Passive Components – Resistors

Sri Sudheera

6 years ago

Resistors: These are the electric components which are use to oppose the flow of current. Generally, Resistors are made by the ceramic rod and over that rod, aluminum is coated. For every resistor will have the different colors. So depending on the colors, the value of resistors are calculated. So that value gives the how much current it can resists. When the current flow through the resistance it absorbs that electrical energy and it dissipates in the form of heat.

Formula: R= V/I ( R – resistance, V- Voltage, I – current )

The power which is dissipated is given as P= VI (P – power, V- voltage, I –current)

Units: Ohms

Types of Resistors

1.Linear

a.Fixed resistor

i .Carbon composition resistor

ii.Wire wound resistor

iii.Thick film resistor

Fusible resistor
Cermet film resistor
Metal oxide resistor

iv. Thin film resistor

Carbon film resistor
Metal film resistor

b. Variable resistor

i.potentiometer

ii.rheostrat

iii.trimmer

2. Non-Linear

i.thermistor

ii.Photo resistor LDR

iii.Varistor resistor

iv.Surface mount SMD

1. Linear:

a)Fixed resistors: The values of the resistors are fixed and can not be changed.

Symbolic representation:

i. Carbon composition resistor:

These are very cheap and occupies less place.Its range from 1 ohm to 25 mega ohms. Power rating will be ¼ th watt to 5 watts. These are less stable and makes noise compared to other resistors.

ii. Wire wound resistor

Wound wire is known as resistor wire and it is made of Tungsten, manganin, Nichrome or nickel or a nickel-chromium alloy. the Enamel coating is made of porcelain, Bakelite, press bond paper or ceramic clay material.

Its range from 0.1 ohms to 100 K ohms and power is 2 watts to 100 watts.These are costly and use in the industries.

iii. Thick film resistors

This resistor will have thick conducting material.

metal oxide resistors:
These have very low noise and are used at high voltage levels.
cermet oxide resistorThese are very stable and they may be in square and rectangular shape
Fusible resistorsThese are same as wire wound resistor that is when the power is increased the resistor will be fused.so it is called fused resistors. Its resistance range is less than 10 ohms. Used in the TV sets.

iv. Thin film resistors:

The conducting material is very thin
carbon film resistorsThese have negligible noise so widely used in electronic circuit
Metal film resistorsThese are same as carbon film resistors but instead of carbon, we use the metal.
b.Variable resistors:The value of the resistors can be changed through the dial, knob, screw or manually.

i. Potentiometer

Potentiometer used for the controlling the voltage level. It is of 3 terminals two are constant connections ad other one is the slider.By moving the slider we can the change the value of a resistor. The range of them varies up to 10 mega ohms.

Types of the potentiometer

ii. Rheostats
Symbolic representation

Rheostat other name is tapped resistor. These are used to control the current level.
And in this, there is wire wound rheostat and its range is from 1 ohm to 150 Ohm and power is 3 to 200 watts.

iii.Trimmer Potential meter

These will have additional screw and by moving that screw by screwdriver we can change the value of resistance

2. Nonlinear resistors:

The flow of current changes with a change in temperature or the applied voltage.

i. Thermister:

The flow current changes with the change in temperature are known as the thermister. So thermister is the temperature sensitive device.

The resistance is inversely proportional to temperature so it is called as negative temperature coefficient.But there also positive temperature coefficients. So that type of thermistors made up of the pid barium titanate semiconductor materials.

Symbolic representation:

Types of thermistors:

ii. Varistors(VDR)

The flow of current changes with the change in the applied voltage is known as the Varistors.

iii.Photo Resistor or Photo Conductive Cell or LDR (Light Dependent Resistors)

Depending on the intensity of the light the resistance value changes. I.e, when the light falls on the LDR the flow electrons increases then the resistance of semiconductor material decreases. So LDR is the negative temperature coefficient.

Symbolic Representation:

iv.SMD

SMD stands for Surface Mounted Device. An SMD is any electronic component that is made to use with SMT or Surface Mount Technology. SMT was developed to meet the ongoing desire for printed circuit board manufacture to use smaller components and be faster, more efficient, and cheaper.

Calculation of SMD Value

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)

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)

Below is the table (1) to shows the multiplier values of different Letters using in the EIA-96 coding system for SMD Resistor Codes.

Table (1)

Letters	Multipliers
Z	0.001
R or Y	0.01
S or X	0.1
A	1
B or H	10
C	100
D	1000
E	10000
F	100000

Also, look in the examples of reading EIA-96 SMD Resistor Codes for importance the use of table (2)

Table (2)…

Table (2)

Code	Value	Code	Value	Code	Value	Code	Value
01	100	25	178	49	316	73	562
02	102	26	182	50	324	74	576
03	105	27	187	51	332	75	590
04	107	28	191	52	340	76	604
05	110	29	196	53	348	77	619
06	113	30	200	54	357	78	634
07	115	31	205	55	365	79	649
08	118	32	210	56	374	80	665
09	121	33	215	57	383	81	681
10	124	34	221	58	392	82	698
11	127	35	226	59	402	83	715
12	130	36	232	60	412	84	732
13	133	37	237	61	422	85	750
14	137	38	243	62	432	86	768
15	140	39	249	63	442	87	787
16	143	40	255	64	453	88	806
17	147	41	261	65	464	89	825
18	150	42	267	66	475	90	845
19	154	43	274	67	487	91	866
20	158	44	280	68	499	92	887
21	162	45	287	69	511	93	909
22	165	46	294	70	523	94	931
23	169	47	301	71	536	95	953
24	174	48	309	72	549	96	976

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)

Calculation of resistors:

Note: these calculations are applicable only to that resistors which are with color bands.