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THEORY OF OPERATION
FIGURE E-9 – TYPICAL FET OUTPUTS
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| 50 | sec |
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MINIMUM OUTPUT
24sec
2sec
24
sec
50sec
MAXIMUM OUTPUT
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PULSE WIDTH MODULATION
The term PULSE WIDTH MODULATION is used to describe how much time is devoted to conduction in the positive and negative portions of the cycle. Changing the pulse width is known as MODULATION. Pulse Width Modulation (PWM) is the varying of the pulse width over the allowed range of a cycle to affect the output of the machine.
MINIMUM OUTPUT
By controlling the duration of the gate signal, the FET is turned on and off for different durations during a cycle. The top drawing above shows the minimum out- put signal possible over a
The positive portion of the signal represents one FET group1 conducting for 1 microsecond. The negative portion is the other FET group1. The dwell time (off time) is 48 microseconds (both FET groups off). Since only 2 microseconds of the
MAXIMUM OUTPUT
By holding the gate signals on for 24 microseconds each and allowing only 2 microseconds of dwell time (off time) during the
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1A FET group consists of the sets of FET modules grouped onto one switch board.