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Old 3rd February 2012, 09:18 PM   #11
! is offline !  United States
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^ What current does the load consume? It is normal for linear regulators to get hot shedding heat. That the input voltage is higher is what should be happening when using the right VA capacity transformer, it is probably a sign everything is working as expected.

The one you mentioned last does not appear to have a problem, 13.78V in and 5.64V out seems right. The other one seems to have a problem, it should not droop all the way to 9V rectified with ~ 12VAC transformer, assuming you used the same transformers and the same load (or without a load.

It is too confusing talking about two different PSU. Let's stop talking about one of them completely and decide one at a time if something is wrong.

As someone already mentioned, it is good to put a small ~ 0.1uF capacitor (non-electrolytic) right before the regulator.

Last edited by !; 3rd February 2012 at 09:20 PM.
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Old 3rd February 2012, 09:22 PM   #12
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mjock--

The phasing is basically the polarity between primary and secondary windings. The dots on the transformer diagram should match up. You can get uneven output if the wiring isn't correct. Do have pins 8 and 11 jumpered, and are you taking output from pins 7 (positive) and 12 (negative)?
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Old 3rd February 2012, 09:33 PM   #13
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by ChicagoJTW View Post
.......... are you taking output from pins 7 (positive) and 12 (negative)?
Pins 7 & 12 cannot be positive nor negative.
They are the output of a transformer and thus must be AC.
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Old 3rd February 2012, 09:39 PM   #14
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AndrewT--

Thanks, I know that. He has pin 7 leading to the positive rail and pin 12 leading to the negative in his schematic. The question is whether he has jumpered the middle two pins as Hammond's data sheet specifies for series connection, or whether they might have been hooked up some other way.
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Old 3rd February 2012, 09:46 PM   #15
AndrewT is offline AndrewT  Scotland
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No.

Those pins 7 & 12 feed to the AC inputs of the bridge rectifier.
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Old 4th February 2012, 12:13 AM   #16
mjock3 is offline mjock3  United States
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Here are the measurements on other supply: with load 9.42 volts in reg and 4.98 volts out. No load is 16.22 volts in and 4.99 volts out.
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Old 4th February 2012, 12:40 AM   #17
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^ are both power supplies reading this powering the exact same load?

The numbers make it look like the load on the one reading 13.85V is only a mild overload on the transformer (transformer current rating or true current capability below what the load consumes) so it causes higher voltage input to the regulator, so the regulator has to drop more voltage thus it runs hotter. This is normal.

The other PSU reading 9.4V input, would appear to have too much of an overload on the transformer, a higher current transformer should be used instead, UNLESS there is something else wrong with the circuit. What is the current used by the load and what is the current rating of the transformer?

If it is merely a case of an overloaded transformer, it will allow the regulator to stay cooler due to lower voltage drop but for a bad reason, you may end up blowing the thermal fuse on the transformer if it were operated for extended periods or in warm weather, in an enclosure, etc.
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Old 4th February 2012, 01:39 AM   #18
mjock3 is offline mjock3  United States
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I measured the current @ 400-430mA both supplies gave same draw, but I suppose that is what they should do right? Transformer is rated at 2.5A 10 volt. This measurement is taken at the output.

Last edited by mjock3; 4th February 2012 at 02:05 AM.
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Old 4th February 2012, 03:37 AM   #19
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With 400mA current into the load and 13.78V in and 5.64V out, and 8.14V drop * 0.4A = 3.3W, that will make a regulator run on the warm side. Avid 531202B02500G (assuming you used that part # as listed on the schematic) is rated for 7.5C/W (convection) so that's 25C rise. That is approaching 50C in some room ambient conditions, which will feel pretty warm but not painfully hot.

The mystery is why the other supply is being pulled down to 9VDC after the bridge rectifier you may need to pull parts one at a time then take measurements to figure out what is wrong.

Last edited by !; 4th February 2012 at 03:57 AM.
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Old 4th February 2012, 11:05 AM   #20
DF96 is offline DF96  England
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I think the problem is that the one with the 10mH choke is behaving a bit like a choke input PSU, even though the choke seems too small for that. The first capacitor is quite small, 120uF, so will have a high ripple voltage. The reactance of the choke means that you can't generate the large pulse needed to charge the second cap. Have you modelled it with PSUD2?
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