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LM317 Voltage Regulator: 11 Simple Circuits (With Example)

Author: Irene Date: 20 Feb 2021  7333

lm317 voltage regulator

Introduction

The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37V. In addition, it has the advantages of wide voltage regulation range, good voltage stability performance, low noise and high ripple suppression ratio.

A Tutorial of LM317 Adjustable Voltage Regulator

Catalog

Introduction

Catalog

I Basic Circuit

II Minimum Stable Operating Current

III Soft-Start Circuit

IV Basic Protection Circuit

V Charging Circuit

VI Overcurrent Protection Circuit

VII Extending Current Circuit

VIII High Voltage Output Circuit

IX Constant Current Circuit

X Programmable Circuit

XI Adjustable Voltage Calibrator

Component Datasheet

FAQ

Ordering & Quantity

I Basic Circuit

Figure 1. LM317 basic circuit diagram

The basic circuit of LM317 is shown in Figure 1. C1 is the input capacitance. When the capacitance distance between the voltage regulator and the rectifier filter is less than 5 ~ 10cm, C1 is not necessary. The recommended value is 0.1 μF. C2 is the output capacitance, which can improve the transient response. The recommended value is 1 μF.

II Minimum Stable Operating Current

LM317 voltage regulator block has a minimum stable working current. Some data call it the minimum output current, and some data call it the minimum discharge current. The minimum stable operating current is generally 1.5mA. Due to the different manufacturers and models of the LM317 voltage regulator block, the minimum stable operating current is also different, but it is generally not greater than 5mA. When the output current of LM317 voltage regulator block is less than its minimum stable working current, LM317 voltage regulator block can not function. When the output current of LM317 voltage regulator block is greater than its minimum stable working current, LM317 voltage regulator block can output stable DC voltage. If you do not pay attention to the minimum stable working current when making voltage stabilized power supply with LM317 voltage regulator block (as shown in Figure 2), the following abnormal phenomena may occur in your regulated power supply: The load voltage and no-load voltage output are different.

Figure 2. LM317 regulated power supply diagram

III Soft-Start Circuit

Figure 3 is a soft-start circuit using LM317. At the moment of power-on, the voltage of CE1 cannot change suddenly. Q1 is biased by R1 and R2 to be saturated and conduction, so that RP1 is short-circuited, which is equivalent to the grounding of the adjustment terminal of LM317. The power output is 1.25V. As the charging time of C2 increases, the output voltage gradually rises. The function of D1 is to quickly release the charge on C2 after the power is turned off, ensuring a normal soft start for the next startup.

Figure 3. Soft-Start Circuit

IV Basic Protection Circuit

D2 is the input short-circuit protection diode. CE1 is the filter capacitor at the regulating end, which has the function of stabilizing output and soft starting circuit. D1 is the output short-circuit protection diode. When the output terminal is short-circuited, CE1 discharges through D1. If there is no D1, CE1 discharges through LM317, which is easy to damage LM317. C1 is the input filter capacitor and C2 is the output filter capacitor. In actual use, the input and output are best connected in parallel by large and small capacitors.

Figure 4. Basic protection circuit

V Charging Circuit

The constant current charging circuit is shown in Figure 5. The constant current I = I=1.25/R1

Figure 5. Circuit diagram of constant current charging

The current-limiting charging circuit is shown in Figure 6. The current-limiting value = 0.7/R3

Figure 6. Current limiting charging circuit diagram

VI Overcurrent Protection Circuit

RSC=0.7/ISC (ISC is over-current protection current)

Figure 7. Over current protection circuit diagram

VII Extending Current Circuit

When the maximum output current is 2A and the output current of LM317 is assumed to be 1A, Q1 is on. The value of R can be calculated according to the following formula: R=UBE/(2-1)=0.7Ω

Figure 8. Extending Current Circuit

VIII High Voltage Output Circuit

If the VZ value of the regulator tube is less than the maximum voltage difference between input and output (40V), the output voltage can be increased. When the output is short circuited, VZ and U1 are easy to be damaged, which is the disadvantage of basic high voltage output circuit.

  

Figure 9. High voltage output circuit

IX Constant Current Circuit

Constant current IL=1.25/R1

Figure 10. Constant current circuit

X Programmable Circuit

Figure 11. Programmable Circuit

XI Adjustable Voltage Calibrator

Figure 12. Adjustable voltage calibrator


Component Datasheet

LM317 Datasheet


FAQ

  • What is lm317 used for?

The LM317 serves a wide variety of applications including local, on card regulation. This device can also be used to make a programmable output regulator, or by connecting a fixed resistor between the adjustment and output, the LM317 can be used as a precision current regulator.

  • What is the maximum input voltage of lm317?

The LM317 is an adjustable voltage linear regulator that can output 1.25 – 37V at up to 1.5A current with an input voltage range of 3 – 40V.

  • What is the difference between lm317 and lm317t?

Member. There is no functional difference as they are one in the same. The T at the end just indicates that it's in a TO-220 package. They usually tag on extra things after the part name to reference things like package, temp range, etc.

  • Is lm317 a transistor?

The LM317 is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 32 V. ... By using a heat-sinked pass transistor such as a 2N3055 (Q1) we can produce several amps of current far above the 1.5 amps of the LM317.

  • How does an lm317 work?

The circuit consists of a low-side resistor and high-side resistor connected in series forming a resistive voltage divider which is a passive linear circuit used to produce an output voltage which is a fraction of its input voltage. 

  • What is IC lm317?

The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V. It requires only two external resistors to set the output voltage. The device features a typical line regulation of 0.01% and typical load regulation of 0.1%.

  • How do I know if my lm317 is working?

Testing lm317t.
If you look to the ic, the legs towards you, the right one is the input pin. you must see a difference of minimum 1.2V between the two pins, otherwise the IC is faulty. furthermore, the first test is to see if you have input voltage !

  • What is the working priciple of lm317?

LM 317 works on a very simple principle. It is a variable voltage regulator i.e. supports different output voltage levels for a constant applied input voltage supply.

  • How to make a simple voltage regulator circuit using LM317?

 

Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
(USD)
LM317AEMP-NOPB LM317AEMP-NOPB Company:Texas Instruments Remark:IC REG LIN POS ADJ 1.5A SOT223-4 Package:TO-261-4, TO-261AA
DataSheet
In Stock:61000
Inquiry
Price:
1000+: $0.77220
2000+: $0.74360
5000+: $0.71500
10000+: $0.70356
25000+: $0.68640
Inquiry
LM317AEMPX-NOPB LM317AEMPX-NOPB Company:Texas Instruments Remark:IC REG LIN POS ADJ 1.5A SOT223-4 Package:TO-261-4, TO-261AA
DataSheet
In Stock:10000
Inquiry
Price:
2000+: $0.74360
6000+: $0.71500
10000+: $0.70356
50000+: $0.68640
Inquiry
LM317AH LM317AH Company:Texas Instruments Remark:Linear Voltage Regulator IC 1 Output 1.5A TO-39-3 Package:TO-205AD, TO-39-3 Metal Can
N/A
In Stock:On Order
Inquiry
Price:
500+: $7.66126
Inquiry
LM317AHVT LM317AHVT Company:ON Semiconductor Remark:IC REG LIN POS ADJ 1.5A TO220-3 Package:TO-220-3
DataSheet
In Stock:On Order
Inquiry
Price:
Call
Inquiry
LM317AT LM317AT Company:Texas Instruments Remark:Linear Voltage Regulators 3-Term Adj Reg Package:N/A
N/A
In Stock:On Order
Inquiry
Price:
1+: $1.51000
10+: $1.28000
100+: $1.02000
250+: $0.89300
500+: $0.86700
1000+: $0.68900
2500+: $0.66300
5000+: $0.63800
10000+: $0.62800
Inquiry
LM317AT-NOPB LM317AT-NOPB Company:Texas Instruments Remark:IC REG LIN POS ADJ 1.5A TO220-3 Package:TO-220-3
DataSheet
In Stock:6411
Inquiry
Price:
1+: $1.58000
10+: $1.42300
25+: $1.34240
100+: $1.07400
250+: $0.93976
500+: $0.91290
1000+: $0.72495
2500+: $0.69810
5000+: $0.67125
Inquiry
LM317BD2T LM317BD2T Company:ON Semiconductor Remark:Linear Voltage Regulator IC 1 Output 1.5A D2PAK Package:TO-263-3, D²Pak (2 Leads + Tab), TO-263AB
DataSheet
In Stock:On Order
Inquiry
Price:
Call
Inquiry
LM317BD2TG LM317BD2TG Company:ON Semiconductor Remark:IC REG LINEAR POS ADJ 1.5A D2PAK Package:TO-263-3, D²Pak (2 Leads + Tab), TO-263AB
DataSheet
In Stock:4372
Inquiry
Price:
1+: $0.88000
10+: $0.77800
25+: $0.73120
100+: $0.55440
250+: $0.47180
500+: $0.44822
1000+: $0.34206
2500+: $0.31846
Inquiry
LM317BD2TR4G LM317BD2TR4G Company:ON Semiconductor Remark:IC REG LINEAR POS ADJ 1.5A D2PAK Package:TO-263-3, D²Pak (2 Leads + Tab), TO-263AB
DataSheet
In Stock:11200
Inquiry
Price:
800+: $0.40338
1600+: $0.30784
4000+: $0.28661
Inquiry
LM317BT LM317BT Company:STMicroelectronics Remark:IC REG LINEAR POS ADJ 1.5A TO220 Package:TO-220-3
DataSheet
In Stock:1194
Inquiry
Price:
1+: $0.53000
10+: $0.45000
25+: $0.42000
100+: $0.31200
250+: $0.26400
500+: $0.25200
1000+: $0.18600
2500+: $0.17400
5000+: $0.16200
Inquiry

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