What is a 100 ohm resistor? 100 ohm resistor color code

What is a 100 ohm resistor? 100 ohm resistor color code

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What is a 100 ohm resistor?

A 100 ohm resistor is one of the most common fixed resistors with a nominal resistance of 100Ω. It is used to limit current, prevent circuit overload, divide voltage or signal conditioning. It is widely used in electronic circuits, signal processing, power management, LED protection and other fields.

According to Ohm's Law:

When current passes through a 100Ω resistor, its voltage drop can be calculated by current (I) and resistance (R).

Main parameters of 100 ohm resistor

When choosing a 100Ω resistor, the following parameters are crucial:

1. Resistance:

• 100Ω (tolerance range ±1%~±5%).

2. Power Rating:

• 1/8W, 1/4W, 1/2W (low-power electronic circuits)


• 1W, 2W, 5W (high-power applications)

3. Temperature Coefficient (TCR):

• Low temperature drift (±50ppm/°C or lower)Suitable for high-precision circuits

4. Material Type:

• Carbon Film Resistor: Low cost, suitable for general electronic products


• Metal Film Resistor: Higher stability, suitable for high-precision circuits


• Wirewound Resistor: High power application, suitable for industrial and power electronics


• SMD (Surface Mount Resistor): Used in modern PCB design

Application of 100 ohm resistor

1. LED current limit

100Ω resistor is often used in LED circuits to prevent LED overload damage. For example, under 5V power supply, a red LED (2V voltage drop) is connected in series with a 100Ω resistor, and its current is:

This current is within the allowable range of the LED to prevent overload and burnout.

2. Power supply current limiting

In DC power supply circuits, 100Ω resistors can be used to limit current and prevent transient shocks from damaging the circuit.

3. Voltage divider circuits

100Ω resistors are often used in voltage dividers, and work with another resistor to divide the voltage to provide a stable reference voltage. For example:

100Ω and 200Ω can be used to form a 1:2 voltage divider ratio.

4. Low-pass filter

100Ω resistors combined with capacitors can form an RC filter to filter out high-frequency noise. For example:

If paired with a 1µF capacitor, the cutoff frequency is about 1.59 kHz.

5. Terminal matching (signal processing)

100Ω resistors are used for impedance matching, especially in Ethernet circuits, matching 100Ω balanced transmission lines to reduce signal reflections.

6. Sensor bias

In a bridge circuit (such as a Wheatstone bridge), a 100Ω resistor is used to provide a reference resistor to ensure that the sensor output is accurate and stable.

How to choose a suitable 100 ohm resistor?

When selecting a 100Ω resistor, the following factors need to be considered:

Parameter	Selection basis
Power	Calculate the power consumption based on the current to ensure that the resistor will not burn
Accuracy	±1% (high accuracy) or ±5% (general application)
Material	Carbon film (general purpose), metal film (high accuracy), wirewound (high power)
Package	SMD (automatic welding), THT (manual welding)

Power consumption calculation formula:



If a 100Ω resistor passes a 100mA current:



At this time, a resistor with a rated power of at least 1W is required.

Package specifications of 100 ohm resistors

100Ω resistors have different package types:

1. Plug-in (THT, Through-Hole)

• Common specifications: 1/4W, 1/2W, 1W, 2W, 5W


• Suitable for manual welding, power circuits

2. Surface mount (SMD)

• Size: 0201, 0402, 0603, 0805, 1206


• Suitable for automated welding, compact circuits

3. Power resistors

• Using ceramic or aluminum shell packaging


• Used for industrial circuits, motor control, power electronics

 

Color code of 100 ohm resistors

The color code of resistors follows the electronic color coding system. Common four-color ring resistors (tolerance ±5% or ±10%) and five-color ring resistors (tolerance ±1% or higher) have different coding methods.

1. Four-color band color code for 100 ohm resistors

For common carbon film resistors (±5% tolerance), the color code for 100Ω is:

Color	First band (tens)	Second band (units)	Third band (multiplier)	Fourth band (tolerance)
Brown	1	-	-	-
Black	-	0	-	-
Brown	-	-	×10	-
Gold (or Silver)	-	-	-	±5% (Gold) or ±10% (Silver)

Final code: Brown - Black - Brown - Gold (or Silver)

Explanation:

• Brown (1)


• Black (0)


• Brown (×10)


• Tolerance: ±5% (Gold), ±10% (Silver)

Example: A 100Ω ±5% resistor, the colors are Brown - Black - Brown - Gold.

2. Five-color ring color code for 100 ohm resistor

For precision resistors (±1% tolerance), the color code for 100Ω is:

Brown

Color	First ring (hundreds)	Second ring (tens)	Third ring (units)	Fourth ring (multiplier)	Fifth ring (tolerance)
Brown	1	-	-	-	-
Black	-	0	0	-	-
Black	-	-	-	×10	-
Brown	-	-	-	-	-
Brown	-	-	-	-

Final code: Brown - Black - Black - Brown - Brown

Explanation:

• Brown (1)


• Black (0)


• Black (0)


• Brown (×10)


• Tolerance: ±1% (Brown)

Example: 100Ω ±1% resistor, the colors are Brown - Black - Black - Brown - Brown.

3. How to read resistor color code?

• Find the gold or silver ring (tolerance ring), which is usually on the far right.


• Read the color rings from left to right (except the tolerance ring).


• The first two (or three) digits are significant digits, which are then multiplied by the factor and finally checked for tolerance.


• Calculate the resistance value in ohms (Ω).

4. Other related resistor color codes

In SMD (surface mount resistor), 100Ω It may be represented by three or four digits:

• "101" → 10 × 10¹ = 100Ω


• "1000" → 100 × 10⁰ = 100Ω

Summary

• Four-color rings (ordinary resistor): Brown-Black-Brown-Gold (±5%)


• Five-color rings (precision resistor): Brown-Black-Black-Brown-Brown (±1%)


• SMD chip resistor identification: 101 or 1000

100Ω resistor is a common electronic component, widely used in LED circuits, signal matching, power supply current limiting and other occasions. Correctly identifying the color code helps to quickly determine the resistance value and improve circuit design and maintenance efficiency!

Common problems with 100 ohm resistors

1. What is the color code of 100 ohm resistors?

If it is a four-color band resistor:

• Brown (1) Black (0) Brown (×10) Gold (±5%)


• Represents 100Ω, tolerance ±5%

2. How much current can a 100 ohm resistor handle?

Calculate based on power P:

• 1/4W resistor: maximum 50mA


• 1W resistor: maximum 100mA


• 5W resistor: maximum 223mA

3. Can a 100 ohm resistor replace a 120 ohm resistor?

Yes, but it will slightly affect the circuit current and voltage distribution. If high accuracy is required, use a closer value (such as 110Ω).

4. Can 100 ohm resistors be used in parallel or series?

• Two 200Ω in parallel can get 100Ω


• Two 50Ω in series can get 100Ω

5. In which devices are 100 ohm resistors most common?

• LED circuit


• Arduino, Raspberry Pi development board


• Audio equipment


• Power protection


• Industrial automation

 

Summary

100Ω resistor is a common fixed resistor, widely used in LED current limiting, power management, signal processing, filtering and impedance matching. Choosing the right power, precision and package is critical to circuit performance. In various electronic circuits, 100Ω resistor plays a key role in stabilizing current, regulating voltage and protecting components.

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