What is Current Transfer Ratio (CTR) ?
Answer: The current transfer ratio (CTR) is an important parameter in optocoupler selection.
The gain of an optocoupler is expressed as the Current Transfer Ratio (CTR). It is defined as the ratio of the phototransistor output current (Ic) to the LED input current (If), expressed as a percentage.
CTR = (Ic / If) × 100%
Does CTR change with temperature and aging?
Answer: CTR is affected by the forward current, the collector-emitter voltage, and the ambient temperature.
Yes, CTR decreases at high temperatures and degrades over time due to LED aging. Design your loop using the minimum guaranteed CTR to stay safe under worst-case conditions.
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Understanding Optocoupler Biasing for Stable Isolated SMPS Feedback
Compensation Network Design in Isolated SMPS Feedback Loops