HV circuit breaker reference design targets EV

September 29, 2021 // By Christoph Hammerschmidt
HV circuit breaker reference design targets EV
The cooperation between the e-mobility specialists of Rutronik's Automotive Business Unit (ABU) and Vishay's Automotive Division has resulted in a reference design for a high-voltage circuit breaker with a switching capacity of 40 kW. This resettable and low-loss SiC solution with MOSFETs from Rohm replaces existing systems with mechanical relays.

High-voltage switches are an indispensable link in the high-voltage architecture of modern battery electric vehicles (BEV). They serve to safely separate auxiliary units on the high-voltage side with - depending on the platform architecture – 400V or 800V- from the rest of the electrical vehicle architecture and thus prevent damage if necessary.

In terms of circuitry, the HV circuit breaker consists of an isolated 800V power stage with 12V measurement and evaluation electronics and an Aurix TC375 Lite Kit. The concept of the HV circuit breaker is realised in the switching stage with high-performance semiconductors of the latest SiC generation from Rohm, galvanic isolation of the measuring channels, high-precision shunts, optocouplers and all protection components from Vishay. In addition, a second-generation Aurix microcontroller from Infineon controls the device.

With the 1200V SiC MOSFETs from Rohm in the SMD package and a precisely tuned control via a SiC gate driver, the HV circuit breaker can switch powers of up to 40kW. The resulting power loss reaches approx. 16W. The heat can be dissipated passively at room temperature (25°C). Thus, the concept exceeds the requirements of premium OEMs.

Two high-precision shunts in parallel connection from Vishay are used in the output stage, which are characterised by highly accurate bidirectional measurement of the battery current. The current and voltage measurement signals are transmitted galvanically separated (earth-free measurement), processed by measurement signal amplifiers and forwarded to the microcontroller. Vishay's newly developed VOA300 linear optocouplers provide galvanic isolation from the 12V side.

Eight high-voltage MLCCs from Vishay provide the galvanically isolated supply for the operational amplifiers, the SiC driver and the optocouplers. This supply includes a push-pull driver stage with 50 kHz. The Aurix board is connected via a cable connection and, after successful connection, can output the measured and processed values via an already implemented software. The configuration and readout of the measured values of the eFuse with Aurix control is done via an

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