PL317E3 Datasheet, PDF (6/9 Pages) Cystech Electonics Corp. – Three Terminal Adjustable Output Positive Voltage Regulators

CYStech Electronics Corp.
Spec. No. : C513E3
Issued Date : 2003.04.09
Revised Date : . .
Page No. : 6/9
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.
The adjustment terminal may be bypassed to ground to improve ripple rejection. This capacitor (CAdj)
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
high capacitance values (Co>25µF,CAdj>10µF). Diode D1 prevents Co from discharging thru the IC
during an input short circuit. Diode D2 protects against capacitor CAdj discharging through the IC during
an output short circuit. The combination of diodes D1 and D2 prevents CAdj from discharging through the
IC during an input short circuit.
D1
1N4002
Vin
Vout
PL317
Cin
Adjust
R1
D2
1N4002
+
Co
R2
CAdj
Fig 6. Voltage Regulator with Protection Diodes
PL317E3
CYStek Product Specification