Various aspects of home brew inverters

Author	Message
Warpspeed Guru Joined: 09/08/2007 Location: Australia Posts: 4406	Posted: 02:06pm 25 Mar 2017         Revlac said   Deciding the value of the pull-down resistor? Usually the purpose of a pull-down is to keep the FET off during startup, the value of gate to source resistor most inverters i have seen(i haven't seen that many) were 2k-7k resistance. Spot on there Aaron. Power up and power down are absolutely critical periods. This is more usually a problem with higher drain voltage mosfet applications. But really large low voltage devices can have pretty high internal gate to drain capacitance which can be a problem. Agree, 2K to around 10K seem to be popular. Any half decent gate driver should be able to handle a few hundred ohms without breaking into a sweat. If you are as paranoid as I am about all this, a 15v to 20v zener diode between gate and source plus the resistor will provide some additional protection at little cost. There are really two very different problems here. Spurious turn on can cause cross conduction and uncontrolled current flow. Or just the voltage spike on the gate can break down the gate oxide and destroy the device without the huge current. I am now convinced we are being flooded with cheap Chinese fake parts that fall way below data sheet specification. So there may not be a problem with your circuit, but the device itself could be junk. Edited by Warpspeed 2017-03-27 Cheers,  Tony.