thermal problem with asymetrical half-bridge

[vodka]

hello,

i have a mosfet(irfz46n) that it warms up when i switch on the power supply with a load inductor.
The power supply consume 0.22 A with the current limited(tested with multimeter and  display power supply),
 this mosfet warms up a few seconds while the schottky diodes and the other mosfet is as freeze as a fish.
So the hot mosfet and cold mosfet switch on at same time and have heatsink .

Below  is my schematic and the problematic mosfet is  the left

[Andy Watson]

I would include a damping resistor in the gate of each Mosfet to ensure stability.  Q1 is unlikely to turn-on fully thereby dissipating more power than necessary. Q4 is upside-down. 

[T3sl4co1l]

Many basic things wrong with this circuit...

1. Oscillator and comparator are using really slow op-amps as comparators
2. Supply is 12V so the 12V zener is redundant
3. Op-amp supply is +/-15V yet gate signal is apparently intended to be +12/0V, causing U2 to drive short-circuit current (bad) into Q3/Q4 base (worse) all the time
4. Q1 gate drive is insufficient to saturate, gate voltage must be above +12V when 'on'
5. None of this matters anyway, because the load shown is a 0.47uF capacitor, which will charge once, and then do absolutely nothing.  Unless you meant that to be something else...

Tim

[Jay_Diddy_B]

Hi,

The problem is with the Gate drive for Q1. The gate can only go to +12V minus Q3 vbe. The source of Q1 can only go to:

+12V minus Q3 vbe minus Q1 Vgs

So the power lost in Q1 is equal to I drain x (Vgs + Vbe)

look at this post: https://www.eevblog.com/forum/projects/inductor-saturation-tester-alternative-route-to-dump-the-excess-energy/msg181720/#msg181720

I use a P Channel and an N Channel in asymmetrical bridge.

Regards,

Jay_Diddy_B

[vodka]

T3sl4co1l

why is not saturate the gate ? when the datasheet says that the voltage gate is among -20 and + 20 V

Jay_Diddy_B

why is the reason for using the channel p and not channel n?

[Dago]

why is the reason for using the channel p and not channel n?

Because then he'd need a floating or isolated gate drive. Remember gate voltage is referenced to source and for the upper FETs the source is not connected to ground.