IRPLLNR3 查看數據表（PDF） - International Rectifier

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IRPLLNR3

Universal Input Linear Fluorescent Ballast using the IR2167

International Rectifier 

RPLLNR3

Figure 5: Typical lamp voltage at startup:

fStartup = fPreheat

Figure 6: Improved lamp voltage at startup:

fStartup > fPreheat

The duration of the Preheat mode as well as the mode of operation of the ballast are determined by

the voltage on the CPH pin of the IR2167. At the completion of the UVLO mode, Preheat mode is

entered and an internal current source is activated at the CPH pin of the IR2167, which begins to

charge up capacitor CPH. The ballast remains in the Preheat mode until the voltage on the CPH pin

exceeds the Ignition Ramp mode threshold (4V).

Ignition Ramp Mode

At the completion of the Preheat mode (4V < CPH pin < 5.1V) the ballast switches to the Ignition

Ramp mode and the frequency ramps down to the ignition frequency. The frequency ramping is

accomplished by turning off the internal open drain MOSFET on the RPH pin of the IR2167 (see

IR2167 block diagram). Resistor RPH is no longer connected directly in parallel with resistor RT. The

shift in frequency does not occur in a step function but rather with an exponential decay because of

capacitor CRAMP in series with resistor RPH to COM. The duration of this frequency ramp is

determined by the time constant of the RC combination of capacitor CRAMP and resistor RPH. The

minimum frequency of oscillation occurs at the end of this ramp and is determined by resistor RT and

capacitor CT. During this ramping downward of the frequency, the voltage across the lamp increases

in magnitude as the frequency approaches the resonant frequency of the LC load circuit until the

lamp ignition voltage is exceeded and the lamp ignites. Figure 7 shows the ramping of voltage appear-

ing across the lamp. Note that the sudden drop in lamp voltage indicates that the lamp has ignited.

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