SMD Resistor – Surface Mount Resistor Guide:

What is SMD Resistor?

SMD Resistor or Surface Mount Chip Resistor is an electronic component with the properties of both obstruction as well as resistance. The property of this component is called resistance.

What is Resistance?

The obstruction or resistance created by any matter in the flow of current is called resistance.

What is the Graphical Symbol of Resistor?

Resistance Symbol:

Which Alphabetic Character Denotes a Resistor?

A resistor is denoted by the character: R

What Is The Function Of a Resistor?

The Function of a resistor is to decrease current.

What is the Unit of Resistance?

The unit of resistance is: Ohm

What is the Power Rating of Resistor?

The power rating of resistor is Watt.

What does a SMD Resistor looks like?

A SMD resistor appears black from top with some blue colour. The colour at the bottom is white.

Facts About SMD Resistor

1. Resistor can be open.

2. Value of resistor can be high.

3. Resistor is available with or without code. Mostly resistors without code are used in mobile phones.

4. R and E alphabets in the resistor denote Ohms.

Different Types of SMD Resistors

1. Network Resistor: Combination of more than one resistor groups is called network resistor. They are made in a single package.

2. Chip Jumper (Zero Ohm) Type Resistor: This type of chip resistor is used as jumper in mobile phones.

3. Thermistor-Type Resistor: The rating of this type of resistor depends on temperature. It is black in colour from all sides. These resistors are of two types – NTC Thermistor (Negative Temperature Co-efficient type Thermistor) and PTC Thermistor (Positive Temperature (Co-efficient type Thermistor).

4. LDR (Light Dependent Resistor): This resistance is dependent upon light. Resistance of a LDR may be several mega Ohms in dark, but is reduced to few Ohms under light.

Coding of SMD Resistor:

Generally a number equivalent to three band color code is written on a resistor. Like resistors of normal terminal, a 4 digit code is provided to denominate tolerance. First 2 or 3 digits denote the first two or three digits of values of the resistor and the third or last digit represents the numbers of zero. R is written before or after the value to denote the position of decibel point in the resistor below 10 Ohm value. Read the following examples:

Code : 221 = 220 Ohm

Code : 683 = 68000 Ohm or 68 K Ohm

Code : 105 = 10,00000 Ohm or 1 M Ohm

Code : 8R2 = 8.2 Ohm

Code : 1000 = 100 Ohm

Code : 4992 = 49900 Ohm or 49.9 K Ohm

Code : 16234 = 162000 or 162 K Ohm

Three digit system

273 = 27 Ω x 103 is 27,000 Ω (27 kΩ)

Four digit system

7992 = 799 Ω x 102 is 79,900 Ω (79.9 kΩ)

1733 = 173 Ω x 103 is 173,000 Ω (173 kΩ)

Examples of converting EIA-96 markings to a resistance value:

01A ⇒ Code 01 = 100 with Multiplier A = 1 ⇒ 100 x 1 = 100 Ω ±1%

38C ⇒ Code 38 = 243 with Multiplier C = 100 ⇒ 243 x 100 = 24,300 Ω ±1%

92Z ⇒ Code 92 = 887 with Multiplier Z = 0.001 ⇒ 887 x 0.001 = 0.887 Ω ±1%

SMD Resistor Multiplication Factors

Code Multiplication Factor

Y / R = 0.01

X / S = 0.1

A = 1

B / H = 10

C = 100

D =1000

E 10,000

F 100,000

Tolerance of SMD Resistor

During manufacturing of resistors, some deficiency or excess may take place in its value. The tolerance of resistors used in mobile phones is almost zero.

Examples of 3-Digit SMD Resistor Codes

250 = 25 x 100 = 25 x 1 = 25 Ω (This is only and only 25Ω not 250 Ω)

100 = 10 x 100 = 10 x 1 = 10 Ω

721 = 72 x 101 = 72 x 10 = 720 Ω

102 = 10 × 102 =10 x 100 = 1000Ω or 1kΩ 915 = 91 x 105 = 91 x 100000 = 9,100,000 Ω = 9.1MΩ

4R7 = 4.7Ω

R12 = 0.12 Ω

Examples of 4-Digit SMD Resistor Codes

2500 = 250 x 100 = 250 x 1 = 250 Ω (This is only and only 250Ω not 2500 Ω)

1000 = 100 x 100 = 100x 1 = 100 Ω

7201 = 720 x 101 = 720 x 10 = 7200 Ω or 7.2kΩ

1001 = 100 × 101 =100 x 10 = 1000 Ω or 1kΩ

1004 = 100 × 104 =100 x 10000 = 1000,000 Ω or 1MΩ

R102 = 0.102 Ω (4-digit SMD resistors (E96 series)

0R10 = 0.1 x 100 = 0.1 x 1 = 0.1 Ω (4-digit SMD resistors (E24 series)

Examples of EIA-96 SMD Resistor Codes

01F = 10M

01E = 1MΩ

01C= 10kΩ

01B = 1kΩ

01A = 100Ω

01X = 10Ω

01Y = 1Ω

66X = 475 x 0.1 = 47.5 …→ (in table (2), 66 = 475 and in table (1), X = 0.1. so 475 x 0.1 = 47.1Ω)

85Z = 750 x 0.001 = 0.75Ω → (in table (2), 85 = 750 and in table (1), Z = 0.001. so 750 x 0.001 = 0.75Ω)

36H = 232 x10 = 2320Ω = 2.32kΩ → (in table (2), 36 = 232 and in table (1), H = 10. so 232 x 10= 2.32kΩ)

How to Check a SMD Resistor with a Multimeter

If the value of a resistor to be checked is 100 Ohm, then place probes of the Multimeter at both the soldering tips of the resistor and select knob of the Multimeter at 200 Ohm. Value of the resistor is displayed on the display screen of the Multimeter. If only 1 is displayed on the screen then it means that the resistor is OPEN and if the reading is too high then it means that the resistor is out of order or it is faulty. Resistors do not get shorted. Value of a resistor is considered OK within its tolerance limit.