How do I find my VBE value?
Calculate the emitter current, which is the current flowing from the emitter to ground. Use the formula Ie = (Vbb – Vbe)/[Rb/(Beta + 1) + Re] where Ie is the variable for the emitter current and Vbe is the base to emitter voltage. Set Vbe to 0.7 volts, which is the standard for most transistor circuits.
What is the value of the Teh voltage VBE?
Generally the VBE will be around 0.65 V for most transistors while operated at ‘normal’ collector currents.
What is VBE in circuit?
Vbe in a silicon transistor, acts like a silicon diode would. The Forward Voltage Drop, after a certain amount of current is passed, rises sharply. Increasing the current makes a negligible Vf difference at that point. Note that the Vf is different for Germanium Diodes, and Transistors, naturally.
What does VBE = VBE ( on ) mean in a BJT?
For a BJT as you say if VBE < VBE (ON) the transistor is in cut-off, when you get to VBE = VBE (ON) the base and the emiter of the transistor behave like a diode, with the voltage drop of a diode (0.6-0.7V) it means you “can’t” have more than VBE = VBE (ON), you only can have the voltage drop across the diode.
How to calculate the real value of VBE?
The “real” VBE value – for a given collector current Ic – can be calculated only – based on Shockleys equation Ic=Is* [exp (Vbe/Vt)-1] – if you know the value of the saturation current Is. However, this current has very large tolerances and a rather large dependency on temperature. Hence, this value is normally unknown.
What happens when VBE is higher than VBE?
Likewise, having VBE slightly lower/higher than VBE (ON) will only allow less/more current to flow through the collector. The voltage across base is a logarithmic function of the current. About 0.058 volts increase, per 10:1 current increase.
How to calculate the current of a BJT?
Take a few measurements of your BJT, where you set V C E = V B E (without actually shorting the collector to the base!) Then just take out some graph paper and plot the logarithm of the collector current at these several measurement points, against the voltage V B E = V C E. Draw a line with a ruler back to the y-axis.