# Question: How Do You Select A Resistor For A Transistor?

## What is transistor diagram?

Diagram ‘A’ shows an NPN transistor which is often used as a type of switch.

A small current or voltage at the base allows a larger voltage to flow through the other two leads (from the collector to the emitter).

The circuit shown in diagram B is based on an NPN transistor..

## Which transistor is best for switching?

Best Transistors: BJTs#1 NPN – 2N3904. You can find most often NPN Transistors in low-side switch circuits. … #2 PNP – 2N3906. For high-side switch circuits, you need a PNP style BJT. … #3 Power – TIP120. … #4 N-Channel (Logic Level) – FQP30N06L.Apr 21, 2014

## What happens if you don’t use a resistor with an LED?

When hooking up an LED, you are always supposed to use a current-limiting resistor to protect the LED from the full voltage. If you hook the LED up directly to the 5 volts without a resistor, the LED will be over-driven, it will be very bright for a while, and then it will burn out.

## Do you need a resistor for every LED?

An LED (Light Emitting Diode) emits light when an electric current passes through it. The simplest circuit to power an LED is a voltage source with a resistor and an LED in series. Such a resistor is often called a ballast resistor. … If the voltage source is equal to the voltage drop of the LED, no resistor is required.

## Which is faster BJT or FET?

Therefore BJTs are more suitable than MOSFETs for driving low-power LEDs and similar devices from Micro Controllers Unit (e.g. Arduino). BJT can switch faster than MOSFET due to the less capacitance at the control pin. However MOSFET is more tolerant to heat (stable to thermal changes) and can simulate a good resistor.

## How do I know what size resistor I need?

To calculate the resistor you need, just add the voltage: we need 4V (2V + 2V), and we have 5V. So we need to drop 1V. For the current, just use the 20mA. In a series circuit, the amperage is the same for the entire circuit.

## How do you choose a resistor?

Resistor selection requires three steps:Determine the resistance and the watts to be dissipated by the resistor.Determine the proper “Watt Size” (physical size) as controlled by watts, volts, permissible temperatures, mounting conditions and circuit conditions.More items…

## What happens if I use the wrong resistor?

If you are using such a resistor in a current-sensing application in a switch-mode circuit, you will get spurious readings or inaccurate behaviour. … For a simple LED circuit there are no bad consequences of using a resistor of higher power.

## Which is the fastest switching device?

MOSFETWhich of the following is the fastest switching device? Explanation: MOSFET is the fastest switching device among the given four options.

## Is 2N7000 NPN or PNP?

2N7000 is a N-channel mosfet. NPN or PNP indicated BJT type transistor. unlike BJTs mosfets are symmetrical devices and S and D is actually defined by connection of the bulk. in case of 3-pin packaged mosfets, you no longer have control of how the bulk is connected so make sure to verify pinout using correct datasheet.

## How do you choose a base resistor for a transistor?

To calculate the base resistor, subtract the B-E 0.7V from the driver voltage and divide by the base current: 4.5-0.7 = 3.8V / 400uA = ~9.5K ohms max. The difference in CE drop between a factor of ten and using the beta is neglible for relatively slow on/off circuits, and it lowers the driver current requirement.

## How do you find the resistance of a transistor?

Yes the simplest method to figure out the equivalent resistance is to measure the collector voltage Vc and the emitter voltage Ve and subtract: V=Vc-Ve, and then measure the current through the collector Ic. The approximate resistance (neglecting the base current) is: R=V/Ic.