Publication 700-AT001A-EN-E June 2002
4-2
Q & A
Why Does the Input Current
Vary With the SSR?
Due to design characteristics, a SSR with photocoupler isolation has
different input current requirements from an SSR with phototriac
isolation.
An SSR with photocoupler isolation does not require as high an input
current as a phototriac ensures efficient signal transmission. The SSR,
however, requires a drive circuit of complicated construction therefore
both versions are offered.
Photocoupler input current < Phototriac input current
What Is The Difference in
Switching with a Thyristor
and a Triac?
There is no difference between them as long as resistive loads are
switched. For inductive loads, however, thyristors are superior to
triacs due to the back-to-back connection of the thyristors.
For the switching element, an SSR uses either a triac or a pair of
thyristors connected back-to-back.
There is a difference between thyristors and triacs in response time to
rapid voltage rises or drops. This difference is expressed by dv/dt
(V/ms) (Refer to “What is a Snubber Circuit” on page 4-3 ). This value
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