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Power FET Driver (MEC120E)

This article was adapted from the book Robotics, Mechatronics and Artificial Intelligence (sold out) that I published in the United States. On the site the reader will find several articles in this series with variations of this project and information about the original book.

The block shown in Figure 1 can drive loads up to several amperes from a voltage source that is typically between 2 and 12 V, depending on the power supply voltage.



Figure 1 – Power driver using a MOSFET
Figure 1 – Power driver using a MOSFET



When the input is positive, the power FET conducts, and the load is powered on. The most important characteristic of this block is the low Rds on. Rds is the resistance between the drain and source of a power FET. This resistance can fall to values as low as fraction of an ohm (0.01 ? is found in some devices). This means that practically no power is dissipated in the transistor, which can control high currents easily.

However, the reader must bear in mind that low Rds on is valid only when high control voltages are used. When operating with low-voltage sources, the power FET has the same characteristics of the bipolar transistor when conducing the current, and some power is converted into heat. Another important characteristic of this circuit is its very high input impedance.