How do I make a transistor turn on at a certain voltage?
So, increasing the base resistor (R2) will make the transistor turn on at higher voltage than 1.5V). If you want the LED to turn on when the voltage is below 1.5V *that is, invert what it is now) then you can do it like this: Now when the transistor turns on, it shorts out the LED so the LED goes dark.
Why do we use a comparator in an IC?
This IC is a low-component-count way to compare two signal voltages or a signal and a reference, and switch the output either on or off. Comparators do a very specific job that presents some advantages to the maker which may not be immediately obvious.
How does a base emitter affect a transistor?
So by driving the CTRL input with a voltage that will create a base current, which will cause a current through LED D3. As D3’s current increases D4’s current will decrease, because the sum of the currents is constant. Remember that the base-emitter junction has a 0.7 V voltage drop.
How is a voltage comparator used in a sensor?
The other is used to measure the target signal, such as the voltage on a sensor. The output will go high or low, depending on set-up, as the sensor voltage goes above or below the reference. Voltage comparators like the LM311 do this with high accuracy, fast response, and minimum external component count.
What happens when you use a transistor as a switch?
Transistors that are fully “ON” are said to be in their Saturation region. Transistors that are fully “OFF” are said to be in their Cut-off region. When using the transistor as a switch, a small Base current controls a much larger Collector load current.
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.