Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
OFF-LINE FLYBACK REGULATOR
T1
4.7 1W
4.7k
4W
56k
1W
0.01µF
400V
USD735
+
220µF
250V
673-3
4700µF
10V
DC (5V 2–5A)
OUT
1N3613
–
1N3613
AC
INPUT
16V
0.01µF
UC3842
20k
2
150k
V
FB
1
COMP
3.6k
100pF
8
V
REF
10k
4
R
T
/C
T
0.01µF
0.0047µF
GND
5
3
CUR
SEN
470pF
1k
0.85
6
OUT
20k
NOTES:
T1: Coilcraft E-4140-B
Primary – 97 turns
single AWG24
Secondary – 4 turns
4 parallel
AWG22
control – 9 turns
–3 parallel AWG28
27
UFN432
V
CC
7
10µF
20V
820pF
1N3613
2.5k
ISOLATION
BOUNDARY
SPECIFICATIONS
Input line voltage:
Input frequency:
Switching frequency:
Output power:
Output voltage:
Output current:
Line regulation:
Load regulation:
Efficiency @ 25 W,
V
IN
=90V
AC
:
V
IN
=130V
AC
:
Output short-circuit current:
70%
65%
2.5A average
90V
AC
to 130V
AC
50 or 60Hz
40kHz±10%
25W maximum
5V±5%
2 to 5A
0.01%/V
8%/A
*
NOTE:
This circuit uses a low-cost feedback scheme in which the DC
voltage developed from the primary-side control winding is sensed
by the UC3842 error amplifier. Load regulation is therefore
dependent on the coupling between secondary and control
windings, and on transformer leakage inductance. For applications
requiring better load regulation, a UC1901 Isolated Feedback
Generator can be used to directly sense the output voltage.
August 31, 1994
1106
PHILIPS [ NXP SEMICONDUCTORS ]
