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Optocoupler LED Resistor & CTR Margin Calculator

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Optocoupler LED Resistor & CTR Margin

Example datasheet values

LED side

Drive voltage (V)

Drive tolerance (±%)

LED VF typ (V)

LED VF max (V)

Target LED current (mA)

LED current abs max (mA)

Coupler and output side

CTR minimum (%)

CTR loss allowance (%)

Output supply (V)

Pull-up resistor (kΩ)

VCE(sat) max (V)

VCE(sat) test ratio IC/IF (%)

Readout

LED SERIES RESISTOR (E24, AT OR BELOW)

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COLLECTOR CURRENT AVAILABLE, END OF LIFE

—mA

OUTPUT-LOW MARGIN

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CHECKS

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Worst case uses the low drive voltage, maximum LED VF, minimum CTR and the loss allowance together. Default 50% loss is a conservative allowance for LED ageing and temperature; use your part's degradation data if you have it.