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| E-UC3843BD1 Datasheet, PDF (5/15 Pages) STMicroelectronics – HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER | |||
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Figure 1: Open Loop Test Circuit.
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
4.7Kâ¦
ERROR AMP.
ADJUST
4.7Kâ¦
2N2222
100Kâ¦
1Kâ¦
ISENSE
ADJUST
5Kâ¦
RT
COMP
VFB
ISENSE
RT/CT
VREF
8
1
7
2
UC2842B
3
6
4
5
0.1µF
Vi
OUTPUT
0.1µF
GROUND
CT
D95IN343
A
1W
1Kâ¦
VREF
Vi
OUTPUT
GROUND
High peak currents associated with capacitive loads
necessitate careful grounding techniques. Timing
and bypass capacitors should be connected close
to pin 5 in a single point ground. The transistor and
5 K⦠potentiometer are used to sample the oscillator
waveform and apply an adjustable ramp to pin 3.
Figure 2: Timing Resistor vs. Oscillator Fre-
quency
RT
(Kâ¦)
50
20
CT=5nF
10
D95IN333
C
T=200pF
CT=C1nTF=500pF
C
T=100pF
5
2
Vi=15V
TA=25ËC
1
0.8
10K
20K
CT=10nF
30K 50K
CT=2nF
100K
200K 300K 500K fOSC(KHz)
Figure 3: Output Dead-Time vs. Oscillator Fre-
quency
D95IN334
%
50
30
20
10
5
3
2
1
10K
CT=1nF
CT=500pF
CT=200pF
CT=2nF
CT=5nF
CT=10nF
CT=100pF
Vi=15V
TA=25ËC
20K 30K 50K
100K 200K 300K 500K fOSC(KHz)
5/15
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