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0-30 Vdc Stabilized Power Supply


Sallala
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  • 6 months later...

The TL081 opamp used for U2 in the original project has a problem called "Opamp Phase Inversion". If its input went too close to its negative power supply voltage (within about 3V) then its output suddenly goes high.

The new opamps do not have the phase inversion problem so Q1 is not needed.


Audioguru, thank you for your prompt response. I
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Hi I am in need of your help. How do I parallel two 2N3055 power transistor? Is it looks like E-E, B-B, C-C are connected?

The two output transistors each must have a 0.33 ohm/2W resistor in series with its emitter to allow the transistors to equally share the current. The other ends of the emitter resistors are joined at the output of the project.
They are shown on the latest schematic and described in the latest parts list. You should not make the project without having these important documents.
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Big knob? can you explain audigur a litle bit the meaning of big knob ;D (sorry), and does this mean for bouth current and voltage?

A big knob has a large diameter so your hand can turn it easily a lot or a tiny amount. Because you can turn it a tiny amount then a fine tuning pot is not needed.
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  • 2 weeks later...

Hello everyone!

I'm going to make this very nice power supply, mainly after lot of modifications to improve its quality!

I was thinking if is possible to use a 15+15 VAC xformer... but with a relay to switch beetween 15Vac or 30Vac to feed the AC input and keep it away from excessive heat...

The idea is to place a comparator on central pin of P1, if U is less than 5V (15V at out) relay remains OFF and feeds power supply with 15VAC at the bridge... if greather than 5V (15V at out) then the relay turns on and feeds the bridge with 30VAC.

What you guys think about it ?

Will the power supply works with 15VAC ? (maybe use lower value for 10V 1W zener?)

thanks!

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With an input voltage that is much lower than the design needs, you must analyse each and every part value to see if the voltages and currents are too low. The negative supply voltage will probably be too low and will need to have its current increased to increase its voltage which will cause its parts to be hotter when the supply voltage is normal.

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  • 2 weeks later...

I think 24V AC is a standard Voltage Output of common transformers, that's why this circuit was designed for this voltage. A few volts up or down(maybe +-5V) aren't going to produce any fault but it is recommended that you use a 24V AC transformer.
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I think 24V AC is a standard Voltage Output of common transformers, that's why this circuit was designed for this voltage. A few volts up or down(maybe +-5V) aren't going to produce any fault but it is recommended that you use a 24V AC transformer.

But the output of the project with a transformer that is only 24VAC is only about 25V at 3A, not 30V.
The opamps in the original project have a supply voltage that is higher than their max allowed voltage.

28V and 30V transformer are common in Canada and the US. Maybe also in europe.
44V opamps are also common.
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  • 1 month later...

Hey,

couldn't you replace the 2n3055 with an MJ2955? This would reduce the dropout voltage ... like this:

http://www.elektronik-kompendium.de/public/schaerer/kdarl2.htm

What do you think?

The 2N3055 is an emitter-follower without voltage gain. Its dropout voltage might be only 2V. Because it has no voltage gain then the stability (possible oscillations) of opamp U2 is not affected.
Using a PNP common-emitter transistor adds voltage gain which might cause U2 to oscillate.

Our project uses a fast opamp and a fast driver transistor for good transient response. Your circuit uses an extremely slow LM358 opamp and the same driver as our circuit so it might have a slow transient response.

You do not gain much but try it and let us know if it works.
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Hi.

I'm gathering parts for this project, and I have a 2x15VAC 4A trafo at hand. Unloaded it delivers 34,4 VAC with the two sides in series. Will this be too much for the circuit?

I've seen 30vac mentioned for the trafo, so I hope this isn't a stupid question  :-[


Regards
soje

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The latest version uses a 28V or 30V transformer.
The voltage regulation of your transformer is poor. A 30V Hammond transformer is 31.5V without a load, not 34.4V.

Simply calculate if it will cause damage:
1) 34.4VAC has a peak voltage of 48.6V and the full-wave bridge rectifier drops 1.4V to 47.2VDC with no load. But the opamps have a max allowed voltage of 44V so they might be destroyed.

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