Problem with optocouplers!

[kappa_am]

Hi;
I try to implement a multilevel inverter step by step! to understand how opto transistor/darlington is working I implement a circuit in proteus! the program is well working but I have problem with optocouplers. I have attached picture of my circuit. is there a problem? any comment to implementing of this circuit is appreciated, also.

thank you

 

[Qaisar Azeemi]

I only come to know form your circuit is by activating any optocoupler will cause nothing but to make tow batteries of different potential in parallel which is not a good idea. please explain problem with optocouplers. why not you use lm338 Regulator if you want different output voltages. the output voltage of this regulator can be easily changed using a microcontroller.

 

[kappa_am]

actually, by appropriate switching we put DC source in series. by adding or subtracting dc values from each other we can obtain a multilevel sine wave! this is just a start, if problems get solved all dc sources will be replaced with capacitor except last one and will be expanded to 3 phase!!
the problem is some optocouplers when are active, have high voltage drop. I consider current transfer ratio but I don't know what else can be cause of this problem.

thank you

 

[ghost1xx]

Hi
For the start I would suggest to try complete one control block (so optocoupler, driver and power switch) than try to expand the diagram as many blocks as you need. In terms of optocoupler problem I think you need to ground the emitter of the internal transistor of the optocoupler. Also you would need some pull up resistor at the output of the optocoupler. Check datasheet for example 6N138/6N139 optocoupler.

 

[miyop]

Do you know is there any 4 pin optocouplers in PROTEUS - ISIS.
I could find only OPTOCOUPLER - NPN, which has 6 pins.
In real life, there are 4 pin opto's, but in Proteus I couldn't find. Can you help me with this?

 

[ghost1xx]

H miyop,

I have not seen any 4 pin optocouplers in Proteus.
It would be very difficult to do because you need 2 pins as input, Vcc, GND, and output so minimum is five.
Either way maybe try newest update of Proteus.

 

[alexan_e]

H miyop,

It would be very difficult to do because you need 2 pins as input, Vcc, GND, and output so minimum is five.

I disagree, there is a diode in the input that has two pins and a transistor in the output (assuming the optocoupler has a transistor output).
The needed transistor pins are the emitter and collector and that gives a total of four pins.
There are cases when the optocoupler also has a pin connected to the base of the transistor which is optional.

**broken link removed**

 

[miyop]

OK, then how can I find it in ISIS alexan_e ? Has it ARES package or what is the name of it's package type?
Thanks for your answers.

 

[udhay_cit]

My opinion is not advisable to use only optocoulpers for multilevel inverter. you should use BJT or MOSFET as a switch to get the proper output... I have some good experience with multilevel inverters[IEEE papers] & i mostly use MOSFET...

 

[miyop]

I won't use it for multilevel inverter, that is an old question from kappa_am. I will use it for isolation. I saw a 4 pin opto called pc817 but it is not found in ISIS.

 

[alexan_e]

OK, then how can I find it in ISIS alexan_e ? Has it ARES package or what is the name of it's package type?
Thanks for your answers.

PC817 has four pins\
Also PC827, PC829, PC837,PC847 etc

 

[miyop]

PC817 has four pins\
Also PC827, PC829, PC837,PC847 etc

And then how can I find those on ISIS?

 

[alexan_e]

open the pick device dialog and type the part code, these are already included in ISIS.

 

[miyop]

I tried already. But it is not there. Can it be because of the version of my proteus (7.2 sp2). If it is how can I fix it -except installing the newer version-?

 

[alexan_e]

You either have to upgrade or modify an existing device and assign a four pin footprint

 

[miyop]

You either have to upgrade or modify an existing device and assign a four pin footprint

OK. Thanks. I don't know how to do it but I'll learn.

 

[alexan_e]

Youtube is full of videos, for example https://www.youtube.com/watch?v=8-cv1bCiuKM

 

[miyop]

Thanks for your help.