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Old 17th May 2013, 12:37 PM   #1
Hushang is offline Hushang  Iran
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Post 7815 and 7915 output problems

hi all, I built this ps and added a 7815 and 7915 regs at the end of it but.. when I plug both regs i have +15 in 7815reg's out but the 7915's output dosent work, and when I disconnect 7815, 7915 works fine, input is double 32v. help
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Old 17th May 2013, 03:42 PM   #2
macboy is offline macboy  Canada
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The 7815 input pin should connect to "Red output", it's ground to "A", and the output should be +15V measured to "A".

The 7915 input pin should connect to "Blue output", it's ground to "A", and the output should be -15V measured to "A" (meter's black probe to "A", red to the 7915 output).

Don't forget to notice that the pin configuration of the two regulators is not the same, the 7915 ground pin is not in the middle as it is for the 7815.
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Old 17th May 2013, 04:01 PM   #3
AndrewT is offline AndrewT  Scotland
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Hush,
looks like D1 & D2 need to be able to pass Fault Current to Chassis.
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Old 17th May 2013, 05:28 PM   #4
Hushang is offline Hushang  Iran
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thanks a lot for reply guys, I checked pins are correct, 7915 "has" output if i disconnect 7815, but when plug 7815, 7915 is not working, is it because of the filters i used?
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Old 17th May 2013, 05:41 PM   #5
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Hi Hushang,

What are the voltages you measure before and after the regulators, in each of the two cases (7815 connected and disconnected) ?

Do you only have the regulators, or any extra hardware ?

What's the load in the regulators ?
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Old 17th May 2013, 06:01 PM   #6
Mooly is online now Mooly  United Kingdom
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I seem to remember Andrew mentioning a while back that some 79 regs need a minimum load of a few milliamps.

Also consider adding diodes (reverse polarity) between each 15 volt reg output and ground and across each reg to prevent a reverse bias situation if the rails rise at slightly different rates. That can cause a latch up on switch on.
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Old 17th May 2013, 06:02 PM   #7
Hushang is offline Hushang  Iran
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Quote:
Originally Posted by AndrewT View Post
Hush,
looks like D1 & D2 need to be able to pass Fault Current to Chassis.
anrew, I did not asemble that part, should I?
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Old 17th May 2013, 06:30 PM   #8
Hushang is offline Hushang  Iran
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Quote:
Originally Posted by pfigueiredo View Post
Hi Hushang,

What are the voltages you measure before and after the regulators, in each of the two cases (7815 connected and disconnected) ?

Do you only have the regulators, or any extra hardware ?

What's the load in the regulators ?
tnx alot, without regs i have +/- 34 volts, this ps also have +-34 v output, when i connect both regs +34 and +15 works but other not, why is that so?
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Old 17th May 2013, 07:21 PM   #9
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What I meant was:

Situation 1: Both Regulators there
Input Voltage of 7815 = ??
Output Voltage of 7815 = ??
Input Voltage of 7915 = ??
Output Voltage of 7915 = ??

Situation 2: 7815 removed
Voltage at Red output = ??
Input Voltage of 7915 = ??
Output Voltage of 7915 = ??

All these voltages measured with respect to node 'A', of course
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Old 17th May 2013, 08:29 PM   #10
Hushang is offline Hushang  Iran
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in sit. 1 :
input voltage of 7815 34
output 15
input voltage of 7915 is 0
output 0
in sit. 2:
about 36
input 7915 about -36 too
output of 7915 about -17.5

Last edited by Hushang; 17th May 2013 at 08:45 PM.
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