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LM2596 Adjustable Voltage Regulator Schematic

  • Contents

I Description

The switching power supply chip LM2596 is compact, low-cost, low-power, high-efficiency and easy to use compared with specialized instruments. The power supply described in this blog is a stepless adjustable DC regulated voltage supply based on the switching power supply chip LM2596.

lm2596

Figure 1. LM2596

Catalog

I Description

II LM2596 Circuit and Design Process

2.1 Circuit of Stepless Adjustable DC Power Supply

2.2 Design Process of Adjustable DC Voltage Source

III How to Apply and Use LM2596 Stepless Adjustable DC Power Supply

3.1 How to Apply?

3.2 How to Use?

FAQ

Ordering & Quantity

II LM2596 Circuit and Design Process

2.1 Circuit of Stepless Adjustable DC Power Supply

This power supply circuit mainly uses LM2596-ADJ. LM2596-ADJ is a step-down switching power supply chip. Its output voltage range is 1.2V-37V, and its maximum load current is 3A, with excellent linearity and load regulation characteristics. Only 4 external components are needed in the main circuit to adjust the output voltage.

The LM2596-ADJ chip integrates frequency compensation and a fixed frequency generator, and the switching frequency is 150KHz, which facilitates the use of smaller filter components, thereby reducing volume, weight, loss and cost. Under certain input voltage and output load conditions, the output voltage error is within 4%, the oscillation frequency error range is within 15%, and the standby current can be only 80uA. It can realize external power-off and has a self-protection circuit (a two-stage frequency reduction current-limiting protection circuit and an over-temperature complete protection circuit that is cut off in abnormal cases). The LM2596-ADJ package in this article is TO220(T), which requires an external heat sink.

 VOUT=1.23V*(1+R2/R1)

When designing the PCB board, the external components should be as close as possible to the LM2596-ADJ, and use ground wire shielding or single-point grounding, and use magnetic shielding inductors. If the inductor core used is open, and the inductance flux crosses the sensitive feedback line, the ground line of the integrated chip and the connection of the output capacitor COUT may have problems. The feedback resistor should be close to the LM2596-ADJ IC, and the related wiring should be far away from the inductor.

  

LM 2596 adjustable DC voltage source circuit
Figure 2. Adjustable DC Voltage Source Circuit

2.2 Design Process of Adjustable DC Voltage Source

  • VOUT is the adjustable output voltage
  • VIN(max) is the maximum DC input voltage,
  • ILOAD(max) is the maximum load current,
  • F=switching frequency (150KHz)

1) Output Voltage Calculation  

VOUT=VREF*(1+R2/R1)

Among them, VREF=1.23V. In this blog, R1 is a 1KΩ metal film resistor with a lower temperature coefficient of 1% accuracy; R2 uses a 30KΩ potentiometer.

2) Inductor Selection

Calculate the product E*T of the inductor voltage and microseconds by the following formula:

  E*T=(VIN-VOUT-VSAT)*(VOUT +VD)/(VIN-VSAT+VD)*1000/150KHz (V· uS)

  • VSAT is the internal saturation voltage of the switch,
  • VSAT=1.16V
  • VD is the forward voltage drop of the diode
  • VD=0.5V

Use the E*T value in the formula to find the matching inductor number from the ordinate in Figure 3, and select the maximum load current of the circuit on the abscissa; determine an inductance area by the intersection of the E*T value, and the maximum load current,and each area is corresponding to an inductance value and an inductance serial number (LXX).  Select the appropriate inductor from the component number of the manufacturer listed in Table 1 for LM2596-ADJ circuit, preferably a magnetic shield inductor.

This blog chooses 68uH inductance.

  

LM2596-ADJ application information
Figure 3. LM2596-ADJ Application Information

3) Output Capacitor COUT

Number

/ Inductance(μH)

/ Current (A)

Schott

Renco

Pulse Engineering

Coilcraft

In-Line

Surface Mount

In-Line

Surface Mount

In-Line

Surface Mount

Surface Mount

L15/22/0.99

67148350

67148460

RL-1284-22-43

RL 1500-22

PE-53815

PE-53815-S

DO3308-223

L21/68/0.99

67144070

67144450

RL-5417-5

RL 1500-68

PE-53821

PE-53821-S

DO3316-683

L22/47/1.17

67144080

67144460

RL-5417-6

-

PE-53822

PE-53822-S

DO3316-473

L23/33/1.40

67144090

67144470

RL-5417-6

-

PE-53823

PE-53823-S

DO3316-333

L24/22/1.70

67148370

67148480

RL-1283-22-43

-

PE-53824

PE-53825-S

DO3316-223

L25/15/2.10

67148380

67148490

RL-1283-15-43

-

PE-53825

PE-53824-S

DO3316-153

L26/330/0.80

67144100

67144480

RL-5471-1

-

PE-53826

PE-53826-S

DO5022P·334

L27/220/1.00

67144110

67144490

RL-5471-2

-

PE-53827

PE-53827-S

DO5022P·224

L28/150/1.20

67144120

67144500

RL-5471-3

-

PE-53828

PE-53828-S

DO5022P·154

L29/100/1.47

67144130

67144510

RL-5471-4

-

PE-53829

PE-53829-S

DO5022P·104

L30/68/1.78

67144140

67144520

RL-5471-5

-

PE-53830

PE-53830-S

DO5022P·683

L31/47/2.20

67144150

67144530

RL-5471-6

-

PE-53831

PE-53831-S

DO5022P·473

L32/33/2.50

67144160

67144540

RL-5471-7

-

PE-53932

PE-53832-S

DO5022P·333

L33/22/3.10

67144390

67144500

RL-1283-22-43

-

PE-53933

PE-53833-S

DO5022P·223

L34/15/3.40

67144400

67144790

RL-1283-15-43

-

PE-53934

PE-53834-S

DO5022P·153

L35/220/1.70

67144170

-

RL-5473-1

-

PE-53935

PE-53835-S

-

L36/150/2.10

67144180

-

RL-5473-4

-

PE-54036

PE-53836-S

-

L37/100/2.50

67144190

-

RL-5472-1

-

PE-54037

PE-53837-S

-

L38/68/3.10

67144200

-

RL-5472-2

-

PE-54038

PE-53838-S

-

L39/47/3.50

67144210

-

RL-5472-3

-

PE-54039

PE-53839-S

-

L40/33/3.50

67144220

67148290

RL-5472-4

-

PE-54040

PE-53840-S

-

L41/22/3.50

67144230

67148300

RL-5472-5

-

PE-54041

PE-53841-S

-

L42/150/2.70

67144410

-

RL-5473-4

-

PE-54042

PE-53842-S

-

L43/100/3.40

67144240

-

RL-5473-2

-

PE-54043

 

-

L44/68/3.40

67144250

-

RL-5473-3

-

PE-54044

 

-

  Table 1. Product model of an inductor manufacturer

In most cases, we can use low equivalent resistance electrolytic capacitors or solid tantalum capacitors between 82uF~820uF. When in use, the capacitor should be close to the for LM2596-ADJ IC, and the pins and connecting copper wires should be as short as possible.

See Table 2 below. In order to simplify the selection of capacitors, Table 1 contains the different output voltages and output capacitors required for the best design. The withstand voltage of the capacitor is at least 5 times the output voltage. Sometimes, in order to obtain a lower ripple output voltage, a higher capacitor withstand voltage value is required.

This blog chooses 220uF/50V electrolytic capacitors.

VOUT

In-Line Capacitor

Surface Mount Capacitor

PANASONIC HFQ

(μF/V)

NICHICON PL

(μF/V)

Feedforward Capacitor

AVX TPS

(μF/V)

VISHAY 595D

(μF/V)

Feedforward Capacitor

2

820/35

820/35

33nF

330/6.3

470/4

33nF

4

560/35

470/35

10nF

330/6.3

390/6.3

10nF

6

470/25

470/25

3.3nF

220/10

330/10

33nF

9

330/25

330/25

1.5nF

100/16

180/16

1.5nF

12

330/25

330/25

1nF

100/16

180/16

1nF

15

220/35

220/35

680 pF

68/20

120/20

680 pF

24

220/35

150/35

560 pF

33/25

33/25

220 pF

28

100/50

100/50

390 pF

10/35

15/50

220 pF

  Table 2. Output Capacitor and Feedforward Capacitor Selection 

4) Feedforward Capacitor CFF

When the output voltage is large, a compensation capacitor with a typical value between 100pF and 33nF is required, which is connected in parallel with the output voltage adjustment resistor R2. Its function is to compensate the feedback loop and increase the phase margin to improve the stability of the loop. For high output voltage, low input-output voltage and/or low equivalent resistance output capacitors, this capacitor makes the circuit more stable, such as solid tantalum capacitors. The selection still refers to the corresponding feedforward capacitor value in Table 1.

This blog chooses 33nF ceramic capacitors.

  CFF=1/(31*1000*R2)

This capacitor can be a ceramic capacitor, plastic or mica capacitor.

5) Zener Diode (D1) Selection

The maximum current capacity of the Zener diode is at least 1.3 times the maximum load current. If the designed power supply is to withstand continuous short-circuit output, the maximum current capacity of the Zener diode is equal to the limit output of LM2596 Current. Its function is to provide a path for the inductor current when the switch is closed. The reverse voltage of the Zener diode is at least 1.25 times the maximum output voltage; the Zener diode must be a fast recovery diode and must be close to the LM2596-ADJ IC. At the same time, the pins and the connected copper wires should be short. Therefore, we should first choose Schottky diodes.

This blog chooses 1N5825 Schottky diode here.

6)Input Capacitance CIN

The input capacitor is an electrolytic capacitor or tantalum capacitor with a low equivalent resistance, which is also close to the IC, and the DC load current must exceed twice the root mean square of the input capacitor current. For aluminum electrolytic capacitors, the maximum input voltage is 2/3 of the withstand voltage; for tantalum capacitors, select capacitors that the manufacturer has tested for surge current. We can select the appropriate input capacitance according to the graph shown. This capacitor prevents excessive transient voltage from appearing at the input, and at the same time provides transient current for LM2596-ADJ every time it switches.

This blog uses 680uF/50V electrolytic capacitors.

VR

Output Current: 3A

Output Current: 4A~6A

Lnline

Surface Mount

Lnline

Surface Mount

Schottky

Super Fast Recovery

Schottky

Super Fast Recovery

Schottky

Super Fast Recovery

Schottky

Super Fast Recovery

20V

 

The minimum withstand voltage of all such diodes is 50V

 

MURS320

30WF10

IN5820

The minimum withstand voltage of all such diodes is 50V

 

MURS320

 

The minimum withstand voltage of all such diodes is 50V

 

MURS620

50WF10

SR502

The minimum withstand voltage of all such diodes is 50V

 

MURS620

HER601

SK32

SR302

 

IN5823

 

MBR320

 

SB520

30V

30WQ03

IN5821

 

 

SK33

MBR330

50WQ03

SR503

 

31DQ03

 

IN5824

40V

 

IN5822

 

SB530

SK34

SR304

50WQ04

SR504

MBRS340

MBR340

 

IN5825

30WQ04

31DQ04

 

SB540

50V or Higher

SK35

SR305

 

 

MBRS360

MBR350

50WQ05

SB550

30WQ05

31DQ05

 

50SQ080

 Table 3. Choice of Diode

  LM2596-ADJ application information

Figure 4. LM2596-ADJ application information

III How to Apply and Use LM2596 Stepless Adjustable DC Power Supply

3.1 How to Apply?

The device can be used as a power supply that requires a DC voltage source kit:

  • radio power supply
  • doorbell power supply
  • alarm power supply
  • power amplifier power supply
  • 51 single-chip power supply, etc.

3.2 How to Use?

The anode of the output end (red alligator clip) is connected to the anode of the circuit, and the cathode of the output end (black alligator clip) is connected to the cathode of the circuit. Plug the 220V power cord into the mains socket. Turn on the power switch, the DC voltage source indicator (red) will light up, adjust the knob to output the voltage change, and its value will be displayed on the voltmeter head.


FAQ

  • What is lm2596?

The LM2596 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 3-A load with excellent line and load regulation.

  • What is the difference between LM2596 and LM2595?

LM2596: The highest output current is 3A, 1PIN-VOUT, 2PIN-VIN;

LM2595: The highest output current is 1A, 1PIN-VIN, 2PIN-VOUT.

  • What is the voltage of each pin of LM2596-12? What is the function of each pin?

Pin 1 is the input terminal, 12V, the normal working voltage range should be 14V~37V under the output condition; pin 2 is the output terminal, here is the high-frequency oscillation output, not DC voltage, so there is no definite voltage; pin 3 is grounded, 0V ; Pin 5 is the enable control terminal, LM2596 works normally when connected to a low level, and no output is turned off when connected to a high level, usually directly grounded; Pin 4 is the feedback control signal input terminal, connected to the middle connection point of the proportional resistor, where the voltage It is proportional to the actual output.

  • Can LM2596 output negative voltage?

LM2596 can output negative voltage.

LM2596 has different application circuits, which can output positive voltage or negative voltage, but it has no boost function, and the absolute value of its output voltage must be less than the absolute value of the input voltage.

  • In the circuit with adjustable output voltage of lm2596, can the output voltage be greater than the input voltage?

The LM2596 switching voltage regulator is a step-down power management monolithic integrated circuit, which can output 3A drive current and has good linearity and load regulation characteristics. The output voltage will not be greater than the input voltage. If the output voltage is greater than the input voltage, it is best to use a step-up power chip. Such as XL6009, VT1050.

After reading the blog, have you better understand LM2596?

Finally, if you have any questions about LM2596, please do not hesitate to leave a message in the comment section below!

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