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0-30V Stabilized Power Supply

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audioguru

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Re: 0-30V Stabilized Power Supply
« Reply #1484 on: April 04, 2013, 07:33:21 AM »
Hello,I have checked the circuit with and without ground the 28VAC power source but it  gives the same results so ground does not makes any difference.
It makes a HUGE difference.
Without the ground at the 28VAC then the full-wave rectifier works properly and the negative supply works properly.
With the ground then the rectifier is half-wave and the negative supply does not work.

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External Negative 1.3V supply is necessary for U3? If it is necessary so  Why it is?
Yes it is necessary for the U3 current regulator to cause the output voltage to go to zero volts when the current is high and the output is shorted. For the output to be zero volts then the output of U3 must go a diode drop (D9) negative.
Without the negative supply, when the output is shorted then there is nothing to limit the current and many parts will burn.

Remove the ground at the 28VAC and remove the 1.3V battery.

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What is the modern model of TLE2141?
Texas Instruments make the TLE2141. Get the simulation model of it from them.

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Which software is better for the simulation of this circuit?
I haver never simulated this project. If I did then I would use the LTspiceIV program that is free from Linear Technology and Yahoo has a user group that provides help and models.

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Re: 0-30V Stabilized Power Supply
« Reply #1484 on: April 04, 2013, 07:33:21 AM »

sobol

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Re: 0-30V Stabilized Power Supply
« Reply #1485 on: April 09, 2013, 03:50:07 PM »
So, I have built that power supply, but after test run i've found what follows:

P1 (voltage control pot) - without a load on the output i've got 7mV to 5V, and at maximum pot position current limiting turns on (while P2 is on the maximum, while less, current limiting is constantly turned on and output voltage is about -200mV).
U1 gets too hot in my opinion - after 10 minutes of test run it was about 80-90 celsius degrees.

Any ideas what could be wrong?

audioguru

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Re: 0-30V Stabilized Power Supply
« Reply #1486 on: April 09, 2013, 04:36:15 PM »
So, I have built that power supply
Which version? The original, a modified one or the latest modification?
Which transformer? 24VAC, 28VAC or 30VAC?
Which opamps? TL081, MC34071 or TLE2141?

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P1 (voltage control pot) - without a load on the output i've got 7mV to 5V
The output should be able to go from calibrated 0V to calibrated 30.0V.
Measure the output voltage of U1. It should be about 11.2V. The output amplifier has a calibrated gain of 2.68 times to make the output 30.0V max.

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at maximum voltage pot position, current limiting turns on (while P2 is on the maximum, while less, current limiting is constantly turned on and output voltage is about -200mV).
Your current regulator U3 is not working correctly. Its output should be high (so that D9 cannot reduce the output voltage and does not turn on the LED) until the load current in R7 causes as voltage drop that is more than the amount of voltage set by P2. 

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U1 gets too hot in my opinion - after 10 minutes of test run it was about 80-90 celsius degrees.
If you used DIP 14 pins case opamps then their maximum allowed dissipation is 1000mW when the anbient is 25 degrees C.
The MC34071 will dissipate a maximum of 302mW and the TLE2141 will dissipate a max of 470mW. Not too hot.

sobol

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Re: 0-30V Stabilized Power Supply
« Reply #1487 on: April 09, 2013, 04:56:10 PM »
Which version? The original, a modified one or the latest modification?
Which transformer? 24VAC, 28VAC or 30VAC?
Which opamps? TL081, MC34071 or TLE2141?

Version from the first post (latest i believe), 28VAC transformer, TLE2141 opamps.

The output should be able to go from calibrated 0V to calibrated 30.0V.
Measure the output voltage of U1. It should be about 11.2V. The output amplifier has a calibrated gain of 2.68 times to make the output 30.0V max.
I'll check it tomorrow and i'll post measurements.

Your current regulator U3 is not working correctly. Its output should be high (so that D9 cannot reduce the output voltage and does not turn on the LED) until the load current in R7 causes as voltage drop that is more than the amount of voltage set by P2. 

I'll focus on the U3 neighbourhood, maybe I will find a mistake.

If you used DIP 14 pins case opamps then their maximum allowed dissipation is 1000mW when the anbient is 25 degrees C.
The MC34071 will dissipate a maximum of 302mW and the TLE2141 will dissipate a max of 470mW. Not too hot.

If its ok, i'm ok too. : D

audioguru

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Re: 0-30V Stabilized Power Supply
« Reply #1488 on: April 09, 2013, 05:35:34 PM »
If you made the circuit on a solderless breadboard then the opamps are probably oscillating which makes them maqlfunction and get hot.

sobol

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Re: 0-30V Stabilized Power Supply
« Reply #1489 on: April 10, 2013, 02:57:46 PM »
Power supply is soldered on normal PCB.
OK, I've made some measurements, look at the result:

U1 pin 6 (output) - 11.2V.
U3 pin 3 - varies from 0 to 1.3V, depends on P2 position.
10V zener diode works properly, there is 29V on emitter of Q3 while current limiter works, and 29V on pin 7 of U3.
U3 pin 6 - 29V while current limiting off, -1V while current limiting on.

And still power supply does not work properly. Any ideas? Can't see any bad soldering or something like that.

audioguru

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Re: 0-30V Stabilized Power Supply
« Reply #1490 on: April 10, 2013, 06:49:40 PM »
R7 is 0.47 0hms and is in series with the load. Load current causes a voltage drop across R7. 3A x 0.47 ohms= 1.41V. With a low load current then the voltage across R7 is very low.
The voltage across R7 is fed to pin 2 input of U3.

U3 is used as a comparator. Normally its output is high so the LED is turned off and D9 does not reduce the output voltage.
When the voltage across R7 exceeds the voltage of P2 then the output of U3 goes low enough to reduce the output voltage so that the load current is reduced to the setting of P2.

Your U3 is not detecting the voltage across R7, it acts like an on-off switch. Maybe R7 is the wrong value or is connected wrong.

What is the part number of your opamps?

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Re: 0-30V Stabilized Power Supply
« Reply #1491 on: April 11, 2013, 05:51:53 AM »
Hi, does the wires to mounted out of PCB potentiometers P1 and P2 should be rated for high current? Or those can be thin wires.

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Re: 0-30V Stabilized Power Supply
« Reply #1492 on: April 11, 2013, 08:29:06 AM »
The current in the pots is very low so thin wires can be used.

sobol

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Re: 0-30V Stabilized Power Supply
« Reply #1493 on: April 11, 2013, 08:52:14 AM »
R7 is 0.47 0hms and is in series with the load. Load current causes a voltage drop across R7. 3A x 0.47 ohms= 1.41V. With a low load current then the voltage across R7 is very low.
The voltage across R7 is fed to pin 2 input of U3.

U3 is used as a comparator. Normally its output is high so the LED is turned off and D9 does not reduce the output voltage.
When the voltage across R7 exceeds the voltage of P2 then the output of U3 goes low enough to reduce the output voltage so that the load current is reduced to the setting of P2.

Your U3 is not detecting the voltage across R7, it acts like an on-off switch. Maybe R7 is the wrong value or is connected wrong.

What is the part number of your opamps?

TLE2141IP opamps.

So...
R7 looks good to me, its 0,47ohm, 10W resistor, connected from the GND "cross" on the pcb to the output GND pad.
I've checked this U3 and it works in weird way. As i wrote before, voltage on the 3rd pin of U3 changes from 0 to 1,3V depending on P2 position. BUT on the 2nd pin of U3 is 20mV to 30mV (depends on P1 position), and at 30mV current limiting turns on(while P2 sets 1,3V on pin 3). That 2nd pin voltage was measured between "Cross" ground and 2nd pin. It should work as comparator, but it's not, and I don't have any idea why.

sobol

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Re: 0-30V Stabilized Power Supply
« Reply #1494 on: April 12, 2013, 03:07:57 PM »
Does someone have any ideas what's wrong with my circuit?

KevinIV

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Re: 0-30V Stabilized Power Supply
« Reply #1495 on: April 12, 2013, 11:38:50 PM »
Are there still problems with this general purpose power supply. Give some better designs or a link to better ones.

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Re: 0-30V Stabilized Power Supply
« Reply #1496 on: April 13, 2013, 01:22:36 PM »
Hi, is there any place in the circuit of this project, where safely, without any harmful consequencies or bad interference to other parts of the circuit, could be added additional LED diode, which should be on all the time, when the power supply is on? Thanks.

audioguru

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Re: 0-30V Stabilized Power Supply
« Reply #1497 on: April 13, 2013, 02:08:40 PM »
Does someone have any ideas what's wrong with my circuit?
Since your U3 opamp does not perform correctly as a comparator then replace it.

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Re: 0-30V Stabilized Power Supply
« Reply #1497 on: April 13, 2013, 02:08:40 PM »