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0-30V Stabilized Power Supply


redwire
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the powersupply worked great right up until i hooked up my 18v dewalt drill test motor .....
now i get 34 volts through the output nothing less

Maybe the current regulation is not working and you overloaded this power supply circuit. Then the output transistors and/or driver transistor and/or opamp are shorted.

ive disconected the driver transister and output transistors and still get 34 volts at pin 6.

That is normal because you disconnected the negative feedback from the output to pin 2 so the voltage on pin 2 is much too low which causes the output pin 6 to go as high as it can.

in audiogurus version c9,c6,r12,r11are all that are connected to pin 6

R11 and R12 are a volage divider that divide the output voltage by about 2.68 times to feed negative feedback to pin 2. When pin 3 is +11.2V then the output of the project will be +30V and pin 2 will also be +11.2V.

Measure the output transistors and driver transistor with an ohm meter to see if they are shorted. If they are not shorted then connect them in the circuit and with the voltage setting pot at zero tell us the voltages at pin 2, pin 3 and pin 6 of the opamp and the voltage at the output of the project.
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alright it happened again i fried my driver chip right away now this is after i ran the supply with just a led as a load. i hooked up my ampmeter and and showed from voltages 0 to 30v, 0 to 93 millamps my current limiter was funtioning correctlly cause i was able to set my current at 20 millamps and my voltage would come up i cant remember but i think it was about 6 some volts and then it would go no higher unless i adjusted current limiter.  the light was working properly. everything was great until i hooked up my motor. it was only on ten sec or so i preset my voltage to 18v cause its a 18v motor. then i turned my current down to almost nothing. then hooked in the motor. nothing. so i turned up the current regulator and after so far the motor kicked in and almost immediattly bd139 started to smoke. the ampmeter read only 83 milliamps. but it almost seemed to me like it fried right away and was just running on 30v which is where my mains are at. im not sure it all happened so fast. i built this supply to operate this motor. i actually built 2 side by side one to run the pic chip and circutry. and one to power the motor that the pic controlls with pwm. i kept frying the motor controller chip L6203 when ever i stop the pic cycling which some times you cant stop the moter during testing so it may be running one direction then you stop the pic its outputs go 0v which 0v is a full speed reverse signal to the l6203 throwing the motor in full reverse next thing i know the l6203 is fried. so i wanted some current limiting thus this circuit. i believe this power supply should work for my prototype its just why does it fry bd139 thers no current  flowing here except for maybe through r16. in all fairness i should say i didnt put heat transfer compound under my chip to heatsink i planned to but i was only running it for a few seconds.

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Hi J Rhodes,
The BD139 powers the load if the two 2N3055 output transistors are shorted, are wired wrong or their 0.33 ohm emitter resistors have a value much too high. Then it will burn.
If the 2N3055 output transistors have minimum gain then the max current in the BD139 is 75mA and is 38mA when the 2N3055 transistors have typical gain. Then when the output voltage is 18V the BD139 has about 22V across it then it dissipates 38mA x 22V= 0.8W to 75mA x 22V= 1.7W which is not much. With a little heatsink it will be fine but without a heatsink its junction will be above its allowed max temperature.

Maybe the BD139 is failing because the motor produces an inductive voltage spike each time the PWM turns it off unless it has a fast free-wheeling diode connected to it.

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i guess its the same..
because they have same ...4071..
therefore CD4071 can be substituted to MC34071..

No.
They are completely different. Why don't you look at their datasheets?
The CD4071 is a Cmos digital quad 2-input OR gate. It has 14 pins.
An MC34071 is a single linear bipolar opamp with some special features that ordinary opamps do not have. It has 8 pins.

A TLE2141 is also an opamp with the same special features as an MC34071. 
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ok.. how about this?

MC33071/72/74, MC34071/72/74. Are they all the same?

Their datasheet show that thew xxxxx1 is a single opamp, the xxxxx2 is a dual opamp and the xxxxx4 is a quad opamp.
The datasdheet shows that the MC33xxxx has a very wide spec'd ambient temperature range for NASA but the MC34xxxxx has a tempreature range that is reasonable on earth. Guess why the MC33xxxx costs much more?

i cant find a 12000uF 63V.. can i just put a 10000uF+1000uF+1000uF in a parallel as substitution?

It is a simple filter so 10,000uF in parallel with one 2200uf or 3300uf capacitor is good. You can use one 15,000uF capacitor or 10,000uF plus two 1000uF capacitors to make 12,000uF if you want.
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Can I use MC33171? It's slower (1.8MHz, 2.1V/uS) and has less Capacitance Drive Capability (500pF).

The MC33171 is low power so its idling power supply current is 1/9th the current of an MC34071 (I use them in low power battery-powered circuits) and its output high current is too low for this project at 1/9th as much as from an MC34071.
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audioguru, you can tell me what the special features mc34071 have?

I noticed that when the current control operates (at minimum), still have 0.7 volts in the input of oamp (due to the diode), multiplying by the gain, we have ~ 1.8 V, so in case of short-circuit 0.6A pass because of the output resistor of the 2n3055. is there any way to reduce it?

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audioguru, you can tell me what the special features mc34071 have?

Unlike most opamps, the MC34071 and the TLE2141 have inputs that work as low as the negative supply which can be ground in some circuits. So U1 and U2 do not use a negaive supply and the negative supply for U3 is only -1.3V.
Their max allowed supply is 44V.

I noticed that when the current control operates (at minimum), still have 0.7 volts in the input of oamp (due to the diode), multiplying by the gain, we have ~ 1.8 V, so in case of short-circuit 0.6A pass because of the output resistor of the 2n3055. is there any way to reduce it?

No.
When the current control is set to maximum then 3A flows through R7 which is 0.47 ohms so it has a voltage of 1.41V across it which is one input to U3. The other input to U3 is a voltage from the current-setting pot. If more than 3A tries to flow then U3 reduces its output voltage which reduces the output voltage of the project until exactly 3A flows. If the output is shorted then the output is reduced to 0V with 3A flowing.

When the current control is set to minimum then only the idle current of the U1 (a few milliamps) and the low current of the feedback for U2 flows in the output of the project.
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I used the UA741. With the tension he'd never zero, so I put a third diode to the negative input is -2.1 V and also linked to the negative pin of u2, This worked perfectly for the tension, but not to the current, I was wondering if u3 can put a negative output? let say -0.7 V? this could solve the problem I think.

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The uA741C opamp is 43 years old. Its max supply is only 36V but the supply for U1 and U2 in this fixed project is 40VDC when it has no load and is higher if the mains voltage is a little high so it will fail soon. Its inputs must be 3V above its negative supply so your -2.7V negative supply is too low. The output of U2 must go down to about 1V but the 741 opamp cannot. It is much too slow which results in undershoots and overshoots when the load current quickly changes.

If you used an MC34071 or TLE2141 opamp for U3 then with a -1.3V negative supply its output can go as low as -0.9V to -1V to make the output voltage exactly zero. Your old 741 opamp cannot do that even when its negative supply is -2.8V.

Every opamp is different. Maybe you are lucky to find an old 741 opamp that works with your changes. But I design circuits that work properly with any passing opamp. 

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I have two working PCBs for the PSU. Now I'm trying to make LCDs which will display the voltage and the current. I'm going to use Arduino for measurment and voltage deviders. My question is, could I use only one Arduino board to measure voltage and current from both PCBs (because of the common ground, which I should use for the Arduino board)?

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Could one of the smarties here point me to the page in this thread that has a final working version of this power supply? Could this final version be made into a sticky so the less electronically endowed of us don't have to wade through 78 possibly problem-filled pages to get to the bits that are accurate and valid?

This looks like a great project. Thanks.

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