Dorian,
We are talking about the peak voltage being 24V, so the peak-to-peak when
using a GDT would be 48V. The gates are typically rated for at least 20V,
but some manufacturers spec up to 30V. The actual breakdown voltage is
quite a bit higher (at least 40V), but its essential to protect the gates
with a bidirectional TVS diode (1.5KE27CA for example).
If you run the gate voltage too low, the conduction isnt as strong so the
IGBT will run hotter. Collector current capability is a function of gate
voltage, so if you try to run too much current for a given gate voltage,
the junction "de-saturates" and goes into a linear mode where the voltage
drop and current are both very high. The resulting power dissipation is
enough to overheat and blow the junctions within micro-seconds. Driving
the gates beyond the typical 15V range gives some headroom in terms of
current conduction capacity. I once pulsed a "300A" IGBT brick to 5200A
using 36V gate voltage... a little bit higher current caused it to fail.
Steve
On Fri, Jul 25, 2014 at 2:12 AM, Dorian Black via Tesla <tesla@xxxxxxxxxx>
wrote:
> Hi,
>
> Apologies if this sounds too rudimentary a question, but when igbt brick
> gates (in drsstc) are said to be driven with 24V, are we talking about 24V
> peak to peak (12V for charging and -12 for discharging), or 48V peak to
> peak (24V charging, -24 discharging)? The fact that brick IGBT datasheets
> dont seem to mention 30V pulsed as a maximum absolute rating is making me
> hesitant to apply +-24V across the gate. Or am I being a gate-oxide sissy?
>
> Many thanks.
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