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- I have some low voltage SMD mosfets that I thought should be tried on my one and only Zip Zap. Naturally I am extra careful not to destroy it. So, after verifying voltages and currents I disconnected a NPN transistor and replaced it with my mosfet. And I could not believe it. It worked! So I tried two mosfets and got even better results.
- Measuring from battery negative to the blue motor wire, running the motor forwards and holding the wheels this is what I got on the oscilloscope:
Original configuration: 0.42v
Shorting R20 and R21: 0.35v
Replaced NPNs with N-Mosfets: 0.2v
Stacked 2 Mosfets: 0.09v
(I suspect that 3 Mosfets would give even better results, but I have gained 0.3v and that is enough for me)
The advantages to this mod are more voltage to the motor, less power wasted in the transistor, and less strain on the IC. My mosfets were pin-for-pin compatable and only cost 44 cents each. The values of R20 and R21 have no effect on the performance. It should also be noted that apparently the IC can sink and source current, so there is no need for a pulldown resistor to turn the mosfets off.
- The mosfets I used were N-Channel 25v SOT-23 from Digikey. But I somehow don't expect too many people to try this mod out.
Oh I almost forgot, I can pull 260mA from the H-bridge. But I have no idea why anyone would wan't to do that.
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