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Sunday, 17 July 2011

It's running Hot Hot Hot!

I've been fiddling some more with my BITX:

http://g0mgx.blogspot.com/2011/01/boxing-bitx.html

and more specifically with the PSU that's built into it. I was using a 9-0-9 transformer, taking the 18V into the BITX. Once rectified and smoothed this was generating a basic DC supply of about 24V. Now, the 24V is a good value to feed directly to the IRF510 PA to get a good output, however, when I passed the 24V into the LM317 to regulate the value down to 12-13V the regulator was running really hot.

Thinking about the maths; then we have 24v in - 13v out = 11 * 0.8 (800mA) = 8.8 watts power dispassion! That's loads for a little LM317 to cope with even with the heatsync I've given it. I've been looking around for some time to try and find a suitable multi-voltage transformer such that I can have separate AC windings for the 13V regulated board supply and the PA. I found this on e-bay:


It was only the transformer I found on ebay, but I've built myself a power pack with a cabled 11.5V, +21V and 0V to the BITX. I'm about to drill the BITX case to take a 4-pin DIN socket and plug to act as the power pack DC connector so later today I'll be BITXing...



I'll keep you posted, but should be nice and cool!

Good egh?

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