WS3241 datasheet(5/8 Pages) ETC2

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WS3241 ProductDescription

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Application Information

WS3241 is a constant current driver for LED lighting,

adopted advanced constant current control method.It

integrates 650V power switch. Only need a few peripheral

components can achieve excellent constant current

characteristic. With the primary side feedback technology,

WS3241 do not need optocoupler and TL431, also need not

the auxiliary winding for power supply and detection. Thus

achieve the low systemcost.

Low operation current

The operating current of WS3241 is very low. The

typical value is 150uA. The low operating current improves

the efficiency of the system, while reducing the VDD

capacitor requirements.

Primary Feedback PSR Technology

Assume that the system works in DCM flyback mode,

the power transmission equations can be expressed











Where, P is the output power, Vo and Io is the system

output voltage and current, η is the system power

conversion efficiency, Ipk is the primary side peak current,

fixed 185mA.

In DCM mode, Demagnetization time Tdem can be

expressed as:

dem







Where, Np and Ns is the transformer primary and

secondary turns, respectively. Combination of the above two

formula, the average output current can be expressed as:

dem







dem







Where Ts is the switch cycle. WS3241 adopts PFM

mode to realize constant current, making the peak inductor

current of primary side constant, also remains the ratio of

the demagnetization time and the cycle time, which can

realize constant output current, but also independent with

the line input voltage and transformer inductance. The ratio

of the demagnetization time and the cycle time is 0.5:



dem

Single Chip Built-in 650V High Voltage Power

Supply, Start time less than 100ms

Fig.1 shows the internal high voltage power supply

module. When the system access AC power, VDD capacitor

is charged by the internal 650V high voltage MOS. It will not

reset and start working until the VDD voltage reaches 5.8V.

The start time is less than 100ms, which means that the light

achieves instant bright. In normal operation, VDD is

dynamically charged by Drain, which can save the power

supply auxiliary Winding.

Demagnetization Detection

WS3241 detects the demagnetization time through the

drainterminal waveform, which can save auxiliary winding.

Cycle by Cycle Current Protection and Lead

Edge Blanking

Cycle-by-cycle current limiting is offered in WS3241. An

internal leading edge blanking circuit chops off the sense

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