
LM2576
http://onsemi.com
21
Figure 32. Undervoltage Lockout Circuit for
Buck Converter
R2
10 k
Z1
1N5242B
R1
10 k
Q1
2N3904
R3
47 k
Vth ≈ 13 V
Cin
100
mF
LM2576XX
1
3
5GN
D
ON/OFF
+Vin
NOTE: This picture does not show the complete circuit.
The following formula is used to obtain the peak inductor
current:
where ton +
|V
O
|
V
in )
|V
O
|
x
1.0
fosc
, and fosc + 52 kHz.
I
peak [
I
Load
(V
in )
|V
O
|)
V
in
)
V
in
xton
2L
1
Under normal continuous inductor current operating
conditions, the worst case occurs when Vin is minimal.
Figure 33. Undervoltage Lockout Circuit for
BuckBoost Converter
R2
15 k
Z1
1N5242B
R1
15 k
Q1
2N3904
R3
47 k
Vth ≈ 13 V
Cin
100
mF
LM2576XX
1
3
5GN
D
ON/OFF
+Vin
Vout
NOTE: This picture does not show the complete circuit.
Adjustable Output, LowRipple Power Supply
A 3.0 A output current capability power supply that
features an adjustable output voltage is shown in Figure
34.This regulator delivers 3.0 A into 1.2 V to 35 V output.
The input voltage ranges from roughly 3.0 V to 40 V. In order
to achieve a 10 or more times reduction of output ripple, an
additional LC filter is included in this circuit.
Figure 34. 1.2 to 35 V Adjustable 3.0 A Power Supply with Low Output Ripple
D1
1N5822
L1
150
mH
Output
2
4
Feedback
R2
50 k
R1
1.21 k
L2
20
mH
Output
Voltage
1.2 to 35 V @ 3.0 A
Optional Output
Ripple Filter
40 V Max
Unregulated
DC Input
Cout
2200
mF
C1
100
mF
Cin
100
mF
LM2574Adj
1
5
3ON/OFF
GN
D
+Vin