IR2157 データシートの表示（PDF） - International Rectifier

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IR2157

FULLY INTEGRATED BALLAST CONTROL IC

International Rectifier 

ADVANCED INFORMATION

IR2157

Thus, for a lamp removal and replacement, the ballast

automatically restarts the lamp in the proper manner,

maximizing lamp life and minimizing stress on the

power MOSFETs or IGBTs. The SD pin contains an

internal 7.5V zener diode clamp, thereby reducing

the number of external components required.

Half-Bridge Current Sensing and

Protection

and under-resonance conditions, there is a negative-

going threshold of 0.2V which is enabled at the onset

of the run mode. The sensing of this 0.2V threshold

is synchronized with the falling edge of the LO output.

Figures 15, 16 and 17 are oscillographs of fault

conditions. Figure 15 shows a failure of the lamp to

strike, Figure 16 shows a hard switching condition

and Figure 17 shows an under-current condition.

The third pin used for protection is the CS pin, which

is normally connected to a resistor in the source of

the lower power MOSFET, as shown in Figure 14.

The CS pin is used to sense fault conditions such a

failure of a lamp to strike, over-current during normal

operation, hard switching, no load, and operation

below resonance. If any one of these conditions is

sensed, the fault latch is set, the oscillator is disabled,

the gate driver outputs go low, and the chip is put

into the micropower mode. The CS pin performs its

sensing functions on a cycle-by-cycle basis in order

to maximize ballast reliability. failure-to-strike, and

For the over-current, hard switching fault conditions,

the 1V, positive-going CS threshold is enabled at

the end of the preheat time. For the under-current

VDC

1

CPH

2

RPH

3

RT

4

RUN

5

CT

6

DT

7

SD

8

rectified

AC line

+V BUS

HO

16

Q1

VS

15

RGHS

VB

14

N/C

13

VCC

12

CBOOT

R SUPPLY

DBOOT

D1

COM

11

CVCC

LO

10

CS

9

Q2

RGLS

R3

RCS

1/2 Bridge output

R SNUBBER

C SNUBBER

D2

Figure 15: Lamp failure to strike

VBUS return

Figure 14: Half-bridge current sensing circuit

connection (shaded area)

15

Figure 16: Hard switching condition

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