ON Semiconductor LM2575 Technical data

LM2575

1.0 A, Adjustable Output
Voltage, Step−Down
Switching Regulator

The LM2575 series of regulators are monolithic integrated circuits
ideally suited for easy and convenient design of a step−down
switching regulator (buck converter). All circuits of this series are
capable of driving a 1.0 A load with excellent line and load regulation.
These devices are available in fixed output voltages of 3.3 V, 5.0 V,
12 V, 15 V, and an adjustable output version.

These regulators were designed to minimize the number of external
components to simplify the power supply design. Standard series of
inductors optimized for use with the LM2575 are offered by several
different inductor manufacturers.

Since the LM2575 converter is a switch−mode power supply, its
efficiency is significantly higher in comparison with popular
three−terminal linear regulators, especially with higher input voltages.
In many cases, the power dissipated by the LM2575 regulator is so
low, that no heatsink is required or its size could be reduced
dramatically.

The LM2575 features include a guaranteed ±4% tolerance on output
voltage within specified input voltages and output load conditions, and
±10% on the oscillator frequency (±2% over 0°C to 125°C). External
shutdown is included, featuring 80 mA typical standby current. The
output switch includes cycle−by−cycle current limiting, as well as
thermal shutdown for full protection under fault conditions.

Features

• 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions

• Adjustable Version Output Voltage Range of 1.23 V to 37 V ±4%

Maximum Over Line and Load Conditions

• Guaranteed 1.0 A Output Current

• Wide Input Voltage Range: 4.75 V to 40 V

• Requires Only 4 External Components

• 52 kHz Fixed Frequency Internal Oscillator

• TTL Shutdown Capability, Low Power Standby Mode

• High Efficiency

• Uses Readily Available Standard Inductors

• Thermal Shutdown and Current Limit Protection

• Moisture Sensitivity Level (MSL) Equals 1

• Pb−Free Packages are Available*

Applications

• Simple and High−Efficiency Step−Down (Buck) Regulators

• Efficient Pre−Regulator for Linear Regulators

• On−Card Switching Regulators

• Positive to Negative Converters (Buck−Boost)

• Negative Step−Up Converters

• Power Supply for Battery Chargers

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TO−220

1

5

Heatsink surface connected to Pin 3

1

5

Pin 1. V

2. Output

3. Ground

4. Feedback

5. ON/OFF

1

5

Heatsink surface (shown as terminal 6 in
case outline drawing) is connected to Pin 3

ORDERING INFORMATION

See detailed ordering and shipping information in the package
dimensions section on page 24 of this data sheet.

DEVICE MARKING INFORMATION

See general marking information in the device marking
section on page 25 of this data sheet.

TV SUFFIX

CASE 314B

TO−220

T SUFFIX

CASE 314D

in

D2PAK

D2T SUFFIX

CASE 936A

*For additional information on our Pb−Free strategy and soldering details, please

download the ON Semiconductor Soldering and Mounting Techniques
Reference Manual, SOLDERRM/D.

© Semiconductor Components Industries, LLC, 2005

November, 2005 − Rev. 8

1 Publication Order Number:

LM2575/D

Typical Application (Fixed Output Voltage Versions)

Unregulated

DC Input

C

in

+V

Feedback

in

1

4

LM2575

Feedback

L1

330 mH

D1
1N5819

Driver

1.0 Amp
Switch

Thermal

/OFF5

4

Output

2

7.0 V − 40 V

Unregulated

DC Input

C

100 mF

+V

in

LM2575

1

in

GND

3ON

Representative Block Diagram and Typical Application

R2

R1

1.0 k

1.235 V

Band−Gap

Reference

Fixed Gain
Error Amplifier

Freq
Shift

18 kHz

Oscillator

3.1 V Internal
Regulator

Comparator

52 kHz

Current

Latch

Reset

ON/OFF

Limit

Shutdown

C

out

330 mF

ON/OFF

5

Output

2
GND

3

5.0 V Regulated
Output 1.0 A Load

Output

Voltage Versions

3.3 V

5.0 V
12 V
15 V

For adjustable version
R1 = open, R2 = 0 W

D1

R2

(W)

1.7 k

3.1 k

8.84 k

11.3 k

Regulated

L1

Output

V

out

C

out

Load

This device contains 162 active transistors.

Figure 1. Block Diagram and Typical Application

ABSOLUTE MAXIMUM RATINGS (Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.)

Rating Symbol Value Unit

Maximum Supply Voltage V

in

ON/OFF Pin Input Voltage − −0.3 V ≤ V ≤ +V
Output Voltage to Ground (Steady−State) − −1.0 V
Power Dissipation

Case 314B and 314D (TO−220, 5−Lead) P

Thermal Resistance, Junction−to−Ambient
Thermal Resistance, Junction−to−Case

Case 936A (D2PAK) P

Thermal Resistance, Junction−to−Ambient (Figure 34)

Thermal Resistance, Junction−to−Case
Storage Temperature Range T
Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)

D

R

q

JA

R

q

JC
D

R

q

JA

R

q

JC

stg

− 3.0 kV
Lead Temperature (Soldering, 10 s) − 260 °C
Maximum Junction Temperature T

J

Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit
values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied,
damage may occur and reliability may be affected.

45 V

in

Internally Limited W

65 °C/W

5.0 °C/W

Internally Limited W

70 °C/W

5.0 °C/W

−65 to +150 °C

150 °C

V

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LM2575

OPERATING RATINGS (Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee

specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.)

Rating Symbol Value Unit

Operating Junction Temperature Range T
Supply Voltage V

J

in

SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 14)

ELECTRICAL CHARACTERISTICS (Unless otherwise specified, V

for the 12 V version, and Vin = 30 V for the 15 V version. I
operating junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics Symbol Min Typ Max Unit

LM2575−3.3 (Note 1 Test Circuit Figure 14)

Output Voltage (Vin = 12 V, I

= 0.2 A, T

Load

Output Voltage (4.75 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

= 25°C) V

J

≤ 1.0 A) V

Load

TJ = 25°C 3.168 3.3 3.432
TJ = −40 to +125°C 3.135 − 3.465

Efficiency (V

= 12 V, I

in

= 1.0 A) η − 75 − %

Load

LM2575−5 ([Note 1] Test Circuit Figure 14)

Output Voltage (Vin = 12 V, I
Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

= 0.2 A, TJ = 25°C) V

Load

≤ 1.0 A) V

Load

TJ = 25°C 4.8 5.0 5.2
TJ = −40 to +125°C 4.75 − 5.25

Efficiency (Vin = 12 V, I

= 1.0 A) η − 77 − %

Load

LM2575−12 (Note 1 Test Circuit Figure 14)

Output Voltage (Vin = 25 V, I
Output Voltage (15 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

= 0.2 A, TJ = 25°C) V

Load

≤ 1.0 A) V

Load

TJ = 25°C 11.52 12 12.48
TJ = −40 to +125°C 11.4 − 12.6

Efficiency (Vin = 15V, I

= 1.0 A) η − 88 − %

Load

LM2575−15 (Note 1 Test Circuit Figure 14)

Output Voltage (V

= 30 V, I

in

Output Voltage (18 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

= 0.2 A, TJ = 25°C) V

Load

≤ 1.0 A) V

Load

TJ = 25°C 14.4 15 15.6
T

= −40 to +125°C 14.25 − 15.75

J

Efficiency (Vin = 18 V, I

= 1.0 A) η − 88 − %

Load

LM2575 ADJUSTABLE VERSION (Note 1 Test Circuit Figure 14)

Feedback Voltage (V
Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

= 12 V, I

in

= 0.2 A, V

Load

= 5.0 V, TJ = 25°C) V

out

≤ 1.0 A, V

Load

TJ = 25°C 1.193 1.23 1.267
T

= −40 to +125°C 1.18 − 1.28

J

Efficiency (V

= 12 V, I

in

= 1.0 A, V

Load

= 5.0 V) η − 77 − %

out

1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2575 is used as shown in the Figure 14 test circuit, system performance will be as shown in system parameters section.

2. Tested junction temperature range for the LM2575: T

= 200 mA. For typical values T

Load

out

= −40°C T

low

= 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V

in

= 5.0 V) V

out
out

out
out

out
out

out
out

FB
FB

= +125°C

high

= 25°C, for min/max values TJ is the

J

3.234 3.3 3.366 V

4.9 5.0 5.1 V

11.76 12 12.24 V

14.7 15 15.3 V

1.217 1.23 1.243 V

−40 to +125 °C
40 V

V

V

V

V

V

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LM2575

DEVICE PARAMETERS

ELECTRICAL CHARACTERISTICS (Unless otherwise specified, V

for the 12 V version, and Vin = 30 V for the 15 V version. I
operating junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics Symbol Min Typ Max Unit

ALL OUTPUT VOLTAGE VERSIONS

Feedback Bias Current (V

= 5.0 V Adjustable Version Only) I

out

TJ = 25°C − 25 100
TJ = −40 to +125°C − − 200

Oscillator Frequency Note 3 f

TJ = 25°C − 52 −
TJ = 0 to +125°C 47 − 58
TJ = −40 to +125°C 42 − 63

Saturation Voltage (I

= 1.0 A Note 4) V

out

TJ = 25°C − 1.0 1.2
TJ = −40 to +125°C − − 1.3

Max Duty Cycle (“on”) Note 5 DC 94 98 − %
Current Limit (Peak Current Notes 4 and 3) I

TJ = 25°C 1.7 2.3 3.0
TJ = −40 to +125°C 1.4 − 3.2

Output Leakage Current Notes 6 and 7, TJ = 25°C I

Output = 0 V − 0.8 2.0
Output = −1.0 V − 6.0 20

Quiescent Current Note 6 I

TJ = 25°C − 5.0 9.0
TJ = −40 to +125°C − − 11

Standby Quiescent Current (ON/OFF Pin = 5.0 V (“off”)) I

TJ = 25°C 15 80 200
TJ = −40 to +125°C − − 400

ON/OFF Pin Logic Input Level (Test Circuit Figure 14) V

V

= 0 V V

out

TJ = 25°C 2.2 1.4 −
TJ = −40 to +125°C 2.4 − −

V

= Nominal Output Voltage V

out

TJ = 25°C − 1.2 1.0
TJ = −40 to +125°C − − 0.8

ON/OFF Pin Input Current (Test Circuit Figure 14)

ON/OFF Pin = 5.0 V (“off”), TJ = 25°C I
ON/OFF Pin = 0 V (“on”), TJ = 25°C I

3. The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated output
voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average dissipation of the IC by
lowering the minimum duty cycle from 5% down to approximately 2%.

4. Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.

5. Feedback (Pin 4) removed from output and connected to 0 V.

6. Feedback (Pin 4) removed from output and connected to +12 V for the Adjustable, 3.3 V, and 5.0 V versions, and +25 V for the 12 V and
15 V versions, to force the output transistor “off”.

7. V

= 40 V.

in

= 200 mA. For typical values T

Load

= 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V

in

b

osc

sat

CL

L

Q

stby

IH

IL

IH
IL

= 25°C, for min/max values TJ is the

J

− 15 30

− 0 5.0

kHz

mA

mA

nA

V

A

mA

mA

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4

0.4

0.2

Vin = 20 V
I

= 200 mA

Load

Normalized at
TJ = 25°C

LM2575

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 14)

1.00.6
I

= 200 mA

Load

TJ = 25°C

0.8

0.6

3.3 V, 5.0 V and Adj

0

−0.2

, OUTPUT VOLTAGE CHANGE (%)

−0.4

out

V

−0.6

−50

Figure 2. Normalized Output Voltage

1.2

1.1

1.0

, SATURATION VOLTAGE (V)

V

sat

0.9

0.8

0.7

0.6

0.5

0.4

−40°C

25°C

125°C

0

TJ, JUNCTION TEMPERATURE (°C)

SWITCH CURRENT (A)

0.8 0.9 1.0

0.4

0.2

, OUTPUT VOLTAGE CHANGE (%)

0

out

V

−0.2
0

5.0−25 100 201525 257550 3530 40100 125

3.0

2.5

2.0

1.5

1.0

, OUTPUT CURRENT (A)

O

I

0.5

0

−50

−250.1 00.2 250.3 500.4 750.5 1000.6 1250.7

12 V and 15 V

Vin, INPUT VOLTAGE (V)

Figure 3. Line Regulation

Vin = 25 V

TJ, JUNCTION TEMPERATURE (°C)

INPUT−OUTPUT DIFFERENTIAL (V)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

−50

Figure 4. Switch Saturation Voltage Figure 5. Current Limit

, QUIESCENT CURRENT (mA)

Q

I

8.0

6.0

4.0

20

18

16

14

I

Load

= 1.0 A

12

10

I

= 200 mA

Load

0

5.0−25 100 1525 2050 2575 30100 35125

Vin, INPUT VOLTAGE (V)

I

Load

I

Load

= 1.0 A

= 200 mA

TJ, JUNCTION TEMPERATURE (°C)

DV
R

ind

= 5%

out

= 0.2 W

Figure 6. Dropout Voltage Figure 7. Quiescent Current

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5

V

= 5.0 V

out

Measured at
Ground Pin
TJ = 25°C

40

LM2575

, STANDBY QUIESCENT CURRENT ( A)μ

I

stby

−2.0

120

100

2.0

80

60

40

20

0

0

0

TJ = 25°C

5.0

10

15

20

25

Vin, INPUT VOLTAGE (V)

Figure 8. Standby Quiescent Current

Vin = 12 V
Normalized at 25°C

120

Vin = 12 V
V

= 5.0 V

ON/OFF

100

80

60

40

20

, STANDBY QUIESCENT CURRENT ( A)μ

0

stby

I

−50

30

4035

−25

0

25

50

75

100

125

TJ, JUNCTION TEMPERATURE (°C)

Figure 9. Standby Quiescent Current

40

Adjustable
Version Only

20

−4.0

−6.0

NORMALIZED FREQUENCY (%)

−8.0

−10

−50

OUTPUT
VOLTAGE
(PIN 2)

OUTPUT
CURRENT
(PIN 2)

INDUCTOR
CURRENT

OUTPUT
RIPPLE
VOLTAGE

0

−20

, FEEDBACK PIN CURRENT (nA)

FB

I

−40

−50

−25

0

25

TJ, JUNCTION TEMPERATURE (°C)

50

75

100

125

−25

0

25

TJ, JUNCTION TEMPERATURE (°C)

Figure 10. Oscillator Frequency Figure 11. Feedback Pin Current

10 V

1.0 A

0.5 A

20 mV

/DIV

0

5.0 ms/DIV

100

00

CHANGE (mV)

, OUTPUT VOLTAGE

−1001.0 A

out

V

1.0

0.5

0

, LOAD CURRENT (A)

Load

I

100 ms/DIV

Figure 12. Switching Waveforms Figure 13. Load Transient Response

50

75

100

125

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Unregulated

5.0 Output Voltage Versions

DC Input

8.0 V − 40 V

Unregulated

DC Input

8.0 V − 40 V

LM2575

Feedback

53ON/OFFGND

Feedback

4

Output

2

4

Output

2

L1

330 mH

D1
1N5819

L1

330 mH

D1
1N5819

C

out

330 mF
/16 V

C

out

330 mF
/16 V

V

out

Regulated

Output

Load

R2

R1

V

out

Regulated

Output

Load

V

in

LM2575−5

+

V

in

−

1

C

in

100 mF/50 V

Adjustable Output Voltage Versions

V

in

LM2575

Adjustable

+

1

C

in

100 mF/50 V

53ON/OFFGND

−

V

+ V

out

R2 + R1ǒ

Where V
between 1.0 kW and 5.0 kW

Figure 14. Typical Test Circuit

PCB LAYOUT GUIDELINES

As in any switching regulator, the layout of the printed
circuit board is very important. Rapidly switching currents
associated with wiring inductance, stray capacitance and
parasitic inductance of the printed circuit board traces can
generate voltage transients which can generate
electromagnetic interferences (EMI) and affect the desired
operation. As indicated in the Figure 14, to minimize
inductance and ground loops, the length of the leads
indicated by heavy lines should be kept as short as possible.
For best results, single−point grounding (as indicated) or
ground plane construction should be used.

ref

ref

R1

V

out

–1Ǔ

V

ref

= 1.23 V, R1

R2

ǒ

Ǔ

1 )

On the other hand, the PCB area connected to the Pin 2
(emitter of the internal switch) of the LM2575 should be
kept to a minimum in order to minimize coupling to sensitive
circuitry.

Another sensitive part of the circuit is the feedback. It is
important to keep the sensitive feedback wiring short. To
assure this, physically locate the programming resistors near
to the regulator, when using the adjustable version of the
LM2575 regulator.

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LM2575

PIN FUNCTION DESCRIPTION

Pin Symbol Description (Refer to Figure 1)

1 V

2 Output This is the emitter of the internal switch. The saturation voltage V

3 GND Circuit ground pin. See the information about the printed circuit board layout.
4 Feedback This pin senses regulated output voltage to complete the feedback loop. The signal is divided by the

5 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total

in

This pin is the positive input supply for the LM2575 step−down switching regulator. In order to minimize
voltage transients and to supply the switching currents needed by the regulator, a suitable input bypass
capacitor must be present (Cin in Figure 1).

of this output switch is typically 1.0 V.
It should be kept in mind that the PCB area connected to this pin should be kept to a minimum in order to
minimize coupling to sensitive circuitry.

internal resistor divider network R2, R1 and applied to the non−inverting input of the internal error amplifier.
In the Adjustable version of the LM2575 switching regulator this pin is the direct input of the error amplifier
and the resistor network R2, R1 is connected externally to allow programming of the output voltage.

input supply current to approximately 80 mA. The input threshold voltage is typically 1.4 V. Applying a
voltage above this value (up to +Vin) shuts the regulator off. If the voltage applied to this pin is lower than

1.4 V or if this pin is connected to ground, the regulator will be in the “on” condition.

sat

DESIGN PROCEDURE

Buck Converter Basics

The LM2575 is a “Buck” or Step−Down Converter which
is the most elementary forward−mode converter. Its basic
schematic can be seen in Figure 15.

The operation of this regulator topology has two distinct
time periods. The first one occurs when the series switch is
on, the input voltage is connected to the input of the inductor.

The output of the inductor is the output voltage, and the
rectifier (or catch diode) is reverse biased. During this
period, since there is a constant voltage source connected
across the inductor, the inductor current begins to linearly
ramp upwards, as described by the following equation:

I

L(on)

+

ǒ

Vin–V

L

out

Ǔ

t

on

During this “on” period, energy is stored within the core
material in the form of magnetic flux. If the inductor is
properly designed, there is sufficient energy stored to carry
the requirements of the load during the “off” period.

Power
Switch

V

in

D1

L

C

out

V

out

R

Load

The inductor current during this time is:

I

L(off)

+

ǒ

V

out

–V

L

Ǔ

t

D

off

This period ends when the power switch is once again
turned on. Regulation of the converter is accomplished by
varying the duty cycle of the power switch. It is possible to
describe the duty cycle as follows:

t

on

d +

, where T is the period of switching.

T

For the buck converter with ideal components, the duty
cycle can also be described as:

V

out

d +

V

in

Figure 16 shows the buck converter idealized waveforms
of the catch diode voltage and the inductor current.

V

on(SW)

Power

Switch

Off

Diode VoltageInductor Current

Power

Switch

On

Power
Switch

Off

Power
Switch

On

Time

Figure 15. Basic Buck Converter

The next period is the “off” period of the power switch.
When the power switch turns off, the voltage across the
inductor reverses its polarity and is clamped at one diode
voltage drop below ground by catch dioded. Current now
flows through the catch diode thus maintaining the load
current loop. This removes the stored energy from the
inductor.

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VD(FWD)

I

I

min

Diode Diode

Power
Switch

pk

Power

Switch

I

Load

(AV)

Time

Figure 16. Buck Converter Idealized Waveforms

8

LM2575

Procedure (Fixed Output Voltage Version) In order to simplify the switching regulator design, a step−by−step design

procedure and example is provided.

Procedure Example

Given Parameters:

V

= Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V)

out

V

= Maximum DC Input Voltage

in(max)

I

Load(max)

= Maximum Load Current

1. Controller IC Selection

According to the required input voltage, output voltage and
current, select the appropriate type of the controller IC output
voltage version.

2. Input Capacitor Selection (Cin)

To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +Vin and ground pin GND. This capacitor should be
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.

3. Catch Diode Selection (D1)

A.Since the diode maximum peak current exceeds the

regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design the diode should have a
current rating equal to the maximum current limit of the
LM2575 to be able to withstand a continuous output short

B.The reverse voltage rating of the diode should be at least

1.25 times the maximum input voltage.

4. Inductor Selection (L1)

A.According to the required working conditions, select the

correct inductor value using the selection guide from
Figures 17 to 21.

B.From the appropriate inductor selection guide, identify the

inductance region intersected by the Maximum Input
Voltage line and the Maximum Load Current line. Each
region is identified by an inductance value and an inductor
code.

C.Select an appropriate inductor from the several different

manufacturers part numbers listed in Table 1 or Table 2.
When using Table 2 for selecting the right inductor the
designer must realize that the inductor current rating must
be higher than the maximum peak current flowing through
the inductor. This maximum peak current can be calculated
as follows:

I

p(max)

+ I

Load(max)

)

ǒ

Vin–V

2L

out

Ǔ

t

on

where ton is the “on” time of the power switch and

V

out

t

+

on

V

1

x

f

osc

in
For additional information about the inductor, see the
inductor section in the “External Components” section of

this data sheet.

Given Parameters:

V

= 5.0 V

out

V

= 20 V

in(max)

I

Load(max)

= 0.8 A

1. Controller IC Selection

According to the required input voltage, output voltage,
current polarity and current value, use the LM2575−5
controller IC

2. Input Capacitor Selection (Cin)

A 47 mF, 25 V aluminium electrolytic capacitor located near
to the input and ground pins provides sufficient bypassing.

3. Catch Diode Selection (D1)

A.For this example the current rating of the diode is 1.0 A.

B.Use a 30 V 1N5818 Schottky diode, or any of the

suggested fast recovery diodes shown in the Table 4.

4. Inductor Selection (L1)

A.Use the inductor selection guide shown in Figures 17

to 21.

B.From the selection guide, the inductance area intersected
by the 20 V line and 0.8 A line is L330.

C.Inductor value required is 330 mH. From the Table 1 or

Table 2, choose an inductor from any of the listed
manufacturers.

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