Yes. That helps

 

Thanks, Ray.

Ken W7EKB

Morning, Ray.

I know it's a big job, but I and many others

would be grateful to hear your wisdom on silencing

the nasty RF noise from some of these DC/DC inverters.

I haven't had much success- some better than others.

TNX OM ES 73 DE Dave AB5S

 

Have to say that wisdom would be a stretch! I wasted a lot of time playing around with inverters, somehow have developed a thing for running old radios in the field so that requires providing high voltage DC from limited sources. Think maybe the biggest issue that perplexes me is the worship of size; everyone is driven to try to build up something small. Imagine if you are doing something like a BC-611 that’s a real factor but for everything I do that’s not been a problem yet.

Because of size we are driven to use high frequency devices, the advantages are the higher the frequency the smaller and lighter the transformer and the smaller the size of the filters required on the output of the power supply. The disadvantage of this is that the higher the frequency the greater the issues with radiated noise from the power supply itself.

Look around your house, all the wall warts that power your stuff are high frequency switching supplies, not because they are better then regular transformer and series regulated power supplies but because they use less copper, iron and are smaller.

Things like ballast transformers for florescent lights are now all solid state inverters instead of transformers, not because it’s smaller but just because it cost less in terms of material. Lot of the first generation florescent ballast generated huge amounts of RFI often well up into the VHF band.

If size and weight will accommodate why do high frequency?

The last several inverters I have done worked at relatively low frequency, sixty cycles because there are lots sixty cycle transformers out there. Working with low frequencies produces a minimum of RFI or spurious and with modern devices you can get just about as good efficiencies as the high frequency cousins.

This simple circuit with a sixty cycle transformer may be a good candidate for replacing dynamotors on field radios. I would like to round up some four hundred cycle transformers and do some work with them thinking they will be lighter and smaller. Consider the PRC-47 being that has a internal four hundred cycle power supply that powers the radio in the DC mode, in AC operation it’s the same transformer as in the inverter that powers the radio.

If on the other hand you just got to have a modern Chinese PWM high frequency device be careful to get one rated around two thirds of your current drain so the PWM width won’t become an issue and be prepared to do lots of shielding and bypassing. Also I noticed sometimes you can do a small bypass on the gate drive to drain and that reduces a lot of the spurious byproducts.