IGBT Gate Driver Selection

Thread Starter

Dimbel36

Joined Sep 22, 2020
8
Hello,

I'm designing a resistive load bank. Currently, I am designing the switch that will be controlled by a control signal via Arduino uno rev 3. The bidirectional switch is composed of two back-to-back igbts connected by their emitters with anti-parallel diodes. (Due to cost, there are two igbts instead of a single igbt module).

My question is:

How do I select the appropriate gate driver for a back-to-back igbt switch?

As shown, The gates are connected together.

Based on my research, the following parameters are needed: gate charge, Iout, Iout pk., Vce, and number of channels? But to calculate Iout, we need switching frequency.
This load bank does not require PWM. Therefore, what is an appropriate switching frequency to calc. current requirements?
Additionally, since the gate is shared between two IGBTs, will I have to account for current division?
Total Gate Charge: 100nC at 15V per device

Any help will be greatly appreciated!

IGBT datasheet: https://www.microsemi.com/document-portal/doc_download/6730-apt20gt60brdq1g-datasheet

1611191357340.png1611191370470.png
 

shortbus

Joined Sep 30, 2009
8,578
Not sure what your trying to do here? Why as shown in your partial schematic do you use two IGBT's? The bottom one is in what would be considered 'shoot through mode'. Why not just use one IGBT?
 

Thread Starter

Dimbel36

Joined Sep 22, 2020
8
Not sure what your trying to do here? Why as shown in your partial schematic do you use two IGBT's? The bottom one is in what would be considered 'shoot through mode'. Why not just use one IGBT?

IGBTs are used for switching load values for a load box rating to 250V ac/dc.
The switch is made of two IGBTs and two diodes in antiparallel. The switch is a common-emitter IGBT connection (CE-IGBT).
The IGBTs are wired back-to-back so each one is controlling a half sine wave.
 

shortbus

Joined Sep 30, 2009
8,578
Doesn't help much without a data sheet for what your using, that should have the information you want in it.

Another thought, you have the IGBT in what is called a "high side switch" configuration. It's called that because you have the resistor after the IGBT. That makes the gate driver more complicated for you, needing a bootstrap circuit to work. Any reason why you did it that way? Google high side switch.
 

Thread Starter

Dimbel36

Joined Sep 22, 2020
8
I'm assuming you mean the IGBT datasheet which I attached in the question. I'll attach it again below.
IGBT datasheet: https://www.microsemi.com/document-portal/doc_download/6730-apt20gt60brdq1g-datasheet

I googled the high side switch and bootstrap operation. I will put the resistor behind the switch for simplicity. (Thanks for pointing it out)
Doesn't help much without a data sheet for what your using, that should have the information you want in it.

Another thought, you have the IGBT in what is called a "high side switch" configuration. It's called that because you have the resistor after the IGBT. That makes the gate driver more complicated for you, needing a bootstrap circuit to work. Any reason why you did it that way? Google high side switch.
 

rod-e

Joined Jun 17, 2016
9
You can use an isolated gate driver, such as the Si8751 or Si8752. These eliminate any requirement for high-side drivers, bootstrapping, etc. They aren't ultra-fast, but are much better than photovoltaic couplers.
 

Thread Starter

Dimbel36

Joined Sep 22, 2020
8
You can use an isolated gate driver, such as the Si8751 or Si8752. These eliminate any requirement for high-side drivers, bootstrapping, etc. They aren't ultra-fast, but are much better than photovoltaic couplers.
Thanks rod e
May I ask what are the considerations for selecting that gate driver? How do you know it will work for this particular configuration?
 

prepka

Joined Oct 5, 2020
13
You can use the HCPL-316J to drive it with isolated 20-24VDC regulated to provide +15/-5Vor-9V with 10ohms in the gate. The circuit is in the data sheet how to make the IGBT driver. This device has everything you need to control it.
 

Thread Starter

Dimbel36

Joined Sep 22, 2020
8
You can use the HCPL-316J to drive it with isolated 20-24VDC regulated to provide +15/-5Vor-9V with 10ohms in the gate. The circuit is in the data sheet how to make the IGBT driver. This device has everything you need to control it.
I appreciate it. I will take a look into this
 

Sensacell

Joined Jun 19, 2012
2,821
I cannot help but suggest using a bridge rectifier as the input then using simple NFETS to switch the pulsating DC into the resistor loads? Far fewer parts. You can use simple low-side drivers, all the Source terminals can be common - perhaps supply the circuit with a tiny isolated DC to DC converter for the gate drive, with standard optocouplers for the input. If the switching speed is low, you dont even need gate drivers.
 
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Thread Starter

Dimbel36

Joined Sep 22, 2020
8
You can use an isolated gate driver, such as the Si8751 or Si8752. These eliminate any requirement for high-side drivers, bootstrapping, etc.
When you mention that an isolated gate driver eliminates any requirement for high-side driver/bootstrapping, does that mean it is okay to leave it as a high-side switch as shown in the schematic? or does that mean I need to put the resistors before the switch (make it low side)?
 

rod-e

Joined Jun 17, 2016
9
When you mention that an isolated gate driver eliminates any requirement for high-side driver/bootstrapping, does that mean it is okay to leave it as a high-side switch as shown in the schematic? or does that mean I need to put the resistors before the switch (make it low side)?
Please read the datasheet - it explains how to use the IC. It is by far the easiest way to achieve an isolated gate drive.
 

shortbus

Joined Sep 30, 2009
8,578
You can use an isolated gate driver, such as the Si8751 or Si8752. These eliminate any requirement for high-side drivers, bootstrapping, etc. They aren't ultra-fast, but are much better than photovoltaic couplers.
Hi and than you for your website, I've learned from a lot of what you have on it.

Now my question. Have never heard of this component, but it's billed as for a solid state relay, but, could it be used in motor driver circuits? To eliminate the need for a bootstrap circuit?

Looking at the "evaluation" boards they sell, it seems like one of these also need a lot of extra components for the circuit. Or is this just when used as a relay?
 

rod-e

Joined Jun 17, 2016
9
Hi and than you for your website, I've learned from a lot of what you have on it.

Now my question. Have never heard of this component, but it's billed as for a solid state relay, but, could it be used in motor driver circuits? To eliminate the need for a bootstrap circuit?

Looking at the "evaluation" boards they sell, it seems like one of these also need a lot of extra components for the circuit. Or is this just when used as a relay?
You need to be aware of its speed. While it is much faster than photovoltaic optocouplers, it is NOT suitable for PWM applications. It is ideal for on-off switching, but it will work at up to 50-60Hz (as a light dimmer for example - I've tested this and it works well).
 

Thread Starter

Dimbel36

Joined Sep 22, 2020
8
Yes, that is my website.
I noticed that the Si8751 provides 10V to the gate drive. For an IGBT to act as a switch, what region must it operate?
For instance, the threshold gate voltage is 5V and its maximum is 30V. So, for the IGBT to conduct, it needs greater than 5V. Looking at the Vce, Ic graph, it appears it needs 15V to be in saturation. My question is what gate voltage is needed for the IGBT to act as a switch? Is 10V gate drive okay?
 

rod-e

Joined Jun 17, 2016
9
I noticed that the Si8751 provides 10V to the gate drive. For an IGBT to act as a switch, what region must it operate?
For instance, the threshold gate voltage is 5V and its maximum is 30V. So, for the IGBT to conduct, it needs greater than 5V. Looking at the Vce, Ic graph, it appears it needs 15V to be in saturation. My question is what gate voltage is needed for the IGBT to act as a switch? Is 10V gate drive okay?
Please learn how to read and understand datasheets. The data for the APT20GT60BRDQ1 indicates that with 10V on the gate it can conduct up to 60A, but to be safe that should be no more than 20A. You don't appear to have disclosed the operating voltage or current.

When you fail to provide the details, no-one can answer the question properly. You keep asking questions, but provide no details of what you are trying to switch. Since your application appears to be switching AC, you can just use a TRIAC with a TRIAC driver optocoupler such as a MOC3020. Lack of details means that answers can only be guesses.
 
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