7815 and 7915 output problems

Hushang

Member
2012-05-03 7:17 pm
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:confused::(
 

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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.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 

Hushang

Member
2012-05-03 7:17 pm
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?
 
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
 

pilli

Member
2006-08-15 9:46 pm
Sorry if I dare...
somebody already said it:
you did pay attention to the fact that 78xx and 79xx have a different pinout, right?

78xx has 1=IN, 2=GND, 3=OUT
79xx has 1=GND, 2=IN, 3=OUT

Did you also put the input and output caps caps?
(edit: I just saw your latest post, taht came while I was typing...)

In case there is a heatsink, remember that the tab of the TO-220 package is connected to the center pin. If the two regulators share the heatsink, you want the tabs to be insulated from the heatsink, otherwise the IN of 7915 goes to ground...

Really, don't get mad if I recall thee basics and you had already done it properly :eek:


-
 
Last edited:

Hushang

Member
2012-05-03 7:17 pm
Sorry if I dare...
somebody already said it:
you did pay attention to the fact that 78xx and 79xx have a different pinout, right?

78xx has 1=IN, 2=GND, 3=OUT
79xx has 1=GND, 2=IN, 3=OUT

Did you also put the input and output caps caps?
(edit: I just saw your latest post, taht came while I was typing...)

In case there is a heatsink, remember that the tab of the TO-220 package is connected to the center pin. If the two regulators share the heatsink, you want the tabs to be insulated from the heatsink, otherwise the IN of 7915 goes to ground...

Really, don't get mad if I recall thee basics and you had already done it properly :eek:


-

bro your right, :d ,tnx so much bro it was heatsink, didnt know that,
(F) omg tnx alot:D tow days i'm thinking checking...
tnx alot (F)
 

Hushang

Member
2012-05-03 7:17 pm
and for last thing is it better to use output caps?
in 7915's datasheet i saw this circuit, are output caps like this? or should be same size?
and is it better to use "d1,d2 and r10 ohm 5w" part for chasis?
 

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is it better to use "d1,d2 and r10 ohm 5w" part for chasis?
this is your Main Audio Ground to Chassis connection.
It can be used to reduce hum.
It can also be used with a bypass switch to short out the components, i.e. switchable between Disconnecting Network and direct zero ohms.
Or you can make a direct wire link from Main Audio Ground to Chassis.

BUT:
This link may have to pass Fault Current until the Mains fuse ruptures.
That Fault Current can approach and even exceed 1kA. The components MUST survive long enough to guarantee that the fuse ruptures and the arc extinguishes.