# Bootstrapping with Opto Driver

1. ## Bootstrapping with Opto Driver

Hi team!

There is a bootstrap gate drive circuit for a inverter that I take the project of a graduate student as a reference and it works. But there are a few things that I don't understand in this circuit.

Like ;

-Why does the PWM signal come from the cathode to the anode?
-Why is a capacitor placed between the cathode and the anode?
-Why 12V is given externally to the anode? or
( Doesn't the opto coupler work without biasing the Anode? )

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2. ## Re: Bootstrapping with Opto Driver

Hi,

this is an inclomplete circuit. I donīt think it is correct. It does not make sens to discuss abut an incomplete circuit.

Where is it from? --> give a link ..
and give full description.

Klaus

1 members found this post helpful.

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3. ## Re: Bootstrapping with Opto Driver

Hi sır ,

The Opto Driver IC is the HCPL-3120 above ,

Also i will send another picture below wich includes 2 pre-bias supplies like the picture above.
He got the same things , only the difference is that they give 5V instead of 12V.
the driver section is taken by EG8010+TLP250.

https://www.lz2gl.com/data/power-inv...tasheet_en.pdf

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4. ## Re: Bootstrapping with Opto Driver

Hi,

This circuit makes more sense:

It differs to the first one:
* Now there is no capacitor beween A nd C of the LED. It is between pin2 and GND. Mind the junction dot.
* It seems to be a low side driver and a high side driver
* low side driver pin5 is connected to GND
* high side driver pin5 is connected to the half bridge
* LED power supply now is 5V.
* maybe others...

Now to your questions.
-Why does the PWM signal come from the cathode to the anode?
what does this mean?

-Why is a capacitor placed between the cathode and the anode?
No. The capacitor is NOT connected between C and A.

-Why 12V is given externally to the anode?
What is the alternatice you see? Why do you ask?

or( Doesn't the opto coupler work without biasing the Anode? )
the input of the optocoupler is a LED. It needs current to flow, it needs some power.
It is very basic knowledge that any LED will need both pins connected to be able to work.

... or did I misunderstand the question?

Klaus

5. ## Re: Bootstrapping with Opto Driver

First of all, thank you very much for answering very quickly sir!

What is the alternatice you see? Why do you ask?
I want to explain the reason by giving an example ,
when the PWM signals are applied, a voltage of 12V comes already to the anode of the IC.
In addition, I could not understand why it was directly powered by 12V with a pre-biased supply.

I mean , can't i just feed the opto - driver with the amplitude of the pwm signal?

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6. ## Re: Bootstrapping with Opto Driver

Hi,

I want to explain the reason by giving an example ,
when the PWM signals are applied, a voltage of 12V comes already to the anode of the IC.
In addition, I could not understand why it was directly powered by 12V with a pre-biased supply.

I mean , can't i just feed the opto - driver with the amplitude of the pwm signal?
This all makes no sense to me.

--> Show a sketch/circuit about your idea.

Klaus

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