LM2576T 查看數據表（PDF） - Motorola => Freescale
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LM2576T Datasheet PDF : 28 Pages
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LM2576
predetermined threshold level with respect to the ground
[ ) ǒ ) Ǔ Pin 3, which is determined by the following expression:
Vth VZ1
1.0
R2
R1
VBE (Q1)
Figure 32. Undervoltage Lockout Circuit for
Buck Converter
+Vin
R2
R3
10 k 47 k
+Vin
LM2576–XX
1
Cin
100 µF 5 ON/OFF 3 Gnd
Z1
1N5242B
R1
10 k
Q1
2N3904
Vth ≈ 13 V
Under normal continuous inductor current operating
conditions, the worst case occurs when Vin is minimal.
Figure 33. Undervoltage Lockout Circuit for
Buck–Boost Converter
+Vin
R2
R3
15 k 47 k
+Vin
LM2576–XX
1
Cin
100 µF 5 ON/OFF 3 Gnd
Z1
1N5242B
R1
15 k
Q1
2N3904
Vth ≈ 13 V
Vout
NOTE: This picture does not show the complete circuit.
NOTE: This picture does not show the complete circuit.
The following formula is used to obtain the peak inductor
[ ) ) current:
Ipeak
ILoad (Vin |VO|)
Vin
Vin x ton
2L1
+ ) + where ton
|VO|
Vin |VO|
x
1.0
fosc
,
and
fosc
52 kHz.
Adjustable Output, Low–Ripple 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 L–C filter is included in this circuit.
Figure 34. 1.2 to 35 V Adjustable 3.0 A Power Supply with Low Output Ripple
40 V Max
Unregulated
DC Input
+Vin
1
LM2574–Adj
Feedback
4
Output
Cin
100 µF
3 Gnd
2
5 ON/OFF
L1
150 µH
D1
1N5822
Cout
2200 µF
R2
50 k
R1
1.21 k
L2
20 µH
C1
100 µF
Output
Voltage
1.2 to 35 V @ 3.0 A
Optional Output
Ripple Filter
MOTOROLA ANALOG IC DEVICE DATA
21
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