AN3372 datasheet(5/37 Pages) STMICROELECTRONICS

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AN3372

General circuit description

Doc ID 018625 Rev 1

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General circuit description

The block diagram of the ballast is shown in Figure 2. The complete circuit is composed of

two stages:

●

The boost converter which regulates the DC bus voltage and corrects the power factor.

●

The inverter stage composed of a full bridge that converts the DC current coming from

the PFC stage into an AC current for the lamp.

Operation mode of the full bridge realizes a buck converter. The full bridge, moreover,

supplies the igniter block to generate the high voltage pulses.

Figure 2.

150 W HID ballast block diagram

To generate a square wave current in the lamp, the circuit is driven in the following way:

When low-side PMOS Ls is switched ON, the current increase linearly, the voltage across

the inductor L is:

Equation 1

where:

●

VL = inductor voltage

●

Vdc = DC bus voltage

●

Vlamp = lamp voltage.

The duty cycle D is established by a current mode control circuit (see Figure 3).

lamp

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