IR2159S datasheet(16/25 Pages) IRF

16 / 25 page

IR21592/IR21593(S)

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Brown-out Protection

In addition to the voltage on VCC being above

the start-up threshold, pin VDC must also be

above 5.1V for HO and LO to begin oscillating. A

voltage divider (R3,RVDC) from the rectified AC

line connected to pin VDC measures the rectified

AC line input voltage to the ballast and programs

the turn-on and turn-off line voltages. A filter

capacitor (CVDC) is also connected to pin VDC

that must be chosen such that the ripple is low

enough and the lower turn-off threshold of 3V is

not crossed during normal line conditions. This

detection is necessary due to the possibility of

the lamp extinguishing during low-line conditions

before the IC is properly reset. Should a brown-

out occur, the DC bus can drop to a level below

the minimum required for the tank circuit to

maintain the necessary lamp voltage. This

detection will insure a clean turn-off before the

DC bus drops too low and properly resets the

IC to the preheat mode when the line returns.

Preheat (PH)

The IR21592/IR21593 enters preheat mode

when VCC exceeds the UVLO+ threshold and

VDC exceeds 5.1V.

HO and LO begin to

oscillate at the maximum operating frequency

with 50% duty cycle and at the internally set

dead-time of 2us (IR21592) or 1

µs (IR21593). Pin

CPH is disconnected from COM and an internal

1uA current source (Figure 7) charges the external

timing capacitor on CPH linearly.

7.6V

1uA

CPH

FMIN

IPH

VCO

COM

1uA

60uA

FMIN

1/R

FMIN

5.1V

RCS

VCO

LOGIC

FMIN

IPH

CPH

VCO

Half

Bridge

Output

LOAD

BUS(+)

BUS(-)

Load

Return

Half

Bridge

Driver

IR21592/IR21593

Figure 7, IR21592/IR21593 preheat circuitry.

An internal 1uA current source slowly discharges

the external capacitor on pin VCO and the voltage

on pin VCO begins to decrease. This decreases

the frequency, which, for operating frequencies

above resonance, increases the load current.

When the peak voltage measured on pin CS,

produced by a portion of the load current flowing

through an external sense resistor (RCS), exceeds

the voltage level on pin IPH, a 60uA internal

current source is connected to pin VCO and the

capacitor charges (Figure 8). This forces the

frequency to increase and the load current to

decrease. When the voltage on pin CS decreases

below the voltge on pin IPH, the 60uA current

source is disconnected and the frequency

decreases again.

IR2159S Datasheet(PDF) 16 Page - International Rectifier

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