Chris

Use a separate pwr supply for the fan, not the same supply that runs the FETS or driver ccts. This is what I do and never had a problem.

mal/g3kev

 

----- Original Message -----

From: Chris Osborn

To: LF Group

Sent: Saturday, June 20, 2009 7:34 AM

Subject: LF: 500 kHz - Fans

LF,

I've nearly completed my new PA for 500 kHz and have now managed to

stop destroying FET's.

 

Unfortunately I have an unusual problem in that the heatsink cooling fans

are going U/S.

 

I have used 24 volts brushless PC-type fans and after a while they

either die completely or start to go backwards slowly. . .

 

The fans may be slightly over-run but only by a volt or so and on key-up

(unregulated supply) and are situated about 50 mm (2 inches) from the heatsink.

I have rf decoupled them from the supply but maybe not well enough !

 

Any suggestions in curing this problem would be most welcome.

 

73 Chris G3XIZ