✔ Why Diode Is Connected Across Mosfet

Why Diode Is Connected Across Mosfet

- September 05, 2019

The backward connected diode has the function to clamp the reverse voltage of the transistor to the on voltage value of the diode. So in normal operation both the source and the drain are in fact diode junctions to the substrate.

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Current source using mosfet in diode configuration current source easily synthesized from current source using current mirror circuit.

Why diode is connected across mosfet. In a n channel mosfet you have a p doped silicon substrate and the source and drain are n doped regions within the substrate. Dont rely on any internal body diode in the mosfet for this. A schottky diode connected in parallel to the body diode will conduct with a lower forward voltage preventing the body pn junction from becoming forward biased.

Sometimes an external diode is connected across the mosfet low power rated in parallel as a body diode for high speed switching applications because the internal diode cannot work properly in high speed switching or h bridge applications. Be sure to use short wide traces to connect the schottky and the mosfet. Just remember the polarity of the relay coil and its diode.

The schottky diode is a majority carrier device and exhibits no recombination. The body of the mosfet is frequently connected to the source terminal so making it a three terminal device like field effect transistor. Also it makes the composite device reverse conducting.

Multiple current sources and sinks with different magnitudes can be synthesized from a single current source. The mosfet is a four terminal device with sources gate g drain d and body b terminals. Voltage source easily synthesized from reference.

The mosfet is very far the most common transistor and can be used in both analog and digital circuits. Yes you need a diode across the relay coil if there is none. Check the schematics twice is it top view or solder view.

If there already is an internal diode in the relay youre ok.