UC184xA/284xA/384xA

PRODUCT DA T ABOOK 1996/1997

Copyright © 1995

Rev. 1.2

12/95

8

TYPICAL APPLICA TION CIRCUITS

(continued)

FIGURE 8. — OFF-LINE FLYBACK REGULATOR

SPECIFICATIONS

Input line voltage:

90VAC to 130VAC

Input frequency:

50 or 60Hz

Switching frequency:

40KHz ±10%

Output power:

25W maximum

Output voltage:

5V +5%

Output current:

2 to 5A

Line regulation:

0.01%/V

Load regulation:

8%/A*

Efficiency @ 25 Watts,

V

70%

V

65%

Output short-circuit current:

2.5Amp average

* This circuit uses a low-cost feedback scheme in which the DC

voltage developed from the primary-side control winding is

sensed by the UC3844A error amplifier. Load regulation is

therefore dependent on the coupling between secondary and

control windings, and on transformer leakage inductance.

7

150k

W

100pF

V

FB

COMP

V

REF

R

4700µF

10V

5V

2-5A

ISOLATION

BOUNDARY

3600pF

400V

1N4935

820pF

2.5k

W

27k

W

0.01µF

10µF

20V

1N4935

1k

W

470pF

0.85k

W

MBR735

TI

4.7k

W

2W

140k

W

1/2W

220µF

250V

4.7k

W

1W

1N4004

1N4004

1N4004

1N4004

AC

INPUT

V

CC

OUT

CUR

SEN

GND

UC3844A

20k

W

3.6k

W

10k

W

.0022µF

0.01µF

16V

3

6

2

1

8

4

5