
User’s Manual G12702EJ8V0UM00
16
Figure 4-4. Example of Typical Connection Circuit (Adjustable Output Power Supply)
VO
CO
D1
R1
R2
CIN
CADJ
+
ADJ
PC317
240
OUTPUT
INPUT
Input
Output
1 F
0.1 F
+
Note This example is for a positive voltage.
For a negative voltage (
PC337), D1 and capacitor polarity are reversed.
CIN
: Since there may be oscillation if the wire leading from a smoothing circuit to a three-terminal regulator is
long (15 cm or more), add a capacitor near the input pin.
CO
: For an application in which the load current changes suddenly, add a 10
F or more capacitor for output
voltage transient response improvement (and add 10
F to CADJ at the same time).
CADJ
: Connecting a 10
F capacitor parallel to R2 can improve the ripple rejection rate (approximately 20 dB)
and increase oscillation stability.
In this case, diode D1 is needed for to prevent application of backward voltage on an output short circuit.
R1, R2 : These are resistors for setting the output voltage. The output voltage VO is determined as follows.
VO = 1 +
VREF + IADJ R2
= 1 +
VREF
Table 4-1 shows the relationship between typical output voltages and R2.
Table 4-1. Settings of Output Voltage Setting Resistor R2
Output Voltage VO (V)
R2 Setting
Note (
)
2.5
240
5.0
720
12
2064
24
4368
30
5520
Note TYP. values
<3> Low saturation type
The standard method of use is the same as for a general fixed output voltage type (see Figure 4-1).
However, the capacitor connected to the output must have a greater capacity than in a general power supply
IC. In addition, note that the output voltage cannot be adjusted by inserting a resistor or the like in the GND
pin as described later.
.
R2
R1
R2
R1