Optical isolation and common ground

Thread Starter

LAOADAM

Joined Nov 21, 2018
541
Hi,
The picture attached shown a IGBT driver circuit got online, which used a 6N136, drive a Triode and then drive the IGBT.
It is clear that the circuit used common ground, my question is can the circuit achieve isolation somehow? and how to modify it better?
Thanks
Adam
igbt test.png
 

ronsimpson

Joined Oct 7, 2019
1,228
Here is the isolation.
I don't like the circuit.
1)R1, 1k turns off IGBT2. But it will not pull to ground. It stops working at the turn on voltage of LED2. (1.5 volts)
2)MCU1 probably can not pull up hard on IO13. It can pull down better.
3)ISO & Q1 = Darlington which is not known for speed. It turns off slowly! What is the PWM frequency?
4)Why not use a Schottky diode for IGBT1?
1622413065041.png
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
541
Here is the isolation.
I don't like the circuit.
1)R1, 1k turns off IGBT2. But it will not pull to ground. It stops working at the turn on voltage of LED2. (1.5 volts)
2)MCU1 probably can not pull up hard on IO13. It can pull down better.
3)ISO & Q1 = Darlington which is not known for speed. It turns off slowly! What is the PWM frequency?
4)Why not use a Schottky diode for IGBT1?
View attachment 240052
Thanks.
I'll modify it and test.
BTW, why the IGBT generally used in pairs?
 
Last edited:

Reloadron

Joined Jan 15, 2015
5,934
The picture attached shown a IGBT driver circuit got online, which used a 6N136, drive a Triode and then drive the IGBT.
Just as a side note the "picture" is a schematic or drawing and Q1 is a BJT NPN Transistor and not a triode. The BJT Transistor is a solid state device and a triode vacuum tube or valve is not. Terminology is sort of important. :)

Ron
 

dendad

Joined Feb 20, 2016
3,835
A couple of points I would change for a start.
There should be a resistor in series with the OPTO LED.
And add a resistor from the FET gate to the FET 0V line, across the LED2/R1 series combo, as the LED does not allow a pull down to the 0V level.
 

LowQCab

Joined Nov 6, 2012
552
I must have missed the 12-Volts part, oops.
Yeah, if I had looked more carefully, I should have noticed the Gate being driven from the Rail.
In that case, IGBTs are not the best choice, they would have a ~10% Voltage-Drop,
a regular ol' FET with a proper FET-Driver would be better, and fewer parts.
LED Isolated FET Driver 4 Amp SI-826X
 

Ramussons

Joined May 3, 2013
973
Hi,
The picture attached shown a IGBT driver circuit got online, which used a 6N136, drive a Triode and then drive the IGBT.
It is clear that the circuit used common ground, my question is can the circuit achieve isolation somehow? and how to modify it better?
Thanks
Adam
View attachment 240047
If the Controller and Controlled parts share the same power supply, you cannot get Isolation in spite of the Opto coupler.
You will need separate power supplies for these.
 

LowQCab

Joined Nov 6, 2012
552
Instead of the top IGBT, use a .....
VS-60EPU02-N3 Fast-Recovery-Diode and a 100nf, and a 10nf, Ceramic-Capacitors.
The Capacitors are to reduce RFI from the Motor Brushes which can easily pop things.
Drive the FET with a .....
LED Isolated FET Driver 4 Amp SI-826X.
.
.
.
 
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