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jscherer 17th March 2009 07:19 AM

Problem with capacitance multiplier power supply
 
I've built a capacitance multiplier power supply for testing/learning/measuring and Its not quite working right.

The circuit is the from here and looks like this:

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I'm getting 58.3 volts across the rectifier, 29.1V across the filter caps. From Gnd to -Ve I get
-26.8V, but from gnd to +Ve I only get 8.1v. I have tried the circuit with 2N3055's at Q3 & Q4 and with MJ15003's but the voltages are similar

The pages says I should adjust VR for 3v across the pass transistors - I get 21V across Q3 and 2.2V across Q4

I suspect this circuit was designed with a lower voltage secondary and that the resistor values will need to be adjusted to reflect this. I'm hoping for some guidance before I dive in. I have been looking at this page as a reference as well.

Cheers

Samuel Jayaraj 17th March 2009 07:48 AM

Check the voltage at the base of Q1 and at its emmiter.

h_a 17th March 2009 03:15 PM

You haven't tried to run that without load, have you? ;)

Have fun, Hannes

PS: didn't check resistor values, but without load it's not going to work.

AMV8 17th March 2009 04:56 PM

Hi

I have built capacitance multipliers that are similar to those in the first circuit that Rod Elliot shows and they work.

I have not tried the layout shown in figure 2. However in figure 2 the relationship between Q2/Q4 the pass transistor does not seem right.

Don

mjf 17th March 2009 09:42 PM

hello.
perhaps you have changed r5 with r3 or so.............
greetings.............

jscherer 18th March 2009 03:50 PM

Samuel: I'll measure the voltage at the base of Q1 and its emitter tonight,

h_a: ahh, ya I guess I was testing without a load. I do have some 5, 10, and 20 ohm 50W resistors. When you say it's not going to work without a load, can you be more specific? I do measure 29.1 volts at the -Ve side which is about what I would expect. It's just the +Ve side that I'm having a problem with.

mjf: I have checked the wiring about 6 different times, on 6 different days - I'm reasonably certain that the wiring is correct. On both sides of the circuit I have the 6.8k resistor going to the 5k pot. I also verified that the wiper of the pot is connected correctly on both sides.

on the outside chance that I did something to the BD139 I replace it as well but the voltages do not change. I also swapped the pass transistors to see if the problem followed them but it did not.

mjf 18th March 2009 07:59 PM

hello.
you can compare the voltage values of the working neg. side with the voltages of the pos. side............that should show the flaw.......(draw it in a schematic).
greetings.............

jscherer 18th March 2009 08:54 PM

Quote:

Originally posted by mjf
hello.
you can compare the voltage values of the working neg. side with the voltages of the pos. side............that should show the flaw.......(draw it in a schematic).
greetings.............

Hello to you mjf,

Great idea, I'll do that tonight as well!

-John

jscherer 19th March 2009 03:39 AM

2 Attachment(s)
Ok, I have attached the schematic with some voltages on it (without load for now until I find my big resistors). I think I may try build the first circuit on that page just for comparison to see if the results are different.

kaos 19th March 2009 04:09 AM

The 20.8 V across Q4 doesnít make sense relative to your other measurements, Iím guessing a typo? 27.3 V on the emitter of Q1 and 8 V on the emitter of Q3 sort of narrows it down to a faulty connection or trace at Q3, or a bad Q3. Any chance the base and emitter are interchanged on Q3 (easy to do on a TO-3 package thatís been hand wired)? I'm assuming nothing's getting hot.


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