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NCP1654BD133R2G датащи(PDF) 14 Page - ON Semiconductor |
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NCP1654BD133R2G датащи(HTML) 14 Page - ON Semiconductor |
14 / 23 page NCP1654 http://onsemi.com 14 Vramp is the internal ramp voltage, the positive input of the PFC modulation comparator, Vm is the multiplier voltage appearing on Vm pin, Ich is the internal charging current, Cramp is the internal ramp capacitor, and VREF is the internal reference voltage, the negative input of the PFC modulation comparator. Ich, Cramp, and VREF also act as the ramp signal of switching frequency. Hence the charging current Ich is specially designed as in (Equation 5). The multiplier voltage Vm is therefore expressed in terms of t1 in (Equation 6). (eq. 5) Ich + CrampVREF T (eq. 6) Vm + VREF * t1 Cramp CrampVREF T + VREF T * t1 T From (Equation 3) and (Equation 6), the input impedance Zin is re−formulated in (Equation 7). (eq. 7) Zin + Vm VREF Vout IL*50 Because VREF and Vout are roughly constant versus time, the multiplier voltage Vm is designed to be proportional to the IL−50 in order to have a constant Zin for PFC purpose. It is illustrated in Figure 34. Figure 34. Multiplier Voltage Timing Diagram Time Time Time VM IL Iin Vin It can be seen in the timing diagram in Figure 33 that Vm originally consists of a switching frequency ripple coming from the inductor current IL. The duty ratio can be inaccurately generated due to this ripple. This modulation is the so−called “peak current mode”. Hence, an external capacitor CM connected to the multiplier voltage Vm pin is essential to bypass the high−frequency component of Vm. The modulation becomes the so−called “average current mode” with a better accuracy for PFC. Figure 35. External Connection on the Multiplier Voltage Pin PFC Duty Modulation Vm + RMIcsVbo 4(Vcontrol * VCONTROL(min)) RM CM Vm Im 2 The multiplier voltage Vm is generated according to (Equation 8). (eq. 8) Vm + RMIcsVbo 4(Vcontrol * VCONTROL(min)) Where, RM is the external multiplier resistor connected to Vm pin, which is constant. Vbo is the input voltage signal appearing on the BO pin, which is proportional to the rms input voltage, Ics is the sense current proportional to the inductor current IL as described in (Equation 11). Vcontrol is the control voltage signal, the output voltage of Operational Trans−conductance Amplifier (OTA), as described in (Equation 12). RM directly limits the maximum input power capability and hence its value affects the NCP1654 to operate in either “follower boost mode” or “constant output voltage mode”. Figure 36. External Connection on the Brown Out Pin Vbo BO 4 + RboL Vin RboU CBO + - VboH / VboL VboH = 1.3 V, VboL = 0.7 V Refer to Figure 36, (eq. 9) Vbo + KBO(Vin) + KBO @ 22 p Vac (eq. 10) KBO + RboL RboU ) RboL where Vbo is the voltage on BO pin. KBO is the decay ratio of Vin to Vbo. <Vin> is the average voltage signal of Vin, the voltage appearing on Cfilter. Vac is the RMS input voltage. |
Аналогичный номер детали - NCP1654BD133R2G |
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Аналогичное описание - NCP1654BD133R2G |
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