Photocouplers with high-speed switching operation and integrated IGBT protection function deliver IGBT gate drive benefits

January 31, 2013 // By Paul Buckley
Renesas Electronics has introduced two new photocouplers PS9332L and PS9332L2, with an integrated insulated-gate bipolar transistor (IGBT) protection function, for applications such as industrial machinery and solar power systems.

The new PS9332L and PS9332L2 feature an integrated active Miller clamp circuit to prevent IGBT malfunction, world-top-class high-speed switching (20 percent faster than conventional products) among IGBT drive photocouplers with integrated IGBT protection function, compact 8-pin SDIP (shrink dual inline package), and guaranteed high-temperature operation. The photocouplers can be used for gate drive of IGBT devices used in inverter circuits for motor control.
 
A photocoupler combines in a single package a light emitting diode (LED) on the input side, to convert an electrical signal into light, and a photo detector on the output side, to convert the light into an electrical signal. The input and output sides are electrically isolated from each other because the signal is conveyed between them in the form of light. Types of photocouplers include general-purpose photocouplers (transistor output) for applications such as power supply, and IGBT drive photocouplers, which are used for gate drive of IGBT devices in applications such as solar power generators or general-purpose inverters.
 
The new PS9332L and PS9332L2 are IGBT drive photocouplers consisting of a gallium-aluminum-arsenide (GaAlAs) LED as the light emitting diode, photo detector IC, and an IGBT protection circuit. They are designed to drive the gate of an IGBT device while at the same time providing an integrated protection function (active Miller clamp) to prevent destruction due to malfunction of the IGBT. In a conventional system this protection function must be implemented by means of external components, resulting in a more complex system design and making miniaturization difficult.
 
When the IGBT connected to the photocoupler turns off, current flow (Miller current) between the collector and gate can cause a gate voltage, resulting in malfunction. The integrated active Miller clamp circuit shortens the gate charge to ground, suppressing any rise in the gate voltage and preventing malfunction. Integrating the protection circuit into the photocoupler simplifies system design and enables the system to be more compact overall.