With today's MOS drivers, there are several extraordinary requirements:
1. Low voltage application
When the application of 5V switching power supply, at this time if the use of traditional totem pole structure, because the triode be only 0.7V up and down loss, resulting in a specific final load gate on the voltage is only 4.3V, at this time, the use of allowable gate voltage of 4.5V MOSFETs there is a certain degree of risk. The same situation also occurs in the application of 3V or other low-voltage switching power supply.
2.Wide voltage application
The keying voltage does not have a numerical value, it varies from time to time or due to other factors. This variation causes the drive voltage given to the MOSFET by the PWM circuit to be unstable.
In order to better secure the MOSFET at high gate voltages, many MOSFETs have embedded voltage regulators to force a limit on the magnitude of the gate voltage. In this case, when the drive voltage is brought to exceed the voltage of the regulator, a large static function loss is caused.
At the same time, if the basic principle of resistor voltage divider is used to reduce the gate voltage, it will happen that if the keyed voltage is higher, the MOSFET works well, and if the keyed voltage is reduced, the gate voltage is not enough, resulting in insufficient turn-on and turn-off, which will enhance the functional loss.
3. Dual voltage applications
In some control circuits, the logic portion of the circuit applies the typical 5V or 3.3V data voltage, while the output power portion applies 12V or more, and the two voltages are connected to common ground.
This makes it clear that a power supply circuit must be utilized so that the low voltage side can reasonably manipulate the high voltage MOSFET, while the high voltage MOSFET will be able to cope with the same difficulties mentioned in 1 and 2.
In these three cases, the totem pole construction cannot meet the output requirements, and many existing MOS driver ICs do not seem to include a gate voltage limiting construction.
Post time: Jul-24-2024
