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Common Gate Drive for IGBTs?

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digi001

digi001

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Do i need a separate isolated gate drive for a string of IGBTs with Common Emitter?

Their collectors are not common but each pulled up with various values of low-valued power resistors.
 

Are the emitters connected to ground? If they are, you can drive them without an isolated gate drive circuit. But if they're not, ie, they source current to the load at the emitter, then you need an isolated gate drive circuit. In short, if it's acting as a low-side switch, you don't need an isolated gate drive circuit, but if it's acting as a high-side switch, you need an isolated gate drive circuit.

You can read a little on high-side and low-side here:

High-Low Side PDF

Hope this helps.
Tahmid.
 
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    digi001

    digi001

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No, you don't need that if all Emitters are referenced to the same "ground point".
However, take special care with routing and avoid having ground loops. Some gate drivers (like the -traditional in this forum- IR2110) allow some voltage offset between logic and power. If you are switching high currents the emitters of your IGBTS may have slightly different voltages due to track or wire resistances and specially during transients (due to parasitic inductances).

Good luck!

Ernest
 
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    digi001

    digi001

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You're going to have to clarify your question... the thread title says common gate, you say common emitter in your post. And what do you mean by a "string?" Are they in series or parallel?
 

Sorry the gate is what I am trying to decide whether can be common or not. The Emitters are all common. The Collectors are not common but all pulled up to a single bus via various resistor sizes.
 

The gate can be common. However, don't short the gates. Each gate has a current limiting resistor. Connect the gates through the resistor like this:

79_1327598932.png


Hope this helps.
Tahmid.
 
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digi001 said:
Sorry the gate is what I am trying to decide whether can be common or not. The Emitters are all common. The Collectors are not common but all pulled up to a single bus via various resistor sizes.
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In that case yes it should be fine to drive them all with one gate driver. But as Tahmid points out you should have gate resistors for each IGBT, which prevents them from interacting with each other. Also you should try and separate their emitter return paths as much as possible, especially if you're switching at a high frequency.
 
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