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18 \ VISHAY An Automotive Grade Above I n today's electric/hybrid vehicle applications, a high-voltage DC/ DC converter (Figure 1) is typically required to transfer power from the high-voltage battery pack (400V in this design) to the 12V vehicle bus. A key function of this design is maintaining a safe galvanic isolation barrier between the high-voltage and low- voltage buses. To transmit low-voltage measurements over the barrier to the controller on the high-voltage side, an optocoupler with a phototransistor output can be utilized. Optocoupler Regulates a 400V/12V DC/DC Converter VISHAY INTERTECHNOLOGY Figure 1: 2kW 400V/12V DC/DC converter (Source: Vishay) In terms of the overall converter operation, the 400V DC input voltage is filtered with L1 and C1 (Figure 2) to suppress any ripple on the bus. The high-voltage MOSFETs (TR1-TR4 in Figure 2) are connected in a full-bridge arrangement to drive the main transformer (T1 in Figure 2) and are controlled by an integrated circuit that generates the necessary pulse-width modulation (PWM) signals. The transformer is a Vishay PQ40/40 custom planar design that can transmit up to 2.5kW of power and is in a 65mm x 42mm x 28mm package. On the low-voltage side, the AC voltage from the transformer output is actively rectified using Vishay SQJQ144AE MOSFETs "To transmit low-voltage measurements over the barrier to the controller on the high- voltage side, an optocoupler with a phototransistor output can be utilized."