How to Identify the Direction of Field Effect Transistors

How to Identify the Direction of Field Effect Transistors

Field effect Transistors are important devices in electronic products that protect circuits from ESD static electricity. Since their inception, they have quickly swept the electronic component market and are loved and sought after everywhere they go. For example, field-effect Transistors protect product circuits in our common mobile phones, tablets, and other devices.

The application range is very wide. However, there is a problem that has puzzled many new procurement and electronic engineers. That is, how to accurately identify the direction of the field effect transistor. Only by solving this problem, we can be more skillful in using the field effect transistor. If we want to know, we can enter the exploration of the field effect transistor direction identification together.

1. Field effect transistor switching circuit:

Those who have studied analog circuits know that a transistor is a flow control device, which controls the current between the collector and emitter by the base current; Field effectTransistors are voltage controlled current devices, which control the current between the drain and source electrodes by the voltage applied to the gate. A field-effect transistor is a type of protective voltage that can be manufactured into four types: enhanced or depleted, P-channel or N-channel. However, only enhanced N-channel field-effect Transistors and enhanced P-channel field-effect transistors are used in practice. In practical use, N field-effect Transistors are the majority.

How to determine the direction of the N-channel field-effect transistor and the P-channel field-effect transistor on the right? Its judgment rule is about the N channel, from the S pole to the D pole; Regarding the P-channel, it points from the D-pole to the S-pole.

How to distinguish the three poles? The D-pole is located on one side alone, while the G-pole is the 4th PIN. The remaining three feet are S-poles. It is useful to remember that their positions are relatively fixed. Please note that regardless of whether N field-effect transistor or P field-effect transistor, the method for determining the PIN pin mentioned above is the same.

The conduction characteristic of a field-effect transistor means to act as a switch, equivalent to a closed switch. The characteristics of N field-effect transistor: When Vgs is greater than a certain value, the transistor will conduct, suitable for use in the case of source grounding (low end drive), as long as the gate voltage reaches 4V. The characteristics of P-field-effect transistor: When Vgs is less than a certain value, the  will conduct, suitable for use in the case of source connected VCC (high-end drive).

2. Barrier effect of field-effect Transistors:

The effect of voltage blocking achieved by field-effect Transistors is another very important and common function. The importance of blocking lies in the concern that the current from the previous pole may leak into the subsequent circuit, causing misjudgment of the power-on timing of the circuit system, the operation of the processor or logic equipment, and ultimately leading to the system being unable to function properly. Therefore, in practical circuit systems, the effect of blocking is very important.

 By controlling the on/off of the field-effect transistor through the high and low levels of the source, the signal level barrier is achieved, because the field-effect transistor has a body diode and is reverse, so no signal will leak through the field-effect transistor. This is a very classic circuit, and many useful circuits can be derived through pairing.