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Download R6 size for wattage requirement
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Do you have any details for the transformer T1? R6 Nominal voltage = AC03 VCC = 12V Less Q2 Vt(minimum) of 2V from FET datasheet Voltage across R6 (VR6) = VCC – Vt(minimum) = 12 – 2 = 10V R6 value = 47 ohms Estimated maximum current = (VR6)/R6 = 10/47 = 213mA Power = VR62/R = 102/47 = 100/47 = 2.13W Typical chopper circuit duty cycle is 10-15% (use 15% (worst case) for this calculation) Power(duty cycle) = 2.13W(.15) = 0.320W Minimum package size to handle the power is 1210 (from Vishay D/CRCW e3 datasheet) Startup power of 2.13W is on the single pulse chart. Operation power of 0.32W is on the continuous pulse chart. Scope image of Voltage across R6 during startup. The AC03 specifies a minimum of four AC=1/2 cycles during startup. This image shows a little over four AC-1/2 cycles appear across R6 during startup. For worst-case evaluation, we will use five AC-1/2 cycles or 50m seconds for startup time. The image also shows the voltage across R6 is decreasing during the startup time. This is expected as all power for the AC03 is from the VCC capacitor. For the calculations above, the VCC is kept at 10V for worst case evaluation. Scope image of Q2 gate drive pin from AC03. The image shows approximately 15% duty cycle during Q2 chopper operation. R6 power during startup Table below from Vishay D/CRCW e3 datasheet. This table is for allowable single pulse wattage versus time. I placed red markers to locate the approximate point of operation. The markers are approximately 50m seconds and approximately 2.13W. The table indicates a 1206 package is not capable of withstanding the power during startup, so the 1210 package is the recommended minimum size for R6. R6 power during operation Table below from Vishay D/CRCW e3 datasheet. This table is for allowable continuous pulse wattage versus time. I placed red markers to locate the approximate point of operation. The markers are approximately 3u seconds and approximately 0.32W. The table indicates a 1206 package is not capable of withstanding the power during startup, so the 1210 package is the recommended minimum size for R6.
