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What do you do when designing a transistor switch?
To use a transistor as a switch, all you have to do is increase the current at the base terminal to a certain level, and the transistor will go into a state commonly known as “saturation.” This is a state (mode of operation) where no matter how much additional current is pumped into the base terminal of the transistor.
When a transistor is used as a switch?
One of the most common uses for transistors in an electronic circuit is as simple switches. In short, a transistor conducts current across the collector-emitter path only when a voltage is applied to the base. When no base voltage is present, the switch is off. When base voltage is present, the switch is on.
What is switching speed of transistor?
1 Transistor scaling issues. It is worth reviewing the parameters that control transistor performance (Sze, 2000). The switching speed is given by τsw = CGVDD/ION, where CG is the controlling gate capacitance, VDD is the power supply voltage, and ION is the on current.
How can you tell how fast a transistor can switch?
Using the datasheet (these parameters are usually listed), you can figure out how fast a transistor can switch between the two states. * This is what transistor can theoretically do, but there are tricks that can be done to improve the switching speed.
What’s the difference between a transistor and a NPN switch?
The equations for calculating the Base resistance, Collector current and voltages are exactly the same as for the previous NPN transistor switch. The difference this time is that we are switching power with a PNP transistor (sourcing current) instead of switching ground with an NPN transistor (sinking current).
How are saturated transistors used in switching applications?
In switching application design, in order to have a saturated transistor it is often required to find an appropriate value of the base current. By looking at the questions answered on the subject, people tend to use a ratio Ic/Ib much smaller than the parameter hFE,min found on the specific transistor datasheet.
Why are multiple transistors used in a bipolar transistor?
Sometimes the DC current gain of the bipolar transistor is too low to directly switch the load current or voltage, so multiple switching transistors are used. Here, one small input transistor is used to switch “ON” or “OFF” a much larger current handling output transistor.