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Design Ideas |
With
PWM control of power factor, you need a continuous check on excess pulse width
and dead periods to protect a variety of systems that may not incorporate such
protection. You also need regular pulsed power to ensure good averaged,
reconstructed power-signal waveforms for which the dead period for the PWM
signal must not exceed limits. The circuit in Figure
1 monitors both excess high-level pulse width and excess dead period and
visually warns the user of problems in the PWM function.
Excess high-level pulse width turns on the normally off, red LED, and excess dead period turns on the normally off, green LED. If the PWM function suffers from both excess high-level pulse width and excess dead period, both the red and green LEDs glow. The circuit compares the upper bounds on pulse width and dead period with the charging time of capacitors C1 and C2. Variable resistors R1 and R2 control the capacitors' charging rates. The resistors set the upper-boundary limits at 10 µsec to 1 msec, according to user requirements. R1 sets the high pulse-width limit, and R2 sets the dead-period limit. C1 and C2 are fixed, 0.01-µF, low-leakage Teflon or polypropylene capacitors. (DI #1941)
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