How to choose a good MOS tube

How to choose a good MOS diode

The first step is to decide whether to adopt N-channel or P-channel MOS transistor. In the normal power use, when the MOS diode is grounded once and the load is connected to the branch voltage, the MOS diode constitutes the high-voltage side switch. N-channel MOS transistor should be adopted in the high-voltage side switch, which is out of consideration for the voltage required to open or conduct the parts. When the MOS diode is connected to the bus and the load is grounded, the low-voltage side switch is used. Generally, P-channel MOS transistors are being adopted in a certain topology, which is also due to the consideration of voltage drive.

Confirm the extra voltage required, or the maximum voltage acceptable to the parts. The greater the extra voltage, the higher the profit of the parts. According to theoretical experience, the extra voltage should be greater than the branch voltage or bus voltage. That ability needs the remaining cover, so that the MOS diode will not take effect. As far as the selection of MOS transistors is concerned, it is necessary to confirm the maximum acceptable voltage between the drain and the source, that is, the maximum VDS. It is very important to know that the maximum voltage that MOS diode can accept will change with measurement. We have to test the range of voltage changes in the whole task measurement range. The extra voltage must have a residual margin to cover a certain transition range to ensure that the channel will not take effect. The remaining insurance elements of demand consideration include voltage transients induced by electronic devices such as generators or transformers. The extra voltage that is not used together is also different; Generally, portable facilities are 20V, FPGA power supply is 20 ~ 30 V, and 85 ~ 220 VAC is 450 ~ 600 V.. The MOS diode conceived by KIA semi-superconductor has strong withstand voltage and wide application range, which is well received by vast depositors.

Two: affirm the extra DC of MOS diode.

The additional DC should be the maximum DC that the load can accept under all conditions. Similar to the voltage situation, make sure that the selected MOS transistor can accept some extra DC, even when the peak DC is happening sporadically. Two contemplated DC conditions are successive forms and pulse spikes. In the form of continuous conduction, the MOS diode is in a steady state, at which time the direct current passes through the parts one after another. Pulse spike refers to a small amount of surge (or spike current) flowing through the machine. Once the maximum DC in the environment of the department is confirmed, it is only necessary to indirectly choose the parts that can accept a certain maximum DC.

After selecting the extra DC, you must also plan to conduct consumption. In practice, MOS diode is not a real part, because there will be kinetic energy consumption in the process of heat conduction, which is called conduction consumption. When the MOS diode is "conducting", it is like a one-degree variable resistor, which is determined by the RDS(ON) of the part and changes significantly with the measurement. The power consumption of machine parts can be calculated by Iload2×RDS(ON), because the return resistance changes with the measurement, so the power consumption will also change correspondingly. The higher the voltage VGS applied to MOS transistor, the smaller RDS(ON) will be. On the contrary, RDS(ON) will be higher. Note that the RDS(ON) resistance will drop slightly with the direct current.

Third, the next step in choosing MOS diodes is piecemeal cooling request.

We must consider two different situations, namely, the worst situation and the real situation. It is proposed to adopt the intended consequences aimed at the worst situation, because a certain consequence requires a larger insurance margin, which can ensure that the piecemeal will not take effect. The junction temperature of the machine is equal to the maximum conditional metric plus the product of thermal resistance and power dissipation (junction temperature = maximum conditional metric+[thermal resistance × power dissipation]). According to a certain formula, we can solve the fragmentary maximum power dissipation, that is, it is the same as I2×RDS(ON) by definition. We have already passed the maximum direct current of the parts, and we can work out the RD(ON) without the same measurement. In addition, the heat dissipation of the via board and its MOS diode should be done well.

Landslide breakdown means that the reverse voltage on semi-superconducting parts exceeds the maximum value and forms a strong magnetic field to increase the direct current in the parts. The increase of chip size will improve the anti-wind and collapse power, and finally improve the stability of the parts. Therefore, choosing a larger package can effectively prevent landslides.

Four: The first step in choosing MOS diode is to decide the switch function of MOS diode.

There are many parameters for the function of the reaction switch, but the most important ones are electrode/drain, electrode/source and drain/source storage capacity. The storage capacity of the department will be consumed by switches in the parts, because they have to be inflated when the switches are switched. As a result, the switch progress of MOS diode is increased, and the frequency of parts is also decreased. In order to plan the total consumption of parts in the process of switching, it is necessary to plan the consumption in the process of opening warp (Eon) and the consumption in the process of opening warp (Eoff). The total power of MOSFET switch can be expressed by the following equation: Psw=(Eon+Eoff)× switch frequency. The electrode point charge (Qgd) has the greatest response to the switch function.