SC4810BIMLTRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
Manufacturer
SC4810BIMLTRT
Semtech Corporation
SC4810BIMLTRT Datasheet PDF : 24 Pages
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SC4810B/E
POWER MANAGEMENT
Application Information
Introduction
Circuit Description
The SC4810B/E is a 16 pin BICMOS peak current mode
controlled PWM controller for isolated DC-DC and off-
line switching power supplies. It features a high switching
frequency of operation, programmable limits for both
power transformer voltage-second product and maximum
PWM duty cycle, line under-voltage lockout, auxiliary switch
activation complementary to main power switch drive,
programmable leading-edge delay time between
activation of each switch, multiple protection features
with programmable cycle -by-cycle current limit and hiccup
mode over-current protection plus soft-restart. It
operates in a fixed frequency programmed by external
components. The separate sync pin simplifies
synchronization to an external clock. Feeding the oscillator
of one device to the sync of another forces biphase
operation which reduces input ripple and input and output
filter size.
The SC4810 can be applied in an active clamp forward
topology with the input voltage ranging from 36V to 72V.
This topology allows the converter to achieve an efficiency
of 92.4% at normal input voltage of 48V.
The schematic of the active clamp forward converter is
illustrated in Figure. 1 below. T4 is the power transformer.
M17 is the N-channel main switching MOSFET and M15
is the auxiliary N-channel MOSFET. C35 is the reset
capacitor for resetting the power transformer’s core. M14
and M16 construct the synchronous rectification circuit.
L2 and C32 and C33 construct the low-pass output
filtering circuit. T6 is the current sensing transformer. R62
is the reset resistor for resetting the magnetic core of
the current sensing transformer. D18 is the rectifying
diode. R63 is the current sensing resistor. R60 and C41
construct the low-pass filtering circuit for the sensed
current signal. The primary bias circuit consists of R55,
R58, D17, Q8, C40, C31, D14 and R51. R55 and R58
construct a voltage divider, which limits the bias voltage
to 6.9V until the line voltage reach 36V. D17 is a zener
diode that limits the bias voltage to under 8V. R51, D14
and C31 construct the peak charge circuit. The peak
charge circuit will provide bias to the PWM IC U9 (SC4810)
and the driver U8 (SC1302A) after the converter starts
Figure 1: Active Clamp Forward Converter
48V
C34
1u,100V
R55
30K
Q8
F Z T458
R58
8K
D17
open
C35
3300pF
R54
20K
C40
10uF
R61
1.1M
D14
1N4148W S
C31
0.1uF
R51
5.11
8
1 M15
7
6
2
3
Si4488DY
5
4
R53 10K
D15
1N4148W S
C36
0.1uF
C37
0.1uF
T5
PE68386
R59
10
D19
1N5819HW
T4
10
1
11
7
6
8
2
9
R50
5.11
1N 4148W S
D13
M14
Si4842DY
4
10K
R52
M16
Si4842DY
8
1
7
2
6
3
5
4
R56
10K
P8208T
8 T6
1
7
3
1N4148W S
D18
R62
10K
1K
R60
R63
6.8
330pF
C41
R64
165k
C43
100pF
R65
100K
SC1302A
U8
2
7
U9
C44 220pF
6 RAMP
OUT2 13 4
5
R71
10K
3
SYNC
15
OUT1
4 RCT
SC4810
CS 10
R74
4.3K
C49
180pF
Q9
F MMT718
R77
18K
R80
1.47K
100K
R75
R78
5.6K
5
DMAX
7 DELAY1
8 DELAY2
R79
100K
11
FB
VREF 16
SS 9
0.1uF
C48
1000pF
C50
D20
1N5819HW
R82
5.11K
C51
0.01uF
M17
Si4488DY
R69
10K
R81
4.7K
U11
MOC207
1
6
5
2
2006 Semtech Corp.
9
3.3 V/30A
1.3uH
L2
100uF
C32
C33
680uF
Q7
F Z T458
R57
0.1uF
C38
5.11K
D16
open
C39
0.1uF
C42
open
R66
open
R68
1K
R67
50
R73
C45
open
3.01K
U10
C47
0.01uF
SC431
R70
open
R72
5.11K
C46
open
R76
3.01K
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