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NCP1653AP Datasheet(PDF) 11 Page - ON Semiconductor |
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NCP1653AP Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 19 page NCP1653, NCP1653A http://onsemi.com 11 stands for the RMS. Ivac is a constant in the 50 or 60 Hz bandwidth. Multiplier resistor RM is the external resistor connected to the multiplier voltage VM pin (Pin 5). It is also constant. RM directly limits the maximum input power capability and hence its value affects the NCP1653 to operate in either “follower boost mode” or “ constant output voltage mode”. Ivac + 2 Vac * 4V (Rvac ) 12 kW) [ Vac R vac (eq.9) Sense current IS is proportional to the inductor current IL as described in (eq.10). IL consists of the high−frequency component (which depends on di/dt or inductor L) and low−frequency component (which is IL−50). IS + RCS RS IL (eq.10) Control current Icontrol is a roughly constant current that comes from the PFC output voltage Vout that is a slowly varying signal. The bandwidth of Icontrol can be additionally limited by inserting an external capacitor Ccontrol to the control voltage Vcontrol pin (Pin 2) in Figure 30. It is recommended to limit fcontrol, that is the bandwidth of Vcontrol (or Icontrol), below 20 Hz typically to achieve power factor correction purpose. Typical value of Ccontrol is between 0.1 mF and 0.33 mF. Figure 30. Vcontrol Low−Pass Filtering FB ref ref reg 300 k Ccontrol V I I 96% I Regulation Block 2 Vcontrol I = control Vcontrol R 1 (eq.11) Ccontrol u 1 2 p 300 kW fcontrol From (eq.7)−(eq.10), the input impedance Zin is re−formulated in (eq.12). Zin + RM RCS Vac Vout IL 2RS R vac Icontrol Vref IL−50 Zin + RM RCS Vac Vout 2RS R vac Icontrol Vref whenIL + IL−50 (eq.12) The multiplier capacitor CM is the one to filter the high−frequency component of the multiplier voltage VM. The high−frequency component is basically coming from the inductor current IL. On the other hand, the filter capacitor Cfilter similarly removes the high−frequency component of inductor current IL. If the capacitors CM and Cfilter match with each other in terms of filtering capability, IL becomes IL−50. Input impedance Zin is roughly constant over the bandwidth of 50 or 60 Hz and power factor is corrected. Practically, the differential−mode inductance in the front−ended EMI filter improves the filtering performance of capacitor Cfilter. Therefore, the multiplier capacitor CM is generally with a larger value comparing to the filter capacitor Cfilter. Input and output power (Pin and Pout) are derived in (eq.13) when the circuit efficiency η is obtained or assumed. The variable Vac stands for the RMS input voltage. Pin + Vac2 Zin + 2RS R vac Icontrol Vref Vac RM RCS Vout (eq.13a) T Icontrol Vac Vout Pout + hPin + h 2RS R vac Icontrol Vref Vac RM RCS Vout (eq.13b) T Icontrol Vac Vout Follower Boost The NCP1653 operates in follower boost mode when Icontrol is constant. If Icontrol is constant based on (eq.13), for a constant load or power demand the output voltage Vout of the converter is proportional to the RMS input voltage Vac. It means the output voltage Vout becomes lower when the RMS input voltage Vac becomes lower. On the other hand, the output voltage Vout becomes lower when the load or power demand becomes higher. It is illustrated in Figure 31. Figure 31. Follower Boost Characteristics Vin V (Follower boost) out time time V (Traditional boost) out Pout Follower Boost Benefits The follower boost circuit offers an opportunity to reduce the output voltage Vout whenever the RMS input voltage Vac is lower or the power demand Pout is higher. Because of the step−up characteristics of boost converter, the output voltage Vout will always be higher than the input voltage |
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