# High Side Switching of IGBT

#### MMayur

Joined Aug 25, 2022
9
I am using a IR2101 gate driver circuitry to switch the high side IGBT ON (I do not want it to be periodic). Hence I found out that since I am not frequently switching the IGBT, the bootstrap circuitry doesnt not work since the capacitor cannot charge up.

I therefore found out 2 ways I can achieve non-periodic switching of high side IGBT:

1) Use an isolated/floating power supply
2) I can add a charge pump circuitry to my current gater driver circuitry.

However, I do not understand how should I incorporate/ use the above two methods with my gate driver to switch the high side IGBT. Please help me with some circuit configurations for the above two methods, as that would make things very clear for me, rather than explaining the circuitry connections with words.

My circuit application looks as follows:

The problem, however, is when I apply 3.3V to the gate driver, I measure the voltage VB-Vs I get 12 V (correct since my 4.4 μF tantalum cap charges). If I measure VB-HO I get 12 V (I don't know why this happens), and the voltage at HO-Vs (emitter of Q1) is 0 V.

Here I dont undertand couple of things:

1) Why is the voltage at HO-Vs (emitter of Q1) is 0 V when I give 3.3V to HIN?
2) I expect the capacitor to discharge when I supply 3.3V to HIN, however when I measure the voltage across the capacitor (VB-VS) it stays 12V, and this means that the capacitor doesnt discharge, hence the 3.3V signal isnt turning the IGBT ON (even for a short while, which would discharge the capacitor fully, and therefore even if I continue to apply 3.3V at HIN, after a short while I should measure 0V across the capacitor, which I do not).

- I would like to stick with N channel and not P channel (because I have them ready for implementation).
- Would really like to use isolated DC-DC converter power supply (either use it individually to connect it to the gate and emitter of the IGBT and switch the converter ON and OFF) or integrate it with IR2101 somehow. (Need help in this application)
- Lastly if nothing works try using charge pump circuitry and integrate that circuitry with the current gate driver I have. (Need help in this application)

#### Ian0

Joined Aug 7, 2020
9,533
Have a look at LTC7001.
But why are you using 600V IGBTs on 20V, what’s wrong with a P-channel MOSFET?
and why are you charging a huge capacitor with no surge current limitation?

#### MMayur

Joined Aug 25, 2022
9
Have a look at LTC7001.
But why are you using 600V IGBTs on 20V, what’s wrong with a P-channel MOSFET?
and why are you charging a huge capacitor with no surge current limitation?
Thank you will look at LTC7001.
I just happen to have N channel IGBT, and later on shall use a suitable switch. For now I have it on me for implementation.
Charging a huge capacitor I have some protection, just showed a simplified circuit, as I wanted to look for ways to switch a N- channel IGBT and not worry about the rest of the circuit application.

Any advice on how I can use isolated DC-DC power supply to switch the IGBT?

#### Ian0

Joined Aug 7, 2020
9,533
Any advice on how I can use isolated DC-DC power supply to switch the IGBT?
Use it in conjunction with an isolated MOSFET driver such as FOD3180. Broadcom makes one as well - can’t remember the number.

#### MMayur

Joined Aug 25, 2022
9
Use it in conjunction with an isolated MOSFET driver such as FOD3180. Broadcom makes one as well - can’t remember the number.
FOD3180 you suggested is like VOD3120AD. I also tried using this optocoupler. Should I then connect the output of the isolated converter to pin VCC and VEE

Or only connect to VCC to +ve output of the isolated supply and leave the -ve floating and then connect VEE to the emitter of the IGBT?

#### Ian0

Joined Aug 7, 2020
9,533
FOD3180 you suggested is like VOD3120AD. I also tried using this optocoupler. Should I then connect the output of the isolated converter to pin VCC and VEE

Or only connect to VCC to +ve output of the isolated supply and leave the -ve floating and then connect VEE to the emitter of the IGBT?
Vcc goes to the positive of the isolated supply. Vee goes to the negative of the isolated supply, and also connects to the emitter or the IGBT

#### ronsimpson

Joined Oct 7, 2019
2,904
vishay.com
Here is a datasheet. " Photovoltaic MOSFET Driver Solid-State Relay "
It is very simply some LEDs to make light and a photocell to get the light and make current to turn on the Gate.
They are not fast switching for PWM but do fine for "relay" type circuits.
The problem is that they do not turn off well. In this example a JFET is added to turn off. I think there is a way of using a dual channel Driver, one channel makes power for turn on and the other makes power to turn on a small MOSFET that shorts out the Gate. I have not thought enough about it. Search for Photovoltaic Gate Driers might turn op a good idea.
ronsimpson

#### MMayur

Joined Aug 25, 2022
9
vishay.com
Here is a datasheet. " Photovoltaic MOSFET Driver Solid-State Relay "
It is very simply some LEDs to make light and a photocell to get the light and make current to turn on the Gate.
They are not fast switching for PWM but do fine for "relay" type circuits.
The problem is that they do not turn off well. In this example a JFET is added to turn off. I think there is a way of using a dual channel Driver, one channel makes power for turn on and the other makes power to turn on a small MOSFET that shorts out the Gate. I have not thought enough about it. Search for Photovoltaic Gate Driers might turn op a good idea.
ronsimpson
View attachment 274673
Thank you.

Any advise specifically related to the gate driver I am using. Maybe how I can use it with isolated dc-dc converter?

#### Irving

Joined Jan 30, 2016
3,814
I believe this works:

#### MMayur

Joined Aug 25, 2022
9
Thank you very much.

Its the concept of adding an isolated converter to the gate driver circuitry.

Really like the way you have responded with a circuit!

#### Irving

Joined Jan 30, 2016
3,814
No charge pump, just an isolated DC-DC converter replacing the boost capacitor which would be the DC source for the high-side gate charge. You'll need to check what output current you need to drive the gate. The TRACO TMR_1-1212 is a 12v in, 12v out 1watt unit (other manufacturers make similar devices). It can deliver 83mA, but a 10uF - 100uF capacitor from VB to VS will help give more gate drive; what frequency/duty cycle are you driving the upper IGBT?

#### MMayur

Joined Aug 25, 2022
9
No charge pump, just an isolated DC-DC converter replacing the boost capacitor which would be the DC source for the high-side gate charge. You'll need to check what output current you need to drive the gate. The TRACO TMR_1-1212 is a 12v in, 12v out 1watt unit (other manufacturers make similar devices). It can deliver 83mA, but a 10uF - 100uF capacitor from VB to VS will help give more gate drive; what frequency/duty cycle are you driving the upper IGBT?
I am not driving it at any frequency, its more switching the high side IGBT when needed (non-periodic). How would I go about calculating the current requirement, and therefore choosing the correct isolated DC-DC converter?

#### Ian0

Joined Aug 7, 2020
9,533
I am not driving it at any frequency, its more switching the high side IGBT when needed (non-periodic). How would I go about calculating the current requirement, and therefore choosing the correct isolated DC-DC converter?
It will be the smallest one.
Current =MOSFET gate charge x frequency + standing current of gate driver.

#### crutschow

Joined Mar 14, 2008
34,078
If you want to roll your own, below is the LTspice simulation of a 555 bootstrap charge-pump circuit that should also work:
E1 simulates the voltage VS at the IGBT emitter (yellow trace).
Note that VB (green trace) tracks at about 10V above VS to provide the desired gate voltage.

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#### Irving

Joined Jan 30, 2016
3,814
If its very occasional and you have no switching time (or switching loss) consideration then 83mA gives a turn-on time of approx 1.6uS. A 10uF capacitor will help improve that, but the 100R resistor limits it to 120mA anyway.

#### Irving

Joined Jan 30, 2016
3,814
Below is the LTspice simulation of a 555 bootstrap charge pump circuit that should also work:
E1 simulates the voltage VS at the IGBT emitter (yellow trace).
Note that VB (green trace) tracks at about 10V above VS to provide the desired gate voltage.

View attachment 274699
Interesting, can you post the ASC file please...

#### crutschow

Joined Mar 14, 2008
34,078
can you post the ASC file please...
Here it is.
It uses a transistor-level model of the 555.

#### Attachments

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#### MMayur

Joined Aug 25, 2022
9
If its very occasional and you have no switching time (or switching loss) consideration then 83mA gives a turn-on time of approx 1.6uS. A 10uF capacitor will help improve that, but the 100R resistor limits it to 120mA anyway.
This is good to know.

I would like to know how you were able to calculate 83mA, turn-on time, the 10uF capacitor value and how did you figure out that having 100R resistor is limiting the current to 120mA.

Please share some indepth calculation you did. I know it will take a significant amount of your time to show all this calculations, but it might just help me in my project.

#### MMayur

Joined Aug 25, 2022
9
If you want to roll your own, below is the LTspice simulation of a 555 bootstrap charge-pump circuit that should also work:
E1 simulates the voltage VS at the IGBT emitter (yellow trace).
Note that VB (green trace) tracks at about 10V above VS to provide the desired gate voltage.

View attachment 274699
Thank you.

I can use a timer to provide charge pump and therefore no need for me to switch the high-side switch at a certain frequency but rather occasionally.

So the 3.3V signal from the micro-controller, only needs to be applied to the gate driver, and not the timer? I thought probably there's some way to also inform the timer that the micro-controller signal is low.

#### crutschow

Joined Mar 14, 2008
34,078
Upon further simulation, I noticed a transient overvoltage on the 555 output when the output VS is rapidly switched (as when the IGBT turns on), so below is the modified circuit with an added diode to clip the overvoltage and resistor to limit the peak transient current.

Edit: Also noticed a problem with the voltage continuing to increase after the the IGBT VS turns on and off, so added a Zener at the output to limit the peak voltage to 10V (below):

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