Philips Semiconductors

Product specification

NE/SE5560

Switched-mode power supply control circuit

1994 Aug 31

7

1000

100

90

80

70

60

50

40

30

20

10

9

8

7

6

5

4

3

2

1

R=10k

Ω

R=20k

Ω

R=40k

Ω

R=5k

Ω

2

2.5

3

3.5

4

4.5

CnF)

f(kHz)

100

90

80

70

60

50

40

30

20

10

1

1.5

2

2.5

V

16

V

Z

δ

SL00364

Figure 5. Typical Performance Characteristics

THEORY OF OPERATION

The following functions are incorporated:

– A temperature-compensated reference source.

– An error amplifier with Pin 3 as input. The output is connected

to Pin 4 so that the gain is adjustable with external resistors.

– A sawtooth generator with a TTL-compatible synchronization

input (Pins 7, 8, 9).

– A pulse-width modulator with a duty cycle range from 0 to 95%.

The PWM has two additional inputs:

Pin 6 can be used for a precise setting of

Pin 5 gives a direct access to the modulator, allowing for real

constant-current operation:

– A gate at the output of the PWM provides a simple dynamic

current limit.

– A latch that is set by the flyback of the sawtooth and reset by

the output pulse of the above mentioned gate prohibits double

pulsing.

– Another latch functions as a start-stop circuit; it provides a fast

switch-off and a slow start.

– A current protection circuit that operates via the start-stop

circuit. This is a combined function with the current limit circuit,

therefore Pin 11 has two trip-on levels; the lower one for

cycle-by-cycle current limiting, the upper one for current

protection by means of switch-off and slow-start.

– A TTL-compatible remote on/off input at Pin 10, also operating

via the start-stop circuit.

– An inhibit input at Pin 13. The output pulse can be inhibited

immediately.

– An output gate that is commanded by the latches and the inhibit

circuit.

– An output transistor of which both the collector (Pin 15) and the

emitter (Pin 14) are externally available. This allows for normal

or inverse output pulses.

– A power supply that can be either voltage- or current-driven

(Pins 1 and 12). The internally-generated stabilized output

voltage VZ is connected to Pin 2.

– A special function is the so-called feed-forward at Pin 16. The

amplitude of the sawtooth generator is modulated in such a way

that the duty cycle becomes inversely proportional to the

voltage on this pin:

δ ~ 1/V16.

– Loop fault protection circuits assure that the duty cycle is

reduced to zero or a low value for open- or short-circuited

feedback loops.

Stabilized Power Supply (Pins 1, 2, 12)

The power supply of the NE5560 is of the well known series

regulation type and provides a stabilized output voltage of typically

8.5V.

setting of

capability is 5mA.

The circuit can be fed directly from a DC voltage source between

10.5V and 18V or can be current-driven via a limiting resistor. In the

latter case, internal pinch-off resistors will limit the maximum supply

voltage: typical 23V for 10mA and max. 30V for 30mA.

10.5V and inhibits the output pulse (no hysteresis).

When the supply voltage surpasses the 10.5V level, the IC starts

delivering output pulses via the slow-start function.