0-30 Vdc Stabilized Power Supply

[audioguru]

Thanks, Mongseng. ;D
It is best to keep with the modified project.
Are you going to make it for 3A or 5A? ???

[Guest Alun]

It will take me a few hours or days to redesign this project for your low-voltage transformer.
Just about every resistor wil need to be analysed. :'( :'( :'(

Just use a voltage doulbler on the output of the transformer, but you'll need to double the current rating of the transformer or half the output current.

[audioguru]

Hi Alun,
A voltage full-wave voltage doubler for a 3A output would need 3 (or 4?) huge capacitors and powerful rectifiers. Another low-current doubler might be needed for the negative supply but instead a few resistors can have their values reduced.

[Guest Alun]

I thought it'd take you hours to redesign it.  ;D Perhaps halving the output current (as I also suggested) miight be more sensible if you want to use a voltage doubler, but you'd still need pretty big capacitors anyhow.

[ruden]

there components with working voltage limits(like capacitors with WV of 50 volts,resistors of 1/4 W) that should br considered in applying other than the prescribed ivput AC voltage

[audioguru]

Hi Ruden,
If you give the circuit an input voltage too low, the resistors won't supply enough current unless their value is reduced. Also the parts for the negative DC voltage will need adjustment.
If the input voltage is too high then the currents will be too high and cause resistors and transistors to overheat. Of course the max voltage limits of capacitors, ICs and transistors must be considered as well. ;D 

[Spagbol]

Hi all,

I like the design for this PSU and would like to build it, but with some changes.

It seems only U2 needs a high supply voltage to drive the output to 30v, U1 & U3 would be happy with a lower supply voltage. I'm wondering about changing the transistor o/p stage to have a voltage gain of 3 and then clamping the opamps supply voltage at say 20v using a zener so that any stock opamps can be used? (I have loads of TL082s and LM358s etc. so I'd like to use those).

I have 2 transformers I can use, a 24v ~100va and a 2x14v ~300va, as this limits the max o/p voltage I thought I'd add a preset pot to the top of P1 to limit the max output voltage according to what the transformer can cope with?

As I'm using dual op amps I thought the leftover amp could become a comparator with a thermistor for a thermal shutdown if the pass transistor becomes too hot?

I'm a bit rusty, so any comments on changing the transistor o/p stage (if feasible) would be welcome!

[audioguru]

Hi Spagbol,
Welcome to our forum. ;D
You have an excellent idea to use gain in the supply circuit's output stage to reduce the high supply voltage requirement for the driver opamp. I have seen high power audio amps with very high supply voltages, gain in the output stages and opamp drivers. I have some circuits in the many on my hard drive and I will post one when I find them.

However, adding gain to a high power transistor stage reduces its bandwidth which might interact with the bandwidth of the opamp and make a nice oscillator!
Carefullly planned frequency compensation must be used.

You also have an excellent idea to use a preset control to fine-tune the voltage pot's max output voltage at its max setting.

You don't need a true thermistor to measure temperature. Since you have a spare opamp then an ordinary diode or a junction in a transistor can be used instead. A silicon junction's voltage drop decreases about 3mV for each degree C of increased temp. The opamp could amplify it perfectly. ;D
I would use the temp sensing circuit to control the speed of a fan.

[cyw1984]

Hello,
I am sorry for my poor English...also I am a newbie of electronic...
I really want to make this project for my first and serious project..


I want to ask somting abt this project...hope anybody can answer me...thanks you.

1. Which precise part is control current and control voltage..??How to separate them??

2. I would like to separate to make it. How can i separate the circuit and test for it??

3. If I use 0-10 V DAC's Vref to repace P1 and P2 ...how can i change the circuit..?
please draw the circuit for me...please..

4. And how to caculate the change part if I use another Vref of DAC??

5. Does any body have a right schematic??? coz i read the post know that the original schmeatic have some bug

Thanks for answering

[audioguru]

1. Which precise part is control current and control voltage? How to separate them?

P1 controls the voltage and P2 controls the current. They are completely separate but the project's output voltage is reduced by the current regulator.

2. I would like to separate to make it. How can i separate the circuit and test for it?

Make it with the pots and measure the voltages at the pots. Then program your DACs to produce the same voltages.

3. If I use 0-10 V DAC's Vref to repace P1 and P2 ...how can i change the circuit..?
please draw the circuit for me...please..

You don't want to use your DAC's Vref, you want to use its outputs to replace the voltages from the pots. Simply remove the pots and apply the voltage from the output of each DAC to where the pot's slider was connected.
You will need to re-arrange the parts for external current control. P2 should be changed to a fixed resistor then the output from your DAC could be connected to the grounded end of R21.

4. And how to caculate the change part if I use another Vref of DAC?

Calculations won't be accurate due to the tolerance of resistors in the circuit. Just build it with pots and measure their voltages.

5. Does any body have a right schematic??? coz i read the post know that the original schmeatic have some bug.

The updated schematic is here in this forum, I am sorry I lost my copy on my old computer's broken hard drive. Here is the modified one's parts list:

0-30V_Mod_parts_list.txt

[cyw1984]

Thanks audioguru, then
which part is Voltage reference and linear Voltage regulator???
I would like to test one by one~~Thanks




Is it all the part is voltage regulator??

Am I worng???

[audioguru]

Hi Cyw,
That part of the circuit is more than only the voltage regulator.
U2 drives the darlington emitter followers connection of Q2 and Q4 and the ratio of R12/R11 plus 1 is the voltage gain. They have an extremely low output impedance and good voltage regulation because the open-loop gain of U2 is at least 200,000 and is reduced to just a few with the negative feedback through R12.
R7 is the current sensing resistor.
Q1 shuts down the output immediately when the project is turned off.

The voltage reference is fixed at 11.2V and feeds the voltage adjust pot. ;D

[cyw1984]

Hi Cyw,
That part of the circuit is more than only the voltage regulator.
U2 drives the darlington emitter followers connection of Q2 and Q4 and the ratio of R12/R11 plus 1 is the voltage gain. They have an extremely low output impedance and good voltage regulation because the open-loop gain of U2 is at least 200,000 and is reduced to just a few with the negative feedback through R12.
R7 is the current sensing resistor.
Q1 shuts down the output immediately when the project is turned off.

The voltage reference is fixed at 11.2V and feeds the voltage adjust pot. ;D

O...IC~~~

Can help me to remove the thing which not a voltage regulator....Thanks a lot

[audioguru]

[Can help me to remove the thing which not a voltage regulator.

Why? All the parts are needed in the voltage regulator circuit.
If you use a DAC to provide a reference voltage, then you don't need the project's zener diode/opamp reference voltage circuit.

[Sallala]

Hi!

Finally I built the circuit.
It started working and I was very happy.
Without a load, I can adjust the voltage from 0-31,8V, tested with a multimeter.
I use an old 32VAC transformer. The DC voltage is 46V at the rectifier.
The negative supply is -5V exactly.
I use OPA445 it's max supply +-45V  :o but the absolute maximum rating at +-50V.


My happyness gone when I tryed to test the circuit under a load  :'(
I started to test the circuit, with an 1 Ohm resistance at 2-3V.

1. I adjusted the voltage
2. cureant adjsutment potentiometer at the center
3 turn on the corcuit. Everithing seems to be ok.
4. I tryed to adjust the voltage and something happend:
Current supply mode led flash ones, and the output is jumped to 13V

Now, I can adjust the voltage only from 13V-31,8V DC.
The DC voltage at the rectifier decreased to 42V

What happend?
Where can I find the bug?

[Sallala]

OK, I unsoldier the 2n3055 and the circuit now 0-31,5V again.
I'm happy, that my opa455"s  alive :-)

The 2n3055 have a split between it's collector and base.

But what happend? It's a very big problem, when the 2n3055 go wrong, the output jump to 13v isn't it?
If I use the supply for an expensive circuit to supply 5V for example, and the 3055-> die.

Now, I start to find another one in my boxes....

[Sallala]

Ehh, I solved my problem.
1. I measured wrong the 2n3055. But is still dead. There is a split between it's emitter and base.
2. I think it was wrong before I soldered it. (I have got three 2n3055 at home. I remember, once I test one of them. Maybe this was, beacuse I remember it's red painted text)

OK, now I try to start testing the circuit under heavy load.

[Spagbol]

Sallala, before you blow up another transistor......

If you test with a 1 Ohm resistor at 2-3 volts as you say, the 2N3055 will have to disspate a lot of power! (~100W!!) You really need to use more than 1 2n3055 (like in the cct in the thread for the 5A version) and they will need a very effective heatsink!

[audioguru]

How can a 2N3055 in a metal TO-3 case split? ???
Maybe you are using a 2N3055 in a plastic case, that can't dissipate up to 60W like one in a metal case.

It failed very quickly. I expected it to take a few seconds to overheat before failing.
Don't you have the 2N3055 bolted to a huge heatsink with some thermal grease?

Maybe your circuit's current regulator doesn't work. It detects the high current and lights the LED but maybe D9 is open so it doesn't pull the voltage down.

[Sallala]

Thank you for the reply Audioguru!

I have a very poor English knowledge.
I mean:
split = not conduct  ::)

Of yourse, I use a metal case 2n3055, as the picture that you attached.

Spagbol: thank you, I know that, and use a heatshink with a fan. But it' true, not a good resistor value for the start :-)

I'am go to eat something, and after start a correct exact test with oscilloscope.

The fast tests with an 50W 12V bulb:
- Circuit can drive more than 4Amps at ~11V
- The curent regulator regulate ~4,8A at the maximum potentiometer turn
- With a 2-3Amp load, the voltage jump 10-20mV if I remove the load
(Now, I used only one 2n3055)

I made many photos whlie I building.
I made small modification on the original PCB according to Audioguru's posts. (Q2 emitter, dual 2n3055, recifier diode bridge, BD139 feet layout. I will upload everithyng soon.

Thank you!
Gábor Salamon

[audioguru]

- The current regulator regulates ~4,8A at the maximum potentiometer turn.

There is your problem.
With your 46V supply (your transformer's voltage is too high) and 11V output at 4.8A, the power dissipated in the 2N3055 is 157W!

The pot shouldn't give 4.8A anyway.
The 11.2V reference at the output of U1 is applied to the voltage divider of R18 (56k), P2 (10k) and R17 (33 ohms) producing 1.7V max at P2. 1.7V across R7 (0.47 ohms) is only 3.6A and should be the max that the current regulator can supply.
Maybe your pot is 14k instead of 10k.

[Sallala]

I measured the DC voltage again. It's 42VDC on C1.
(I measured the 46V before I put the IC's into the panel. Maybe this makes the difference?)

My pots are 10K. (as the label says)
U1 output is just 10,56V for me. (I sed BZX 5v6 as D8)
U(D8) is 5,25V
Something wrong with my reference?


I'am sorry. My old RFT scope dead. I must to go to the service :-S
I can't measure the ripple now.  :-[

[audioguru]

I measured the DC voltage again. It's 42VDC on C1.
(I measured the 46V before I put the IC's into the panel. Maybe this makes the difference?)

42VDC when loaded is normal for your 32V transformer. The 30V transformer that we recommend would produce 40VDC and reduce max heating in the output transistor by only 6W.

My pots are 10K. (as the label says)

Measure the current-regulator's pot. Your 4.8A max output indicates that its value is more than 14k, or the resistance of R7 (0.47 ohms) is too low.

U1 output is just 10,56V for me. (I used BZX 5v6 as D8)

The BZX79C5V6 zener D8 is rated from 5.2V to 6V when the circuit uses a 1k resistor for R4. If you used the original 4.7k for R4, its voltage will be a little lower. The U1 opamp doubles its voltage.

[Sallala]

Ok, I will unsoldier the potentiometers, and measure they.
My R4 is 1k, as according to the modified part list.

I promised the pcb plans.
Here they are:


My finished PCB's picture.


My modified soldier side plan


My modified pcb side


My finished circuit, and my transformator. This time, with only one power transistor.


My finished circuit, closer look.


PCB side, with the bypass capacitors for the OPAMP's. You can see, I use a shortcut for the powertransistor's emitter resistance. I will replace this with an 0,1 Ohm R, if I place a second 2n3055


The PCB plans are contain the "Q1's emitter" modification, and ready for bridge rectifier. They are draw for the BD139 transistors and ready for two 2n3055. Contain two fuse.

Sallala

[Spagbol]

What's the Q2 emitter modification you mention? I've skimmed this thread, maybe I missed something?

I've built the Op-amp bits with a pair of TL082s with their supply rail clamped at 22v by a zener. So far so good, but not sure how to change the output stage to give it some voltage gain?

Audioguru: thanks for the suggestion for temp sensing with a diode, will have a go at this once I get the PS working.