Apr 3rd, 2008
by Electronics Online.
Resistors can play any of numerous different roles in electrical and electronic equipment. Here are a few of the more common ways resistors are used.
Voltage division
You’ve already learned a little about how voltage dividers can be designed using resistors. The resistors dissipate some power in doing this job, but the resulting voltages are needed for the proper biasing of electronic transistors or vacuum tubes. This ensures that an amplifier or oscillator will do its job in the most efficient, reliable possible way.
Biasing
In order to work efficiently, transistors or tubes need the right bias. This means that the control electrode—the base, gate, or grid—must have a certain voltage or current. Networks of resistors accomplish this. Different bias levels are needed for different types of circuits. A radio transmitting amplifier would usually be biased differently than an oscillator or a low-level receiving amplifier. Sometimes voltage division is required for biasing. Other times it isn’t necessary. Figure 6-1 shows a transistor whose base is biased using a pair of resistors in a voltage-dividing configuration.
Apr 3rd, 2008
by Electronics Online.
WHAT A TRANSFORMER TAP CHANGER IS AND WHAT IT DOES.
A tap changer is a device fitted to power transformers for regulation of the output voltage to required levels. This is normally achieved by changing the ratios of the transformers on the system by altering the number of turns in one winding of the appropriate transformer/s. Supply authorities are under obligation to their customers to maintain the supply voltage between certain limits. Tap changers offer variable control to keep the supply voltage within these limits. About 96% of all power transformers today above 10MVA incorporate on load tap changers as a means of voltage regulation. Tap changers can be on load or off load.
On load tap changers generally consist of a diverter switch and a selector switch operating as a unit to effect transfer current from one voltage tap to the next. It was more than 60 years ago on load tap changers were introduced to power transformers as a means of on load voltage control.
Apr 3rd, 2008
by Electronics Online.
Here the resistor color code for 4 band color and 5 band color.
Usually the 5 band color resistor also known as metalfilm resistor (blue body color).
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Resistor Color Code »
