30V Internal Switch LCD Bias Supply

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9

saturation region. When shut down, the input voltage

exceeds the emitter voltage so the inactive transistor

provides high-impedance isolation between the input

and output. Efficiency will be slightly degraded due to

the PNP transistor saturation voltage and base current.

0.8V TO

-19V

2.4V TO

5.5V

D3**

D2*

D1*

R1

240k

Ω

R2

16.5k

Ω

ON

OFF

SHDN

LIM

GND

LX

FB

MAX1605

L1

10

µH

C3

0.1

µF

C6

0.1

µF

C4

0.01

µF

C1

1000pF

C2

1

µF

R3

1

Ω

C5

1

µF

*D1, D2 = CENTRAL SEMICONDUCTOR

CMPD7000 DUAL

**D3 = CENTRAL SEMICONDUCTOR

CMSD4448 (1N4148)

Figure 4. Negative Voltage for LCD Bias

R3 = 180k

Ω

ON

OFF

R1

R2

SHDN

2N2907A

LIM

GND

LX

FB

MAX1605

L1

10

µH

Figure 5. Output Disconnected in Shutdown

Chip Information

TRANSISTOR COUNT: 2329