Contents
How to protect MOSFETs-basics explained, homemade?
Add a decoupling capacitor close to the driver IC supply pinouts, this will reduce the switching transients across the internal supply pinouts which in turn will prevent unnatural output logic to the mosfet gates.
How does a high value resistor protect a MOSFET?
If for any reason, the MOSFET drifts into a high temperature condition, this is sensed by the RTP, and at a predefined temperature, the RTP changes into a high-value resistor. This effectively cuts off the power to the MOSFET, saving it from destruction. Thus, a lower priced resistor sacrifices itself to save a more expensive MOSFET.
What causes a delayed discharging of a MOSFET?
Causing a delayed discharging would mean forcing the mosfet to conduct under stressful conditions, making it unnecessarily warmer.
What should the temperature of a MOSFET be?
Since the RTP has to sense the temperature of the MOSFET, it naturally follows that the two should remain in close proximity. The RTP resistance will allow up to 80A of current at 120V AC through the MOSFET as long as the temperature of the MOSFET remains below the Open Temperature of the RTP, which can be between 135-145ºC.
Why do MOSFETs latch up when voltage is applied?
Well, normally mosfets have the tendency to latch up whenever a switching voltage is applied, this latching effect can sometimes be hard to revert, and by the time an opposite switching current is applied it is already too late.
What should the resistor be on a MOSFET?
The mentioned resistor ensures that as soon as the switching signal is removed the mosfet is able to quickly turn OFF, and prevent a possible damage. This resistor value could be anywhere between 1K and 10K, however lower values would provide better and more effective results.
Why are my MOSFETs so hot after connecting?
Even after connecting everything correctly you find the mosfets in your circuit becoming HOT and blowing off within minutes. This is quite a common issue faced by most new as well as experienced hobbyists while designing and optimizing mosfet based circuits especially the ones which involve high frequencies.
What happens when the voltage of a MOSFET is exceeded?
If the maximum operating voltage of a MOSFET is exceeded, it goes into Avalanche breakdown. This is not necessarily destructive. The MOSFET specifications will state a maximum energy the MOSFET can take in avalanche mode. Energy is 1/ 2LI 2 where L is the inductance and I is the current.
Where does the energy come from to clamp the MOSFET?
Fortunately, in most circuits, the energy the MOSFET may have to clamp is that contained in the rather small (lumped) inductance of the battery and its leads. See the article on PWM controllers in the 4QD TEC archives.
How is the fan speed controlled by the MOSFET?
exclusively controlled by the MOSFET. This means that the MOSFET must be operated in linear mode. voltage will change the current flowing through the motor and thus the fan speed. Fig. 2 the output characteristics of the MOSFET is shown.