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Transistor emitter1/18/2024 ![]() ![]() The transistor turns on and current can flow down to ground is there an established electric potential. It is +9V positive across both terminals of the motor, so, again, there is no electric potential. That is supplied to the DC motor has no electric potential. When a transistor acts an open circuit, no current can flow The transistor acts as an open circuit when it does not receive sufficient base voltage. ![]() Of 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. Receive sufficient current at its base, no current can flow from emitter to collector to power the load, which in this case is a motor. When the PIR sensor detects no motion, it outputs no current, so the transistor does not turn on. So, again, transistors are used when we want electrical current to control the state of switches in a circuit. A transistor is when an electrical current switches something on. A mechanical switch is when a human needs to press down to operate it. 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 worksĬomplementary with the transistor. It can be used to turn on the transistor. Once it detects motion, it outputs current to its outpin pin, which is pin 3. When motion is detected by this sensor, it converts this motion into an electrical current. But the part which detects the motion is the PIR motion sensor. ![]() There are a few different parts in this circuit. ![]() The emitter will connect to ground.īelow is an example of a transistor functioning as a switch in a circuit: The load will be connected to the collector as wellĪs the positive DC voltage for NPNs. The output of the device that outputs a current will be connected to the base of the transistor. The setup to set the transistor up as a switch is shown in the diagram below: And the collector will connect to the load that the transistor will turn on and the supply voltage of the circuit. The emitter will connect to ground of the circuit. To connect the transistor as a switch in a circuit, we connect the output of the device that will switch on the transistor to the base of the transistor. Looking at the back side of the transistor, the emitter is the first pin, the base is the middle, and the collector is the third. So now that we know the theory of why transistors are used as switches, let's go over how to connect a transistor to function as a switch in a circuit.Ī transistor is a 3-pin device composed of a base, collector, and emitter for bipolar junction transistors (BJTs). How to Connect a Transistor as a Switch in a Circuit Transistors are used when we want to switch devices on or off when only current can the on-off state of the transistor.Īs a prime example of where transistors function perfectly as electrical switches, we will go through a few example circuits below. Such as an ON-OFF switch for turning on or off a device, volume control, etc. Mechanical switches are used mostly outside of electronic circuitry where it is desired that humans control various functions Transistors, however, turn on and off, not by physical human intervention, but by electrical current.īoth have their own uses. Mechanical switches, such as knife switches, pushbutton switches, need human intervention- someone to press them down and pull them back up. Unlike all the switches above, which are mechanical switches, a transistor turns on or So why are transistors used so frequently as switches in circuits if these switches above have the same use?Īnd the reason is that transistors are electrical switches. ![]()
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