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The opto-transistor in the PC817 can't disable the LTC3780 PSU without help from another NPN transistor
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The opto-transistor in the PC817 can't disable the LTC3780 PSU without help from another NPN transistor
Had the same issue. With load and low battery, the LTC3780 started to toggle at around the low input voltage threshold. Solved it by using a BC546 NPN over the I-O input and an Attiny45 with voltage devider which debounces the battery voltage using different on and off thresholds. Measured around 50mA to ground the Comparator, so the BC546 with its 100mA + 10mA Attiny pin is about right. Other benefit: also added an LTC output voltage monitoring on the Attiny, which shuts of in case of LTC converter failure.
Would it not be better to shunt to ground before the comparator? So in your schematic, shunting across the bottom divider resistor monitoring battery voltage (so the comparator thinks the input voltage is zero)? Might be easier than the Darlington and the really inefficient shunting of the opamp output? I might be chatting rubbish of course lol
Julian: "My solution doesn't work."
Me: "Why?"
Julian: "Because this board is passing 200mA from VCC to ground when it's in shutdown."
Me: "That's ridiculous. You should do something about it."
Julian: "Yes! Clearly what I need to do here, is implement a *lower-resistance solution*, so this 200mA of wastage can continue without interfering with it."
(Sod Almighty has left the chat)
I would have cut the track from the output of the op amp and put a 1k resistor over it to limit the current it can output so that the opto isolator will win the battle 🙂
I can see a few of them in back 😋👍
Would it not be better to use the opto to adjust the current limit on a PSU and not have the complexity of two power supplies?
Hi, you could instead consider inserting a resistor after the opamp and before the shut-down pin, then pulling down after the resistor just using the opamp. Not much difference, a resistor is slightly cheaper than a transistor, but it is perhaps a little simpler and doesn't put such a strain on the Opamp. Personally I think it's a bit risky pulling down the output of the opamp to ground, looks to me like it might make it fail.
The op-amp will have protection against ouput shorts, but even so, transfering the disable function to the + input would have been the normal design method. Take care if using darlingtons to pull things hard down to chassis. A single transistor can get down to 0.1v or so, but a darlington will struggle to get below 0.7V because it needs sufficient remaining voltage for its first device to continue to "tell" the second device to remain on – they share a common collector connection, of course.
very cool using the 3904 with the opto-isolator but is it really need there. couldn't something be done with it and the op-amp to switch off/on the supply???
Great vid.
I'm cancelling all my subscriptions for content makers with mid roll advertisements.
I stopped watching tv because there were too many adverts and will dump the tube if they persist with more and more advertisements.
you give me an idea using this dc to dc converter and a relay and high wattage bulb or heater eliment to make a dump load to stop batterys overcharging
Why not use a 4n33 opto. it has built in darlington. You can also control the base hold off with a resistor.
would shorting the ground resistor of the V in divider also switch of the power supply ? , if it will maybe the opto isolator will work by itself 🙂
Can you please provide the model of the power supplies used in your video so I can look into it and may purchase some of them? Thanks. Great video as always.
It looks like you can cause the OP-AMP output to go low by using the OPTO to pull the + input of the OP amp so + input Voltage is < – input of the OP-AMP so you basically simulate LOW Vin.
The way you want to do that I would think it would just oscillate on and off on you. This is because there isnt enough hysteresis or is there? I guess you dont know until you try it. Why didn't you just add a resistor before the hard switch to gnd from the lm358?
I thought about a super cap light, radio, and a phone charger, super cap, because it would be hand cranked, and shelved for long stretches of time. So cycling lots, and neglected, caps would last longer, i have a 80's cordless drill, I'm planning to chuck up a crank. And modify it to be a charger for the project I want to keep it low voltage to keep the capacitance up, I been looking for a DC boost converter, to boost from 1.2v or so to 5v, at 2 amps or 10-20 watts, and a disconnect to stop the caps from charging, I found tiny, .5v to 5v but are under 500ma, I thought about just using electrolytic capacitors, and storing higher voltage, use a boost in the crank charger, from 3-4v to 24v-28v or so, and a buck inthe cap device, to 5v wich would be cheaper, since I have salvaged components, I haven't studied the effiencey, or how it would effect run time!😱. Being offgrid I think about things like this often! There is THOUSENDS without power in the US now, from the increasing bad weather, lots of ppl would give their left butt cheek to charge their phone in an emergency, ha,
Even a 1/4 charge from a half hour of cranking is worth it, I think! Or 30 min. Of light, from 10 minutes cranking, with a dimmer, to make it last longer, cheers, and sorry for rambling!
I have some 26650 LiFePo4 batteries that have been shelved to death, they are as bout 160mah 60mah+/-, but the strange thing , some can be discharged, then set a few minutes, then discharge 40-50 mah again, over and over, with less than 500 ma discharge, they were like 3500 mah cells that Sat unused for years, I never seen a battery do that more than a couple times, it seems they are also working like a capacitor, I was hoping to get a 3-4 ah from about 6-8 of them for a solar landscape lighting project, but I doubt it will happen, the capacity is all over the place, especially when I can get used batteries cheap, I gave $0.10 each for these, I can still use them for something!