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RF Protection

Sometimes RF will interfere with voltage regulation. What happens is the RF gets into the 723 by way of the Current Limit pin #2 and the Current Sense pin #3.

Some frequencies never interfere with the power supplies ability to regulate. Other frequencies can really cause a problem. It seems that there are no rules as to when and where this will happen. Many things determine the cause. Try to keep all the power lines going to and from the unit as short as possible.

This is easy to fix. Just put a .001 mylar capacitor across these two pins. It should stop the interference with regulation.

An electrolytic of around 150 mf @ 25 volts across the output terminals helps. A .01 ceramic capacitor across the output and .01 from negative to chassis ground. A .01 from positive to chassis ground.

I always build a power supply with a diode and 3,  .01 caps in a configuration across the output terminals. This is a preventative measure that I use for many things. A detailed schematic and it's function are described on the "Output Protection" page.

I also like to use a .22 ** tubular capacitor across the secondary of the transformer. A  .01 from each input terminal of the power transformer, to chassis ground help with the spike that can occur when switches are dirty or that have a tendency to cause a spike.

Always make sure that the wiring inside of your unit are kept to a minimum length when building them. If you have done all this and are still having problems with RF interference, drop me an eMail and we can try other things. We can come up with all kinds of ideas when given a more detailed view of what your particular situation might be. All RFI problems seem to be unique.

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** This is the one that I use: Cornell Dubilier CDE HV Metallized Polypropylene Film Capacitors 600V .22uF It seems that they do not have the "tubular" types much any more. Tubular caps can be found in the old junk boxes that Hams keep around.



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