LAB

SEME

IP1524 SERIES

Prelim. 3/95

APPLICATIONS INFORMATION

The IP1524 is a fixed-frequency pulse-width

modulation voltage regulator control circuit. The

regulator operates at a frequency that is programmed

which is fed to the comparator providing linear control of

the output pulse width by the error amplifier.

The IP1524 contains an on-board 5V regulator that

serves as a reference as well as powering the IP1524’s

internal control circuitry and is also useful in supplying

external support functions. This reference voltage is

lowered externally by a resistor divider to provide a

reference within the common-mode range of the error

amplifier or an external reference may be used. The

power supply output is sensed by a second resistor

divider network to generate a feedback signal to the

error amplifier. The amplifier output voltage is then

resulting modulated pulse out of the high-gain

comparator is then steered to the appropriate output

which is synchronously toggled by the oscillator output.

The oscillator output pulse also serves as a blanking

pulse to assure both outputs are never on

simultaneously during the transition times.

The width of the blanking pulse is controlled by the

The outputs may be applied in a push-pull

configuration in which their frequency is half that of the

base oscillator, or paralleled for single-ended

applications in which the frequency is equal to that of

the oscillator. The output of the error amplifier shares a

common input to the comparator with the current

limiting and shutdown circuitry and can be overridden

by signals from either of these inputs.

This common point is also available externally and

may be employed to control the gain of, or to

compensate, the error amplifier, or to provide additional

control to the regulator.

RE F

V

INV .

N. I.

OS C .

SH . D O W N

C O M P.

E

A

C +

L

C -

L

IN

V

GN D

+2 8 V

RE T URN

GN D

+5 V

1A

0. 1

µF

0. 02

µF

0.1

Ω

500

µF

1N388 0

Ω

5k

Ω

5k

Ω

5k

Ω

5k

Ω

3k

0.0 0 1

µF

Ω

68

Ω

150

Ω

2k

Ω

50k

0.9 m H

RE F

V

IN V .

N. I.

OS C .

S H . D OW N

C OM P .

E

A

C +

L

C -

L

IN

V

GN D

+2 8 V

RE T URN

0.1

µF

0. 01

µF

Ω

5k

Ω

5k

Ω

5k

Ω

5k

0.001

µF

1m H

Ω

2k

Ω

20k

Ω

1k

1W

Ω

1k

1W

Ω

1k

Ω

1k

20

T

20

T

100

µF

0. 1

Ω

5

T

5

T

5V

5A

100

µF

In this conventional single-ended regulator circuit, the two outputs of

the IP1524 are connected in parallel for effective 0-90% duty cycle

modulation. The use of an output inductor requires an R-C phase

compensation network for loop stability.

Push-pull outputs are used in this transformer-coupled DC-DC

regulating converter. Note that the oscillator must be set at twice the

desired output frequency as the IP1524’s internal flip-flop divides the

frequency by 2 as it switches the PWM signal from one output to the

other. Current limiting is done in the primary so that the pulse width will

be reduced should transformer saturation occur.