The **ISP817AXSMT-R** is a high-performance, single-channel phototransistor output optocoupler manufactured by Isocom Components. It is widely used for signal isolation between high-voltage and low-voltage circuits. --- ### ## 1. Technical Specifications Below are the primary electrical and physical characteristics of the component: | Parameter | Specification | | :--- | :--- | | **Type** | Phototransistor Optocoupler | | **Number of Channels** | 1 | | **Isolation Voltage** | 5000 Vrms | | **Current Transfer Ratio (CTR)** | 80% to 160% (Rank A) | | **Forward Current ($I_F$)** | 50mA | | **Collector-Emitter Voltage ($V_{CEO}$)** | 35V | | **Package Type** | SMT (Surface Mount Technology) | | **Mounting Type** | Gull-wing (SMD) | --- ### ## 2. Pin Configuration The device typically follows a standard 4-pin layout: 1. **Pin 1 (Anode):** Positive terminal of the Input LED. 2. **Pin 2 (Cathode):** Negative terminal of the Input LED. 3. **Pin 3 (Emitter):** Emitter terminal of the Output Phototransistor. 4. **Pin 4 (Collector):** Collector terminal of the Output Phototransistor. --- ### ## 3. Key Features and Part Breakdown The part number **ISP817AXSMT-R** can be broken down to understand its specific features: * **ISP817:** The base series identifier (compatible with PC817). * **A:** Refers to the **CTR Rank**. Rank A indicates a Current Transfer Ratio of 80% - 160% at 5mA $I_F$. * **X:** Often denotes specific internal construction or high-density mounting. * **SMT:** Indicates Surface Mount Technology packaging. * **R:** Indicates **Tape and Reel** packaging for automated pick-and-place assembly. --- ### ## 4. Applications The ISP817AXSMT-R is commonly found in the following environments: * **Switch Mode Power Supplies (SMPS):** Providing feedback loops while maintaining isolation from the AC mains. * **PLC/Industrial Control:** Protecting sensitive microcontrollers from electrical noise or surges on input/output lines. * **Telecommunications:** Signal transmission between circuits with different ground potentials. * **Computer Peripherals:** Isolating high-speed data buses. --- ### ## 5. Design Considerations ```c // Design Tip: Calculating the Current Limiting Resistor (Rin) // Formula: Rin = (V_input - V_forward) / I_forward V_input = 5.0; // Input Logic Voltage V_forward = 1.2; // Typical LED drop I_forward = 0.005; // 5mA for CTR stability Rin = (5.0 - 1.2) / 0.005; // Result: 760 Ohms ```