Page 178 - The Art and Science of Analog Circuit Design

Tripping the Light Fantastic

full V CE saturation without inducing base overdrive or beta starvation. A
procedure for doing this is described in the following section, "General
Measurement and Optimization Considerations."
Figure 11-20's circuit is similar, but uses a transformer with lower cop-
per and core losses to increase efficiency to 91%. The trade-off is slightly
larger transformer size. Value shifts in Cl, L2, and the -base drive resistor
reflect different transformer charaeteristics. This circuit also features shut-
down via Q3 and a DC or pulse width controlled dimming input. Figure
11-21, directly derived from Figure 11-20, produces 10mA output to
drive color LCDs at 92% efficiency. The slight efficiency improvement
comes from a reduction in LT1172 "housekeeping" current as a percentage

Figure 11-20.
A 91% efficient 2ov
CCFL supply for
5mA loads features
shutdown and
dimming inputs.

"—I N ' 03 IMF
+ LL 2N7001
2MF
T f 1
SHUTDOWN DIMMING INPUT
C1 = WIMA MKP-20 ( SEE TEXT )
L1=COILTRONICSCTX150-4
01, Q2 = ZETEX ZTX849 OR ROHM 2SC5001
T1 = COILTRONICS CTX110600-1 OR SUMIDA EPS-207
PIN NUMBERS SHOWN FOR COILTRONICS UNIT
* = 1% FILM RESISTOR
DO NOT SUBSTITUTE COMPONENTS
COILTRONICS (305) 781-8900, SUMIDA (708) 956-0666

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