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45v out of a bridge rectifier, what AV voltage goes in?

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Peter Percival
Guest

Fri Jul 19, 2019 8:45 pm   



If want to get 45v/2amps out of a bridge rectifier, what AV voltage
goes in?
--
"He who will not reason is a bigot;
he who cannot is a fool;
he who dares not is a slave."
- Sir William Drummond

Sjouke Burry
Guest

Fri Jul 19, 2019 8:45 pm   



On 19.07.19 21:20, Peter Percival wrote:
Quote:
If want to get 45v/2amps out of a bridge rectifier, what AV voltage
goes in?

(45 - 2 diodedrops)/sqrt2 and then a but more to compensate for losses.


so (45 - 1.6)/1.141256 + 2= 33Volt more or less.

Peter Percival
Guest

Fri Jul 19, 2019 9:45 pm   



Sjouke Burry wrote:
Quote:
On 19.07.19 21:20, Peter Percival wrote:
If want to get 45v/2amps out of a bridge rectifier, what AV voltage
goes in?

(45 - 2 diodedrops)/sqrt2 and then a but more to compensate for losses.

so (45 - 1.6)/1.141256 + 2= 33Volt more or less.


Thank you.

--
"He who will not reason is a bigot;
he who cannot is a fool;
he who dares not is a slave."
- Sir William Drummond

Look165
Guest

Fri Jul 19, 2019 10:45 pm   



(2^^1.5/pi*)45

Peter Percival a écrit le 19/07/2019 à 21:20 :
Quote:
If want to get 45v/2amps out of a bridge rectifier, what AV voltage
goes in?


Ralph Mowery
Guest

Fri Jul 19, 2019 11:45 pm   



In article <5d321c14$0$26409$e4fe514c_at_textnews.kpn.nl>,
burrynulnulfour_at_ppllaanneett.nnll says...
Quote:

On 19.07.19 21:20, Peter Percival wrote:
If want to get 45v/2amps out of a bridge rectifier, what AV voltage
goes in?

(45 - 2 diodedrops)/sqrt2 and then a but more to compensate for losses.

so (45 - 1.6)/1.141256 + 2= 33Volt more or less.



All of that is well and good.

However, is that going to be peak, average, rms or just what that the
origional question wanted. Is there going to be a capacitor to smooth
out the voltage, or is the full wave rectified DC going to be used ?

Lots of unasked questions in the origional question.

Phil Allison
Guest

Sat Jul 20, 2019 5:45 am   



Ralph Mowery wrote:


Quote:

All of that is well and good.

However, is that going to be peak, average, rms or just what that the
origional question wanted. Is there going to be a capacitor to smooth
out the voltage, or is the full wave rectified DC going to be used ?

Lots of unasked questions in the origional question.



** The original Q is a pile of utterly ambiguous drivel.

If Q posters would simply reveal the PURPOSE of their question, ambiguity would disappear and useful answers become possible.

But no, they want to play at being smart and be in control the answers by NOT revealing any such damn thing.



..... Phil

default
Guest

Sat Jul 20, 2019 11:45 am   



On Fri, 19 Jul 2019 21:08:18 +0100, Peter Percival
<peterxpercival_at_hotmail.com> wrote:

Quote:
Sjouke Burry wrote:
On 19.07.19 21:20, Peter Percival wrote:
If want to get 45v/2amps out of a bridge rectifier, what AV voltage
goes in?

(45 - 2 diodedrops)/sqrt2 and then a but more to compensate for losses.

so (45 - 1.6)/1.141256 + 2= 33Volt more or less.

Thank you.


And depending on how the transformer is spec'd (assuming you are
running off the mains) you should probably go with a current of 3
amps.

I was fresh out of navy boot camp assigned to an electronics shop and
had the place to myself after hours. I wanted some music and found a
junked turntable and FM radio front end. I modified our junked
cannibalized donor transceiver into a stereo amp. One night listening
to music the transformer vented (sealed steel case potted in tar,
military grade thing) it was impressive, lot of noise and smoke
literally shot out of it. Turns out I didn't allow for the true
current the transformer could supply. The nameplate gave the
milliamps it could supply as an AC rated part, but when you convert to
DC the amps has to drop proportionately. Many transformers are rated
in Volt-Amperes for that reason.

Peter Percival
Guest

Sat Jul 20, 2019 6:45 pm   



Phil Allison wrote:
Quote:
Ralph Mowery wrote:



All of that is well and good.

However, is that going to be peak, average, rms or just what that the
origional question wanted. Is there going to be a capacitor to smooth
out the voltage, or is the full wave rectified DC going to be used ?

Lots of unasked questions in the origional question.



** The original Q is a pile of utterly ambiguous drivel.

If Q posters would simply reveal the PURPOSE of their question, ambiguity would disappear and useful answers become possible.

But no, they want to play at being smart and be in control the answers by NOT revealing any such damn thing.



.... Phil


Oh dear.

I am looking at Fig 3.6 on p 42 of Marston's /110 operational amplifier
projects for the home constructor/. The circuit depicted is that of a
power supply delivering 3-30V at 0-1A. It is to be supplied with "+40
to 45V (unregulated)". The text has nothing to say about where that
comes from. I have decided to use a bridge rectifier attached to the
secondary of a transformer with 240(ish)V primary; and I wish to know
what secondary I need.

The "2amps" in my OP was a guess of mine that if the PS delivers 1amp,
then 2amps in would be more than enough.


--
"He who will not reason is a bigot;
he who cannot is a fool;
he who dares not is a slave."
- Sir William Drummond

Phil Allison
Guest

Sun Jul 21, 2019 3:45 am   



Peter Percival wrote:
Quote:

Phil Allison wrote:
Ralph Mowery wrote:



All of that is well and good.

However, is that going to be peak, average, rms or just what that the
origional question wanted. Is there going to be a capacitor to smooth
out the voltage, or is the full wave rectified DC going to be used ?

Lots of unasked questions in the origional question.



** The original Q is a pile of utterly ambiguous drivel.

If Q posters would simply reveal the PURPOSE of their question, ambiguity would disappear and useful answers become possible.

But no, they want to play at being smart and be in control the answers by NOT revealing any such damn thing.



.... Phil

Oh dear.


** Shit, somebody actually took notice of my complaint - never happened before.


Quote:
I am looking at Fig 3.6 on p 42 of Marston's /110 operational amplifier
projects for the home constructor/. The circuit depicted is that of a
power supply delivering 3-30V at 0-1A. It is to be supplied with "+40
to 45V (unregulated)". The text has nothing to say about where that
comes from.


**But it is easy to infer that the author means a transformer isolated supply of rectified AC with adequate smoothing for one or more electro caps - with 1 amp DC capacity and 43 volts average output under load and nominal house supply voltage.


Quote:
I have decided to use a bridge rectifier attached to the
secondary of a transformer with 240(ish)V primary; and I wish to know
what secondary I need.


** The transformer will need to have 2 amps AC capacity and a rated secondary voltage of 32 volts AC. This will give about 47V DC off load dropping to 42 under full(1A)load. About 4700uF(63V) filter capacitance should be OK.


Quote:
The "2amps" in my OP was a guess of mine that if the PS delivers 1amp,
then 2amps in would be more than enough.


** But there was no way previously for us to know what the heck you were up to.


..... Phil

Peter Percival
Guest

Mon Oct 14, 2019 8:45 pm   



tabbypurr_at_gmail.com wrote:
Quote:
On Saturday, 20 July 2019 18:35:38 UTC+1, Peter Percival wrote:
Phil Allison wrote:
Ralph Mowery wrote:



All of that is well and good.

However, is that going to be peak, average, rms or just what that the
origional question wanted. Is there going to be a capacitor to smooth
out the voltage, or is the full wave rectified DC going to be used ?

Lots of unasked questions in the origional question.



** The original Q is a pile of utterly ambiguous drivel.

If Q posters would simply reveal the PURPOSE of their question, ambiguity would disappear and useful answers become possible.

But no, they want to play at being smart and be in control the answers by NOT revealing any such damn thing.



.... Phil

Oh dear.

I am looking at Fig 3.6 on p 42 of Marston's /110 operational amplifier
projects for the home constructor/. The circuit depicted is that of a
power supply delivering 3-30V at 0-1A. It is to be supplied with "+40
to 45V (unregulated)". The text has nothing to say about where that
comes from. I have decided to use a bridge rectifier attached to the
secondary of a transformer with 240(ish)V primary; and I wish to know
what secondary I need.

The "2amps" in my OP was a guess of mine that if the PS delivers 1amp,
then 2amps in would be more than enough.

A bit of an old post, but one that never got a fair answer.
To get 40v out, you need 40x 0.707 ac input = 28.3v rms plus the diode drop of the bridge which under load will be 2x 1-2v. If we guess 1.5v diode drops under load then you'd need 31.3v in. That much has mostly been covered already, though a lot of EEs mistakenly think diodes drop 0.65v all the time.

However there are 2 other factors not so far addressed.
First, the reservoir cap will charge to its peak v but then decay until recharged. You need to supply a bit more V to counter the decay for 100th of a second.
Second, there is mains voltage variation to consider. If you want the psu to be reliable & meet mains voltage specs it needs to get enough V to the regulator when V_mains is at the lowest it is permitted to go, which is a fair bit under nominal voltage.

Finally you should only need a 1A supply, parasitic drain is trivial in any normal 1A V reg.

And really finally, check the reg can dissipate the power at full load when mains V is max, I_out is max & V_out is min. And ensure you have sound short/overload protection.


NT

Thank you. Much obliged!



Guest

Mon Oct 14, 2019 8:45 pm   



On Saturday, 20 July 2019 18:35:38 UTC+1, Peter Percival wrote:
Quote:
Phil Allison wrote:
Ralph Mowery wrote:



All of that is well and good.

However, is that going to be peak, average, rms or just what that the
origional question wanted. Is there going to be a capacitor to smooth
out the voltage, or is the full wave rectified DC going to be used ?

Lots of unasked questions in the origional question.



** The original Q is a pile of utterly ambiguous drivel.

If Q posters would simply reveal the PURPOSE of their question, ambiguity would disappear and useful answers become possible.

But no, they want to play at being smart and be in control the answers by NOT revealing any such damn thing.



.... Phil

Oh dear.

I am looking at Fig 3.6 on p 42 of Marston's /110 operational amplifier
projects for the home constructor/. The circuit depicted is that of a
power supply delivering 3-30V at 0-1A. It is to be supplied with "+40
to 45V (unregulated)". The text has nothing to say about where that
comes from. I have decided to use a bridge rectifier attached to the
secondary of a transformer with 240(ish)V primary; and I wish to know
what secondary I need.

The "2amps" in my OP was a guess of mine that if the PS delivers 1amp,
then 2amps in would be more than enough.


A bit of an old post, but one that never got a fair answer.
To get 40v out, you need 40x 0.707 ac input = 28.3v rms plus the diode drop of the bridge which under load will be 2x 1-2v. If we guess 1.5v diode drops under load then you'd need 31.3v in. That much has mostly been covered already, though a lot of EEs mistakenly think diodes drop 0.65v all the time.

However there are 2 other factors not so far addressed.
First, the reservoir cap will charge to its peak v but then decay until recharged. You need to supply a bit more V to counter the decay for 100th of a second.
Second, there is mains voltage variation to consider. If you want the psu to be reliable & meet mains voltage specs it needs to get enough V to the regulator when V_mains is at the lowest it is permitted to go, which is a fair bit under nominal voltage.

Finally you should only need a 1A supply, parasitic drain is trivial in any normal 1A V reg.

And really finally, check the reg can dissipate the power at full load when mains V is max, I_out is max & V_out is min. And ensure you have sound short/overload protection.


NT

Phil Allison
Guest

Tue Oct 15, 2019 2:45 am   



tabb...@gmail.com wrote:

--------------------------

Quote:

A bit of an old post, but one that never got a fair answer.


** I beg to difefr...

Quote:

However there are 2 other factors not so far addressed.
First, the reservoir cap will charge to its peak v but then decay until recharged. You need to supply a bit more V to counter the decay for 100th of a second.


** In my post, I allowed 2V for that.

The formula I = C dv/dt covers it,

where I =1, C =4700exp-6 and dt = 0.008


Quote:
Second, there is mains voltage variation to consider.
If you want the psu to be reliable & meet mains voltage
specs it needs to get enough V to the regulator when V_mains
is at the lowest it is permitted to go, which is a fair bit
under nominal voltage.


** Designing a mains transformer, linear, regulated DC supply is a non-trivial exercise if done entirely on paper. Coming up with an accurate spec for the tranny being the hardest thing.

Secondary AC too low and the PSU will hum under low mains.

Secondary VAC too high and the regulator IC or BJT will cook with high mains.

Tranny VA too small and it will cook.

A few clever designers installed a pre-regulator using a Triac and feedback in front to ease the requirements on the poor tranny and heatsinking.


...... Phil









Quote:

Finally you should only need a 1A supply, parasitic drain is trivial in any normal 1A V reg.

And really finally, check the reg can dissipate the power at full load when mains V is max, I_out is max & V_out is min. And ensure you have sound short/overload protection.


NT



Guest

Wed Oct 16, 2019 1:45 pm   



On Tuesday, 15 October 2019 02:20:01 UTC+1, Phil Allison wrote:
Quote:
tabby wrote:

--------------------------


A bit of an old post, but one that never got a fair answer.


** I beg to difefr...


However there are 2 other factors not so far addressed.
First, the reservoir cap will charge to its peak v but then decay until recharged. You need to supply a bit more V to counter the decay for 100th of a second.


** In my post, I allowed 2V for that.

The formula I = C dv/dt covers it,

where I =1, C =4700exp-6 and dt = 0.008


Second, there is mains voltage variation to consider.
If you want the psu to be reliable & meet mains voltage
specs it needs to get enough V to the regulator when V_mains
is at the lowest it is permitted to go, which is a fair bit
under nominal voltage.


** Designing a mains transformer, linear, regulated DC supply is a non-trivial exercise if done entirely on paper. Coming up with an accurate spec for the tranny being the hardest thing.

Secondary AC too low and the PSU will hum under low mains.

Secondary VAC too high and the regulator IC or BJT will cook with high mains.


just means a bigger pass tr & heatsink are needed.

Quote:
Tranny VA too small and it will cook.

A few clever designers installed a pre-regulator using a Triac and feedback in front to ease the requirements on the poor tranny and heatsinking.


..... Phil


There are others ways to do it too, but for someone needing a 'how to' it's easier to stick to dissing the heat in the pass tran.


NT

Phil Allison
Guest

Wed Oct 16, 2019 10:45 pm   



Some Trolling Lunatic Stalker called tabb...@gmail.com wrote:

---------------------------------------------------------

Quote:

Secondary VAC too high and the regulator IC or BJT will cook with high mains.

just means a bigger pass tr & heatsink are needed.


** A fuckwit's worthless solution.



Quote:
A few clever designers installed a pre-regulator using a Triac and
feedback in front to ease the requirements on the poor tranny
and heatsinking.


There are others ways to do it too,


** A fuckwit's worthless comment.




...... Phil


Guest

Fri Oct 18, 2019 3:45 am   



On Wednesday, 16 October 2019 22:39:53 UTC+1, Phil Allison wrote:
Quote:
Some Trolling Lunatic Stalker called tabby wrote:

Secondary VAC too high and the regulator IC or BJT will cook with high mains.

just means a bigger pass tr & heatsink are needed.

** A fuckwit's worthless solution.


it's the standard solution for a linear reg.


Quote:
A few clever designers installed a pre-regulator using a Triac and
feedback in front to ease the requirements on the poor tranny
and heatsinking.

There are others ways to do it too,

** A fuckwit's worthless comment.


that comment certainly is of no worth.

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