Constant resistor in electronics
 Resistance
is defined by Ohm's Law I = V / R where R is the resistance. In electronic
components are used with normalized values, the purpose of this definition. Both
types are used:
1. Carbon resistors.
Values are chosen in a range type
called "Renard Series". The most common range is geometric progression of
ratio 
(About 1.21) which is rounded values. These are the so-called values Standard 1
- 1.2 to 1.5 - 1.8 - 2.2 to 2.7 - 3.3 - 3.9 to 4.7 - 5.6 - 6.8 - 8.2 to 10 - ...
For this type of component, power dissipated
is low: 0.25 to 2 Watts. The maximum voltage applicable to a resistance value R
and can dissipate a puisance P is under the Joule's
law  Or
The tolerance the values can be
1, 2, 5, 10 or 20%, only three possible values for carbon
resistors common.
| Black |
0 |
| Brown |
1 |
| Red |
2 |
| Orange |
3 |
| Yellow |
4 |
| Green |
5 |
| Blue |
6 |
| Purple |
7 |
| Gray |
8 |
| White |
0 |
Values are given either plain or by
coding standard based on the colors.
On resistance are four rings of color: the first
gives the first digit, second band give next and third exponent of 10. The
fourth gives the tolerance (or-> 5% argent -> 10% and white (or absent)
-> 20%).
In the example above, the value is red-red-red-white,
2.2 * 10 ² = 220 Ohm with a tolerance of 20 %. Green-blue-gray-gold gives a
value of 5.6 * 108=560 megaohms.
2. The bobined resistors.
The values are identical to the
resistance carbons. The big difference is the power dissipation that can reach
for the largest up to hundreds of Watts. By cons, they have a significant
coefficient of self-induction high frequency.
Definitions Annexes: Ohm's Law, Kirchhoff, potentiometer
(Variable), diode, LED
Last update, 06/25/2011 |
