Various aspects of home brew inverters

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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 01:27pm 08 May 2017      

Heaps of bandwidth for this.

We will usually be switching at quite a low frequency, and the gentle ramping up and down is a very slow change with no fast edges anywhere. But as there are some very high circulating currents, and the mosfets and diodes do switch fast, there can potentially be a lot of switching noise and nowhere a clean ground reference.

A sense resistor is going to only produce a low voltage unless its very lossy, and differential measurement of a low amplitude noisy signal is difficult, unless you have really good equipment.
All sorts of problems with current transformers, although in theory it should be possible.

Hall device gives complete isolation, frequency response down to zero, and usually several volts of nice clean output. A further advantage is you can very easily increase the sensitivity by looping several turns through a high current Hall sensor.

I have a 75 amp Hall sensor (LA55P) glued onto the end of a plastic box which contains a +/-15v dc power supply inside. I just grab that and plug it into the mains, and plug the coax output into my oscilloscope. Its my "big" current probe ready for instant use at any time.

Often quite useful for many other things besides choke testing.

My tester is in another plastic box. It has an opto isolator input driving a divide by two flip flop. That feeds into an IR2110 gate driver. There are a pair of small mains power supplies to provide two separate 12v supplies.
The mosfets and diodes are sized for an easy peak 80 amps.
No point in going higher as that is about where my Hall sensor tops out.

I initially blew up quite a few mosfets until I became much more careful in using this tester. But with a bit of care and some familiarity it has served me very well.
Sorry still no camera here.
Cheers,  Tony.