Here's a simple dual opto-isolator driver for an N-channel MOSFET on the high side of the load. A very simple bootstrap circuit (capacitor/diode) provides a gate voltage twice that of the load power supply. Opto-isolators are PC817C.
By Julian
Youtuber, shed dweller, solar charge controller aficionado
This video is garbage. Don't have the schematic. I see a a blinking bulb. No clear indication how it is used. And why a high side switching is used. watch 1000 videos before you upload your lousy circuit and video. I DISLIKED YOUR GARBAGE.
Please add all video in use schimetic and connection easy to everyone guys.
A picture (for picture read schematic) is equivalent to a thousand words.
I am really glad you have shared this with everyone. I have very limited knowledge of electronics but I've picked this circuit to experiment with.
My experiments revolve around high freaquency inverters, so I used the complementary action of the dcoi circuit to drive the gates of two mosfets which are tied to ground with 10k resistors. Each drain feeds power to separate coils of the same (repurposed) gate drive transformer and then read the output of a tertiary coil on the GDT.
In this manor I was able to visualize and tweak the performance. The resulting product was a very inefficient square wave inverter but it did work. The largest issue is the turn on time of the optocouplers which caused a distorted signal above 1kHz, ignoring the distortion, I could drive them up to 14kHz.
To compensate for the on time lag in the couplers it was necessary to tweak the duty cycle to such extremes as 95% to acquire a relatively clean square wave.
I really do enjoy your channels and look forward to more brain teasing projects. Thanks, Jason
julian, is there a limit on how fast (often) this can switch because of the tantalum cap?
Could you show the voltage across the gate – source and gate – ground on a scope?
This is a very clever and useful circuit, and it's beautifully explained thanks Julian. I reproduced it and used it to switch a 12V power supply on and off with an arduino, and it worked perfectly. However I noticed that the bootstrap capacitor / diode is acting as a voltage doubler, so it works with these voltages; but if you want to switch say 1000V (as I do) then the source / gate voltage will get up to 1000V too (source at 1000V and gate at 2000V) and fry the mosfet. Any suggestions as to how to keep the gate switching to source +5V instead of source x2?
Do you have a circuit diagram for the full thing? I've got the LEDs switching, but I'm trying to work out how the capacitor, diode and NMOS (high sided) connect to the optocoupler.
Forgive my noobiness, I'm a code junkie trying to bash my way through into electronics
I couldn't understand why the voltage would increase across the capacitor. But then I realized when you wire 2 AA battery in series the voltage also increases. The tantalum capacitor could be replaced by a non-polarized capacitor.
That's it. The four LEDs together have a forward voltage greater than 5v, so they don't light at all (even with no series resistor). Connecting the Arduino output pin to the mid-point of the LEDs (via a resistor) creates a complementary drive – the upper 2 are on when the digital pin is low and vice versa. I'm still waiting for a whole load of 3mm LEDs to arrive from China. As soon as I get them, I'll make a part 4 with a step by step explanation of how it works. Cheers.
It took me two days of pondering to figure out how the Arduino pin could switch the LEDs. The four LEDs can't burn together on 5V because they're wired in series. When an Arduino digital pin is DOWN that pin is connected to GND (!!!!). When the Arduino pin is LOW this connects the first two LEDs to GND and hence pulls them up. When the Arduino pin is HIGH this supplies LEDs 3 & 4 with 5V while LED 2 acts as a diode. In essence the Arduino pin constantly switches between 5V & GND. That was fun!
I'll be returning to the MPPT project soon. I'm rebuilding it on a larger board, so it's easier to see what's going on. The MOSFET tutorial is proving very useful – it's giving me ideas for advancing the MPPT controller circuitry.
Thanks very much for your comments and support.
Many thanks.
I'm looking forward the next video's of the MPPT controller.
I like the way you cut the project into pieces and explain all the "modules" bit by bit.
Thank you. I'll make a #4 video with instructions on how to make it and including a schematic.
Would be very nice and instructive to have a schematic !
Keep going. Your tutorials are very good !