WS21351
Lamp ignites successfully, the voltage on pin CPH
continues to increase until it internally limits at 6V
(V
CPH_MAX
). The frequency stops decreasing when
V
CPH
reach 5V and stays at the minimum frequency
as programmed by an external resistor, on pin RMIN
(as show in Fig 4). The minimum frequency should
be set below the High-Q resonance frequency of the
ballast output stage to ensure that the frequency
ramps through resonance for lamp Ignition
.The desired preheat time can be set by adjusting
the slope of the V
CPH
ramp with the external
capacitor on pin CPH. The relation of LCC tank
frequency and Pin CPH voltage V
CPH
as show in
Fig5.
Run Mode
TheWS21351 enters RUN mode when the voltage
on pin CPH exceeds 5V . The lamp has ignited and
the ballast output stage becomes a low-Q, series-L,
parallel-RC circuit. The voltage on the CPH pin
continues to increase but the frequency don't change
as the minimum frequency is reached. The resonant
inductor, resonant capacitor, DC bus voltage and
minimum frequency determine the running lamp
power. The relation of minimum run frequency and
the setting resistor R
RMIN
as show in Fig 6. The IC
stays at this minimum frequency unless VDD
decreases below the V
DDTH–
threshold
5/7
Steady, keep you advance
WINSEMI [ SHENZHEN WINSEMI MICROELECTRONICS CO., LTD ]
