Hi,

Assuming that I want switch on a circuit 3/4 times daily, using a mosfet associated with a driver ( for instance MOS FDP075N and FAN 7371 ), when I try to calculate the capacitor of bootstrap circuit based on Qtotal ( Fairchild AN-6076), what shall be the Ton used?
As it's a very high value, the Qtotal became very high as well the Cboot!

Any suggestions?
thanks in advance

 

How long will you need the switch to be on? A bootstrap circuit is not practical for ON times longer than a few minutes, due to the discharge of the boot capacitor from the circuit leakage currents.

 

A battery might be a better choice to replace the capacitor. It could last a very long time before needing replacement, but it would fail at some point.

 

Thanks for your help.
Time on about 10 hours
time off 14 hours

If it's not the best way, shall we use an IGBT or other solution?
A relay is not a good solution due the power lost to maintain the coil on/off


The circuit has vinmax 120V and Imax 10A

Any other ideia is welcome.

 

Put the load before the switch/mosfet. This is known as a "low side switch", and no bootstrap circuit is needed.

If a low side switch can't be used for some reason, look into a "charge pump" circuit to keep the boot capacitor charged. A good example is here, page #18 - http://www.google.com/url?sa=t&rct=...F_G6P5rcv6Kyd_fjU1B__Rg&bvm=bv.53537100,d.aWM