Re: H-bridge diodes

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Alex,

Im assuming you are referring to the parallel diodes on the switching
devices.  Under ideal ZCS (zero current switching) conditions the
diodes dont see any current when driving the coil (note that they will
see current when all switches shut off and energy returns back to the
DC supply).  But, you probably wont get exactly ZCS.  So at worst you
could expect the diodes to be in conduction for say 50% of the time
(this is at worst!), and diodes have similar losses as an IGBT for
example.  If the IGBTs need heatsinking, the diodes do too.

If you are using schottky diodes to block the reverse current from
getting through the fet, then they will see the same current that the
fet does.  Schottky diodes have very low voltage drop, but may still
need heatsinking if you are running a lot of power (say 500W or more).
 I never use these extra diodes...

Really, i cant even answer your question directly since you gave no
indication of the power levels or devices being used.  But in general,
they will need heatsinking (unless its a very low power and high
efficient setup).

Steve

On 2/1/06, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "Alexander Turkin" <alex_3@xxxxxxx>
>
> Hi all
>
> Simple question: do the diodes (ultrafast, shottky) in the H-bridge
> get hot while operating?
> Do they need to be mounted on a heatsink?
>
> Thanks
>
>
>