over voltage and reverse voltage protection circuit

Hi all,

I've been developing an over voltage and reverse voltage protection circuits for small bike powered systems. I want to use the system for educational purposes as well as for running small sound systems or charging phones. Because the bike is going to be used for educational purposes, I don't want to use a big battery to limit over voltage.

This circuit is in it's 4th iteration so far. It has been tested a fair amount on the bench and somewhat in "real life". I'd really appreciate it if any members could point to any likely failure as it's important to protect the downstream voltage from anything larger than 25V DC.

It seems to me that when the mosfets connect and disconnect is when I'll get spikes due to the inductance of the DC motor that is in front of the circuit. I've got a large (1000uf) cap in the middle that soaks these up. I've checked what happens on the output with a 60MHz storage scope and can see the voltage on the output never rises above 24V.

The circuit should be good up to about 120V (depends on max gate drain voltage of the mosfets).

Operation notes:

F1 is a fuse for basic circuit protection.
Q1 is a P channel mosfet with gate tied via a zener to ground. This protects from reverse voltage. The zener protects vgs from being above 10v.
C1 is to soak up voltage spikes due to connection and disconnection of the mosfet Q6
D1 is a zener diode set to your over voltage level. When input voltage is beyond this Q2 and Q5 turn on.
Q5 turns on a warning LED
Q2 turns off Q4, which turns off the over voltage mosfet Q6.
D5 is to protect vgs of Q6.

Thanks for any feedback, and I hope someone finds it useful!
Matt

circuit and SMD board layout are available here via github:
https://github.com/mattvenn/eagle-circuit-designs/tree/master/over voltage protection

no one interested in this? I think the reverse voltage protection is pretty cool, as it works up to 100V!
Matt

LOts of zeners!!

I would consider a different approach of dumping generator power to drive universal cell phone charger station or power large fan and 100W LED with CPU fan & Heat sink.

Enough that would limit speed by load on gnerator

Thanks for the reply. It sounds like the method typically used for wind turbines (a dump load). It is used in turbines because if they spin to fast the mechanics break, so an electrical load is used. I did consider that (and have used it in other bike applications). However I think there is no need to do that with a bike as a rider can't break the mechanics by over pedalling. In which case we can benefit from smaller, lighter, cheaper electronics.

I know, lots of zeners!The reason for the zeners are:
D3, D4 to protect the mosfet gates
D1 to set the trip voltage
D2 to protect the LED

Here's a pic of the whole thing, with USB dc/dc converters:
https://www.flickr.com/photos/matthewvenn/7181432985/in/photostream