The **PC933** (often identified as the TLP933 or similar series depending on the manufacturer, such as Sharp or Toshiba) is a high-speed **Photocoupler (Optocoupler)** specifically designed for driving Power MOSFETs or IGBTs. It serves as a bridge that transfers electrical signals between two isolated circuits using light, preventing high voltage from the power side from damaging the control side (like a microcontroller). --- ### 1. Internal Components and Construction The PC933 consists of two primary electronic elements housed within a single package: | Component | Description | Function | | :--- | :--- | :--- | | **Input Side** | AlGaAs Infrared Emitting Diode (LED) | Converts the electrical input signal into light pulses. | | **Output Side** | Integrated Photodetector & Signal Processing | Includes a photodiode, an amplifier, and a totem-pole output stage. | --- ### 2. Key Technical Specifications Below are the typical electronic characteristics found in the PC933 datasheet: | Parameter | Value (Typical) | | :--- | :--- | | **Isolation Voltage** | 5,000 Vrms | | **Output Peak Current** | ±0.5 A to ±1.0 A (depending on specific sub-model) | | **Supply Voltage ($V_{CC}$)** | 15V to 30V | | **Switching Speed ($t_{PLH} / t_{PHL}$)** | < 0.5 µs (High Speed) | | **Common Mode Rejection (CMR)** | 10 kV/µs to 15 kV/µs | --- ### 3. Core Electronic Functions #### A. Totem-Pole Output Unlike standard optocouplers that use a single transistor, the PC933 features a **Totem-Pole (Push-Pull)** output stage. * **Why it matters:** It can both "source" (supply) and "sink" (absorb) current. This is critical for charging and discharging the gate capacitance of a MOSFET/IGBT rapidly to ensure clean switching. #### B. High Common Mode Rejection (CMR) In high-power environments, rapid voltage changes ($dv/dt$) can create noise that triggers "ghost" signals. The PC933 includes internal shielding to ignore these spikes, ensuring the output only changes when the input LED is actually triggered. #### C. Threshold Input Current The LED typically requires a forward current ($I_F$) of about **5mA to 10mA** to activate the output. This makes it compatible with most standard logic circuits and microcontrollers. --- ### 4. Typical Application Circuit When wiring the PC933, the following electronic parts are usually required: 1. **Input Resistor ($R_{in}$):** Limits current to the internal LED. 2. **Bypass Capacitor ($C_b$):** A 0.1µF capacitor placed close to the $V_{CC}$ pin to stabilize the high-speed switching current. 3. **Gate Resistor ($R_g$):** Placed between the PC933 output and the IGBT/MOSFET gate to control switching speed and prevent oscillations. ---