Power MOSFET Gate Driver
Power MOSFET Gate Driver
(OP)
I am using a gate driver as an interface between a power FET and a microcontroller. The power FET controls a coil that operates at 48V. The gate driver is powered by 12 V with input voltages that are TTL compatible. Any ideas why the gate drivers could be getting hot and exploding? They are decoupled using capacitors as mentioned in the data sheet, the only difference is that I'm using electrolytic capacitors instead of a film and ceramic capacitor.





RE: Power MOSFET Gate Driver
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Power MOSFET Gate Driver
FET: IRF1407
RE: Power MOSFET Gate Driver
Got a schematic snippet?
Have you looked at the Driver's output pin with a scope to see if something is coming back at the driver?
Have you done the the device power calculation which includes switching losses, etc?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Power MOSFET Gate Driver
http://w
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Power MOSFET Gate Driver
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Power MOSFET Gate Driver
1) You must use adequate decoupling which provides a very low impedance at very high frequencies. This is due to the very fast switching of the FET and drive circuit. There can be a lot of energy to decouple in a very short period of time. Small Ceramic capacitors provided a low impedance path at high frequencies. Film capacitors (physically small) provide a low impedance path at medium frequencies. Electrolytic capacitors provide a low impedance path at low frequencies. I would suggest that you add 100nF ceramic decoupling capacitors as close to the supply pins as possible.
2) The printed circuit layout is vitally important. It is essential that the drive circuit is not influenced by the load current. That means that you need to be aware of the current paths and how they affect the inputs. Ground plane layouts are a solution if implemented correctly.
3) Heatsinking. These drivers need to be cooled. If you do not apply sufficient heatsinking, they will over heat. The drivers often rely on large copper areas on the pcb to act as heatsinks.
4) Limit the operating frequency and see if the temperature drops.
It is possible that the drive circuitry and FET are oscillating due to poor decoupling and circuit layout and are effectively operating at a very high frequency and this is causing your problem. Check the FET Drain with a scope.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Power MOSFET Gate Driver
Heres the overall setup:
4 batteries in series provide 48 volts. The 48 volts powers the coil. The low side of the coil is connected to the drain of the power FET so the FET controls when current is allowed to pass through the coil. 12 V is taken from the first battery to power the gate drivers.
The gate of the FET should be insulated from any effects of the coil on the source and drain, correct?
RE: Power MOSFET Gate Driver
An exact replica of this application is currently in place using MOSFETs as gate drivers. The drain of the FET is connected to 12V via a 10K resistor. The gate of the power FET receives its signal from the drain of the previous FET. Same coil, same voltages. These FETs do not seem to have any problems. They do not get hot while the system is running and they have lasted a very long time. It just not the best way for the system to run because the logic has to be inverted from the microcontroller.
Why does the gate driver have problems but not the MOSFET?
Is it because when the gate of the power FET needs to discharge, there is a clear path to ground through the MOSFET?
RE: Power MOSFET Gate Driver
What overvoltage protection and snubbing protection have you provided for the solenoid?
When the solenoid opens, there will be a very high voltage with a steep wavefront developed across the solenoid to try to prevent it from opening. This can result in a large voltage transient on the drain of the FET and this can be capacitively coupled through into the gate of the FET. The driver has to keep the gate low enough to prevent a turn ON at this point. If the design is not correct, there can be oscillations at this point with the gate driver having to absorb a lot of energy. A scope on the drain of the FET may give a clue.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Power MOSFET Gate Driver
RE: Power MOSFET Gate Driver
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com