At zero crossing the current flow is zero. That means the load current
comes up as the voltage phase comes back up, which means you can switch
larger currents with smaller (cheaper) devices, make less (or zero)
switching noise for the same reason, and interface with lower voltage
drivers such as low current computer stuff, since the gate signal can be
smaller.

"Vaughn" wrote in message
...
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| "Robert Swinney" wrote in message
| ...
| The point in time where a harmonic wave (can you say "sine wave")
intersects
| the ordinate, or "x" axis. Voltage is zero at that time thus it is
desireable
| for switching to occur at that time rather than earlier or later. There
can be
| no transient voltage at the time of zero crossing; no chance of
transient
| voltage damage to the switch.
|
| I always thought the main reason for the zero switching was to
reduce
| generation of electrical/RF noise caused by switching. Back in my traffic
| signal tech days, I used thousands of those things.
|
| Vaughn
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