From
http://www.angelfire.com/sd/paulkemble/sound5c.html


I want to use this schematic for 80V instead of 25V power supply.

For switching at tens of KHz.
I want to not destroy gate of MOSFET.

My IC driver offers PWM with 12V amplitude.

How to modify for 80V supply ?(first schematic-with speaker)

Note - P-MOSFET is in the lower part. They "repeat" signals.

 

You need to rebuild the inverter of input from ic to bjts of npn inverter, and choosing the vce of bjt and Vds of mosfet could withstand over 120V, so you still could keep the input as 12V pwm signal.

You can see the bjt inverter circuit as below:
Using transistor as switch.

You can redraw the circuit and try to setup the values of resistors.

 

BJT (bipolars) switch slower that MOSFETs.

Turn off slower and however they not have dead time.

 

I'm not suggest you to use bjt to replace mosfet, so don't worry about the dead time and working frequency of bjt. (Using mosfet still has Cgs problem, so don't think that it is fast than bjt)

For the upper circuit:
1. From the left input, using npn bjt to replace the ic inverter, the method was described in the last posted.

2. The speaker side that the mosfet still using mosfet, just peak up some Vds over 120V.

3. Redraw the new curcuit and label the values of resistors, so I can make sure how much you know about what I said.

Where did you get the 80V?

 

Where did you get the 80V?

12V->80V inverter(Elliott project89)'

 

I tried this-


The online simulation works.
In practice, it did not work.

D2 is a fast UF4007 diode.

I suppose the zener diode does not switch very fast and that's why it did not work.

What other element could I put in place of D3?

 

Why not use a dedicated gate driver IC such as the usual IR2110?

 

Why not use a dedicated gate driver IC such as the usual IR2110?

I have version with MOSFET driver and it works.

I'm looking to make a cheaper version.

I am wrong that scheme from # 1 is working at a higher voltages.
If anyone wants to explain the conditions in which that scheme from post #1 can work at 80V.

 

IRF640/irf9640
ABSOLUTE MAXIMUM RATINGS (TC = 25 °C, unless otherwise noted)
Gate-Source Voltage VGS ± 20V

 

The mosfets are arranged as emmiter followers (drain followers actually) so they will be hugely inefficient at large currents. I would add a zener between G and S of each mosfet, not sure what D2 is for but it doesn´t seem right to me.

 

As drain followers you have the "same" voltage at the output, but the output power is much higher.

<I would add a zener between G and S of each mosfet>
12V or 15V zener ?

And I thought how could the voltage between G and S exceed 20V? if they are followers.

 

As drain followers you have the "same" voltage at the output, but the output power is much higher.

"same" meaning ~4V drop on the mosfet when it should be switched hard on, mind you this is not a linear amp an the output should be either Vcc or gnd and nothing in between.

And I thought how could the voltage between G and S exceed 20V? if they are followers.

Yes, but I think there is a possibility to swing the gate high wihout the source following in suit, due to capacitive load or a short circuit or something, even a short time discrepancy would destroy the fet. I would use a 15V zener.

 

As drain followers you have the

http://www.falstad.com/circuit/e-mosfollower.html
Perhaps the correct term is source followers(as emitter followers), the rest is correct.