CYStech Electronics Corp.

Spec. No. : C513F3

Issued Date : 2003.05.24

Revised Date :

. .

Page No. : 6/9

PL317F3

CYStek Product Specification

Load Regulation

The PL317 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

A 0.1µF disc or 1.0µF tantalum input bypass capacitor (Cin) is recommended to reduce the sensitivity to

input line impedance.

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

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

Although the PL317 is stable with no output capacitance, like any feedback circuit, certain values of

external capacitance can cause excessive ringing. An output capacitance (Co) in the form of a 1.0µF

tantalum or 25µF 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.

Fig 6 shows the PL317 with the recommended protection diodes for output voltages in excess of 25V or

IC during an input short circuit.

R1

R2

Vout

Adjust

Vin

PL317

+

Co

CAdj

D2

D1

1N4002

Cin

1N4002

Fig 6. Voltage Regulator with Protection Diodes