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Sci.Electronics.Basics -> Explanation of Parallel Resistor and Diode
There are 3 messages in this thread.
You are currently looking at messages 1 to 3.
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I had difficulty choosing keywords to narrow the search enough to give
me any solid hits for this, and I hope this question isn't too
advanced for the basics group.
I'm looking at a full-bridge IGBT switching amplifier circuit (eg.,
from Eastern Voltage Research's DRSSTC-2 schematic, drawing number
SC2045, page 1), and I'm trying to understand the use for putting a
diode (Schottky) and a resistor in parallel (eg., CR1 and R1 in the
cited document). I've seen this sub-circuit in other places, but I
haven't found an explanation for it.
I tried breaking down the problem, but it didn't get me very far. When
the [conventional] current flows toward the gate, the current flows
through both the resistor and the diode. When the current flows away
from the gate, the current only flows through the resistor. The
resistor limits the current, with an associated voltage drop, and the
diode has a small voltage drop (and I would assume an associated
current drop, though I haven't found it mentioned in any reference)
when current flows through it. Unless I have missed something, this
sub-circuit does nothing more than drop the voltage (and probably the
current) more in one direction than the other.
Is that all there is to it, or did I miss something? If that is all
there is to it, then what use is it, when the voltage drop across the
Schottky is almost neglible? I can see the possibility of protecting
the IGBT gate from over- or under-voltage or -current... of .14V to .
46 volts (according to wikipedia)? If you need more voltage or current
protection in one direction than the other, it might make sense from
an efficiency standpoint. But why do I feel that I'm missing
something?.
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Author: John LarkinDate: 19:00 07-08-08
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On Thu, 7 Aug 2008 15:45:54 -0700 (PDT), jackpanella@yahoo.com wrote:
>I had difficulty choosing keywords to narrow the search enough to give
>me any solid hits for this, and I hope this question isn't too
>advanced for the basics group.
>
>I'm looking at a full-bridge IGBT switching amplifier circuit (eg.,
>from Eastern Voltage Research's DRSSTC-2 schematic, drawing number
>SC2045, page 1), and I'm trying to understand the use for putting a
>diode (Schottky) and a resistor in parallel (eg., CR1 and R1 in the
>cited document). I've seen this sub-circuit in other places, but I
>haven't found an explanation for it.
>
>I tried breaking down the problem, but it didn't get me very far. When
>the [conventional] current flows toward the gate, the current flows
>through both the resistor and the diode. When the current flows away
>from the gate, the current only flows through the resistor. The
>resistor limits the current, with an associated voltage drop, and the
>diode has a small voltage drop (and I would assume an associated
>current drop, though I haven't found it mentioned in any reference)
>when current flows through it. Unless I have missed something, this
>sub-circuit does nothing more than drop the voltage (and probably the
>current) more in one direction than the other.
>
>Is that all there is to it, or did I miss something? If that is all
>there is to it, then what use is it, when the voltage drop across the
>Schottky is almost neglible? I can see the possibility of protecting
>the IGBT gate from over- or under-voltage or -current... of .14V to .
>46 volts (according to wikipedia)? If you need more voltage or current
>protection in one direction than the other, it might make sense from
>an efficiency standpoint. But why do I feel that I'm missing
>something?.
Probably fast turn-off, slow turn-on. Or vice versa, depending on the
diode direction. Anti-shoot-through maybe.
John
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On Aug 7, 4:00=A0pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Thu, 7 Aug 2008 15:45:54 -0700 (PDT), jackpane...@yahoo.com wrote:
> >I had difficulty choosing keywords to narrow the search enough to give
> >me any solid hits for this, and I hope this question isn't too
> >advanced for the basics group.
>
> >I'm looking at a full-bridge IGBT switching amplifier circuit (eg.,
> >from Eastern Voltage Research's DRSSTC-2 schematic, drawing number
> >SC2045, page 1), and I'm trying to understand the use for putting a
> >diode (Schottky) and a resistor in parallel (eg., CR1 and R1 in the
> >cited document). I've seen this sub-circuit in other places, but I
> >haven't found an explanation for it.
>
> >I tried breaking down the problem, but it didn't get me very far. When
> >the [conventional] current flows toward the gate, the current flows
> >through both the resistor and the diode. When the current flows away
> >from the gate, the current only flows through the resistor. The
> >resistor limits the current, with an associated voltage drop, and the
> >diode has a small voltage drop (and I would assume an associated
> >current drop, though I haven't found it mentioned in any reference)
> >when current flows through it. Unless I have missed something, this
> >sub-circuit does nothing more than drop the voltage (and probably the
> >current) more in one direction than the other.
>
> >Is that all there is to it, or did I miss something? If that is all
> >there is to it, then what use is it, when the voltage drop across the
> >Schottky is almost neglible? I can see the possibility of protecting
> >the IGBT gate from over- or under-voltage or -current... of .14V to .
> >46 volts (according to wikipedia)? If you need more voltage or current
> >protection in one direction than the other, it might make sense from
> >an efficiency standpoint. But why do I feel that I'm missing
> >something?.
>
> Probably fast turn-off, slow turn-on. Or vice versa, depending on the
> diode direction. Anti-shoot-through maybe.
>
> John
Sorry, blonde moment. Thanks, John. That makes more sense than my
suggestion.
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