Philips Semiconductors

Product specification

NE/SE5560

Switched-mode power supply control circuit

1994 Aug 31

10

a. Duty Cycle —

δ — % Regulation

b. Pulse-Width Modulation

(+)

8

3.72V

3

+

–

ERROR

AMP

PWM

OUT

(–)

(–) O.C.

(–)

START/

STOP

RESET

4

5

6

–

+

7

6

5

4

3

2

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

4

3

RS

R1

VREF(3.72V)

δ

∆VO/VREF (%)

10

20

30

40

50

60

70

80

90

R

f

R

S

+ 20

R

f

R

S

+ 100

R

f

R

S

+ 500

SL00369

Figure 10.

100

90

80

70

60

50

40

30

20

10

0

1

2

3

4

5

6

δ (%)

V4,5,6 (V)

SL00370

Figure 11. Transfer Curve of Pulse-Width Modulator

Duty Cycle vs Input Voltage

Extra PWM Input (Pin 5)

The PWM has an additional inverting input: Pin 5. It allows for

attacking the duty cycle via the PWM circuit, independently from the

feedback and the

SMPS must have a real constant-current behavior, possibly with a

fold-back characteristic. However, the realization of this feature must

be done with additional external components. When not used, Pin 5

should be tied to Pin 6.