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FSBH0170W 数据表(PDF) 11 Page - Fairchild Semiconductor |
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FSBH0170W 数据表(HTML) 11 Page - Fairchild Semiconductor |
11 / 14 page © 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com FSBH0F70WA/0170W/0270W • Rev. 1.0.2 11 Functional Description Startup Operation The HV pin is connected to bulk voltage through an external resistor, RHV, as shown in Figure 22. When AC voltage is applied to the power system, an internal HV startup circuit provides a high current (around 3.5mA) to charge an external VDD capacitor until VDD voltage exceeds the turn-on threshold voltage (VDD-ON). For lower power consumption, the HV startup circuit shuts down during normal operation. The external VDD capacitor and auxiliary winding maintain the VDD voltage and provide operating current to controller. Figure 22. Startup Circuit Slope Compensation The FSBH-series is designed for flyback power converters. The peak-current-mode control is used to optimize system performance. Slope compensation is added to reduce current loop gain and improve power system stability. The FSBH-series has a built-in, synchronized, positive slope for each switching cycle. Soft-Start The FSBH-series has an internal soft-start circuit that reduces the SenseFET switching current during power system startup. The characteristic curve of soft-start time versus VLMT level is shown in Figure 1. The VLMT level rises in six steps. By doing so, the power system can smoothly build up the rated output voltage and effectively reduce voltage stress on the PWM switch and output diode. Figure 23. Soft-Start Function Brown-In/Out Function FSBH0170W/0270W has a built-in internal brown-in/out protection comparator monitoring voltage of the VIN pin. Figure 24 shows a resistive divider with low-pass filtering for line-voltage detection on the VIN pin. Figure 24. Brown-In/Out Function on VIN Pin Once the VIN pin voltage is lower than 0.6V and lasts for 500ms, the PWM gate is disabled to protect the system from over current. FSBH0170W/0270W starts up as VIN increases above 1.1V. Because the divider resistors of the VIN pin are connected behind the bridge, the ratio calculations for brownout in PFC and non-PFC system are different, as shown in Figure 1. The formulas are provided in the following equations: Brownout with PFC: _ 2 20.6 C AC OUT AB C R V RR R π ⋅⋅ = ++ (1) Brownout with non-PFC: _ 20.6 C AC OUT AB C R V RR R ⋅= ++ (2) Brown-in level is determined by: _ 1.1 2 A BC AC IN C RR R V R ++ =⋅ (3) Figure 25. VIN Level According to PFC Operation Brown-In Function of FSBH0F70WA The VIN pin functions are disabled from FSBH0F70WA which still exist brown-in protection in VDD pin. There is a discharge current internal from VDD to ground during startup. The HV source current must be larger than IDD- ST to charge the capacitor of VDD. The brown-in level can be determined by RHV according to the equation: 212 AC HV DD ST V R I − − = (4) |
类似零件编号 - FSBH0170W |
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类似说明 - FSBH0170W |
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