Field Effect Transistor for Low Voltage, Wide Voltage, and Dual Voltage Applications in Circuits

Field Effect Transistor for Low Voltage, Wide Voltage, and Dual Voltage Applications in Circuits

Low voltage applications of field-effect transistors:

When using a 5V power supply, if the traditional totem pole structure is used, the voltage drop of the transistor is about 0.7V, resulting in the actual final voltage applied to the gate being only 4.3V. At this point, choosing a field-effect transistor with a nominal gate voltage of 4.5V carries certain risks.

The same problem also occurs when using 3V or other low-voltage power sources.

Wide voltage applications of field-effect transistors:

The input voltage is not a fixed value, it will vary over time or other factors. This change causes the driving voltage provided by the PWM circuit to the field-effect transistor to be unstable.

In order to ensure the safety of field-effect transistors at high gate voltages, many field-effect transistors are equipped with built-in voltage regulators to forcibly limit the amplitude of the gate voltage. In this case, when the provided driving voltage exceeds the voltage of the voltage regulator, it will cause significant static power consumption.

Meanwhile, if the gate voltage is simply reduced using the principle of resistive voltage division, the field-effect transistor will work well when the input voltage is relatively high, but when the input voltage decreases, the gate voltage will be insufficient, causing incomplete conduction and increasing power consumption.

Dual voltage application of field-effect transistor:

In some control circuits, the logic section uses typical 5V or 3.3V digital voltages, while the power section uses 12V or even higher voltages. Two voltages are connected in a common ground manner.

This raises a requirement to use a circuit that allows the low-voltage side to effectively control the high-voltage side field-effect transistor, while the high-voltage side field-effect transistor will also face the problems mentioned in 1 and 2.

In these three cases, the totem pole structure cannot meet the output requirements, and many existing field-effect transistor driver ICs do not seem to include gate voltage limiting structures.