A1458 Optocoupler Datasheet -

| Parameter | Symbol | Conditions | Min | Typ | Max | Unit | |-----------|--------|-------------|-----|-----|-----|------| | Collector-Electron Breakdown | BV_CEO | I_C = 100 μA, I_F = 0 | 80 | - | - | V | | Emitter-Collector Breakdown | BV_ECO | I_E = 100 μA | 6 | - | - | V | | Dark Current (Leakage) | I_CEO | V_CE = 20V, I_F = 0, Ta=25°C | - | 10 | 100 | nA | | Dark Current at 100°C | I_CEO | V_CE = 20V, I_F = 0, Ta=100°C | - | 1 | 10 | μA |

Important: Dark current doubles approximately every 10°C. At high temperatures, it can become significant, so ensure your pull-up resistor and logic threshold account for this.

| Parameter | Symbol | Rating | Unit | | :--- | :--- | :--- | :--- | | Input (LED side) | | | | | Forward Current | IF | 50 | mA | | Peak Forward Current (1µs pulse, 300pps) | IFP | 1 | A | | Reverse Voltage | VR | 6 | V | | Power Dissipation | PD | 70 | mW | | Output (Phototransistor side) | | | | | Collector-Emitter Voltage | VCEO | 80 | V | | Emitter-Collector Voltage | VECO | 6 | V | | Collector Current | IC | 50 | mA | | Collector Power Dissipation | PC | 150 | mW | | Total Device | | | | | Total Power Dissipation | PTOT | 200 | mW | | Isolation Voltage (for 1 min) | VISO | 5000 | Vrms | | Operating Temperature | TOPR | -55 to +110 | °C | | Storage Temperature | TSTG | -55 to +125 | °C | a1458 optocoupler datasheet

Design Alert: Do not exceed the forward current of 50mA on the input diode. Exceeding 60mA will rapidly degrade the LED's light output, permanently lowering the CTR.

Before we dissect the numbers, let’s understand the anatomy. The A1458 is a phototransistor optocoupler. This means it consists of two primary components housed within a single, light-tight package (usually a DIP-4 or SMD format): | Parameter | Symbol | Conditions | Min

This simple mechanism creates an electrical barrier. The input side controls the output side via light, not copper. Therefore, there is no direct electrical connection between your high-voltage side and your low-voltage logic.

In industrial environments, long signal cables act as antennas, picking up noise. By converting the electrical signal to light and back to electricity, the A1458 filters out almost all electromagnetic interference (EMI), ensuring a clean signal reaches your logic board. Design Alert: Do not exceed the forward current

Scenario: Isolating a 24V PLC output to a 3.3V microcontroller input.

Components:

Operation: When PLC output is high (24V), LED turns on, phototransistor conducts, output pin pulled low. When PLC output low, LED off, output pulled high by R2.