0-30V Stabilized Power Supply

[Big zee]

I replace all the 3
And its stil gives me 35 volt
But the 3rd pin for u2 gives me 1.14 volt
And I can't adjust it !

 

[Big zee]

The 6th pin of U1 gives me 4 volt only

 

[audioguru2]

I replace all the 3
And its stil gives me 35 volt
But the 3rd pin for u2 gives me 1.14 volt
And I can't adjust it !

Look at my sketch of U2 Alone. Pin 3 of U2 has:
1) D9 but it is reversed biased so it does nothing.
2) R8 and R9 in series from the voltage setting pot.
3) Filter capacitor C4 to ground.
There is nothing to cause pin 3 to be stuck at +1.14V so check your pcb to make sure there is nothing that should not be there.

As I said earlier, the voltage gain of U2 is set by R11, R12 and the calibration trimpot to be 2.68 times so when pin 3 is +1.14V the output should be only +3.05V, not +35V. Something is wrong.  

 

[audioguru2]

The 6th pin of U1 gives me 4 volt only

U1 has its voltage gain set to 2 times by R5 and R6. So the 5.6V zener diode D8 has its voltage doubled to +11.2V at the output of U1.
Check that D8 is a 5.6V low current (5mA) zener diode and check the values of R4, R5 and R6.

 

[seb1982]

Hi!

I'm about to try making this (as in Audioguru's helpfully modified version), with the addition of a simple microcontroller & LCD V & I readout.

One thing I'm not sure about, though, and I'd appreciate any advice as a noob:  am I right in thinking that in order to set a specific current limit level on the readout, you'd have to short the output for a few seconds, set the level, and then un-short it and carry on?  If so, is this doable for short periods of time do you think, or should I really just buy a commercial lab power supply if I want to be doing that?

Thanks for your help.

Simon

 

[audioguru2]

Am I right in thinking that in order to set a specific current limit level on the readout, you'd have to short the output for a few seconds, set the level, and then un-short it and carry on?  If so, is this doable for short periods of time do you think, or should I really just buy a commercial lab power supply if I want to be doing that?

The knob (or electronic pot) used to set the amount of current is CALIBRATED so that when it is set at maximum the current is exactly 3.0A, set at halfway the current is exactly 1.50A, etc. Usually the knob points at numbers on the dial surrounding it.

The maximum current is simply calibrated to be 3.0A when the output is shorted. Then the maximum current will be 3.0A when the output is 30V with a 10 ohm load, 20V with a 6.67 ohm load, 10V with a 3.33 ohm load etc.

 

[seb1982]

Ah - I see now - yes, of course!

Many thanks for your kind help, Audioguru.

 

[Big zee]

dear AG
I did the PS on a new board and its not PCB
I did it as you sketch it
and the 6th pin still gives me 35 V !!
I removed all the ICs and its gives me almost zero
but the BR1 gives 74volt on the board
and 23.50volt off the board
I changed it and its the same
???

 

[audioguru2]

Hello big Zee,
Two weeks ago you said you used a 24V transformer. The bridge rectifier charges your main filter capacitor to about +35V which is the positive supply voltage for U2. The maximum output voltage of U2 is about 1V less than its positive supply so it might go as high as +34V.

U2 is an amplifier with a voltage gain of 2.68 times. Its output from the voltage-setting pot is from 0V to +11.2V so its output should be from 0V to a little higher than +30V.

 

[Big zee]

yes its still 24v 3amp
but its shows it 74v on the board ! and 23.5 of the board !
how that's happened ? is it because I didnnot connect the 12000 caps ?
ok but the out of the 6th pin its 35 ?
and I cant adjust the volts ! is the potentiometer has a diferent way to connect it ?
and can I drop the Q3 ?

 

[audioguru2]

yes its still 24v 3amp
but its shows it 74v on the board ! and 23.5 of the board !
how that's happened ? is it because I didnnot connect the 12000 caps ?

The 24VAC transformer might produce 25.5VAC with no load. Its peak voltage is (the root of 2) 1.414 times higher at +36V and the bridge rectifier with no load drops it to about +35V.
OF COURSE you MUST connect the main filter capacitor!

Your meter is WRONG to measure 74V!

but the out of the 6th pin its 35?

Then something is shorted or is disconnected.

and I cant adjust the volts! is the potentiometer has a different way to connect it?

The schematic shows the 3 pins of the voltage-setting pot. The input, the slider and ground.
Measure the voltage at the slider when you turn the pot. It should go from 0V to +11.2V.

can I drop the Q3?

I do not know whose schematic you are using. Picmaster and Redwire used different parts numbering than the original one that I use. In the original and in my schematic Q3 simply turns on the current-regulation warning LED. It is a warning that the current regulation is reducing the output voltage.

 

[Big zee]

yes your Q3

 

[Big zee]

the supply for U2 is the main negative supply
and not the same as U1 and U3 !
-1.3v
should it be the same as the rest of them ?

 

[Big zee]

ok
now its canon cam

 

[Big zee]

ignore the blue wire on the back of the board

 

[Big zee]

PS

 

[audioguru2]

The schematic shows that only U3 uses the -1.3V supply because its output must go a little negative due to the forward voltage drop of D9 when the output of the project is shorted.

I cannot trace your stripboard layout since none of the parts in your photo are numbered.

 

[Kevin Weddle]

Hi Big zee. Are you contructing this power supply. Are you almost done!

 

[Big zee]

hello KevinIV
I did the PS for the 6th time and it still gives me the wrong value
I don't know what went wrong everything seems in order .
but I ran of the ICs , and I still into it .

 

[Big zee]

for AG