Electrically Isolated Zero-Crossing Detector

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< Analog Electronic ~ Electrically Isolated Zero-Crossing Detector

eric

Posted: Mon Aug 28, 2006 12:08 pm Post subject: Electrically Isolated Zero-Crossing Detector

Site Admin Joined: 01 Jan 1970 Posts: 311

C. Volt
All power control circuits that use phase
control require an adjustable delay element
synchronised to the mains voltage. The
adjustable delay determines the phase
angle at which the thyristor, triac or transistor
connects the mains voltage to the
load. Simple passive dimmer circuits use
RC phase shifters having a fixed relationship
to the mains frequency. Nowadays,
microprocessors are often used for precision
controllers and complex control tasks.
A zero-crossing detector is thus required
for synchronisation with the mains frequency.
If the microprocessor does not
have to be electrically isolated from the
mains, the detector can be constructed
very simply: a voltage divider and two protection
diodes at the interrupt input of the
microcontroller are sufficient.
However, if the microcontroller must be
electrically isolated from

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