Hello to all, and sorry for my poor English.
This is a Buck converter and I want to control speed of DC Motor by changing the PWM. My question is How can I protect the output from over voltage, I mean It doesn't have any protection when input voltage is over than 75v.
For example I want when the voltage is over than 75 volts Mosfet goes to zero.
What can I do?
Very thank you.
Why make a buck converter yourself. And for a motor. Controlling a motor with PWM is more easier then with voltage. So why not PWM the 75V?
And to protect against over voltage, just use flyback and clamping diodes 
septillion:
Why make a buck converter yourself. And for a motor. Controlling a motor with PWM is more easier then with voltage. So why not PWM the 75V?And to protect against over voltage, just use flyback and clamping diodes
Thanks.
What kind of flyback and clamping diodes I should use?
Very thank you
@leoncorleone, do not cross-post.
leoncorleone:
Hello to all, and sorry for my poor English.
This is a Buck converter and I want to control speed of DC Motor by changing the PWM. My question is How can I protect the output from over voltage, I mean It doesn't have any protection when input voltage is over than 75v.
For example I want when the voltage is over than 75 volts Mosfet goes to zero.
What can I do?
Very thank you.
What is that 1mH inductor and 470uF capacitor doing? Do you know how PWM motor drivers
normally work?
What kind of current are we talking of?
Maximum Power of my DC Motor is about 400 watts and Input current is about 6 amperes.
Firstly you are trying to make a buck-converter instead of a motor driver - you need a motor driver,
the motor itself is the inductor that smooths the current so you just feed PWM straight into the winding,
so no external inductor / capacitor combination is needed (although a small amount of capacitance can
reduce EMI at radio-frequencies).
Switching on the low-side is much simpler as all the circuitry can share ground. Having said that opto-isolation
is a good idea.
At those power levels you have to have good protection circuitry - MOSFETs can fail in sub-millisecond
timescales if large amounts of power are available to dump into them.
For instance:
Momentary over-voltage across the gate-source will instantly destroy a device (sub microsecond
timescale) - zener diode clamp between gate and source right on the terminals is a good idea.
Holding the device in a half-on-half-off condition will cause extremely rapid heating and destroy
the device (sub-millisecond timescale). Use a MOSFET driver chip with under-voltage cut-off.
Over-voltage of drain-source can do the same - inductive voltage spikes can cause this if not
suppressed.
Lack of sufficient deadtime (if a half-bridge or H-bridge) can cause shoot-through - another failure mode
where huge amounts of power are dumped into the MOSFET die.
If you protect against the likely failure modes you can have a robust and reliable circuit, but a
naive circuit is very vulnerable. Use MOSFET driver chips to drive MOSFETs at high power.