Publication 700-AT001A-EN-E June 2002
2-4
Considerations When Designing SSR Control Systems
For SSRs with constant-current input circuits (e.g., 700-SH) calculation
is performed at 0.1 mA.
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The ON/OFF frequency should be set to 10 Hz maximum for an AC
load and 100 Hz maximum for DC load ON/OFF. If ON/OFF occurs
at frequencies exceeding these values, the SSR output will not be able
to follow up.
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In SSRs that have a wide input voltage range (such as 700-SC and
700-SF), the input impedance varies according to the input voltage
and changes in the input current. If the input voltage is low, the
influence of the voltage drop for the input LED is large, and the input
impedance will be higher than expected. If the voltage is so high that
the LED voltage drop can be ignored, the input impedance will be
close to the resistance R.
For semiconductor-driven SSRs, changes in voltage can cause
malfunction of the semiconductor, so be sure to check the actual
device before usage. See the following examples. Refer to the SSR’s
datasheet for the impedance of individual SSR models.
Input
R = 2 k
Ω
R = 1.5 k
Ω
Applicable Input Impedance for a Photocoupler-type SSR
without Indicators (Example)
700-SC (Without Indicators)
Input current (mA)
Input impedance (k )
Ω
Input voltage (V)
Input current
Input impedance
