0-30V Stabilized Power Supply

[WinDTrek]

WinDTrek, everything else you made as in the original circuit, or something changed?
Have you used a resistor with C7?

I did follow redwire's schematic and part list in page 1 of this thread.
No I did not use any resistor with C7.

 

[Kevin Weddle]

WinDTrek, you are on loose ground.

 

[audioguru2]

Hello, could you help me. What do you think about this PCB design?

The traces that carry high currents should be much wider.

 

[audioguru2]

Please, could you draw in red color on original circuit image, what traces must be thicker? Thank you.

Don't you know which parts of the circuit carry high currents?
I am interested in circuit design, not pcb design. I design a circuit then send the schematic to a company that does the pcb design.

 

[gsengul1]

what will happen we use tl081 instead of mc34071 or tle2141 with a low AC input such as 15Vac? thanks in advance

 

[audioguru2]

what will happen we use tl081 instead of mc34071 or tle2141 with a low AC input such as 15Vac?

When rectified and filtered, 15VAC makes about 19VDC. The entire circuit will be starved for current unless the values of many resistors are reduced. The maximum output voltage from the project will be about 12V to 14V.

The old TL081 has a problem called "Opamp Phase Inversion" which was stopped with transistor Q1 in the original circuit. Without the transistor then the output of opamp U2 and the output of the entire circuit goes as high as it can for a few seconds when the power is turned off.

Another problem with the TL081 is that it needs a negative supply of about -5.6V. The MC34071 and TLE2141 do not need a negative supply.View attachment 41942

 

[Guber1]

hi, I'm modifying mi original circuit to adapt it to the last revision, now when i connect the board i get 37,5 V at the output and the pots don't modify this value, i have observed that the U2 circuit is getting to hot very fast then i have checked all the conections and it seems to be ok, i have also measured the tension on U2 and between V- and V+ there is 31 V on the input there is 12V (between IN- and IN+) and i don't know is that values are correct.

Thanks

Edit: I'm using TLE2141

 

[audioguru2]

hi, I'm modifying mi original circuit to adapt it to the last revision, now when i connect the board i get 37,5 V at the output and the pots don't modify this value, i have observed that the U2 circuit is getting to hot very fast then i have checked all the conections and it seems to be ok, i have also measured the tension on U2 and between V- and V+ there is 31 V on the input there is 12V (between IN- and IN+) and i don't know is that values are correct.

If you connected the pins on the driver or output transistors backwards or if they are shorted then you will have your problems.
The driver and output transistors are emitter-followers. Their emitter voltage should be 0.6V to 1V less than their base voltage.

The (-) input and (+) input of a linear opamp amplifier (U2) should always have the same voltage because its open-loop voltage gain is 200,000 times or more.

When the (+) input of U2 is 0V from the voltage-setting pot then negative feedback through R11 and R12 causes the (-) input to also be 0V. Then the opamp turns off the driver and output transistors so that the output voltage of the project is 0V.

When the (+) input of U2 is +5V then the negative feedback causes the (-) input to also be +5V and the voltage gain of 2.68 causes the output voltage of the project to be +13.4V.

Your U2 might be destroyed by the excessive heat. 

 

[Guber1]

Hi,
I've checked the circuit again after your advice and I realized that the BD139 wasn't connected right because in this device the Base pin is in the middle.... , now i have fix this but i still having the same problem, the circuit had been turned on for lees than 30 sec then i don't think the tle2141 could be burned, i just turn it on take a measure and turn it off again, i have also realized that the BD139 have only a 1,2 Ohm between Emitter and Colector i don't know is this is normal in this device or because of the bad connection it may be broken.

Thanks.

 

[audioguru2]

The resistance between the collector and emitter of an unpowered transistor should be so high (tens of Megohms) that it might not be measurable. Your BD139 is shorted.

It takes one second or less to blow up an opamp that is driving a short circuit.

 

[Guber1]

Hi,
after a hundred of tests i finally have found the guilty, one of the 2n3055 was shorted i have tested without it and it works!!!, this was driving me crazy...

Thanks a lot.

 

[Guber1]

Hi again,

Now i realized that is not working at all because of the pot P2 is not limiting the current, it doesn't matter if i increase his value or not

 

[audioguru2]

The pot P2 does not limit the current. Opamp U3 regulates the current determined by the voltage set by pot P2 and the current sensed in R7. If Diode D9 is backwards or is burnt out then the current regulation will not work.

The LED should light to warn that current regulation is reducing the output voltage.

 

[Guber1]

Ok, then it`s working rigth but I have a doubt, I have using PSUs and all of them have the possibility to limit the output current shorting the PSU and then selecting the max current, is it possible to do something like that here?

 

[audioguru2]

Yes you can short the output then set the maximum current to anything from a few mA to 3.0A.
But most people calibrate 3.0A max then mark a dial around the knob on P2 with current settings.

 

[Guber1]

Hi, reading your message again i realized that i misunderstood you, P2 don't limit the current but is used to adjust this limit, i have checked that when i shorted the output the led turn on but the current isn't limited by anything, if i measured the current sense in R7 it reach 8A i think that U3 is not working right.

 

[audioguru2]

Guber,
The (+) input of U3 has a voltage divider including P2 from the reference voltage of 11.2V.
The (-) input of U3 has the voltage across R7 created by the output current.

When the voltage on the (-) input exceeds the voltage on the (+) input then the output of U3 goes low enough to reduce the output voltage through D9 then the output current is also reduced.
When the output of U3 goes low then it turns on Q3 which lights the LED. Your LED turns on so U3 is working correctly.
Maybe your D9 is burnt open or is connected backwards.

 

[Guber1]

Hi, I see U3 is working as comparator between the voltage set by P2 and R7, I have checked D9 and seems to be broken I have replaced it but I still have the same problem, I set P2 to a very low voltage then I connect some LEDs to the output and the indicator of current limit turn on but the current is not limited....

 

[Kevin Weddle]

The voltages and currents aren't what they should be then. You can make a cheap power supply. This is a 30V stabilized power supply. Either the pot or the transistors used are now of out of specification.

 

[Guber1]

hi, i have been studying the circuit and i see that the voltage at the input of U2 must be the 11,2 established by the zener diode and when U3 is turned on because of the Voltage set by P2 is greater than the one in R7 D9 must be open, but this happen is the Voltage in cathode is greater than the Voltage in anode less 1V, I mean, Voltage in D9 have be minor than 1V, then the Voltage in the output of U3 must be greater than 10,2V when is turned on, isn't it?

Edit: of course when P1 is at his Maximum Value.