19 Simple Audio Amplifier using 317IC

Another simple audio amplifier circuit, but this time it uses LM317 regulator IC. The amp can deliver 1W power max and needs only few parts.  This circuit is originally from  vegmatic1966 youtube channel.

schematic diagram of LM317 audio amp

Part List:
C1, C3 - 10uF electrolytic capacitor rated 16V
C2 - 470uF electrolytic capacitor rated 16V
R1 - 470 ohms 1/2W
R2 - 10 ohms 2W
POT1 - 5 kilo-ohms potentiometer
SPK - 8 ohms rated 1W speaker
LM317 - 317 or any similar regulator IC

What to do:
After you assembled the circuit above, adjust potentiometer POT1 until the voltage across R2 is half the supply voltage (around 4.5V). Don't forget adding heatsink in your LM317. Check the polarities and pins of the parts before testing.

Part pinouts:

LM317 pinout

0 Simple LED Lamp (Current Regulated)

This simple lamp circuit is made of very few materials. It uses high intensity white LEDs. The circuit is current regulated thus the LED is protected even the supply voltage is variable. The operation of the circuit is very similar to LED driver using LM317 regulator. The current is controlled by resistor R1 with the formula: Current = 1.2V/R1

Current regulated LED lamp schematic

Part List:

C1 - 220uF electrolytic capacitor rated 16V

R1 - 27 ohms 1W

LM317 - 317 or similar regulator IC

LED - white LED (see LED pinout in case you forget)

LM317 pinout

1 Power Supply with Selectable Output

This simple power supply unit (PSU) uses LM317 IC and can deliver 1.5A current with selectable voltages. Outputs are 1.5V, 3V, 4.5V, 6V, 9V and 12V. The output voltage is controlled only by the resistor combinations. You can use the LM317 calculator to determine these resistor values.

PSU schematic diagram

317 pinout

Part List:
C1 - 2200uF electrolytic capacitor rated 25V
C2, C5 - 100nF Mylar or ceramic capacitor
C3, C5 - 22uF electrolytic capacitor rated 16V
R1, R2, R7 - 120 ohms 1/4W
R3, R4 - 240 ohms 1/4W
R5 - 100 ohms 1/4W
R6 - 20 ohms 1/4W
D1, D2 - 1N4004, 1N4007 or similar silicon diode
317 -  LM317 or similar regulator IC
S1 - rotary switch
DC - see AC to DC converter circuit below

Part List:
Transformer - 220 to 12V center tap rated 15VA minimum
D - Any rectifier diode rated 2A minimum
C - You can omit since we got C1 (2200uF)

Note: I recommend using 220V/15V center tap but excessive heating might occur on when 1.5V is selected and with 1.5A output. The lower the output voltage with higher current, the higher the tendency the LM317 will overheat.

2 LM317 lamp flasher

Another simple flasher circuit that is good for car or vehicle use since its powered by 12V car battery.

Part List:
C1 - 4.7uF electrolytic capacitor rated 16V
C2, C3, C4 - see Flash Rate vs RC table
R1, R2, R3 - see Flash Rate vs RC table
Lamp - 12V bulb maximum 15W power
317 - LM317 or similar regulator IC

Flash Rate vs RC table

Rate is the frequency of the flasher. Changing the values of RC changes the rate. R is the resistance value of R1, R2, R3; and C is the value of C2, C3, and C4.

Similar Flashers:
Bulb Flasher - 12W bulb flasher using power BJT
LED Flasher using 555
Lamp Flasher using FET - high current flasher for bulb or LED

4 Simple 12V UPS circuit

This project is one of the simplest 12V Uninterruptible Power Supply (UPS) using few parts. When AC source is available, the battery is charged and there is dc supply coming from regulator IC. On the other hand, when AC supply is not available, the battery will supply power to its output.

The R3 limits the charging current while R1 and R2 combination limits the output voltage of the IC to 13.9V or 13.2V for the battery. D1, D3, D4 prevents the battery from draining or supplying power to the IC. You can modify the circuit by changing the values of R1 and R2 and Bat only (you can use LM317 calculator to change this values).

Part List:
R1 - 120 ohms 1/4w
R2 - 1.2 kilo ohms 1/4W
R3 - 56 ohms 1/2W
C - 470uF (higher the better) electrolytic capacitor rated 25V
D1, D2, D3, D4 - 1N4004, 1N4007, or similar (ge diode is much better)
Bat - 12V lead acid battery
317 IC - LM317 regulator IC
DC input - see AC to DC converter below

The DC input is made out from a simple circuit shown below.

AC-DC converter

Part List:
Transformer - 220V to 12V center-tap min 12VA
D - 1N4004, 1N4007, or similar diode
C - 470uF (higher the better) electrolytic capacitor rated 25V

19 6V Battery Charger Circuit for Lead Acid battery

This simple charger is good for 6V lead acid batteries.The main part of the circuit is the LM317 regulator IC that limits the output voltage based on R1 and R2 values. The charger automatically turns the supply off when battery reaches its full charge voltage. It has a led indicator that turns on when the battery is fully charge thus help you when are you going to remove the battery from the charger.

charger schematic diagram

Part List:
D1, D2, D3, D4 - 1N4001, 1N4004 or similar diode
Dz - 1N5235B or any 6.8V zener diode
C1 - 1000uF electrolytic capacitor rated min 16V
R1 - 12 kilo ohms 1/4W
R2, R4 - 2.2 kilo ohms 1/4W
R3 - 390 ohms 1/4W
LED - 3mm or 5mm Red or any low power LED
Q1 - 2N2907, 2N4403, CS9012 or similar PNP transistor
Q2 - 2N2222, CS9013 or similar NPN transistor
LM317 - any variable regulator IC
Bat - 6V lead-acid battery
Transformer - 110V/9V-0-9V or 220V/9V-0-9V center tap transformer

LM317 pins

PNP transistor pins

NPN transistor pins

Note: If you need a more improve charger with current and voltage control, try to modify the automatic 12V charger circuit.

1 Constant Current Charger using LM317 regulator

This project is very similar to universal charger that uses constant current charging method.  But this one is much simpler to construct since you can build it using only 2 parts, the LM317 regulator and resistor. The use of diode D is for short circuit protection. Capacitors C1 and C2 is for good voltage regulation. Resistor R2 acts a dummy load when battery is disconnected. The idea of this charger is the output current is equal to 1.2V divided by the value of R1.
In equation:  Current out = 1.2/R1

Charger schematic

LM317 pins

Part List:
LM317
R1 - see the values in table below
R2 - 2.2 kilo-ohms 1/4W
C1,C2 - 47uF/25V, or any value will do, the higher the better
D - 1N4001 or any similar diode at-least 1A rated

R1 vs  Output current table

You can modify the circuit above and make it simpler by omitting some parts. See diagram below.

Simplified charger schematic

Note: This is not an automatic charger so monitor the battery always to avoid damage. You can charge any battery with voltages from 1.2V to 12V but make sure that the DC input is at-least 3V higher than the battery.

Other useful chargers:
Mobile phone charger - very simple charger intended for cellphones
3V charger - charger powered by 3V battery
1.5V charger - charger powered by 1.5V, for emergency purposes
Universal Charger - charge any battery with different voltages with different charging currents.

8 High current variable power supply (1.2V to 30V at 5A)

We are going to design a simple, very cheap, high power, variable power supply unit (PSU) with current control or protection. Diagram below is our design basis. We have three main parts, the voltage regulator, current amplifier, and current controller. Voltage regulator is the one that controls the variable voltage output, which in our case LM317 IC. Current amplifier is an add-on circuit component that boosts the output current. Current controller is the circuitry that protects the entire power supply unit from short circuits and overloading. You can use either ordinary fuse or current limiter circuit as your current controller.

PSU design

Power supply unit below is rated 150W and has an output current of 5A. Output voltage can be varied from 1.2V up to 30V DC, thus very suitable as power source of your electronic projects, devices, battery chargers and others.

High power PSU schematic diagram

Circuit Operation:

DC input is a 35VDC using AC-DC converter below. R1, Q1, and Q2 limits the maximum to 5A (read more on how current limiter works). Q3 and R3 is the current booster that increases the current capacity of LM317 regulator. R4 is the potentiometer that controls the output voltage from 1.2V to 30V (see LM317 calculator to know how these output voltages are arrived).

Part List:
R1 - 0.15 ohms resistor 10W
R2 - 1.8 kilo-ohms 1W
R3 -  4.7 ohms 1/2W
R4 - 5 kilo-ohms potentiometer
R5 - 220 ohms 1/4W
Q1 - 2N4403 or any general purpose PNP transistor
Q2 - IRF4905 power FET or similar power PMOS
Q3 - MJE2955t or similar PNP power transistor
C1 - 220uF electrolytic capacitor rated 50V
C2 - 22uF electrolytic capacitor rated 50V
LM317 - regulator IC
DC input - regulated 35V DC (see AC-DC converter circuit below)

Part list diagrams: click to enlarge

LM317 pin

IFR4905 pins

MJE2955t pins

 The DC input

AC-DC converter

Converter Part List:
X'former - 220V/27V-0V-27V center tap transformer min 180VA
D - rectifier diode min 6A current rating
C - 1000uF electrolytic cap 50V (higher capacitance the better)
Fuse - 1A @ 220V

Similar variable PSU projects:

1. Simple variable PSU - (+1.2V to +28V at 1.5A) positive output

2. Negative variable PSU – (-1.2V to -28V at 1.5A) negative output

3. Dual variable PSU – two outputs positive and negative @ 1.5A, from 0V to 28V

13 Simple LED driver using LM317 regulator

This Led driver is very easy to construct since  you will need only 2 electronic parts, the LM317 IC regulator and 1W resistor. Driver can be powered by any 9 to 20V DC supply. Circuit can drive any  LED ranging from .5W up to 5W by just replacing the value of resistor depending the allowed current specified for the LED using the formula shown below : ( no need for LM317 Calculator).
R =1.25/current(I);    where I is the current specified by LED datasheet
For example:
700mA current is needed to power up a 3W LED, you will have:
R=1.25/0.7A=1.785 or around 1.8-ohms

LED driver circuit

Part List:
1-LM317 regulator
1-resistor
    -3.9-ohms for 1W led
    -1.8-ohms for 3W led

Other LED driver:
1. LED driver using 7805 – one of the cheapest and simplest driver, similar to this driver
2. Cheap Power LED Driver circuit – cheapest, uses only resistor, transistor and diode
3. High current LED driver using FET – stable and  high current led driver

Note: The maximum current of the LM317 regulator is around 1.5A only. Don't forget to add heatsink in the regulator to avoid damage due to overheating. When the DC supply is not regulated, add a 100uF (or higher) capacitor accros  the input positive and negative terminal.