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IRPLDIM2U

Power Factor Control

The power factor correction section consists of a Power Factor Controller IC (IC1), MOSFET (M1), inductor (L2),

diode (D2), capacitor (C6) and additional biasing, sensing and compensation components (see Appendix A: sche-

matics). The power factor correction circuit is a boost converter type running in critical conduction mode. This

means that the inductor current discharges to zero each cycle before the boost MOSFET is turned on. The ST

L6561D PFC IC is used which shapes the input current to the input voltage while regulating the DC bus voltage at

400 VDC. The IC is chosen for its minimal component count, low start-up supply current and robust error amplifier.

Ballast Control

The ballast control section is built around the IR21592 Dimming Ballast Control IC (IC2). The IR21592 is used for

preheating and igniting the lamp, controlling the lamp power and detecting fault condition (over temperature, over

current, VCC fault and DC Bus/ AC line fault). The IR21592 contains a voltage-controlled oscillator (VCO) control-

ling the half-bridge frequency while maintaining a 50% duty cycle, a high voltage half-bridge driver, an amplitude

control, fault circuit and an analog dimming interface.

To preheat the lamp, the amplitude control feature of the IR21592 is used, which regulates the resonant tank

current during the Preheat period. The VCO starts at maximum frequency and then decreases the frequency until the

voltage at the CS pin is equal to the programmed voltage at the IPH pin. The VCO is then adjusted internally (and

therefore the frequency) such that the inductor current remains constant until the external capacitor on pin CPH

charges above 5.1V. The preheat current (voltage) can be adjusted by increasing or decreasing the resistor on the

IPH pin (RIPH) and the preheat time can be adjusted by increasing or decreasing the capacitor on pin CPH (CCPH).

When pin CPH exceeds 5.1V, the IR21592 enables the over-current protection and the next cycle where the CS

pin exceeds the internal threshold of 1.6V the half-bridge is disabled. The VCO voltage decreases to a minimum

value and the IR21592 starts to decreases the frequency to a minimum frequency which is set by the external

resistor on pin FMIN (RFMIN) and the current sensing resistor RCS. In this way it generates a high voltage for

igniting the lamp. This voltage can be adjusted by adjusting RCS.

When the lamp is successfully ignited, The IR21592 regulates the phase angle of the inductor current with respect

to the half bridge voltage to regulate the lamp power. This is done by measuring the zero crossing of the current

and regulating it against the reference angle from the dimming interface. The IR21592 provides a 0-to-5 VDC

dimming interface which converts the analog input voltage to an internal phase angle reference for controlling the

lamp power. The DIM pin is a high impedance analog control input and the RMAX and RMIN pins set the maximum

and minimum angles boundaries. The RMIN resistor sets the minimum lamp power at 1% when VDIM=0V and the

RMAX resistor sets the maximum lamp power at 100% when VDIM=5V.

Digital Control

The digital control section is built around the PIC16F628 Microchip microcontroller. This microcontroller acts as an

interface between the IR21592 ballast controller and the Digitally Addressable Lighting Interface (DALI). Data is

transmitted to the unit and the PIC16F628 collects the data through an isolation circuit. It then interprets the data

and sends the appropriate signals to the ballast controller IR21592 if necessary or sends information back to the

DALI. The PIC16F628 also performs fault detection and disables the IR21592 if a fault is present.