Correct selection of low-pressure MOS diodes

Correct selection of low-pressure MOS diodes

The selection of MOS diodes is a very important link, and poor MOS diode selection may affect the efficiency and cost of the entire circuit, and will also bring a lot of trouble to engineers.

Step 1: Choose N-channel or P-channel

The first step in selecting the right device for your design is to decide whether to use an N-channel or P-channel MOSTRANSISTOR.

In a typical power application, when a MOS diode is grounded and the load is connected to the mains voltage, the MOS diodes constitutes a low-side switch. In low-side switches, N-channel MOS transistors should be used to turn off or turn on the voltage required to turn the device on. When the MOS diode is connected to the bus and the load is grounded, a high-side switch is used. P-channel MOS transistors are often used in this topology, also for voltage drive considerations.

Step 2: Determine the rated current

Depending on the circuit structure, this rated current should be the maximum current that the load can withstand under all conditions. Similar to the case of voltage, the MOS transistor selected needs to be able to withstand this rated current, even when the system generates a current spike. The two current cases considered are continuous mode and pulse spikes. In continuous conduction mode, the MOS transistor is in a steady state, where current flows continuously through the device, and once these conditions are determined, simply select the device that can withstand this maximum current.

Step 3: Determine the thermal requirements

Selecting a MOS diode also requires calculating the thermal requirements of both systems, worst-case and real-case scenarios. The worst-case scenario provides a greater margin of safety and ensures that the system does not fail.

Step 4: Determine the switching performance

The final step in selecting a MOS diodes is to determine the switching performance of the MOS diode. There are many parameters that affect switching performance, but the most important are gate/drain, gate/source, and drain/source capacitance. These capacitors create switching losses in the device because they are charged each time they are switched. As a result, the switching speed of the MOS transistor is reduced and the efficiency of the device is reduced.