MOS tube drive circuit review series (Part 2)

The current MOS driver has several special applications

1. Low voltage application
When using a 5V power supply, if the traditional totem pole structure is used, the voltage added to the gate is only 4.3V due to the 0.7V voltage drop of the transistor be. At this time, there is a certain risk if we choose a MOS tube with a nominal gate voltage of 4.5V.
The same problem also occurs when using a 3V or other low voltage power supply.

2. Wide voltage application
The input voltage is not a fixed value, it will change with time or other factors. This change causes the driving voltage provided by the PWM circuit to the MOS tube to be unstable.
In order to make the MOS tube safe under high gate voltage, many MOS tubes have built-in voltage regulators to forcibly limit the amplitude of the gate voltage. In this case, when the driving voltage provided exceeds the voltage of the voltage regulator, it will cause a large static power consumption. At
the same time, if the gate voltage is simply reduced by the principle of resistor voltage division, the MOS tube will work well when the input voltage is relatively high, and the gate voltage will be insufficient when the input voltage is reduced, causing incomplete conduction, thereby increasing power consumption.

3. Dual voltage application
In some control circuits, the logic part uses a typical 5V or 3.3V digital voltage, while the power part uses a 12V or even higher voltage. The two voltages are connected in a common ground.
This requires the use of a circuit that allows the low-voltage side to effectively control the MOS tube on the high-voltage side. At the same time, the MOS tube on the high-voltage side 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 off-the-shelf MOS driver ICs do not seem to include a gate voltage limitation structure.