MB39C604 Datasheet, PDF (12/36 Pages) Cypress Semiconductor – PSR topology in an isolated flyback circuit

MB39C604
8.2 PFC (Power Factor Correction) Function
Switching on time (T_ON) is generated by comparing V_COMP with an internal sawtooth waveform (refer to Figure 2). Since V_COMP is
slow varying with connecting an external capacitor (C_COMP) from the COMP pin to the GND pin, T_ON is nearly constant within an AC
line cycle. In this state, I_{P_PEAK} is nearly proportional to the AC Line voltage (V_BULK). It can bring the phase differences between the
input voltage and the input current close to zero, so that high Power Factor can be achieved.
8.3 Dimming Function
MB39C604 has the built-in dimmable circuit to control I_LED by changing a reference of Err Amp based on the input voltage level on
the DIM pin (V_DIM), and realizes dimming. Figure 6 shows I_LED dimming ratio based on V_DIM.
Figure 7 shows the input circuit to the DIM pin for PWM dimming. PWM signal is divided and filtered into an analog voltage with RC
network. It is possible to configurate PWM dimmable system by inputting the voltage to the DIM pin.
Figure 6. Dimming Curve
110%
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
V_DIM [V]
Figure 7. DIM Pin Input Circuit
Document Number: 002-08441 Rev.*A
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