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Old 26th February 2007, 05:57 PM   #1
zlast is offline zlast  United States
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Default 12 volt converter

I found this project on the web "Practical voltage converter":

http://web.telia.com/~u85920178/power/vconv_01.htm

I built it and substituted TIP33C and TIP42C for BC547/557. Also I reversed polarity on the electrotyic caps and diodes because the goal was negative 12 volts. Attached is the pcb with component overlay. With 12 volts attached I get no output.
Q1,Q2,Q3 are TIP33C THe PNP is TIP42C
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Old 26th February 2007, 06:59 PM   #2
paulb is offline paulb  Canada
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You need to figure out whether it is oscillating. You'll need an oscilloscope, or maybe you can try to measure its frequency a frequency counter or a DVM that has a frequency measuring capability.
Have you emailed the author of the circuit?
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Old 26th February 2007, 07:00 PM   #3
poynton is offline poynton  United Kingdom
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Default Re: 12 volt converter

Quote:
Originally posted by zlast
................. Also I reversed polarity on the electrotyic caps and diodes because the goal was negative 12 volts. ..................
Hi.


If you read the article carefully, the original circuit gives either +24v or -12v depending on the positioning of the link.

There is no need to change polarity on the caps or diodes.


Andy

EDIT

You have also made errors on the pcb.
The emitters of the output pair are not connected to anything.
The cap goes to the bases of the output pair not the collector.
The diodes are wrong.

redo the board !!!!!!!!!!!!!

Cheers
Andy
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Old 26th February 2007, 10:56 PM   #4
zlast is offline zlast  United States
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Default 12 volt converter

Speaking of careful reading:

The links LK(x) refer to the links on the PCB component overlay. If the LK1 RED wire is removed and the BLUE wire is fitted, then the circuit will provide +12v, +24v, +36v and +48v. The first option (+12v) may not seem very usefull since this is the same as the input voltage, but if all electrolytic caps and diodes are reversed, then the board will provide -12v, -24v, -36v and -48v.
The author also marks the links and outputs in RED and BLUE...if reversing the diodes and caps is not needed then the article is unclear to say the least..

You are correct about the output transistors ...got confused by the parts overlay..
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