CS1601

DS931PP6

9

5. GENERAL DESCRIPTION

The CS1601 offers numerous features, options, and

functional capabilities to the electronic product lighting

designer. This digital PFC control IC is designed to replace

legacy analog PFC controllers with minimal design effort.

5.1 PFC Operation

One key feature of the CS1601 is its operating frequency

profile. Figure 11 illustrates how the frequency varies over half

cycle of the line voltage in steady-state operation. When

power is first applied to the CS1601, it examines the line

voltage and adapts its operating frequency to the line voltage

as shown in Figure 11. The operating frequency is varied from

the peak to the trough of the AC input. During startup, the

control algorithm generates maximum power while operating

in critical conduction mode (CRM), providing an approximate

square-wave current envelop within every half-line cycle.

Figure 11. Switching Frequency vs. Phase Angle

Figure 12 illustrates how the operating frequency of CS1601

(as a percentage of maximum frequency) changes with output

power and the peak of the line voltage.

Figure 12. CS1601 Max Switching Freq vs. Output Power

Figure 13 illustrates how the operating frequency of CS1601H

changes with output power and the peak of the line voltage.

Figure 13. CS1601H Max Switching Freq vs.Output Power

(Refer to Burst Mode section for more information.)

The CS1601 is designed to function as a DCM controller.

However, during peak periods, the controller may interchange

control methods and operate in a quasi-critical-conduction

mode (quasi-CRM) at low line. For example, at 108VAC main

input under full load, the PFC controller will function as a

quasi-CRM controller at the peak of the AC line cycle, as

shown in Figure 14.

Figure 14. DCM and quasi-CRM Operation with CS1601

The zero-current detection (ZCD) of the boost inductor is

achieved using an auxiliary winding. When the stored energy

of the inductor is fully released to the output, the voltage on the

ZCD pin decreases, triggering a new switching cycle. This

quasi-resonant switching allows the active switch to be turned

on with near-zero inductor current, resulting in a nearly

lossless switch event. This minimizes turn-on losses and EMI

noise created by the switching cycle. Power factor correction

control is achieved during light load by using on-time

modulation.

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045

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180

Rectified Line Voltage Phase (Deg.)

Switching Freq. (% of Max.)

Line Voltage (% of Max.)

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40

5

20

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48

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Vin> 156 VAC (Input Voltage 108 –305 VAC , V

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DCM

Quasi CRM

DCM

Quasi CRM

DCM

t [ms]