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Old 15th February 2009, 09:50 PM   #171
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Hello

I finally got around to finishing one of these power supplies.

Click the image to open in full size.

I am feeding 25v secondaries into this power supply via a bridge rectifier. I have connected a 230R resistor between either Vout + or Vout - and I'm getting a reading of 36vdc.

I am using a 27v zener to set the voltage, would I be right in thinking the voltage is too high?

Thanks

Richard
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Old 15th February 2009, 09:58 PM   #172
AndrewT is online now AndrewT  Scotland
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hi Trip,
what have you built?
Help us to help you.
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Old 15th February 2009, 10:15 PM   #173
Nuuk is offline Nuuk  United Kingdom
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Yes Richard, you should be getting around +/-27v. Sounds like you could have a short somewhere allowing the full unregulated voltage through to the output.

Andrew, he is building the Pedja Rogic discrete regulated PSU described here (second diagram down).
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Old 16th February 2009, 07:23 AM   #174
AndrewT is online now AndrewT  Scotland
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Hi trip,
The two followers each drop ~0.6V. the output should be ~27-1.2 ~25.8Vdc.

Start by measuring the voltage from ground to all the components and list them here. Do one channel only. Check to see if any component gets hotter than the rest. The pass transistor should be cold if it is not dropping any voltage.

Is the 230r load resistor getting VERY hot? 36V across 230r is 5.6W and that resistor looks like it might be a 1 or 2W carbon composition. Is it still drawing any current?


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Old 16th February 2009, 08:30 AM   #175
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Quote:
Originally posted by AndrewT
Hi trip,
The two followers each drop ~0.6V. the output should be ~27-1.2 ~25.8Vdc.

Start by measuring the voltage from ground to all the components and list them here. Do one channel only. Check to see if any component gets hotter than the rest. The pass transistor should be cold if it is not dropping any voltage.

Is the 230r load resistor getting VERY hot? 36V across 230r is 5.6W and that resistor looks like it might be a 1 or 2W carbon composition. Is it still drawing any current?



Hi Andrew

I will have a look tonight and will post the results.

The resistor on the output got very hot last night, I turned the power supply on this morning and noticed the 3A fuse in the ‘light bulb tester’ plug top had blown.

I’ve lost count the number of times I have checked this board prior to powering up!

Richard
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Old 16th February 2009, 08:39 AM   #176
AndrewT is online now AndrewT  Scotland
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Hi,
is your light bulb tester properly wired up?

It should be unlit when no load is present.

If the bulb lights when you insert a big load into the output socket then it's probably right, but it should never blow a 3A fuse, that's indicating the bulb passed more than 700W!!!
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Old 16th February 2009, 09:07 AM   #177
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Quote:
Originally posted by AndrewT
Hi,
is your light bulb tester properly wired up?

It should be unlit when no load is present.

If the bulb lights when you insert a big load into the output socket then it's probably right, but it should never blow a 3A fuse, that's indicating the bulb passed more than 700W!!!

As sure I was about the power supply

I have bought the components to make the Nick’s latest light bulb tester (including on-off testing switches) I think this should be the next project!
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Old 16th February 2009, 10:09 PM   #178
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Quote:
Originally posted by Tripmaster



As sure I was about the power supply

I have bought the components to make the Nick’s latest light bulb tester (including on-off testing switches) I think this should be the next project!
Hi

I have attempted to assemble another light bulb tester this evening.

Click the image to open in full size.

Would you mind checking my wiring, I think its ok?

Click the image to open in full size.


Thanks

Richard
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Old 16th February 2009, 10:17 PM   #179
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OK, right then...I have connected the light bulb tester to my power supply and I get 34.2vdc from the output. I then measured the voltage at the 27v zener (pictured below) this read 26.63vdc.

Click the image to open in full size.

When ever I press the 'on button' on the light bulb tester the bulb glows for a second
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Old 16th February 2009, 10:30 PM   #180
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The voltage remains at 26v up to and including the base pin of the first BD140 transistor. The collector and emitter read 34v
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