UC3842A, UC3843A, UC2842A, UC2843A
V
CC
V
in
7(12)
8(14)
+
−
5.0V
ref
+
R
R
R
T
Bias
−
+
−
MPS3904
+
7(11)
6(10)
5(8)
−
4(7)
R
O
Slope
Osc
From V
C
T
+
−m
1.0mA
S
R
R
i
2(3)
+
−
Q
−
+
2R
R
EA
Comp/Latch
C
f
1.0V
R
f
R
d
m
3(5)
R
S
1(1)
−3.0 m
5(9)
The buffered oscillator ramp can be resistively summed with either the voltage feedback or current sense inputs to provide slope compensation.
Figure 33. Slope Compensation
L1
MBR1635
+
4.7ꢃ
3300pF
1N4935
MDA
202
4.7k
250
5.0V/4.0A
T1
+
+
+
+
2200
1000
56k
115Va
c
5.0V RTN
12V/0.3A
MUR110
1000
1N4935
68
L2
10
7(12)
+
+
12V RTN
47
100
1000
10
L3
8(14)
+
−
+
+
5.0V
ref
−12V/0.3A
+
0.01
MUR110
680pF
1N4937
Bias
+
−
+
10k
7(11)
1N4937
2.7k
4(7)
2(3)
22ꢃ
Osc
6(10)
4700pF
+
MTP
4N50
L1 − 15 ꢀH at 5.0 A, Coilcraft Z7156.
L2, L3 − 25 ꢀH at 1.0 A, Coilcraft Z7157.
18k
S
+
−
Q
−
+
5(8)
3(5)
R
EA
Comp/Latch
4.7k
1.0k
T1 − Primary: 45 Turns # 26 AWG
T1 − Secondary 12 V: 9 Turns # 30 AWG
ꢁT1 − (2 strands) Bifiliar Wound
470pF
1(1)
0.5ꢃ
T1 − Secondary 5.0 V: 4 Turns (six strands)
ꢁT1 − #26 Hexfiliar Wound
5(9)
T1 − Secondary Feedback: 10 Turns #30 AWG
ꢁT1 − (2 strands) Bifiliar Wound
T1 − Core: Ferroxcube EC35−3C8
T1 − Bobbin: Ferroxcube EC35PCB1
T1 − Gap ≈ 0.01" for a primary inductance of 1.0 mH
Figure 34. 27 Watt Off−Line Flyback Regulator
Test
Conditions
Results
Line Regulation: 5.0 V
12 V
V
in
= 95 Vac to 130 Vac
ꢂ = 50 mV or 0.5%
ꢂ = 24 mV or 0.1%
Load Regulation: 5.0 V
12 V
V
V
= 115 Vac, I = 1.0 A to 4.0 A
ꢂ = 300 mV or 3.0%
ꢂ = 60 mV or 0.25%
in
out
= 115 Vac, I = 100 mA to 300 mA
in
out
Output Ripple:
5.0 V
12 V
V
in
= 115 Vac
40 mV
80 mV
pp
pp
Efficiency
V
in
= 115 Vac
70%
All outputs are at nominal load currents, unless otherwise noted.
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