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Is the NEC2501 opto any quicker than the low cost Sharp PC817?
Is the NEC2501 opto any quicker than the low cost Sharp PC817?
By Julian
Youtuber, shed dweller, solar charge controller aficionado
You didn't compare them at different frequencies. They might behave quite differently.
what maximum frequency can reel working optocoupler
Why not use a logic level mosfet instead? It would be way faster wouldn’t it?
Can anyone share circuit of this mosfet driver with 2 opto?
Julian, you should read up on making your own gate drive transformers. You can use small, low cost ferrite toroids, and you don’t need many turns of wire. Many people wind them with twisted pairs from lan cables. The only problem is the circuit is more complex, but not ridiculously so.
You can get very nice, sharp waveforms at high frequencies with these transformers.
Hey julian, those standard opto isolators are probably not that good for this application. You can get the speeds higher by using a constant voltage across the output side and sensing the current, but that is going to cause a lot of circuit hassle. Better look at something like the TLP251 instead, it is meant to drive Mosfets or IGBTs.
The used opto couplers are only a small part of the problem. The larger part is how you use them.
Driving them directly from the µC pins is a bad idea, because the µC can't provide enough current. The internal LEDs can be pulsed up to 1A (and 50mA continuous). Optocouplers are current transfer devices. In the PC817 it is about 50%. This means if you drive the LED with 20mA for example you can only get about 10mA through the output transistor. That current is way to low if you are ever thinking about switching a MOSFET. Your rise times on the MOSFET will be horrible.
For switching off you need a decent load on the OC outputs. Look at the data sheet. If you want to use these OCs even at a few tens of kHz, the load must be lower than 100 Ohms.
Get an opto coupler that has a pin for the base of the internal transistor (and preferably has an internal reverse biased photo diode). You will need to use this base if you want fast rise times (<1µs).
so the conclusion of today must be that you are a proud new owner of 50? new opto isolators and you must find yourself a new storage box and a new project to put them in , in guess.. ghihihi . maybe a nice idea for a video julian, a walk in your museum/store/solar shed ? nice video again..
why don't you use a low side switching circuit?
Hi Julian, can you please redo the experiment, but show your input pulse shape.
Also, form your input with PWM and then direct port manipulation.
Also see if having the input LEDs on your PCBs has an influence.
The reason is, in the past I had to bit bang a sensor to get it to communicate at a high comms speed.
I found a big difference in Arduino output depending on how software/firmware was used.
I agree with the speed differences you show, but a bit more input tuning may improve the opto output shape.
Thanks.. Tom…
What size panels do you have for your workshop? Do you use main power in the shop or all battery /solar? Love your channel, all the way from South Carolina.
Possible that the LEDs switch on differently with different colors….
i can't help thinking you'll be better served using a dedicated gate driver. something like the NCP5901BDR2G can be had for $.33*100 and will give you <20ns switching times.
took me a second before Rainham, Cold Aston, Wetton, Miserdon, and Nasty final clicked in my brain. got me chuckling properly.
At least the weather is nice here, warm enough to go out in t-shirt and shorts and still be warm. I wish they would make fast optoisolators, or maybe make some kind 4-pin transistor. That's my dream component: 2 of the pins would be the drain and source, the other 2 pins would be where you connect the signal and it would be completely isolated, like a relay but faster, it would solve everything. I know no such component exists, but I can dream.
I wonder … were the optoisolators driving anything? Driving a load could change your measurements quite a bit. Just a thought.