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For example, this datasheet refers to a 'freewheeling' diode and a 'boost' diode. The upper diode is the freewheeling diode, right?

If you wanted to switch an inductive load with a single such module, the upper diode would act as the flyback (freewheeling?) diode in parallel with your inductance, and the anti-parallel diode would not be doing much.

I'm curious because I recently saw a failure analysis report of an IGBT module in which the the terms 'freewheeling' and 'flyback' we use -not- interchangeably. I've also seen the term 'body diode' used for the anti-parallel diode.

Are these terms contextual? Is there a preferred name for the lower diode?

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    \$\begingroup\$ I use the terms freewheeling diode and anti-parallel diode interchangeably. \$\endgroup\$
    – winny
    Commented Oct 12, 2018 at 20:09
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    \$\begingroup\$ "body diode" is a term that is most often used with FETs because it's an unavoidable part of the construction of a MOSFET between drain/source and the 'body' or 'bulk' silicon, rather than an additional diode added intentionally. I'm not familiar enough with the construction of IGBTs to say whether the same would hold for them. \$\endgroup\$
    – Hearth
    Commented Oct 12, 2018 at 20:37

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schematic

simulate this circuit – Schematic created using CircuitLab

In the h-bridge circuit above, if M1 and M4 are turned on current from V1 flows left to right through L1. If M1 is turned off, the current must flow through "freewheeling" diode D2. This is also called a flyback diode, because if this conduction path was not present the voltage on L1 would increase sharply. Mosfets like the one shown do have a body diode junction which will act in this capacity, but they do dissipate power and sometimes do not have the required response. You can buy mosfets with a separate integral diode (as in the one you selected), and in some cases you may use a separate external diode.

schematic

simulate this circuit

In the boost circuit above, the switch charges up the inductor, which then has a current path to the load through the boost diode when the mosfet is turned off. D1 in this circuit is the "boost diode".

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