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How does a BJT switch work with a driver?
With the driver, the logic circuit will only need to supply base current, not LED current. Here is how it works: If the logic input voltage is zero, there will be no base current. This means that there will be no collector current and therefore the LED will be off. At this point the BJT is in cutoff.
How are transistors used in LED driver circuits?
LEDs is the linear topology, in which the transistor operates in the linear region. You then have the choice of implementing your driver circuits using discrete transistors or transistors integrated in a semiconductor integrated circuit (IC) with other LED- related functionality.
How does an emitter-follower led driver work?
Using the emitter-follower LED driver keeps the PIC supply current to the minimum required and keeps the LED brightness constant even as the supply voltage varies. If your only goal is to get light out of the LED, then the circuit on the left is perfectly fine.
How is a flyback voltage generated in a BJT?
The result is that the winding now generates a large flyback voltage (also called an “inductive kick”) directly across the BJT. That is, the winding momentarily appears as a high voltage source of opposite polarity and, via KVL, this potential appears from collector to emitter.
What kind of circuit consists of a BJT transistor?
Before investigating more complex circuits, we will begin by introducing discrete solid-state switching circuits: those built around BJTs. A switch consists of a BJT transistor that is alternately driven between the saturation and cutoff regions. A simple version of the switch is shown in figure 1.
What is the minimum base current for a BJT?
I C (sat) is the current that the load R C requires. V CE (sat) is specified in the datasheet of the BJT that you are going to use. After calculating I C (sat), the next thing to figure out is the minimum base current, I B (min), needed to make sure to produce I C (sat).