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0-30V Stabilized Power Supply


redwire
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Hi again.
I've just finished the PSu work and I got some problems. U3 gets instantly very very hot after i plug it in. Also The current control potentiometer acts like voltage regulator and it regulates between 15 and 38 V. I really need some help.

U3 has a load of only 3mA through R20. There is no current in D9. Therefore U3 will not get warm.
The current control normally reduces the output voltage when the output current exceeds its setting.
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Is normal to have 45V at the + and - of the bridge diode?  ???
LE:
I use 28V ac transformer.
If P2 shortcuts Pin3 of U3 with R18=U3 gets very hot;
if P2 shortcuts Pin3 of U3 with R17=U2 gets very hot, led also turns on;
I don't know too much electronics and I need someone to help me troubleshoot this power source. I've spent too many hours just to throw it away.  :-\

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Is normal to have 45V at the + and - of the bridge diode?  ???
LE:
I use 28V ac transformer.
If P2 shortcuts Pin3 of U3 with R18=U3 gets very hot;
if P2 shortcuts Pin3 of U3 with R17=U2 gets very hot, led also turns on;
I don't know too much electronics and I need someone to help me troubleshoot this power source. I've spent too many hours just to throw it away.

Your 28V AC transformer might produce 30VAC when it has low load current. 30V AC produces 42.4V peak. The rectifier bridge reduces it to 41.0VDC. Your 45V is a little too high but is OK for opamp U3 if the 10V zener diode that feeds it is not connected backwards. The cathode of the zener diode is marked with a black bar and must be connected to the positive supply. Then the positive supply pin 7 of the opamp will be +31V which is well below its maximum allowed voltage of 44V. Yours might be +35V which is also fine.

P2 is 10k, R18 is 33k and the current-calibration trimpot is about 45k. The trimpot connects to the output of U1 which is +11.2V. Then if P2 connects pin 3 input of U3 to R18 its voltage is only 11.2V x 10k/(33k + 45k)= 1.4V which is fine for U3. With a low load current on the project then the pin 2 input of U3 is 0V. Then the pin 3 input is higher than the pin 2 input so its output is high which turns off the LED and it does not limit the project's output current. U3 will be barely warm. If you are using the tiny surface-mount package then it will be obviously warm but not hot.

When P2 connects pin 3 input of U3 to R17 then its voltage is almost 0V which is fine. a load on the project that has a currernt higher than a few mA will cause the output of U3 to go low which causes 3mA in R20 which turns on the transistor driving the LED. The low at the output of U3 also causes D9 to reduce the voltage to the input pin 3 of U2 which reduces the output voltage of the project so that the output current is reduced. U3 gets a little warmer but not hot and U2 does not get hot unless the driver or output transistor is connected backwards (collector and emitter pins swapped).

You also had the output never less than 15V which might be caused by the driver or output transistor with its collector and emitter pins swapped. Then U2 and the driver transistor will get very hot. 

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  • 2 weeks later...

So i have build the power supply and i replaced sense resitor to 0.27E and i used three paralleled 2n3055 transistor with 0.33E emitor resistor.
I was thinking about max. current, how can i test this most easily??
Other component are unchanged against VER2 of circuit and REV3 of component!

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So i have build the power supply and i replaced sense resitor to 0.27E and i used three paralleled 2n3055 transistor with 0.33E emitor resistor.
I was thinking about max. current, how can i test this most easily??
Other component are unchanged against VER2 of circuit and REV3 of component!

You made the 5A version of the latest circuit. The transformer must be 28V at least 200VA and the heatsink for the output transistors must be huge and maybe have a cooling fan.

Most ordinary inexpensive multi-meters can accurately measure the load current.
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  • 3 weeks later...

I think a large knob should be used for adjusting the voltage so you can see where it is and adjust it fine or coarse.

If you add a fine adjustment pot in series with the coarse adjusting pot then one pot will frequently be at its end.


So i must insert 1k pot in series with existing trim pot and adjustale pin combine together??
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So i must insert 1k pot in series with existing trim pot and adjustale pin combine together??

No.
The trimpot is adjusted only one time for calibration. Adjust the trimpot for an output of exactly 30.0V with the coarse and fine pots set to maximum.
The 1k fine pot is connected in series with the coarse 10k voltage setting pot P1.
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Hi guys
I have trawled through the 123 pages about this project on the first listed subject, and then the 96 pages in this listed project, and I note some confusion and some frustration, so I have spent time trying to filter out a solution for the newcomers to get started and to have success - it's a great project.

Attached is the latest and most commonly used schematic and parts list from Audioguru (a real master!), but it is left up to the enthusiast to design a printed circuit board, and many of us do not have this desire or these skills.

Also attached is the circuit diagram and parts list from Picmaster (the circuits are the same but the part numbering is different!), which also includes a successful printed circuit board design for the 3A or 5A version.

Since I wanted the easy and quickest way forward I made the pcb using the 'laser print and Mommy's iron' method, and then I created a comparison list of how to progress from the Audioguru version to the Picmaster pcb.

I hope that this is helpful to anyone just starting.

Audioguru_schematic_and_parts_list.pdf

Picmaster_0_-_30V_3_-_5A_Power_Supply.pdf

Parts_comparison_0_-_30V_3_or_5A_Power_Supply.pdf

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I have onother question, i don't know exactly where is the negative power supply in the schematic of stabilized power supply?
Therefore which connection in circuit should i use to negative set voltage (oV to -30V)?


Can anyone help me about this??
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I have onother question, i don't know exactly where is the negative power supply in the schematic of stabilized power supply?
Therefore which connection in circuit should i use to negative set voltage (oV to -30V)?

Some of the circuit uses a -1.3V negative supply. It is made from a few parts.

The entire circuit can have an output of 0V to -30V if you connect its + and - outputs in reverse so that the +30V output is used as ground and the 0V output is used as 0V to -30V.

Many people have built two of this project so that the first one has a 0V to +30V output and the second one has a 0V to -30V output. Each project must have its own power transformer.
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  • 3 weeks later...

Can i replace MC34071 to AD711??? or TLE2141 to AD829???,, cause electronic stores here don't have those components.

I selected MC34071 or TLE2141 opamps because their inputs work at their negative supply voltage (0V here) and their outputs go down close to their negative supply voltage, and they are available almost everywhere.

The first opamp you guessed about will not work.
I didn't bother looking at the second opamp you guessed about.
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hi every one. i create the original version and work fine
but i have 2.5A at 30v when turn voltage volume under
7v current get to 1,5 A and overload protection
do not work
please help me
excuse me for poor english

The original version has many errors that cause it to be unreliable and not meet its specs.
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hi every one. i create the original version and work fine
but i have 2.5A at 30v when turn voltage volume under
7v current get to 1,5 A and overload protection
do not work
please help me
excuse me for poor english


Hi Ajax007, forget the original version. You should see the xristost's schematic the following link:
http://diyfan.blogspot.com.br/2012/02/adjustable-lab-power-supply.html
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thank you for reply

my circuit work fine only problem is current not constant. when current volume is max: 30v 3A (short circuit) when current volume ismax and voltage volume is 7v current :2A (short circuit)my transformer is 24v 3A

please help me i dont have new component to create new version .





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When the original circuit has a 24VAC/3A transformer then the transformer can supply 24V x 3A= 72VA. But 24V rectified produces 24V x 1.414V (-2V for the rectifier bridge) which is +32V.
But the circuit needs at least 40VDC instead of only 32V so the voltage from the original transformer is also too low. The transformer must be rated at 42V x 3A= 127VA.

The tiny old 2N2219 driver transistor gets too hot when the output voltage is low and the current is high. The improved circuit uses a modern power transistor with a real heatsink.
The single 2N3055 output transistor also gets too hot. The improved circuit uses two output transistors (with emitter resistors) to share the heat.

When your output is 7V at 2A then maybe the driver and/or output transistor gets too hot and fails. 

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2N2219 and 2n3055 temperature is normali test circuit this way:1-turn current and voltage(30v) volume max2-connect ammeter and read 3.2A3-turn voltage volume to 30 to 8v connect ammeter and read 3.2A4-turn voltage volume to 7v  connect ammeter and read 2.6A5-turn voltage volume to 3v  connect ammeter and read 1.5Ayou think transformer voltage is low i test 28v and i get same result

thank you











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With a +32VDC supply and a 3A load, the voltage across R7 reduces the output voltage 1.41V.
The maximum output of the TL081 opamp U2 is +29.1V but it could be as low as +27.6V.
The maximum output of the 2N2219 driver transistor Q2 is +28.1V but it could be as low as +26.3V.
The maximum output of the 2N3055 output transistor is +27.1V but it could be as low as +24.8V.

But the overloaded transformer probably cannot produce rectified 32VDC so the output voltage will probably be less and be unregulated with a lot of ripple. 

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