Renesas Electronics Introduces Optocoupler with Industry-Leading Fast Switching and Integrated IGBT Protection Function

It is designed to drive IGBTs used in inverter devices for purposes such as motor control. The use of the new optocoupler facilitates the design of IGBT peripheral circuits and enables IGBT direct drive up to the 1,200 volt (V) and 100-ampere (A) class. The compact 16-pin SOP (Small Outline Package) contributes to system compactness.

An optocoupler integrates in a single package a light emitting element (LED) on the input side, which converts an electric signal into light, and a light receiving element on the output side, which converts light into an electric signal. It is an optical coupling device that completely isolates the input and output sides electrically by using light for signal transfer. Optocouplers are used in the inverter circuits of industrial equipment and in electric household appliances to protect the circuits between electronic devices and to shut out noise by electrically isolating the input and output blocks.

General-purpose inverters and inverters for solar power generation systems are a fundamental technology employed in recent years to reduce environmental impact by cutting carbon dioxide emissions and reducing power conversion loss to save energy. The market for these inverters is expected to continue to grow. The inverter circuit comprises a high-voltage circuit block incorporating power devices such as IGBTs or MOSFETs and a control circuit block employing components such as a microcontroller (MCU). Optocouplers designed for use with IGBTs or MOSFETs are needed to electrically isolate the two circuit blocks. An IGBT drive coupler is typically used for the drive control of an IGBT, but a protection circuit is also needed to safeguard the IGBT. This has tended to complicate the overall system design.

The PS9402 optocoupler simplifies system design and contributes to greater compactness by integrating the protection circuit that previously had to be added as an external component.

Key features of the PS9402 optocoupler:
(1) Integrated IGBT protection circuit providing functionality such as short circuit detection
When a fault (short circuit) occurs in the IGBT connected to the optocoupler, the collector-emitter voltage of the IGBT rises and may damage the device. The PS9402 has a function that detects a rise in collector-emitter voltage and turns off the IGBT. It also incorporates a soft turn-off function that suppresses the generation of noise when the IGBT is turned off. A fault signal is output to the MCU to indicate that an abnormal shut-off has occurred, and an auto-reset function performs recovery automatically once a specified time (minimum 5 microseconds) has elapsed after the fault was detected.

Since these protection circuits are built into the PS9402 optocoupler, the design of the system is simplified and it can be made more compact overall.
(2) Integrated active Miller clamp circuit to prevent IGBT malfunctions
When the IGBT connected to the optocoupler turns off, current flow to the collector-gate capacitance (Miller current) can generate a gate voltage that causes a malfunction. The active Miller clamp circuit built into the PS9402 absorbs the Miller current, averting malfunctions by preventing the gate voltage from rising.
(3) High-speed and low-power operation
Renesas Electronics’ exclusive BiCMOS process is employed for the light receiving IC, resulting in reduced parasitic capacitance (Note 2), shorter delay time (tPHL and tPLH ≤ 200 ns), and reduced circuit drive current consumption (Icc ≤ 3 mA). These contribute to an increase in the precision of the inverter control circuit and reduced power consumption. They also enable greater system compactness because keeping circuit current levels low means a smaller power supply can be used for the system driven by the IGBTs.
Renesas Electronics positions the new PS9402 optocoupler as a product that can contribute to simplified development and greater compactness in inverter systems, for which the market is expected to continue to grow in future. The company plans to continue to develop new high-temperature and high-output product versions.