0.5A Step-Down Switching Regulator
TC2574
Adjustable Output, Low-Ripple Power Supply
R2
R1
VTH ≈ VZ1 + 1.0 +
VBE (Q1)
(
)
A 0.5 A output current capability power supply that
features an adjustable output voltage is shown in Figure 16.
Thisregulatordelivers0.5Ainto1.2to35Voutput.Theinput
voltage ranges from roughly 3.0 to 40 V. In order to achieve
a 10 or more times reduction of output ripple, an additional
L–C filter is included in this circuit.
+V
IN
+V
IN
TC2574
(5V)
5
C
R1
10k
R3
47k
IN
22µF
3
ON/OFF
2
GNDs
and Pins
4
+V
IN
+V
IN
TC2574
(5V)
Z1
1N5242B
5
C
in
22mF
R2
15 k
R3
68 k
Q1
2N3904
3
ON/OFF
2
GNDs
and Pins
4
R2
10k
Z1
1N5242
Q1
2N3904
NOTE: This picture does not show the complete circuit.
Figure 14. Undervoltage Lockout Circuit for Buck Converter
R1
15 k
–V
OUT
NOTE: This picture does not show the complete circuit (see Figure 8).
Figure 15. Undervoltage Lockout Circuit for Buck-Boost Converter
Feedback
40V Max
Unregulated
DC Input
1
+V
IN
L1
150µH
L2
20µH
TC2574–ADJ
Output
Voltage
5
Output
7
1.2 to 35V @ 0.5 A
R2
50 k
4
C
IN
22µF
Pwr
GND
2
Sig
GND
3
ON/OFF
C
D1
1N5819
OUT
C1
100µF
1000µF
R1
1.1 k
Optional Output
Ripple Filter
Figure 16. 1.2 to 35V Adjustable 500mA Power Supply with Low Output Ripple
TC2574-1 1/6/00
18
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