# I'm in love with the 4 switch synch topology



## abudabit (Sep 18, 2008)

For when you need buck boost and regenerative braking it seems like a vastly superior option. It's non inverting and bidirectional. It only needs 1 inductor per staggered phase. The peak voltage across the mosfets is gentle. 

The main drawback is that you need 4 switches but that isn't such a problem. One example - a 30 amp 100 v peak stage built with irfp4310 seems very inexpensive and gets less than .75% RDS losses at max voltage and current. On top of that you are only actively switching at most 2 switches in any mode so switching losses aren't a big deal either (unless your timing is flawed). An almost 3 kW stage for well under $10. 

The other drawback of course is you need to implement good switching control - if not you could get horrible inefficiency.

Also if you do a single stage you will get a lot of noise, but since we are doing ev's you will have to do multistage anyways.

It can operate in the following modes:
- regen with buck
- regen with boost
- drive with buck
- drive with boost
- unity (bidirectional)
- unity (unidirectional) (no purpose for this though)
- coast / off

What do you all think? Any other complaints / praises about this topology? 

One caveat is I am only doing simulations and calculations now, I haven't actually gone through the rigours of programming my mcu yet.


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