge pump -- but suggestions are welcome.
--
My liberal friends think I'm a conservative kook. My conservative
friends think I'm a liberal kook. Why am I not happy that they have
found common ground?
Tim Wescott, Communications, Control, Circuits &
Softwarehttp://www.wescottdesign.com
The 34063 is false economy with its low frequency operation, internal
heat dissipation, and primitive PWM architecture.
I hadn't realized just how primitive its PWM architecture is until I
looked closely. Now I know...
Yeah, it's ghastly. However ... it is one of very few chips that is
truly multi-sourced. And that counts for a lot. 15c a pop is also very
hard to beat but in my cases the multi-source argument usually matters more.

--
Regards, Joerg

http://www.analogconsultants.com/- Hide quoted text -

- Show quoted text -

It's Stone Age stuff compared to the modern offerings. Even for a
minimalist design, you have to use L's and C's 10x larger than what's
needed switching at a relatively modest 500KHz- more expensive parts
and more board space.