# Why do we need reverse bias?

## Why do we need reverse bias?

A reverse bias reinforces the potential barrier and impedes the flow of charge carriers. In contrast, a forward bias weakens the potential barrier, thus allowing current to flow more easily across the junction. Forward bias decreases a diode’s resistance, and reverse bias increases a diode’s resistance.

### When a reverse bias is applied to the gate of JFET?

By applying a reverse bias voltage to a gate terminal, the channel is “pinched”, so that the electric current is impeded or switched off completely. A JFET is usually “on” when there is no voltage between its gate and source terminals.

Is a gate signal required when reverse biased?

The thyristor is reverse biased by this voltage and cannot conduct even if a Gate signal is present. So by applying a Gate signal at the appropriate time during the positive half of an AC waveform, the thyristor can be triggered into conduction until the end of the positive half cycle.

What will happen when the gate and source junction is forward biased?

(vgs >0) and finally, if the gate-source junction is forward biased with a small voltage, the channel will open a little further to allow larger currents through it, causing damage to the transistor.

## What happens in reverse bias?

In reverse bias a voltage is applied across the device such that the electric field at the junction increases. The higher electric field in the depletion region decreases the probability that carriers can diffuse from one side of the junction to the other, hence the diffusion current decreases.

### What is pinch off voltage of JFET?

Pinch off voltage: Pinch off voltage is the drain to source voltage after which the drain to source current becomes almost constant and JFET enters into saturation region and is defined only when gate to source voltage is zero.

Which is the drain current in JFET?

For the case vGG=vGS=0, the drain current at pinch-off is called the drain-source saturation current, IDSS. Operation beyond the pinch-off point (vDS > vGS – VP for an n-channel device) defines the normal operating or saturation region of the JFET.

Which device does not have a gate terminal?

DIACs have no gate or trigger electrode, unlike some other thyristors that they are commonly used to trigger, such as TRIACs. Some TRIACs, like Quadrac, contain a built-in DIAC in series with the TRIAC’s gate terminal for this purpose.

## When an SCR is reverse biased?

When a negative voltage is applied to the anode and a positive voltage to the cathode, the SCR is in reverse blocking mode, making J1 and J3 reverse biased and J2 forward biased. The device behaves as two diodes connected in series. A small leakage current flows. This is the reverse blocking mode.

### Why gate current is zero in FET?

We all are aware that the gate current in the IGFET(insulated gate field effect transistor) is always zero owing to the oxide coating present between the gate and the substrate region.

Are source and drain interchangeable?

Theoretically, the drain and source can be swapped, and when you do this, the source becomes the drain and the drain becomes the source. For an N-MOSFET, the source is the lower potential, and the drain is the higher potential.