What this optocoupler does in the design
The Toshiba TLP388(GB-TPL,E is a single-channel transistor-output optocoupler built for galvanic isolation between a DC input and a high-voltage output stage. Its 5000Vrms isolation rating suits it for industrial motor drives, PLC I/O modules, and power-supply feedback loops where safety isolation or ground-loop breaking is required.
Key ratings that drive the BOM decision
The 5000Vrms isolation is the primary spec for safety-critical designs. The 350V VCEO max means this part can handle 24V, 48V, and even 120V DC bus rails with margin, so you don't need a second transistor for level shifting. The current transfer ratio (CTR) spans 100% to 600% at 5mA forward current, giving you a wide operating window: a low CTR still guarantees logic-level output at the minimum drive current, while a high CTR allows the LED to be driven at lower current for reduced power draw. Rise and fall times of 2µs and 3µs respectively are adequate for 100 kHz switching or slower — fine for relay drives, status feedback, and isolated serial communication at moderate baud rates.
Temperature range and deployment environment
The wide temperature range also covers military/aerospace ground-support equipment that must operate across extreme thermal cycles.
Package and footprint notes
Housed in a 6-SOIC package with 4 leads (0.173" body width, 4.40mm), it is a surface-mount device. The 4-lead arrangement — two input-side LED pins and two output-side phototransistor pins — keeps the creepage distance consistent with the 5000Vrms isolation rating. Standard SOIC-4 footprint applies; no special thermal pad or heatsinking is needed at the 50mA output current.