At 18.41 2011.12.26, you wrote:
>> The most important is the latching current. Is it the current=20
>necessary to trigger the
>> device (via anode/cathode, not gate) in case the breakdown voltage=20
>is reached?
>> This sounds logical to me, but when I read that Vd=3D12V then we're=20
>really far away from
>> breakdown.. so I think the above theory cannot be true anymore. :-/
>>
>> This latching current parameter that I'm not sure I understand seems=20
>related to another
>> parameter, the holding current, which I imagine being the current=20
>that must flow between
>> the anode and cathode to keep the previously triggered device=20
>latched, when the gate stops
>> being triggered. Or, in other words, the holding current is the=20
>limit BELOW which the
>> anode/cathode must go for us to "free", unlatch the device.
>>
>
>I understand the latching current to be the value current must reach
>(cathode to anode wise) when applying gate drive to latch the device
>in conduction without further gate drive. Once the current has gone to
>or over the latching current and the gate drive stopped, it may fall
>to the holding current and the device will stay in conduction. If
>current falls below the holding current, it may or may not stop
>conduction. The holding current holds the latch, but only after
>latching. The gate trigger voltage/current is a different parameter
>from latching/holding current.

Very logical, thanks!


>SCRs will self conduct if their breakdown voltage is exceeded, or the
>dV/dt rate of anode-cathode voltage is exceeded. The dI/dt limit is
>usually spec'd at close to maximum gate drive. The dI/dt limit is
>imposed because small areas of the SCR conduct before the whole device
>turns on, and with large currents it will damage the device. A hard
>gate drive allows more area to come into conduction faster.
>
>I don't know about gate sensitivity vs anode-cathode voltage, but SCRs
>vary in sensitivity not only between devices of the same type but by
>temperature. Cold SCRs need a lot more gate current (and
>latching/holding current) than warm ones. Also, cold SCRs are able to
>withstand higher dV/dt in the off state before conducting.

I knew about temperature, but Your whole post says pretty much everything
one needs to know about SCR's in the real world.

Can the post be made sticky? ;D

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.