Overview

The PC817 (PC817X / LTV-817) is a universally deployed 4-pin photocoupler (optocoupler) IC manufactured by Sharp Microelectronics, Lite-On, and Everlight. It consists of an GaAs infrared emitting diode optically coupled to an NPN silicon phototransistor inside a compact 4-pin package.

Providing up to 5000 VRMS5000\text{ V}_{\text{RMS}} of galvanic isolation, the PC817 breaks ground loops and isolates sensitive microcontroller digital logic pins from high-voltage AC/DC noise, noisy motor drivers, relays, and switch-mode power supply (SMPS) feedback circuits.

Quick reference

Component Type4-Pin Photocoupler / Optocoupler
Isolation Voltage (VISOV_{ISO})5000 VRMS5000\text{ V}_{\text{RMS}} (1 minute)
Collector-Emitter Voltage (VCEOV_{CEO})80 V80\text{ V} max
Input LED Forward Current (IFI_F)50 mA50\text{ mA} max (20 mA20\text{ mA} recommended)
Collector Current (ICI_C)50 mA50\text{ mA} max
Current Transfer Ratio (CTR)50% to 600% (Rank A: 80–160%, B: 130–260%, C: 200–400%, D: 300–600%)
Response Time4 μs4\ \mu\text{s} rise time / 3 μs3\ \mu\text{s} fall time
Package4-pin DIP / 4-pin SMD

Pinout (DIP-4 Package)

Looking at the top of the 4-pin package with dot indicator at Pin 1:

text
             ┌───┴───┐
     (A)  1 │ 1   4 │ 4  (C)
  ANODE     │ PC817 │    COLLECTOR
     (K)  2 │ 2   3 │ 3  (E)
  CATHODE   └───────┘    EMITTER
PinNameTypeDescription
1ANODE (A)InputIR LED Anode (+)
2CATHODE (K)InputIR LED Cathode (-)
3EMITTER (E)OutputPhototransistor Emitter (Output ground reference)
4COLLECTOR (C)OutputPhototransistor Collector (Output signal line)

Specifications

ParameterSymbolMinTypMaxUnitConditions
LED Forward VoltageVFV_F1.01.21.4VIF=20mAI_F = 20\text{mA}
LED Reverse VoltageVRV_R——6.0VIR=10 μAI_R = 10\ \mu\text{A}
Collector-Emitter BreakdownV(BR)CEOV_{(BR)CEO}80——VIC=0.1mA,IF=0I_C = 0.1\text{mA}, I_F = 0
Collector Dark CurrentICEOI_{CEO}——100nAVCE=20V,IF=0V_{CE} = 20\text{V}, I_F = 0
Collector Saturation VoltsVCE(sat)V_{CE(sat)}—0.10.2VIF=20mA,IC=1mAI_F = 20\text{mA}, I_C = 1\text{mA}

Typical Applications

Isolated Microcontroller Input Signal Buffer

Reading a 12V12\text{V} or 24V24\text{V} industrial sensor or push-button into a 3.3V3.3\text{V} / 5V5\text{V} MCU GPIO pin:

text
  +24V Sensor Line ───[ R1 = 2.2kΩ ]───► [Pin 1: ANODE]
                                             PC817
  Sensor Ground ──────────────────────► [Pin 2: CATHODE]

  +3.3V MCU Power Rail ───[ R2 = 10kΩ Pullup ]───┬─── [Pin 4: COLLECTOR]
                                                 │
                                                 ├─── MCU GPIO Pin (Active LOW)
                                                 │
  MCU Ground ────────────────────────────────────┴─── [Pin 3: EMITTER]

Common mistakes

  • Forgetting input series current-limiting resistor: Connecting a 5V5\text{V} or 12V12\text{V} control line directly across Pins 1 and 2 without a series resistor burns out the internal IR LED (VF≈1.2VV_F \approx 1.2\text{V}). Always size Rin=(Vin−1.2V)/0.010AR_{in} = (V_{in} - 1.2\text{V}) / 0.010\text{A}.
  • Assuming 100% CTR across all operating temperatures: The Current Transfer Ratio (CTR=ICIF×100%CTR = \frac{I_C}{I_F} \times 100\%) degrades over time and at high temperatures. Design pull-up resistors assuming lower CTRCTR bounds.

Notes

  • PC817 vs 6N137: PC817 is a phototransistor optocoupler for DC and low-speed switching (<10 kHz< 10\text{ kHz}); 6N137 is a high-speed logic gate optocoupler (10 Mbps10\text{ Mbps}) for high-frequency SPI or fast UART isolation.

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