UC3842A, UC3843A, UC2842A, UC2843A
V
CC
7(12)
8(14)
5.0V
ref
R
T
MPS3904
R
R
Slope
From V
O
R
i
C
f
4(7)
Osc
C
T
2(3)
R
f
1(1)
−3.0 m
5(9)
+
−
V
in
+
−
R
+
−
7(11)
Bias
+
−
+
1.0mA
−m
S
2R
R
−
+
+
−
6(10)
Q
EA
R
5(8)
R
d
1.0V
m
Comp/Latch
3(5)
R
S
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
4.7W
115Va
c
MDA
202
+
250
56k
4.7k
3300pF
MBR1635
T1
2200
MUR110
+
L1
1000
+
5.0V/4.0A
5.0V RTN
+
L2
10
+
12V/0.3A
±12V
RTN
1N4935
7(12)
8(14)
5.0V
ref
0.01
Bias
10k
4(7)
Osc
4700pF
18k
2(3)
100pF
150k
4.7k
+
−
+
−
1N4935
1000
+
47
1000
+
100
68
+
−
+
10
L3
+
+
1N4937
MUR110
680pF
2.7k
22W
6(10)
MTP
4N50
−12V/0.3A
+
7(11)
1N4937
+
S
EA
−
+
Q
L1 − 15
mH
at 5.0 A, Coilcraft Z7156.
L2, L3 − 25
mH
at 1.0 A, Coilcraft Z7157.
T1 − Primary: 45 Turns # 26 AWG
T1 −
Secondary
±
12 V: 9 Turns # 30 AWG
T1 −
(2 strands) Bifiliar Wound
T1 −
Secondary 5.0 V: 4 Turns (six strands)
T1 −
#26 Hexfiliar Wound
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
R
Comp/Latch
5(8)
3(5)
1.0k
470pF
0.5W
1(1)
5(9)
Figure 34. 27 Watt Off−Line Flyback Regulator
Test
Line Regulation: 5.0 V
±
12 V
Load Regulation: 5.0 V
±
12 V
Output Ripple:
Efficiency
5.0 V
±
12 V
Conditions
V
in
= 95 Vac to 130 Vac
V
in
= 115 Vac, I
out
= 1.0 A to 4.0 A
V
in
= 115 Vac, I
out
= 100 mA to 300 mA
V
in
= 115 Vac
V
in
= 115 Vac
Results
D
= 50 mV or
±
0.5%
D
= 24 mV or
±
0.1%
D
= 300 mV or
±
3.0%
D
= 60 mV or
±
0.25%
40 mV
pp
80 mV
pp
70%
All outputs are at nominal load currents, unless otherwise noted.
http://onsemi.com
14
ONSEMI [ ON SEMICONDUCTOR ]
