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0-30V Stabilized Power Supply


redwire
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Guest Big zee

dear audioguru
I did the last update of the PS
but the ICs U1 and U2 gets hot and the voltage is 33 and I cant adjust it !
FYI the power supply is 28 volt and 3 amp

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I did the last update of the PS
but the ICs U1 and U2 gets hot and the voltage is 33 and I cant adjust it !
FYI the power supply is 28 volt and 3 amp

Maybe you mean the transformer is 28VAC and 3A? Then without a load it produces a rectified and filtered about +39.6VDC.

U1 has a quiescent current of 3.5mA for a TLE2141, then its quiescent dissipation is 39.6V x 3.5mA= 139mW. Its output voltage is 11.2V and its output current is 5.6mA so it has (39.6V - 11.2V=) 28.4V across its output. Its output power dissipation is 28.4V x 5.6mA= 159mW. Then its total dissipation is 139mW + 159mW= 298mW which is far from its maximum allowed dissipation of 1000mW at room temperature ambient. It will be warm, not too hot.
U2 will be a little warmer but since yours is fighting the transistors then maybe it is destroyed.

The output cannot be controlled when the pins on the driver or output transistors are connected backwards.
These transistors are simply emitter-followers.   
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Guest Big zee

sorry its transformer and its 24v 3 amp
you are right there is problem  and i fixed it with the 2N3055
and replaced the TLE2141 but its stil gets very hot in 2 seconds and i cant adjust the voltage ! it 35 volts
is the U3 gets the U2 hot or its still the 3055  ???

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Hello Big Zee,
Your image of the pcb is too small to read any of the part numbers. I cannot see the pins of the driver transistor.
The 2N3055 has a different and metal case than the transistors you are using. Are they TIP3055 by Motorola/Freescale?

Without a load your 24VAC transformer probably produces a rectified and filtered +35VDC.
With a +35VDC supply and no load current, U2 has a maximum output voltage of +33.8V.
The driver transistor is an emitter-follower with a maximum output of +33.1V.
The output transistors are also emitter-followers with a maximum output of +32.4V.
Then how can your output be +35V unless something is shorted to +35V??

If the driver and output transistors work properly then U2 has a low output current and will not get hot.
U3 simply reduces the input voltage to U2 (through D9) when the output current is higher than the setting of the current-setting pot.

I sketched a test for U2 by disconnecting the driver, output transistors and a few other things.

post-1706-14279144544442_thumb.png

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Guest Guber1

Hi, i'm looking to build the latest circuit update but i have a doubt about the zener diode( D1) that is near to Q3, it seems to be a 10V 1W zener diode but i'm not sure. Thanks

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Big Zee,
Your pcb shows that all the pins on the BD139 driver transistor are shorted together.

Guber,
The 10V zener diode D1 has 7mA for the LED and 3.5mA for opamp U3 in it so its max current is 10.5mA and it dissipates 10V x 10.5mA= 105mW. A 0.5W or 1W zener diode will be fine.
1N758A, 1N961B, 1N5240B, 1N6000B or many BZX European ones. 

post-1706-14279144545606_thumb.png

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Guest Guber1

Big Zee,
Your pcb shows that all the pins on the BD139 driver transistor are shorted together.

Guber,
The 10V zener diode D1 has 7mA for the LED and 3.5mA for opamp U3 in it so its max current is 10.5mA and it dissipates 10V x 10.5mA= 105mW. A 0.5W or 1W zener diode will be fine.
1N758A, 1N961B, 1N5240B, 1N6000B or many BZX European ones. 


Perfect. Thanks
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Guest Big zee

yes
i fixed that with photoshop before print it
but i tried to connect the BD139 and the 2N3055 without the pcb
and the same thing and i disconnect all of them and the IC didnt get hot
and the 6th pin gives me 35 volts !

post-93909-14279144545708_thumb.jpg

post-93909-14279144546022_thumb.jpg

post-93909-14279144546332_thumb.jpg

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Big Zee,
Your camera is not clear enough for us to see any details.
I think since you had wiring problems with the output transistors then that caused U2 to be destroyed. Replace it.

Here is a sketch that shows how U2 should work. It has the driver and output transistors removed but the output voltages should be the same when they are connected.

post-1706-14279144546638_thumb.png

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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.  
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Guest 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

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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.
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Guest 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
???

post-93909-14279144547436_thumb.jpg

post-93909-142791445481_thumb.jpg

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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.

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Guest 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 ?

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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.
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