Weekly PULSE Issue
Kaivan Karimi – Dir. of Global Strategy, Microcontroller Group, at Freescale
Electronics Quiz of the Day
Rise/Fall time
Question:
Answer:
One reason might be that the FETs in the circuit do not turn off and on perfectly with the PWM signal, but instead have delays. This causes the H-bridge circuit to sometimes create the equivalent of a short circuit.
The “turn on delay” is the delayed response of the FET to an on signal, and “rise time” is the time it takes to start to turn on and actually reach the on state.
Likewise there is a “turn-off delay”, the response time for the FET to start to turn off; and a “fall time”, the time for the FET to go from starting to turn off to fully turned off.
Therefore the timing of the MOSFETs needs to be adjusted to prevent the overlapping periods and make the motor control more efficient and cooler.
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