# IGBT

Discussion in 'General Electronics Chat' started by onceinalifetim, Oct 1, 2014.

1. ### onceinalifetim Thread Starter New Member

Feb 9, 2014
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I know that IGBT is combine together with MOSFET and BJT. the common feature is a gate, a collector and a n emitter..

so what is the main different between IGBT vs (MOSFET & BJT)

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Main difference = 1 component instead of 2.

3. ### DerStrom8 Well-Known Member

Feb 20, 2011
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An IGBT can generally handle much higher power with fewer losses, but sacrifices switching speed.

Jan 18, 2008
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5. ### alfacliff Well-Known Member

Dec 13, 2013
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a bipolar transistor with an insulated gate instead of a base connection.

6. ### DerStrom8 Well-Known Member

Feb 20, 2011
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Not exactly. There is a full BJT and a full FET built into an IGBT.

Here is a (simplified) internal circuit diagram (Left: equivalent, Right: effective):

7. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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The IGBT has nearly zero "on" resistance, which makes it ideal for switching applications, plus the input impedance is very high, so driving power is minimal.

8. ### DerStrom8 Well-Known Member

Feb 20, 2011
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I'm just going to add on to this. I was going to mention it this morning but I was in a rush to get to work, and didn't have enough time.

FETs are effectively voltage-controlled resistors. Their on-resistance changes depending on the voltage applied to the gate. If you pass a current through it (from drain to source), your power loss will be (according to Ohm's Law):

$image=http://latex.codecogs.com/gif.latex?P%20%3D%20I%5E%7B2%7D*R&hash=321b422dad31b86881301bb587628b12$

Notice that the power increases exponentially with current, thus the losses will increase significantly at higher currents. On the other hand, an IGBT does not act as a voltage-controlled resistor. As KL7AJ mentioned, it has a very low on-resistance (generally a few milliohms). Its losses are really only determined by the voltage drop of the silicon itself. Therefore, the losses will be (again, according to Ohm's Law):

$image=http://latex.codecogs.com/gif.latex?P%20%3D%20I*V&hash=acb7393f1c9404fbca54435461757579$

As you can see, the power loss does NOT increase exponentially with current, making it much more efficient (less lossy) at higher currents.

Hope this clears some things up.

Regards,
Matt

9. ### clickclack New Member

Sep 30, 2014
5
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At lower voltages where the diode drop is a significant part of the operating voltage isn't the FET generally superior though?

I'm working on a project for harvesting and bucking up power from a 12V solar panel right now and keeping diode drops out of the current path is a concern on the input voltage side. I've looked at a lot of solar designs doing research and I don't recall seeing any IGBTs at all.

10. ### DerStrom8 Well-Known Member

Feb 20, 2011
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Yes, at lower power levels MOSFETs are definitely superior. They are faster and smaller. IGBTs are generally used for large motor drivers, which can see very high currents.

11. ### cmartinez AAC Fanatic!

Jan 17, 2007
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Check this video, it shows how to use a MOSFET as an extremely efficient diode with a very low voltage drop:

Also, the narrator has a knack for keeping it interesting...

DerStrom8 likes this.