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Power-Factor-Slide21

Next an application example will be used to quantify the operating conditions for the semiconductors in a SMPS with output power of 650 watts. This will highlight the challenge for low line operating conditions for the semiconductors. Most important is the input voltage range, requiring 90 Volts AC to 265 Volts AC which is a typical range. 400 V is a very typical value for the bus output voltage feeding a PWM converter. The target efficiency of 92 percent provides the multiplier to determine the total input power. Inductor ripple current affects the size of the inductor required. A smaller ripple current is easier on the semiconductors but requires a larger inductor, so a typical compromise value might be 30% ripple current at full load. In this design example, which assumes CoolMOS CP transistors and Infineon Silicon Carbide diodes, a 250 kHz switching frequency is specified to minimize inductor size. However, the customer requirement for 75 Volts AC line brownout hold up makes this the effective low line design point for the semiconductors, not the 90 Volts AC specification.

PTM Published on: 2011-09-02