Transistor As A Switch
Jan 15, 2013 How can a transistor turn a circuit on and off? This electrical current switches the transistor on, so the transistor can now power its load, which is the motor. In this circuit, the transistor acts as a switch and an amplifier. The same setup to set the transistor as a switch is also to set it up as an amplifier. If using a PNP transistor, negative voltage is supplied to the collector.
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| Subject: Using a transistor as a switch Wed 16 Mar 2011, 9:28 pm | |
Using a transistor as a switch There are three areas of operation of the transistor is an area of segments Cut OFF in which a Transistor is turned off completely Work and the complex stream = Cefromntqp operating active region And the transistor works Like a microphone, where the compound stream Is the enlarged image of the stream Alhadpomntqp saturation Saturation In which a transistor Working to full capacity any Fully ON and the current complex is the largest Can not be here (ie, stream Complex) based on stream Al Qaeda. Use Transistors as the key electrical When the transistor is used As the key electrical, it works either In the blocks or at the Saturation, in short, be either Ergonomics, such as matte or key. When the transistor Ergonomics (saturation region) is the effort VCE almost zero and here we say that Transistor is not saturated any Can pass more of the stream Compound. The device that control the Runs through this Transistor called pregnancy (LOAD) (See figure below). Very important observation here Is that the capacity to be dissipated by transistors are very small You know Why? Because the effort VCE is a very small (approximately Zero) and as we know that the ability Dissipated by the transistor = Stream complex IC × voltage VCE. Mark When Any transistor in the case of Saturation, the voltage VCE is Almost zero, and the stream More complex as possible. Example You are using the transistor 2N3904, in Aldcanivet Special This transistor, we found that Po = 625 mW that any capacity That this transistor can Dissipation (in the form of heat) Equal to 625 mW. Now If we assume that the voltage VCE = 0.4 V at saturation, this Transistor can pass Stream complex = 1.5 amp (Approximately the result of dividing power The voltage VCE, taking into account Units). But the question now is: Can this transistor Pass this much power Note that the Aldata Special Shit It says that the highest Ic can This transistor is a bear 200 mA? Answer Absolutely not. If the stream was passed 1.5 mA in this Sitvhm transistor. | |
How to Connect a Transistor as a Switch in a CircuitIn this article, we go over how to connect a transistor so that it will function as a switch in a circuit.A transistor is a component that can play 2 vital roles. It can function as a switch and an amplifier. Many times,it functions as both in a circuit.Specifically, in this article, we will show how transistors can be used as switches.Why Transistors Are Used as SwitchesBefore we go into how to wire it up, let's go over first why transistors are used in circuits as switches.Think about it for a moment.
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There are tons of different switches.There are pushbutton switches, rocker switches, slide switches, dip switches, key switches, toggle switches, knifeswitches, that play the same function as a transistor. It switches a load on or off that is connected to the output side of the switchThe below circuit uses a knife switch to turn the load, the lamp, on or off. So why are transistors used so frequently as switches in circuits if these switches above have the same use?And the reason is that transistors are electrical switches. Unlike all the switches above, which are mechanical switches, a transistor turns on oroff by electrical current.
Mechanical switches, such as knife switches, pushbutton switches, need human intervention- someone to press them down and pull them back up.Transistors, however, turn on and off, not by physical human intervention, but by electrical current.Both have their own uses. The output of the device that outputs a current will be connected to the base of the transistor.
The load will be connected to the collector as wellas the positive DC voltage for NPNs. The emitter will connect to ground.Below is an example of a transistor functioning as a switch in a circuit:There are a few different parts in this circuit. But the part which detects the motion is the PIR motion sensor.When motion is detected by this sensor, it converts this motion into an electrical current. Many electronic devices do this. They convert mechanicalinto electrical current.
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The PIR motion sensor does this. Once it detects motion, it outputs current to its outpin pin, which is pin 3. Since this output is current,it can be used to turn on the transistor.Since the PIR motion sensor outputs current and the transistor is a switch that turns on by electrical current, it's a perfect switch that workscomplementary with the transistor.
A mechanical switch is when a human needs to press down to operate it. A transistor is when an electrical current switches something on.So, again, transistors are used when we want electrical current to control the state of switches in a circuit.When the PIR sensor detects no motion, it outputs no current, so the transistor does not turn on.
When the transistor does notreceive sufficient current at its base, no current can flow from emitter to collector to power the load, which in this case is a motor.Even though the collectorof the transistor needs positive voltage (for an NPN transistor) in order to operate, it will not turn on just because voltage is attached to it. This is becausethe transistor acts as an open circuit when it does not receive sufficient base voltage. When a transistor acts an open circuit, no current can flowdown to ground. So the +9V of DC voltagethat is supplied to the DC motor has no electric potential. It is +9V positive across both terminals of the motor, so, again, there is no electric potential.
Only whenthe transistor turns on and current can flow down to ground is there an established electric potential. This is now when current can flow.
Current can only flow whenthere is an electrical gradient of voltage.When the motion detector detects motion, it outputs a current from its output pin to the base of the transistor. This electrical current switches thetransistor on, so the transistor can now power its load, which is the motor.In this circuit, the transistor acts as a switch and an amplifier. The same setup to set the transistor as a switch is also to set it up as an amplifier.If using a PNP transistor, negative voltage is supplied to the collector.Related Resources.