Universal PWM SIGNAL ISOLATION MODULE

This PWM (pulse width modulation) signal isolation module is built around the widely adopted 6N137 high-speed optocoupler.

- T.K. HAREENDRAN

The device combines a high-efficiency input LED with an integrated optical photodiode detector IC to ensure robust signal isolation.

The advanced 6N137 variants incorporate an open drain NMOS transistor output (photodetector logic gate), offering lower leakage than traditional open-collector Schottky-clamped transistor outputs (VO). An integrated enable function (VE) also allows the detector to be strobed, improving design flexibility and control.

Optocoupler speed is critical for its performance. According to the Everlight 6N137 datasheet, maximum output rise and fall times are 40ns and 10ns, respectively. These represent the output voltage transition times when the input LED is pulsed with forward current. The inverse of the sum of these times closely approximates the maximum operating frequency under specified drive conditions.

Fig. 1 shows how the 6N137 IC module looks and Fig. 2 shows its internal structure.

PWM resolution defines the number of distinct duty cycles within a given period. A 10-bit resolution yields 1024 steps, while an 8-bit resolution provides 256 discrete duty cycles.