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Published on 30 Nov 2010 | over 7 years ago

Transistor SwitchTransistor switch is used for switching load circuits under the influence of external control signals. A transistor switch can stay in one of its static modes. The transistor is closed in a cutoff mode. In a saturation mode the transistor is open and saturated. Electronic switches are based on the operating principle of bipolar transistors. When there is no voltage in relation to the emitter at the transistor base then the transistor is closed. The current does not pass through it. A maximal signal, i.e. all supply voltage, is in the collector. When an electric signal is supplied to the transistor base then it opens, and a "collector-emitter" current appears. Voltage across the collector resistance drops. Then collector voltage drops. The output voltage drops correspondingly to a low level.Let's take a simple circuit of a transistor switch based on a bipolar transistor. We use КТ817 transistor - a collector power resistor is 1 kOhm, and 270 ohm resistor on the input. There is full voltage in the on-state... When the signal is supplied to the input, i.e. voltage, then voltage across the transistor collector is limited to the minimum...Transistor switches can also be based on field-effect transistors. Their operational principle is similar to that of electronic switches on bipolar transistors. Digital switches on field-effect transistors consume lesser control current. They provide a galvanic isolation of input and output circuits. However, their performance is slower as compared to bipolar transistors.Here is an example of using a field-effect transistor as an electronic switch. We use KP103 transistor. We may use a resistor from 10 to 100 kOhm...Transistor switches are used in various radio-electronic appliances, analog and digital signal switches, automation and monitoring systems, automatic equipment control systems, home radio and TV appliances, as well as in many other devices.
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