UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 1:
Open Loop Test Circuit.
V
REF
4.7KΩ
2N2222
100KΩ
ERROR AMP.
ADJUST
4.7KΩ
COMP
V
FB
1KΩ
I
SENSE
ADJUST
5KΩ
I
SENSE
R
T
/C
T
R
T
V
REF
1
2
8
7
V
i
0.1µF
OUTPUT
GROUND
1W
1KΩ
OUTPUT
A
0.1µF
V
i
UC3842A
3
4
6
5
C
T
D95IN343
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 KΩ potentiometerareusedto samplethe oscillator
waveform and apply an adjustable ramp to pin 3.
Figure 2:
Oscillator Frequency vs Timing Resis-
tance
f
o
(Hz)
D96IN362
Figure 3:
Maximum Duty Cycle vs Timing Resis-
tor
f
o
(Hz)
D96IN363
80
1M
CT
=
1nF
47
0
pF
60
100K
2.2
nF
4.7
nF
40
10K
20
1K
300
1K
3K
10K
30K
R
T
(Ω)
0
300
1K
3K
10K
30K
R
T
(Ω)
5/15
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