Generate Complementary PWM with dead time. ..#2

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rfengineer28

Joined Apr 28, 2021
71
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crutschow

Joined Mar 14, 2008
30,127
If you really need both outputs low, then connect the spare AND-gate in series with the high output.
Applying a low signal to one of the inputs will keep the output low.
Applying a high signal to that input will allow the output to toggle from the input signal.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
If you really need both outputs low, then connect the spare AND-gate in series with the high output.
Applying a low signal to one of the inputs will keep the output low.
Applying a high signal to that input will allow the output to toggle from the input signal.
if I do this, it'll and both and I won't get the output from A
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
So what’s connected to the output of the half bridge?
I am driving a dc brushed motor. I have the dgd2190m gate driver on my power mosfets. It’s an all 4 n-channel mosfet h bridge, each mosfet has a Qg of 268nC. My plan was to set up the pwm controller before the gate drivers.
 

Ian0

Joined Aug 7, 2020
5,553
I am driving a dc brushed motor. I have the dgd2190m gate driver on my power mosfets. It’s an all 4 n-channel mosfet h bridge, each mosfet has a Qg of 268nC. My plan was to set up the pwm controller before the gate drivers.
Is there any situation when the motor must be able to freewheel? i.e. the output shaft can be turned by the load?
If not, then it is an advantage if both lower FETs are switched on, as it will prevent the motor from rotating when it is not required to move.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
Is there any situation when the motor must be able to freewheel? i.e. the output shaft can be turned by the load?
If not, then it is an advantage if both lower FETs are switched on, as it will prevent the motor from rotating when it is not required to move.
The main issue I am having is that with my dead time circuit, even when I am not pulsing , the output that’s inverted remains high and while I am operating in the opposite direction that means both lower fets are on and I am seeing an insane amount of power dissipation when Ieave it like that.
 

Ian0

Joined Aug 7, 2020
5,553
The main issue I am having is that with my dead time circuit, even when I am not pulsing , the output that’s inverted remains high and while I am operating in the opposite direction that means both lower fets are on and I am seeing an insane amount of power dissipation when Ieave it like that.
Something else must be wrong. If the two lower FETs are on, then both sides of the motor are connected to 0V and there is no current path from the supply.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
Something else must be wrong. If the two lower FETs are on, then both sides of the motor are connected to 0V and there is no current path from the supply.
If both lower fets are on am I not creating a path straight to ground on 1 side? Hence shorting the supple?
 

Ian0

Joined Aug 7, 2020
5,553
Did you mention a multiplexer way back a thousand posts ago? Or was that someone else?
You seem to have a clock and a PWM waveform, when you need a direction control and a PWM waveform.
The logic should look like this. 0F7CF175-767E-438E-8057-E421F8CB01E9.jpegApply de Morgan’s laws and you can do it with all NOR gates, but you still need 5. Or alternatively, you can use a 74HC139 demultiplexer and a couple of inverters.
The dead-time networks come at the end, like you have them before.
However, I would recommend a half-bridge driver, especially and adaptive half bridge driver, as it will deal with the dead time for you.
 
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