0-30 Vdc Stabilized Power Supply

[tjille]

Very helpful information, thanks! Will try this.

 

[srecenvid]

hey. i have a problem. i built now 5A power supply, it was working great, until i did not try today it with 48v power transformer. now i have constant 35v voltage, also cant adjust it. anyone have idea what can be wrong?

 

[audioguru2]

hey. i have a problem. i built now 5A power supply, it was working great, until i did not try today it with 48v power transformer. now i have constant 35v voltage, also cant adjust it. anyone have idea what can be wrong?

The MC34071 or TLE2141 opamps operate near their maximum allowed supply voltage (44V) with a transformer that is 30VAC. A 48V transmormer voltage is much too high so the opamps are probably blown up. The transistors also might be blown up. Resistors and capacitors too?

Why did you try the transformer that has a voltage much too high? Using a stick of dynamite would be quicker.

 

[srecenvid]

hey. yeah it was mistake XD actualy i thought its also 30V power transformer. anyway it was not much wrong, only one mc34071 was blown up and 10A trimpot+potentiometer. after changing this enverything work great . i am doing now also ammeter/voltmeter lcd panel... do i post some pictures or project files? thanks for help.


u know maybe if someone tried to do 10A version? or does it need other power transformer (toroidal transformer)?

 

[audioguru2]

u know maybe if someone tried to do 10A version? or does it need other power transformer (toroidal transformer)?

If the output voltage is set low, the load is shorted or draws 10A and the current-setting pot is set to 10A then the output transistors (six of them) will dissipate a total of 390W. How will you cool them?

The driver transistor cannot drive six output transistors so it must be made stronger and opamp u2 will not be able to drive the driver transistor.
The 30VAC transformer must be 424VA which will be enormous, custom made and very expensive.
R7 must also be huge.
It will not be practical. 

 

[mizikono]

Greetings

Created by I will supply the power. I am curious if the components are written on the connection (link), okay, or which is necessary to change the other values

http://www.electronics-lab.com/projects/power/001/index.html

what transformer would be needed for good performance?
220/24V 100VA ali 120VA

 

[audioguru2]

The original project is an old piece of garbage with many errors. It does not produce 30VDC at 3A and is not reliable.
That is why I fixed it. We talk about the latest fixed version on this and on another thread here. Look through this or the other thread to find the latest parts list (Rev 3) and schematic Rev 2, Mar 11/09).

1) The original project used a 24VAC transformer so its max output was about only 25VDC at 3A (not 30V).
Even with a transformer with a voltage too low, the opamps it used have a supply voltage that was much too high for them.

2) The transformer, driver transistor, output transistor, rectifier diodes and many resistors are overloaded and will fail soon.

Therefore the original circuit does not work properly and is not reliable.

 

[srecenvid]

Thanks audioguru.

I have 500 and 1000VA transformer 24V in my small lab and i can try to do also 10A version.

About heat and transistors i have really big cooler with water cooling, so that wont be problem probably, now i have only found enough big resistor for this...will check tomorrow my inventory and see what i have.

about driver transistor i was thinking maybe i can try and use 2 drive transistors and opams, but that will change scheme alot? or is that stupid thinking? or you maybe help me find enough big opamp and driver transistor... anyway good night, i am ready for experiment , will check all needed parts tomorrow and see if it is even possible

 

[audioguru2]

I have 500 and 1000VA transformer 24V in my small lab and i can try to do also 10A version.

A 24VAC transformer voltage is too low.

About heat and transistors i have really big cooler with water cooling, so that wont be problem

I guess some people have liquid nitrogen.

about driver transistor i was thinking maybe i can try and use 2 drive transistors and opams, but that will change scheme alot?

 

[Sparkington]

Ok Im trying to fix my project using the following info.

    Received the following email from Ivan on 02/2010:

    Ok. I bulid your project about a day ago. Mounted all the parts on the pcb and then concluded that there is some serious problems in this schematics. First, 2N3055 will overheat, so you have to connect two of them in parallel with emitter resistors 0.1ohm/5w. Second, maximal voltage between '+' and '-' of TL081 is 36VDC.If you connect them as it is shown in this circuit diagram that voltage will be about 45VDC, so they will burn down immediately. To fix this problem you have to reconnect all pins number 7 of U1, U2 and U3, emitter of Q3 and 'upper' end of R19 to out of an 7809 with 18V zener diode between 'common' pin and '-' of 3300uF cap, and input of 7809 connect to '+' of the same cap. Now, on pin number 7 and mentioned parts you'll have 27VDC, and total voltage will be 32.6VDC. Third, instead of using 3300uF, use 4700 or 6800uF/63VDC to reduce the ripple on higher currents (2-3A). The rest of the circuit is perfect. I like it cause it is so inexpensive and easy to make with those simple reconstructions i mentioned.

I was wonder if I insert the LM7809 into the circuit properly, I dont really understand words sometimes, and if i got it wrong I was wondering you could supply the correct schematic.  I cant buy any other IC listed in fixes expect a MC34072DG and know it wrong IC but it all I got :/

 

[audioguru2]

Sparkington,
You forgot to connect the driver and output transistors to the power supply (the input of the 7809 regulator).

Ivan used the original circuit and most of its parts then added a 7809 regulator and an 18V zener diode so that the maximum unregulated supply voltage to the opamps is only (+27V plus the -5.6V negative supply=) 32.6V then the original opamps rated at 36V maximum can survive.
But then since the positive unregulated supply is 27V then the maximum output voltage from the project at 3A is only about 20VDC, not 30VDC.

An MC34072 is two MC34071 opamps in one case. The surface-mount package might get too hot because it is very small.

 

[Sparkington]

Thank you for the quick reponse, I will remake the PCB and start again. I will use the upgraded parts on the rest circuit describe by one of your early post. 0-20V will get me out trouble for now, I will upgrade transformer to a 30V 3A later on. Time to go to the local electronic store by more parts lol

 

[peckcj]

I've built my PSU and everything works as expected  ;D .  My only issue is as follows...

I have 2 LED panel meters that I will be using for voltage and current displays.  They are both PM129B units (http://www.circuitspecialists.com/images/PM129A&B.pdf).

I got the voltage meter to work fine, but the current meter is giving me a headache.  I am using R7 as the shunt resistor, and since I built the 5 amp version, that resistor is valued at .27 ohm.  When I connect the meter across R7, I get high reads...750-1200mV when I have a loading resistor drawing .5 amps.  The meter is set at the 200mA range.

Should I add another shunt resistor into the scheme that is better suited for this 200mA meter?  I was thinking .40 ohms.

 

[audioguru2]

..... the current meter is giving me a headache.  I am using R7 as the shunt resistor, and since I built the 5 amp version, that resistor is valued at .27 ohm.  When I connect the meter across R7, I get high reads...750-1200mV when I have a loading resistor drawing .5 amps.  The meter is set at the 200mA range.

The meter is a voltmeter so it does not have mA ranges.
If it is set for the 200mV range then it will read 200mV which is too low when a current of (200mV/0.27 ohms)= 0.74A. when the current is 5A then it will try to read over-range at (5A x 0.27 ohms)= 1350mV.
If it is set to 20V range then when the current is 5A it will read (5A x 0.27 ohms)= 1.35 which is too low.

Set it to the 20V range and add a multi-turn cermet 500k calibration trimpot in series with its RA. Adjust the trimpot so that its reading is accurate.

It might need its power supply 0V connected to the power supply 0V, not the output 0V. 

 

[peckcj]

The meter is a voltmeter so it does not have mA ranges.

Yes....my mistake  :-[

Thank you

It might need its power supply 0V connected to the power supply 0V, not the output 0V. 

Could you elaborate on this please?  What is the difference between the output 0V and the PS 0V?

 

[audioguru2]

R7 connects between the power supply 0V and the output 0V.
The output 0V becomes a positive current-sense voltage when there is load current.

 

[peckcj]

Thank you, I'll try that.

Also, my C1 capacitor is a 20,000 mF 63V electrolytic that is holding a charge after I power down, so I need to add a bleeder resistor across the terminals.

Do you have a recommendation on the size of resistor?

 

[audioguru2]

C1 already has a bleeder resistor, R1. It is 2200 ohms so it will take about 3.7 minutes to discharge your capacitor but the electronics will also discharge it so maybe in 1 minute.

 

[peckcj]

Thank you.

Would you have any recommendations on how to deplete that standing voltage faster without having to change my C1 type?

 

[audioguru2]

I don't know why you want to reduce the output voltage when the circuit is turned off.
C1 holds a large charge to reduce ripple in the output.

Maybe a second contact on the on-off switch can discharge it quickly through a low value resistor.