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0-30V Stabilized Power Supply


redwire
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I found a lot of projects using LM317 but I didn't find a good one.

The LM317 reduces its max output current to only 150mA when its input to output voltage is high.
An LM317 does not have adjustable current regulation. Instead it has simple abrupt current limiting at 1.5A to 2.2A when the input to output voltage is 15V or less.
An LM317's output does not go down to zero volts without an additional negative 1.2V regulated supply.
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Hello

I'am french and i speak a basic english
I have a problem with my 0-30V Stabilized Power Supply.
The problem appeared when i use this power supply for charging lipo battery
The problem is a voltage variation is between Approximately 10V to 33V and the intensity variation is broken.
Have you got ideas of my problem?

Florent

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Hi everyone, I finished building this power supply with the three 2N3055 transistors version, but I couldn`t find 0,27/10W ohm resistor for R7 only 0,22 ohm but it works really nice, I measured the output current in short circuit it is adjustable from 0 to 11,38A  ;D, but with the current setting trimmer it can be calibrated to a smaller output current, the minimum output voltage is about 50mV cannot be adjusted with RV1 not even if I replaced C7 with a tantalum capacitor. I had the same problem as some other guys, when the current limit pot. is turned to min. the current limit led lights up,  I thougth if U3 is a comaparator on U3 pin 3 is the reference voltage for the current control, on pin 2 the voltage without a load was 10.6 mV, and when the current control pot. is at min. on U3 pin 3, I had 8.4 mV (the compared value was bigger than the reference value)  from this voltage difference the led was lighting up, so I replaced the 33ohm R17 to 100ohm  ;D (I don`t think I have to change anything else, correct me if I am wrong) so in this case the voltage on U3 pin 3 with the current set. pot. at min. is 11.4 mV finaly the led does not light up when the current set. pot. is at min. :), but in my case from the voltage difference between pin 2 and 3 on U3 the minimum adjustable current is about 4 mA, which I don`t mind. I designed a board in eagle and I would like to make a 7 segment volt and ampere meter using PIC, I`ll upload some pictures of my project soon...

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Hi Nemeszoli,
How can pin 2 of U3 have a voltage when there is no load on the project? Pin 2 is connected to 0V by R7 that has no current in it. Maybe you have leakage current in your 0V printed wire.

If C7 has "dielectric absorption" then there will be an output voltage when the voltage pot is at minimum. The capacitor type with the lowest dielectric absortion is a metallized plastic film type.

Which opamps did you use? 

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Hi

The control voltage on output of U2 is OK but the current control is not ok.
Have you got an idea of my problem?

Florent

What is the problem?
The output voltage is supposed to be regulated when the current regulation is not reducing the output voltage.
Does the warning LED for the current regulator light up when there is no load?
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Hi audioguru,
              I used TLE2141 opamps ordered from farnel.com. Without a load, on R7 I have 2,2mV,
wich means about 10mA passing trough it, I think this is normal because the current supplying U1 is
passing trough R7 and 0V wire. I tried taking out U1 from the circuit, in this way there vas no voltage on
R7 so I think, with this design it is normal to have some current on the 0V wire

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Hy, I made some measurements on my power supply but unfortuneatly I saw that I have a ripple of about 0,8V  ??? at 6A tested with a load of 1.5ohms. I have a transformer with 26V output, I would like to have on the power supplys output at least 24V without ripple I tried also using a 22000uF capacitor but the result was the same as with a 10000uF one

post-55581-14279144254257_thumb.jpg

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Ripple on a power supply is in triangular waves with a quick charge then a slower discharge.
Yours has square-waves maybe from an overloaded transformer or from transformer current in the amplifier circuit or from pickup if the transformer or rectifier is near a sensitive amplifier part.

With an output of 6A then the average transformer current is 8.5A because the rectifiers conduct for only a small portion of the waveform. 

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Hy, I don`t realy understand why but, by changing the place where the 22000uF C1 capacitor is connected my power supply seems to be working now.  I designed a connector for C1 wich was connected on, and in my earlier post I attached a picture of the output voltage form (square wave), now I connected C1 directly on the wires connecting the rectifier (black and red on the picture) and this way the output voltage looks nice, the triangle wave is the voltage on C1, but it doesn`t  seem to influente the output voltage. I gues the problem should be in my PCB design

post-55581-14279144256279_thumb.jpg

post-55581-14279144256998_thumb.png

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Hello everyone. I am looking at building this power supply for a specific use which requires 0-20 volts and typically up to 2 amps, so my question is can I save some money and take some weight off by stepping down the transformer just a bit? Would a 24v 3.3 amp such as the Hammond 185E24 work if I never need to exceed 20 volts?

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Hello everyone. I am looking at building this power supply for a specific use which requires 0-20 volts and typically up to 2 amps, so my question is can I save some money and take some weight off by stepping down the transformer just a bit? Would a 24v 3.3 amp such as the Hammond 185E24 work if I never need to exceed 20 volts?

The original circuit uses many old and parts too small that overheat then the circuit does not make 30VDC at 3A.
The improved circuit will probably work well with a little 24V/3.3A transformer then its max output might be 24VDC at 2.3A.
You should adjust the calibration so that when the voltage pot is at max then the voltage is almost at max.
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Thank you for the feedback audioguru. I am using what appears to be the latest revision you have made with the MC34071/TLE2141 opamps with the parts list using red text to indicate the part changes, I've attached them below to verify they are the correct revision. So if I use a 24v 3.3A transformer and set the voltage pot to my 20v max needs I would not need to make any further changes as far as parts go correct? But could I feasibly reduce the C1 capacitor to less than 12,000uf? Also I'm pretty sure its safe, but using 1/2 watt resistors in place of 1/4 watt would be fine in this circuit as in most, correct?

Thanks for your help

post-57673-14279144257824_thumb.png

post-57673-14279144258081_thumb.gif

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I haven't seen a 1/2W resistor for about 45 years.  If yours are that old then they probably have their values changed.

Hmm... the parts list calls for a 1/2W resistor on D3 (220 ohm). I'm looking at all new parts from Newark, it's just that some values for resistors have a better selection in 500mW or are actually cheaper than 250mW.

Also I noticed the schematic and parts list don't quite agree on the Zener and LED, the parts list calls D12 the Zener and LED1 as the LED, but on the schematic D12 appears to be the LED and the Zener is unmarked? I assume its just the labeling and the schematic placement is correct?
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Am I correct in thinking that if this power supply is turned on even with no load, or a very light load the power transistors will actually be hotter than running at higher output voltages correct? Say if it were at 5 volts of output they would have to burn off more than if they were cranked up to get rid of the difference between their input from the transformer and the output load correct?

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Heating in the output transistors, the driver transistor Q2, bridge rectifier and R7 is caused by the voltage across them times the current through them. If there is no load current then there is no heating in these devices. The most heating is produced when the current is the highest (3A) and the output voltage is low or is shorted. The the output transistors have 35.7V across them x 3A= 107.1W. The driver transistor Q2 has 34.7V across it x as much current as 75mA= 2.6W. The bridge rectifier heats with about 2V x 3A= 6W. R7 heats with 3A squared x 0.47 ohms= 4.23W.

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Starting to make more sense now. Now if the intended load will be typically run at 4-12 volts 50% duty cycle (electromagnetic machine), never exceeding 18v then would it make sense to further step the transformer down to 18v 4a? The load shouldn't exceed 1 amp, 2 at the most. Would 18v with at least 10,000 uf C1 keep the remainder of the circuit functioning properly?

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An 18V transformer produces a rectified and filtered full current voltage of 23.4V but with a couple of volts of ripple so the troughs of the ripple are at 22.4VDC.
The output transistors, their emitter resistors, the driver transistor Q2, the opamp U2, the bridge rectifier and the current sensing resistor R7 need a total of about 5V so for an output of 18VDC the unregulated positive supply must be at least 23VDC and the transformer must be a little higher than 18VAC.

A 4A transformer with a load of only 2A has an output voltage a little higher than its voltage rating so your transformer might or might not work. I would use a 20VAC transformer.   

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