Resistor – a double-ended, passive electronic component. It is a linear component, which means that the voltage drop is directly proportional to the current that flows through it. Resistor is used to reduce or achieve the desired value of the current that flows in the electric circuit. It can operate under direct, alternating or pulse currents (a type of circuit has a significant impact on its properties). In addition, resistor is a component in which the process of converting electric energy into thermal energy takes place.
Resistor – Division
Memory resistor (that is controlled by current) is called memristor. Resistor with adjustable electric resistance is called a potentiometer. It is a triple-ended element used as the voltage divider. On the Fig. 3 you can find more about resistor’s big family.
Resistor – Technical Parameters
The most important technical parameters of the resistor are written below:
- nominal resistance (conductance parameter “G” [S – siemens] is also often used, where G = 1/R) – given by the manufacturer on the housing element that can be measured using a multimeter,
- accuracy class (tolerance) – possible deviation of the actual value of the resistor from the nominal value (given in percentages),
- power rating – the maximum permissible power that can be dissipated as heat from resistor under certain conditions,
- temperature coefficient of resistance (TCR) – it defines resistance variation under the influence of temperature (the smaller the TCR, the more stable resistor is),
- voltage limiting – the maximum value of the DC voltage (or the highest effective value of the alternating current AC), that won’t cause any damage to the component. This value depends on the material from which resistor was manufactured – for popular, low power resistors it ranges from 150 to 500V.
Resistor – Color code chart
I bet that many of you have wondered, what these “colorful stripes” on the resistor actually mean? Below you can find out and “decode” your own resistor’s value.
Let’s take resistor from the Fig. 4. as an example. According to the color chart from Fig. 5., first stripe (purple) has the value of “7”. Second stripe (yellow) has the value of “4”. Third stripe (orange) means the multiplier value, so basically we need to write the first two digits next to each other and multiple that number by 1000 (1k). So, 7 and 4 multiplied by 1000: 74 * 1000 = 74000Ω = = 74kΩ Tolerance of this resistor has the value of +/- 0,05% (grey color).
First stripe (green) has the value of “5”. Second stripe (black) has the value of “0”. Third stripe (orange) means the 1k multiplier value.
5 and 0 multiplied by 1k: 50 * 1000 = 50kΩ. Tolerance of this resistor has the value of +/- 1% (brown color).
First stripe (yellow) has the value of “4”. Second stripe (purple) has the value of “7”. Third stripe (brown) means the 10 multiplier value.
4 and 7 multiplied by 10: 47 * 10 = 470Ω. Tolerance of this resistor has the value of +/- 2% (red color).
That was easy, right?
Resistor – Basic equations
R = V / I
R – resistance (Ω – Ohm)
V – the current between the element ends (V– Volt)
I – current (A – Ampere)
Power dissipated on the resistor:
P = V * I
P – electric power (W – Watt)
Note: More in-depth explanation of Ohm’s Law and more important topics can be found in our 911electronic Basic Electronic Course.
Resistor – Series and Parallel connections
The equivalent resistance of the series connection of several resistors “R” is equal to the sum of the resistance of the resistors forming this connection.
R = R1 + R2 + …Rn
For two, parallel connected resistors, equation for total combined equivalent resistance is shown below:
R = R1,2 = R1 * R2 / R1 + R2
Resistor – Voltage divider
Voltage divider – two resistors in series connection. It is used to separate the voltage supplied to its input, so its output voltage will be the partial input voltage. Input voltage is supplied to the R1 and R2 resistors, while the output voltage is equal to the voltage drop on the resistor R2:
Vout = Vin * R2/R1 + R2