Calculate resistances for LM317 voltage-regulator

LM317 Voltage Regulator Calculator

The basic LM317 circuit. See the datasheet for advice
on adding capacitors and other enhancements.

Enter the required output voltage and value of the R1 resistor to calculate the R2 resistor. Then use the nearest available value (listed at the bottom of the page) or a smaller resistor and series trim-pot for greater accuracy. Maximum output is 37V.

R1 can be changed but should be kept in the range 100-1000 ohms. The regulator should have a minimum load of 10mA for the worst-case specified accuracy; the 240 ohm resistor commonly used gives a 5mA loading which is usually OK.

The second calculator can be used to see the calculated voltage resulting from your stock value resistors. Resistor values must be entered in ohms, '1k' won't work. Sorry.

(Due to voltage losses in the LM317 regulator chip, the input voltage should be at least 2V more than the required output voltage.)

Output Voltage volts

R1 resistor ohms

R2 resistor ohms

R1 resistor ohms

R2 resistor ohms

Output Voltage volts

Why is my output voltage a bit off?

The formula used to calculate the regulated voltage is:

V_out = 1.25(1 + R2/R1)

However,

• The Reference Voltage is only nominally 1.25V and for different components it can vary from 1.20–1.30V; so with a 12V aim, the end result will be 12V ±0.5V.
• The resistors won't be exactly what they say. The cheaper gold-banded are ±5%, brown-banded metal film not much more expensive and ±1%.
• There's a small error term Iq * R2 to add to the result. Iq, the Adjustment pin current, is typically only 50µA (0.00005), so it doesn't usually make much difference compared to the two factors above; only 5mV if R2=1k.

If you need high accuracy, use an adjustable trimpot for all or part of R2.

E24 resistor series

The E24 series is widely available and goes up in roughly 10% steps as below:

10 ohms, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91...

and decades of the above, eg 120 ohms, 4,700 ohms (4.7k).

There are two reasons for adding a diode: 1) To provide reverse polarity protection, in case someone connects the battery backwards. In this case the diode needs to go in series with the input to the LM7805. 2) To prevent a large capacitor connected to the output from discharging back in to the regulator, if the input power supply is removed and short circuits, see the circuit on the bottom of page 8 of the datasheet linked below.LM7805 Datasheet In this case I don't think there's any need for #2 but you might want #1, besides #1 will provide protection against #2.

How to convert dBm to watts to dBms?

dBm to Watts Calculator

Convert dBm to watts or watts to dBm with the use of Digi-Key conversion calculator.

 

dBm		Watts
Watts		dBm

Calculate electric time constant (T or RC)

Time Constant Calculator

Online calculator to calculate the energy (E) and time constant (RC) in a capacitor for the given voltage across it. You can determine two different values from the calculator. Time constant (T) can be determined from the values of capacitance (C) and load resistance (R). Energy stored on a capacitor (E) can be determined by giving all three inputs: voltage (V), capacitance and load resistance.

 

Voltage (V) Optional		Capacitance (uF)		Load Resistance (Ohms)
	×		×
Seconds (S)		Joules (J)

Calculate V = I * R (Ohm's Law)

Ohm's Law Calculator

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.

 

Resistance (Ω)		Current I(A)		Voltage (V)
	×
Voltage (V)		Resistance (Ω)		Current I(A)
	÷
Voltage (V)		Current I(A)		Resistance (Ω)
	÷

Calculate your mobile phone battery life

Battery Life Calculator

Generally, battery life is calculated based on the current rating in milli Ampere per Hour and it is abbreviated as mAh. Ampere is an electrical unit used to measure the current flow towards the load. The battery life or capacity can be calculated from the input current rating of the battery and the load current of the circuit. Battery life will be high when the load current is less and vice versa. The calculation to find out the capacity of battery can be mathematically derived from the following formula:

Battery Life = Battery Capacity in Milli amps per hour / Load Current in Mill amps * 0.70

 

Battery Capacity (mAh)		Device Consumption (mA)
	÷		×	0.7*
Estimated Hours

*The factor of 0.7 makes allowances for external factors which can affect battery life.

Calculate 6-band resistance

6 Band Resistor Color Code Calculator

This tool is used to decode information for color banded axial lead resistors. Select the number of bands, then their colors to determine the value and tolerance of the resistors.

Number of Bands:

Select the color of each band on the resistor:
None Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Gold Silver	None Brown Red Green Blue Violet Gold Silver	None Brown Red Orange Yellow Blue Violet

Resistor Value:

Calculate 5-band resistance

5 Band Resistor Color Code Calculator

This tool is used to decode information for color banded axial lead resistors. Select the number of bands, then their colors to determine the value and tolerance of the resistors.

Number of Bands:

Select the color of each band on the resistor:
None Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Gold Silver	None Brown Red Gold Silver

None Brown Red Orange Yellow Blue Violet

Resistor Value:

Calculate 4-band resistance

4 Band Resistor Color Code Calculator

This tool is used to decode information for color banded axial lead resistors. Select the number of bands, then their colors to determine the value and tolerance of the resistors.

Number of Bands:

Select the color of each band on the resistor:
None Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Green Blue Violet Gray White	None Black Brown Red Orange Yellow Green Blue Gold Silver	None Brown Red Gold Silver

None Black Brown Red Orange Yellow Green Blue Violet Gray White None Brown Red Orange Yellow Blue Violet

Resistor Value:

How to measure the resistance with Resistor Color Code?

Components and wires are coded are with colors to identify their value and function.

 

The colors brown, red, green, blue, and violet are used as tolerance codes on 5-band resistors only. All 5-band resistors use a colored tolerance band. The blank (20%) "band" is only used with the "4-band" code (3 colored bands + a blank "band").

Example #1

 
 A resistor colored Yellow-Violet-Orange-Gold would be 47 kΩ with a tolerance of +/- 5%.

Example #2

  A resistor colored Green-Red-Gold-Silver would be 5.2 Ω with a tolerance of +/- 10%.

Example #3

 A resistor colored White-Violet-Black would be 97 Ω with a tolerance of +/- 20%. When you see only three color bands on a resistor, you know that it is actually a 4-band code with a blank (20%) tolerance band.

Example #4

 A resistor colored Orange-Orange-Black-Brown-Violet would be 3.3 kΩ with a tolerance of +/- 0.1%.

Example #5

 A resistor colored Brown-Green-Grey-Silver-Red would be 1.58 Ω with a tolerance of +/- 2%.

Example #6

 A resistor colored Blue-Brown-Green-Silver-Blue would be 6.15 Ω with a tolerance of +/- 0.25%.