5

GM317

3-TERMINAL 1.5A

ADJUSTABLE REGULATOR

R1

R2

GM317

Adjust

Basic Circuit Configuration

GM317

Adjust

R1

R2

D2

1N4002

D1

1N4002

Application Information

Basic Circuit Operation

The GM317 is a 3- terminal floating regulator. In operation, the GM317 develops and maintains a nominal 1.25V

programming current flow through R2 to ground.

The regulated output voltage is given by:

returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is

less than this minimum, the output voltage will rise.

Since the GM317 is a floating regulator, it is only the voltage differential across the circuit which is important to

performance, and operation at high voltages with respect to ground is possible.

Load Regulation

The GM317 is capable of providing extremely good load regulation, but a few precautions are needed to obtain

maximum performance. For best performance, the programming resistor R1 should be connected as close to

the regulator as possible to minimize line drops which effectively appear in series with the reference, thereby

degrading regulation. The ground end of R2 can be returned near the load ground to provide remote ground

sensing and improve load regulation.

External Capacitors

prevents ripple from being amplified as the output voltage is increased. A 10µF capacitor should improve ripple

rejection about 15 dB at 120Hz in a 10V application.

Although the GM317 is stable with no output capacitance, like any feedback circuit, certain values of external

aluminum electrolytic capacitor on the output swamps this effect and insures stability.

Protection Diodes

When external capacitors are used with any IC regulator, it is sometimes necessary to add protection diodes to

prevent the capacitors from discharging through low current points into the regulator.

The figure below shows the GM317 with the recommended protection diodes for output for output voltage in

IC during an input short circuit.

R1

R2