AN3372 datasheet(7/37 Pages) STMICROELECTRONICS

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AN3372

Lamp power calculation

Doc ID 018625 Rev 1

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Lamp power calculation

The lamp power is obtained multiplying the lamp voltage signal for the lamp current.

The lamp voltage is sensed directly across the lamp and the lamp current is obtained by the

relations reported below.

Starting from peak inductor and considering that the half bridge works in transition mode,

the average value is:

Equation 3

where:

●

Ilamp = lamp current

●

IAV = inductor average current

●

Ipeak = inductor peak current

●

ΔI = inductor current ripple.

The inductor current is sensed with a current transformer and the output signal is

proportional to the average value.

Considering that the inductor current is equal to lamp current, and the lamp voltage is

directly measured by the MCU, in this way it is possible to calculate the lamp power simply

multiplying the current for the lamp voltage:

Equation 4

This relation is valid because the average current is equal to the lamp current. This formula

is implemented in ST7 microcontrollers in order to calculate the lamp power.

peak

lamp

AN3372 Datasheet(PDF) 7 Page - STMicroelectronics