WS21351 データシートの表示（PDF） - Shenzhen Winsemi Microelectronics Co., Ltd

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WS21351

Half-bridge power IC for CFL lamps

Shenzhen Winsemi Microelectronics Co., Ltd 

OPERATION DESCRIPTION

Under-Voltage Lockout (UVLO)Function

The WS21351 has UVLO circuits for both high-side and

low-side circuits. When VDD reaches VDDTH+, UVLO is

released and the WS21351 operates normally. Under

UVLO condition,WS21351 consumes little current, typically

50uA. After UVLO is released,WS21351 operates normally

until VDD goes below VDDTH-, the UVLO has hysteresis

which typically is 2.8V . At UVLO condition, all latches that

determine the status of the IC are reset.

WS21351 has a high-side gate driver circuit. The supply

for the high-side driver is applied between VB and VOUT.

To protect from malfunction of the driver at low supply

voltage between VB and VOUT,WS21351 provides an

additional UVLO circuit between this supply rails. If

VB-VOUT is under VHSTH+, the driver holds low state to

turn off the high-side switch, when VB-VOUT is higher than

VHSTH– after VB-VOUT exceeds VHSTH+, operation of

the driver continues.

WS21351

ignition and improve lamp life longevity.Accordingly,

the oscillation frequency is changed in the following

sequence:

Preheating freq > Ignition freq > running freq.

WS21351

Oscillator Operation

The ballast circuit for a fluorescent lamp is based on the

LCC resonant tank and a half-bridge inverter circuit, as

shown in Fig4 . To accomplish Zero-Voltage Switching

(ZVS) of the half-bridge inverter circuit, the LCC must be

driven at a higher frequency than its resonant Frequency,

which is determined by L, CS, CP, and RL; where RL is the

equivalent lamp's impedance. The transfer function of LCC

resonant tank is heavily dependent on the lamp impedance,

RL, as illustrated in Figure 4. The oscillator inWS21351

generates effective driving frequencies to assist lamp

Preheating and ignition Mode

When VDD exceeds VDDTH+ threshold, theWS21351

enters preheating mode. An internal current source charges

the external capacitor on pin CPH, and the voltage on pin

CPH starts ramping up linearly. The frequency ramps down

towards the resonance frequency of the high-Q ballast

output stage causing the lamp voltage and load current to

Increase.

The voltage on pin CPH continues to increase and the

frequency keeps decreasing until the lamp ignites. If the

4/7

Steady, keep you advance

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