How do you choose a base resistor for a transistor?

How do you choose a base resistor for a transistor?

Choosing a transistor and base resistor for a digital IC output

1. Choose the right type of transistor, NPN or PNP.
2. Find out the supply voltage(s) and load properties.
3. Work out the transistor properties required.
4. Work out a value for the base resistor R.
5. Check if you need a protection diode.

How do I calculate resistor needed?

Resistor = (Battery Voltage – LED voltage) / desired LED current. So assuming a 12-volt power source and a white LED with the desired current of 10 mA; The formula becomes Resistor = (12-3.4)/. 010 which is 860 ohms.

How is VBE calculated in transistor?

This can be done using the formula: Vcc = Vrc + Vrb + Vbe + (Ic + Ib)Rc + IbRb + Vbe, where “Vrc” is the voltage across the collector resistor; “Vrb” is the voltage across the base resistor (connected across the base) and the junction between the collector resistor and the transistor collector; and “Vbe” is the voltage …

What is the formula of transistor?

The Common Emitter Amplifier Circuit A transistors current gain is given the Greek symbol of Beta, ( β ). As the emitter current for a common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek symbol of α.

Why is VBE 0.7 V?

The base emitter junction is a PN junction or you can consider that as a diode. And the voltage drop across a silicon diode when forward biased is ~0.7V. That is why most of the books write VBE=0.7V, for an NPN silicon transistor with forward biased emitter junction at room temperature.

How do you calculate ve?

Minute ventilation (VE) is the total volume of gas entering (or leaving) the lung per minute. It is equal to the tidal volume (TV) multiplied by the respiratory rate (f). Minute ventilation = VE = TV x f At rest, a normal person moves ~450 ml/breath x 10 breath/min = 4500 ml/min.

What is BJT formula?

The current gain Ai of common collector BJT is given by the ratio of output current IE to input Current IB: IE = IC + I.

Can you use transistor as resistor?

Using a transistor in place of a resistor or a capacitor is sometimes done in integrated circuit design, because some processes don’t offer suitable resistors or capacitors or they simply would take up too much area.

How can I determine resistor voltage?

Part 3 of 3: Calculating Voltage across a Resistor (Parallel Circuit) Understand parallel circuits. Imagine a wire leaving one end of a battery, then splitting into two separate wires. Think about how the current flows. In a parallel circuit, the current flows across each path available to it. Use the total voltage to find the voltage across each resistor. Calculate the total current of the circuit.

What is the equation for a resistor?

Ohm’s law formula. The resistor’s current I in amps (A) is equal to the resistor’s voltage V in volts (V) divided by the resistance R in ohms (Ω): V is the voltage drop of the resistor, measured in Volts (V). In some cases Ohm’s law uses the letter E to represent voltage.

How do you calculate circuit resistance?

How to Calculate Total Resistance in Circuits Method 1 of 4: Series Circuit. Identify a series circuit. A series circuit is a single loop, with no branching paths. Method 2 of 4: Parallel Circuit. Understand parallel circuits. Method 3 of 4: Combination Circuit. Break down your circuit into series sections and parallel sections. Method 4 of 4: Formulas Using Power. Learn the formula for power.

What is a base resistor?

“base” resistor, so called because it limits the amount of current that flows through the base of the transistor. Aside: The “larger” current through the LEDs isn’t actually all that much larger.

How is resistance calculated in a transistor circuit?

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.

How is BJT power calculated?

To calculate the power dissipation we have to find the equivalent resistance of the circuit and then according to formula power is given as.. Power (P) = (supply voltage (V))²/ equivalent resistance (R).. Or, Total Power dissipation (P) = ( Circuit current (I))² * Equivalent resistance (R)…

Does a BJT need a base resistor?

Some bipolar transistor circuits (such as common bases and common collector, and those that drive the transistor with a high impedance, such as the collector of another transistor) do not need a series base resistor to limit base current, but would use a base resistor to reduce the Q of the base circuit so that it won’ …

Is highest current in any BJT?

In a BJT , the largest current flow occurs in the emitter.

What are the specifications of BJT?

Specifications of bipolar junction transistor (BJT)

• The bipolar junction transistor (BJT) has small signal current gain, α (hfb).
• Maximum collector current Ic (max).
• Maximum collector to emitter voltage, VCE (max).
• Collector to emitter breakdown voltage, BVCBO.
• Collector cut off current, ICEO.

How to calculate the 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 to calculate bias voltage in a BJT transistor?

Ve= Emitter Voltage . Vb= Base Voltage. Ic= Collector gain x Ib. Ve= ICx Re. Vb= Vex Base to Emitter Drop . Vc= Vs- ICx Rc. If (Vc< Ve) then, . Vc= Ve. Vb= Ve+ Base to Emitter Drop .

What does a base resistor do in a bipolar junction transistor?

Consider a base resistor that controls the amount of current entering the base junction of a bipolar junction transistor (BJT) to cause it to conduct in the saturation region.

What kind of resistor do I need for a switching calculator?

For switching applications, a ¼-watt resistor with 5-% tolerance usually works fine. In order to use this calculator, you will need to know the input switching voltage (Vi), supply voltage Vcc, and the load current iL. Use the Standard Resistor Values chart to find the nearest standard resistor value.