Exploding 7915

[diarav]

Hi,

I constructed a preamp power supply as shown in this schematic.
http://sound.westhost.com/project05.htm
(not exactly - but i have a rectifier instead of the input diodes) and the input is +-35V.

On connecting and powering on, the 7915 exploded. One possibility could be the shorting of the output (I had carelessly laid out the wires), but I am not sure.

My question is : is a load compulsory to test this? that is should the power supply be connected to a preamp or something? Would an open output also cause this explosion?

 

[BWRX]

Are you sure you have the 7915 wired up correctly? The 7815 and 7915 do not have the same pinouts.

An open circuit or a short circuit on the output should not cause the device to explode, but it would get very hot very fast if there were a short circuit.

Also, you mentioned you have +/-35VDC input - is the ground connected?

 

[diarav]

BWRX,

Thanks for your response.

Yes I am aware of the pinout differences between 7815 and 7915 and I have wired them correctly. And yes the ground was connected.

Anyways I think you have answered my question. I'll get a new 7915 and rewire this and try again.

 

[jamesrnz]

what do you mean you have a rectifier instead of input diodes?

full wave or bridge?

is the transformer center tapped and what is the out put voltage of the transformer? and the rms DC?

the 78 and 79 series is generally limited to 35v max

 

[djQUAN]

the 78 and 79 series is generally limited to 35v max

yep. at 35V you're pushing the devices to its limits. it could be that a small spike or the high idle voltage of the main 35V supply simply raised it above the 35V limit of the regulators causing it to blow.

 

[diarav]

hi,

I think you'll are right. I never realized that.

Transformer is at 25-0-25 and the output at caps measured +- 35.4 V. I am having a bridge rectifier and the center tap connects to the ground.
I think I'll add a 220 ohms 5w resistor in series on both supply rails. http://sound.westhost.com/project73.htm

Thanks for your inputs again.

 

[BWRX]

Series resistors work well if you know the max current draw through the regulators. A simple zener reference with an emitter follower pass transistor will work even better.