0-30V Stabilized Power Supply

[zulcao]

what might be the problem if the LED did not light up but the output voltage is around 25v?

and also what might be the problem if a wire connecting the components at the lower left side of the schematic(somewhere around D5 and C1) was burned?

The D12 led only light up when the current passing by R7 is over the limit set by P2 (U3).

In which circumstances the wire burned up ?

[stealthghost]

Sorry but I don't have time to look at the datasheets of your Oriental transistors.
The spec's for a 2N3055 transistor are a Vceo of 60V, a minimum hFE of 20 at 4A and a max power dissipation of 115W. If your transistors are the same or better then they can be used.

ok got it! thanks for the advice..

I didn't know how to compare before but based on your advice and spec requirements, the 2SC5198 is an OK replacement. These are some old transistors I found somewhere.. :D

[fly3rman]

Fly3rman ,    The pcb you reference was copied from the 1st post  on page 1 and is still current.    Given it is a double sided board it is a little more difficult to build at home.   I had some commercially made pcb's  from that board file so I know it works.

Redwire?
Could you please exlain the offboard wiring? Points 7a 7 8 3 and 1.
Also what it is with D7 Diode and if d2+d3 are replacing it? Or are they needed? 4 and 4a are ground? Current outputis wired from Output Transistor?

[jpmhdbest]

can someone tell me what trimmer/s should be adjusted and at how much will you turn it.. thx in advance..

[zulcao]

can someone tell me what trimmer/s should be adjusted and at how much will you turn it.. thx in advance..

once more,

RV3 is to set the maximum current to 3 or 5 amps (one way to set: short the PSU, adjust P2 (amp) to max, adjust the RV3 to desired maximum current, be quick, the transistor will get HOT).
RV2 is to set the maximum voltage to 30v (how to set: in open circuit adjust the P1 (volts) to max, adjust the RV2 to be 30v at the terminals of the PSU).
RV1 is to set the ZERO voltage (how to set: in open circuit adjust the P1 (volts) to min, adjust the RV1 to be 0v at the terminals of the PSU).

[redwire]

fly3rman  

You are correct about the output transistor.     Connections 7a (spare) and 7 for offboard power transistor (collector).   Connection 8 is the base connection for power transistor and point 3 is the backfeed from the power transistor emitter.    Connection 1 is a spare for the lcd display.

connection 4 and 4A (reserved for lcd display)are the same.

If you use an offboard power resistor r7 then connection 4B1 and 4 are used.
If an on board resistor is used then connections 4B and 4 are used.

In regards to D7  (5.6V Zener),  it is not used in the latest design.  It was replaced with the two diodes D2 and D3   for a -1.3 negative rail instead of the older -5.6 negative rail.

There is a small connection between C1 and 4B on the board.  This is just a spare ground for the lcd display or the power resistor can use this hole instead of 4B.

[fly3rman]

Thanks alot redwire, it seems  it got it then.

Here my toner-selfmade-double-side-etched-pcb. I hope you can see it on the pictures.
I will test it tomorrow with the small 18v trafo. If everyone finds any wiring problems ...

[audioguru]

If everyone finds any wiring problems ...

1) The voltage and current from the transformers are much too small.
2) The circuit needs two 2N3055 output transistors not just one.
3) Each output transistor needs a 0.33 ohm emitter resistor, not a 33 ohm resistor.

[fly3rman]

1) The voltage and current from the transformers are much too small.
2) The circuit needs two 2N3055 output transistors not just one.
3) Each output transistor needs a 0.33 ohm emitter resistor, not a 33 ohm resistor.

1) Still it should work or will it not? I meant this transformators just for testing so far. Is it possible to trim it down with RV2? What is the minimum voltage needed for correct working of the voltagecontrol? Putting them in series with 36v is also a little high then :/
2) Yes, but only for higher currents right?
3) thanks, put a wrong on it, will replace.

Questions:

For understanding: So this always need the 3A current and atleast 28V AC and heat up everything not used by the consuming load? Otherwise the control doenst work?

Is it possible to trim it down to lets say 2A? As written before : "RV3 is to set the maximum current to 3 or 5 amps".
And actually i want to use an 120VA Trafo instead of 160VA because its 1/4 cheaper. It should can handle the missing 0.2A right? (someone ask before also)

and another one: Can anybody say something to the stability and possibility to control the current of this powersupply?

[audioguru]

1) Still it should work or will it not? I meant this transformators just for testing so far. Is it possible to trim it down with RV2? What is the minimum voltage needed for correct working of the voltagecontrol?

Nobody knows if the circuit will work with your tiny transformers. If it does not work then you will not know if something in the circuit is wrong so the test will be useless.

Putting them in series with 36v is also a little high, but only for higher currents right?

Your tiny transformers might produce 46V AC without a load then the unregulated supply to the circuit will be 64V DC and blow up most parts in the circuit.

So this always need the 3A current and at least 28V AC and heat up everything not used by the consuming load? Otherwise the control doenst work?

The circuit was designed to produce 0V to 30.0VDC at 3mA to 3A. It uses a 28V AC to 30V AC transformer rated at 126VA. You can reduce its output voltage and current and make it cheaper if you re-design it.

Is it possible to trim it down to lets say 2A? As written before : "RV3 is to set the maximum current to 3 or 5 amps".

I don't know how low the current trimpot can adjust the maximum current but you can increase the value of the resistor in series with it to reduce the maximum current.

And actually i want to use an 120VA Trafo instead of 160VA because its 1/4 cheaper. It should can handle the missing 0.2A right?

A 28V AC transformer at 120VA will allow a max output of 30.0V at 3.0A DC. A 30V AC transformer at 120VA will allow a maximum output of 30.0V DC at 2.83A. The 30V transformer will overheat a little if the output is 3.0A DC continuously.

Can anybody say something to the stability and possibility to control the current of this powersupply?

The fixed and modified circuit is very stable and is very reliable. Its max output current is controlled by a pot.

[fly3rman]

Nobody knows if the circuit will work with your tiny transformers. If it does not work then you will not know if something in the circuit is wrong so the test will be useless.

Iam aware of that. Also on the other side, one 18v/1.5VA transformer couldnt blow anything up, and still possible that it works ;]

Your tiny transformers might produce 46V AC without a load then the unregulated supply to the circuit will be 64V DC and blow up most parts in the circuit.

Yep, got that.

The circuit was designed to produce 0V to 30.0VDC at 3mA to 3A. It uses a 28V AC to 30V AC transformer rated at 126VA. You can reduce its output voltage and current and make it cheaper if you re-design it.

3mA is fine enough.  Redesigning is a little bit problematic at the moment because of the lack of overview and compelte understanding of the cirtcuit, but time will come ;]

I don't know how low the current trimpot can adjust the maximum current but you can increase the value of the resistor in series with it to reduce the maximum current.

But its possible without any problems in stability or something? If i trim down to lets say 1A max Output? (This, as i mentioned, would allow a later upgrade to a highpower transformer)

A 28V AC transformer at 120VA will allow a max output of 30.0V at 3.0A DC. A 30V AC transformer at 120VA will allow a maximum output of 30.0V DC at 2.83A. The 30V transformer will overheat a little if the output is 3.0A DC continuously.

This is fine. Iam actually gonna use it in region of <1A most of the time.

The fixed and modified circuit is very stable and is very reliable. Its max output current is controlled by a pot.

Ive used the latest version. Nice.

Thanks for the input so far.

UPDATE: My Circuit works! Had wrong wiring on current / voltage control, but now it works.
With lower voltage and current transformer i am able to set voltage and current! Tested on 2 leds. Will show pictures later. Of course hard to set the current/voltage on this potis because of wrong dimensions.
But now iam aware its working i can get the expensive transofmer i think =)

[HISPID]

Hi all!
Sorry for my bad English.

I decided to build this PSU under the original scheme. I consider that the original scheme is not too bad, if to make small corrections.

My corrections in the original scheme:
- Replacement of C1 by more capacious 8200mf 63V
- Use of two MJE3055T in parallel connection
- Use of operational amplifiers OP07CP U1, U2, U3
- Use of BD139 in Q2

* For use of operational amplifier OP07CP (U2) in the original scheme, I have changed in places contacts 5 and 8, look at the picture below.
* Also for parallel connection MJE3055T, I have made the small PCB, look at the picture below (7,8,9 are contacts on PCB).

As a result when all has been done, nothing works :(. Target voltage regulates from 0 to 0,65 volt, and U2 strongly heats up.
Also strongly heats up R1, R2, i think replacing them with more powerful resistors will solve the problem of their heating.

My actions:
- Before soldering, all parts were checked on serviceability. So all of them were in working order.
- I have checked PCB on a possible cracks, but found nothing.
- After soldering, i have checked polarity of all parts, all is established correctly.
- I have checked all connections with tester (multimetr). All in contact!

Help me please! I do not know where can be a problem?
Can be some part burned down? Though there are no traces of ignition. Unsolder all parts and to check them, there is no desire.

[HISPID]

All sources are included in link to *.zip file below. PCBs are in *.lay format (Sprint Layout 5.0).
- original PCB with OpAmp OP07CP correction
- PCB for parallel connection of 2N3055 or MJE3055

PSULay.zip

[audioguru]

The OP07 opamps will be destroyed in the original circuit because their maximum supply is plus and minus 18V (a total of 36V) but the 24V AC transformer will be 26V AC with no load and the positive unregulated supply will be +35.4V DC. U2 and U3 also have the -5.6V supply so their maximum supply will be too high at 41V DC.

There is too much voltage loss in the circuit for the output to produce 30.0V at 3A.
Many parts in the original circuit are overloaded (they get too hot) including the transformer.

The latest modified circuit should be used.

[MyTallest]

Just started gathering parts for this project. I thought I'd pass along an idea. I didn't have much luck in finding the right transformer plus I thought I'd like to keep the "box" fairly small. So I went for an external transformer. A lot cheaper and nicely packaged.  :)

http://www.amazon.com/gp/product/B0027BUS0M

The one they sent me was actually rated at 90W instead of 70W as advertised.

[audioguru]

Just started gathering parts for this project. I thought I'd pass along an idea. I didn't have much luck in finding the right transformer plus I thought I'd like to keep the "box" fairly small. So I went for an external transformer. A lot cheaper and nicely packaged. 

You didn't buy a transformer that has a 24V AC or 28V AC output. Instead you bought a switched mode power supply with a choice of DC outputs which is no good for this project.

The modified project has a 28V AC or 30V AC transformer that is rectified and filtered and it produces +40.2V DC and -1.3V DC. Your project will not work when the positive unregulated supply is only +24V DC and with no negative supply.

[HISPID]

Thanks audioguru.

Operational amplifiers OP07CP won't be destroyed, because their maximum voltage + - 22V (total 44V), I attached screenshot from the specification.

Yes I agree that in the original scheme there are voltage losses, and some parts become hot. But with small corrections (replacement of some parts by more powerful analogs) it will work. And it works for many users who built the original scheme.

I have forgotten to mention that i have not polyester C4, C5. And i used their ceramic analog. Whether there can be a problem in it?? I think that isn't present...

[audioguru]

Operational amplifiers OP07CP won't be destroyed, because their maximum voltage + - 22V (total 44V)

The first page of the datasheet from Analog Devices spec's a max supply of only 36V but later it says 44V so it is very confusing. I would not use more than 36V.

Yes I agree that in the original scheme there are voltage losses, and some parts become hot. But with small corrections (replacement of some parts by more powerful analogs) it will work. And it works for many users who built the original scheme.

It is wrong to overload parts. The original circuit cannot produce a regulated (no hum) +30.0V at 3.0A.

I have forgotten to mention that i have not polyester C4, C5. And i used their ceramic analog. Whether there can be a problem in it?? I think that isn't present...

C4 and C5 are simple filters. Their tolerance and type does not matter.

[fly3rman]

Arghs. Crap. Mixed up Base and Emitter of 2n3055 and now somethin weird is happening, but its not working. Output of maximal 3V and extreme hot R1 and R2. But iam able (in a small range) to control voltage and current. extreme strange.
Test everything will be fun :/

I think i saw some picture of "as it should be" voltages and differente places. will look into that.

update: u1 and u2 (tle2141) do have 42.6 volts on pin 7. u3 does have zero.
when shorten the output, ~1.5 amper are flowing and 2n3055s heat up very well, so far working, but cant control current then. But when i set voltage to zero on voltage poti, its no current flowing anymore -> working. Led isnt lighten up.
I think i should replace u3, but maybe its something next to it.

Ideas please =)

[audioguru]

Hi fly3rman,
When the 2N3055 transistors are connected with their base and emitters backwards, then the driver transistor Q2 takes almost the entire output load and probably burns out if the project has a load.

The positive supply pin 7 of U3 has a 10V zener diode in series so its voltage should be about +32.6V. Its output pin 6 is usually as high as it can go (about +31.3) then drops to reduce the output voltage when it regulates the output current.

U2 and the driver and output transistors are an amplifier with a voltage gain of about 2.68. Its input is 0V to +11.2V from the voltage-setting pot that is fed +11.2V from the output of U1.

R1 is supposed to be 2200 ohms/2W. With 42.6V across it then it dissipates 0.82W so it is very warm but not too hot.
R2 is supposed to be 82 ohms/2W. It should also not be too hot. 

[fly3rman]

@ audioguru, thanks for the input, you were right. It was the Q2. I put in a new one and now its working like it was before, but still not right.
I can:
Set voltage from zero to 11.1
Control current and also turn it off completely (led lights on)

Now some data:
- i used redwires pcb with latest values (see picture)
- power is supplied by 2x15 (series) 160VA transformer
- ac voltage is fine: 30v
- dc voltage after rectifier and supplied to 2n3055`s: 42v
- q3 is a bc327, collector:32v, emitter: zero aslong no c.c, base ~32v
- q2: zero to 11v on emitter (reacts on base voltage), 42v on collector, base zero to 11.9v
- negative rail is @  -1.3
- R1 is 2200 Ohm, R2 is 82 Ohm, both 2W, still getting extreme instant-fingerburn hot
- u1 pin7 voltage: 42v, pin6: constant 10.8
- p12: 0-10.9v, p10: zero constant, p5 10.9 constant
- p13:0-0.9v?, p11: zero constant, p6:0.9v
- u3: pin7: 32v, 6:zero to 32
- u2: pin7: 42v, 6: zero to 11.7
- trimmers seem to have no effect at all

It really seems that is dont get the voltage gain of 2.68 times. i start thinking about faulty opamps? they are hard soldered, so not fun to exchange them, but i wanted to put in sockets anyway ....
I hope you can provide some more help.

[audioguru]

Hi fly3rman,
You used Redwire's pcb but my parts list. They have different resistor values but  they should work properly even if the parts are mixed up.
Your output amplifier has a gain of only slightly more than 1 so maybe R11, R12 or RV2 are broken or wrong values. Maybe C6 is shorted.

Here is Redwire's schematic simplified:

[fly3rman]

Hi fly3rman,
You used Redwire's pcb but my parts list. They have different resistor values but  they should work properly even if the parts are mixed up.
Your output amplifier has a gain of only slightly more than 1 so maybe R11, R12 or RV2 are broken or wrong values. Maybe C6 is shorted.

Here is Redwire's schematic simplified:

Hi audoguru,
I have no idea how you could find that problem but you was right, again! I actually double/three time checked all the parts, but this one slipped through ...
R12 was a 56 Ohm instead of 56K Ohm. No wonder it wasnt working.
Now it does freaking work. Voltage goes up to 30+something, i successfully trimmed it down to 30. Shorted Amper measurement was showing 5 Amp, then i stopped turning up =). Trimmed it down successfully to 3Amp!

Zero Voltage is something of 0.33mV. Cant trim it down, but will recheck values around RV1. But actually that Voltage is ok for me first.

Now i will build in the additional fine potentiometers. Do some heatshrink ...
And  then i will think about heating problems, my heatsinks are way not enough ( 3,5'K/W, http://www.segor.de/#Q=SK 63-37,5SA 3S)
For thins i thinking about follwing:
placing these heatsinks inside on the aluminium backplate (se picture), and outside another one big heatsink, conencted with screws/nuts and silicon heatpaste. Maybe a problem: the whole backplate gets hot? Other idea: on the bottom inside on the airholes i just place a 40x40 or 50x50 airfan, maybe controlled with a temperature-sensor.
I posted some pictures of my work so far.


Thanks man, you rock!

[fly3rman]

One more picture:

[audioguru]

Hi fly3rman,
With the output set to a low voltage or is shorted and the current is set to 3.0A then each output transistor has 40.6V and 1.5A which is heating of 60.9W. Your little heatsinks are rated for only about 10W each.

The 2N3055 is rated for a chip to case max thermal resistance of 1.5 degrees C per Watt. Thermal paste is about 0.2 degrees per Watt. 60.9W will heat the chip to (60.9 x 1.7)= 104 degrees C above its case temperature. The max allowed chip temperature is 200 degrees C but 180 degrees is safer. If the ambient free air is 30 degrees C then the heatsink must have a thermal resistance of at least (180 - 30 - 104)/60.9= 0.76 degrees C per Watt which is impossible without having a huge heatsink and a fan.

The original project used only one 2N3055 transistor that tried to dissipate 91.6W. Impossible!