Which is preferable as High Side Mosfet/Igbt driver?

[sohel]

optocupler is best device for high side isolated  switching. ir2110 is very complicated. if u use  optocupler why u need ir2110 ? 

[jzaghal]

Hi,

Previous discrete design should work, but you need a separate supply to power the Hi-Side.

Quote: " While transformers and couplers offer isolation, an isolated (floating)VGH supply may also be required, to swing along with the gate voltage."

Still I prefer pulse transformer.

Cheers.

[tAhm1D]

Hi jzaghal,
If you use separate supply to power Hi-side, then why you require any other circuit? You can drive the low side with any means like optocouplier etc.
Yes Pulse Transformer is better if you get those readily available and can purchase and use. Making those is real troublesome.
Regards.

[jzaghal]

Hi,

The problem is with driving the Hi-Side, which needs to be at a higher potential than the actual supply by

something like 15 to 20V dc in order to drive the Hi-Side Switch.

You don't have this problem with the Low-Side switch since the driving voltage is present using the normal

voltage supply. So you need one more supply for the Hi-Side. Hope it is clear.

You need one supply when you use a pulse transformer, since you get an isolated drive for both sides.

Cheers.

[tAhm1D]

Hi jzaghal,
Requirements and theory for Hi side and Low side mosfet drive is known to me as I have made lot of s.m.p.s. products. I normally use Mosfet/Igbt drivers like IR2110/2113. I tried to use Pulse Transformer but the one constructed by me was not appropriate and here pulse transformers are not available so that I can purchase. I am searching a discreet driver like I use in low voltage and low frequency application but could not make or find one for high voltage and high frequency. But this time I hope to make one with the help of optocouplers as I get the informations from Ichan.
Hope, I could make you understand what I wanted to mean.  

[tAhm1D]

Hi myheadhurts,
This circuit is not completely alright, as you have to provide the VGH for the MOSFET with external bootstrap circuitry. This, I had done earlier, but it is not going to work for high voltage, high frequency (say, 300V, 50kHz), as I would need to provide 310v minimum at VGH, and in turn damage the transistors (unless 400v ones are used). Also the high value resistors would cause a problem for high frequency signals.
Anyway, I appreciate your cooperation.

[Walkura]

Personaly i used several options .
I designed a ac-ac chopper using the HCPL3120.
http://www.bmh.nu/pdf/Opto/HCPL3120.pdf
Depending on the gatecapacity i think the IR2101 is also a quite nice option .
Also from time to time i abuse PC817 optocouplers to isolate my highside driver from the MCU .
The point is a little that with the HP and the PC817 you need to make your own bias supply .
Usualy one of my selection criteria is , what if it goes wrong ?
Otherwise i prototype while using optoisolated gatedrive ,when its *mature* i change to a cheap IR .
This way i can limit the (potential) damage while being in experimental phase .
It depends a little on what you can get in your country .

[tAhm1D]

HI Walkura,
So, you use different drivers as the circuit/situation requires. Yes, that should be the ideal method. Instead of using OPtocoupler and then making high side floating supply seperately, I think it is better to use Highspeed Optocoupler to supply the Microcontroller signal to Mosfet drivers like IR2110 etc. and that can be the suitable system for high frequency and high voltage full bridge circuit. I am using this process. However, I will try to use optocoupler and  separate floating supply with boost capacitor for high frequency and high voltage circuit.

[myheadhurts]

hi

one of the reasons I tried a discrete solution rather than a Mosfet/Igbt driver like IR2110/2113 ,was to solve a problem of voltage spikes (caused by tail-end currents in the h bridge )at the higher than normal frequencies I needed.
I found that under certain conditions shoot-through by erroneous firing could occur and removing the Mosfet/Igbt driver and its bootstrap circuits was a cure...providing power to the high sides from a boost circuit mc34063 and multitap transformer to provide all 12 highside supplies.
I later solved the spike issue by using the pwm drive signal to control the tail-end current towards the end of the commutation cycle..removing the charge pump effect altogether..

Rob

[tAhm1D]

Hi myheadhurts,
Your concept is correct. The way you have described is workable I think. I will work with your idea.

[tAhm1D]

optocupler is best device for high side isolated  switching. ir2110 is very complicated. if u use  optocupler why u need ir2110 ? 

Hi,
Are you convinced that IR2110 is not necessary and only Microcontroller and Optocouplers are enough to drive all 4 Mosfets in a full bridge circuit operating in around 300V? If it is, then how?

[jzaghal]

Hi,

What Sohel is suggesting is possible.

You can use a fast opto_isolator such as 6N136 and, use a separate 12V PSU.

Cheers.

[tAhm1D]

Hi jzaghal,
Using separate power supply for high side virtual ground is the first lesson in full bridge topology in power electronics.If I use separate power supply for high side mosfets, then there is no need for such a long discussions in this thread. Instead of supplying separate power supply to the highside mosfets, creating artificial virtual ground with discreet process is the aim. However, Your system is workable but I prefer IR2113 instead of separate power supply. Your idea is welcome.

[Jehan]

If your duty cycle is less than 50% you can use an isolation transformer type drive , many small drivers transformers are available from Coilcraft, pulse and many manufacturers, you can also manufacture your own transformer using toroids.
Also there are dedicated fully contained drivers from Infinieon if you are going to use high
power IGBTs

[sohel]

using two 6n137 opto for high side and normal low side. can u clear me which product u want make. r u talking 50khz pwm or something else.

[tAhm1D]

Hi,
Do you think that 6n137 opto in highside is enogh for a circuit where voltage is almost 320v? I am considering about an smps circuit to convert 320v DC to 230v sinusoidal AC with > 50khz Freq.

[sohel]

convert 380v DC to 230v/50hz sinusoidal AC with > 50khz pwm Freq ? look at picture for one high side with 6n137.

[tAhm1D]

Hi,
What you are trying to say is not clearly comprehensible from the pcb, so could you please provide the schematic?

[tAhm1D]

Hi sohel,
I have tested your circuit. It works fine at low frequency, below approximately 8khz, but higher frequencies cause distortion of waveform (slow rise time) due to pull up resistor. You cannot discard pullup resistor since 6n137 is an open collector device. Reducing the resistor will destroy the 6n137. so, your circuit can not be used for high frequency applications.

[sohel]

can u show picture from output.

[tAhm1D]

Hi sohel,
I don't have camera in my possession now and hence can not show the output waveform. However, have you not tested the circuit by yourself? What is your observation regarding the circuit?

[lito108]

Hi Ichan
good info !

[qolpa]

can u share ur hardware design

thanks

sohel, sorry for a so late answer, but i missed your reply and i do not have the whole schema, i tried to put some little parts together and hope this helps. this was a 48V to 27,5V battery charger with ~20A output and 20kHz switching freq. it was a school project and had a  basic circuit.