Thread: Power MOSFETs
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Old 14th May 2019, 1:34 am   #42
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Default Re: Power MOSFETs

Originally Posted by julie_m View Post
I'd be tempted to use a cheap microcontroller to generate a PWM signal by simple bit-banging, and a pair of TDA2030-alikes with no feedback to drive the gates of the MOSFETs, for the current sourcing and sinking ability. For 3-phase, make the table with a multiple of 3 entries and start reading 1/3 and 2/3 of the way through to drive the other phases. Software timing should be accurate enough, you know how many cycles the lookups and writes will take, and the only decisions will be in the idle loop.
All true, but it might pay to consider these remarks from my article on my 400Hz 3 phase power source:

I looked at the notion of designing my own inverter and I’m not shy to take on a difficult task. However, it is not a trivial task to design and build a three phase power inverter capable of some hundreds of watts output. Generally, one would start with a DC supply derived from the mains power. Then create three sine wave oscillator outputs, separated by 120 degrees for each phase at the “base” frequency, in this case 400Hz.(of course you don't need that for single phase)

Those outputs would pass to comparators being fed a high frequency switching or “carrier” signal to generate a PWM (pulse width modulated signal). This would then pass to a three phase bridge output stage, typically with IGBT’s.

While the basic design of an inverter like this seems simple enough, there are very important issues in these circuits with isolation required between stages and this often requires an array of separate DC supplies and isolation devices which add to the complexity. There are also the issues of transient snubbing to protect the IGBT’s and often a dead-band circuit is also required to prevent simultaneous conduction and catastrophic failure of the IGBT’s in the bridge.

I also noticed that this sort of project has been presented as a topic for an Electronics Masters thesis by some, giving an indication of the scale of the task, to do it properly that is.

So its a bit more of a task than meets the eye, it is "doable" but not easily if you want it reliable.

(Also about the remark that its not necessary to have a feedback loop leveling the output if it was a power amp system with a sine wave drive signal, I still think it is especially if a home constructed device, that has the potential for more mishaps, maybe not for the work of the professional power engineer)
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