n and p channel mosfet half bridge problem

Thread Starter

nigel200

Joined Nov 27, 2018
3
I am putting a series LCR into resonance using a N and P channel mosfet half bridge.
The circuit is powered by a 20 volt adjustable power supply.When i turn the voltage up
above 12 volts the LCR stops oscillating and the current jumps from 500 ma to 2 amps
I think this is caused by shoot through.Does anyone no of a chip i can use which has dead
time with a single input?
 

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ronv

Joined Nov 12, 2008
3,770
Sometimes you can get away with something like this:
upload_2019-5-15_17-14-4.png

Or better yet you can do something similar on the input to the driver.
What are your FET part numbers?
 

wayneh

Joined Sep 9, 2010
17,498
Sometimes you can get away with something like this:
I used that exact approach on my EL bridge project and it worked. I don't know it if would have worked without the diodes, but I included them and everything is fine.
 
Last edited:

ronv

Joined Nov 12, 2008
3,770
You can not put a current limiting resistor for a MOS. For a MOS you use either pull-ups or pull-downs.
The gate resistors form an RC network with the gate capacitance of the FET. This slows down the turn on and turn off time. By putting the diodes across the resistor only the turn on time is slowed down.
 

Thread Starter

nigel200

Joined Nov 27, 2018
3
Just tried with 10 ohm gate resistors and IN4148 diodes. Definitely works better
but current still jumps up at around 16 volts.
 

ArakelTheDragon

Joined Nov 18, 2016
1,362
MOS transistors are normally controlled by the voltage on the gate. If you want lower current, you will have to switch off the transistor when the current in the load rises. Like this you keep a border off when the current is high, on when the current is from 0 to border.
 
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