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I'm currently trying to operate a supercapacitor that'd be charged up using footstep to energy system, then once the super caps are charged, it's energy is used somewhere to be stored via MPPT module.

You could ask why not go directly to MPPT? I did this because there is an initialization time with the MPPT before it operates, and the time of the generated energy during footstep is not enough to trigger the MPPT module to operate.

I've able to find a work around on this by using a supercap, but I had to do it manually by closing the circuit of the super cap and the MPPT module once the supercaps are fully charged,.

Now I'm having trouble on finding a circuit that would do just that automatically. And also at a low power consumption.

I need a circuit that would close the circuit from let's say, 10 V to 5 V, but open circuit at 5 V to 10 V.

Null
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Aezakmi123
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    I'm not sure I understand what you're looking for. Is a diode not what you need? – Hearth Feb 01 '22 at 16:44
  • A timing diagram and/or block diagram would make this question less confusing. I'm guessing you want to keep the cap disconnected from the MPPT until it reaches a certain voltage, then connect and attach the MPPT until it's discharged, then disconnect the MPPT and continue to charge the cap? The way you describe it in the title it sounds like it only closes the circuit and never opens it. – Cristobol Polychronopolis Feb 01 '22 at 16:57
  • It sounds like you are after an under-voltage-lock-out circuit with hysteresis. So, as the supercap voltage is rising up to 10 volts, the UVLO+H circuit disconnects the supercaps from the MPPT stage until the voltage rises to 10 volts and above then, on the way down, as the voltage drops, it disconnects when the voltage has dropped to 5 volts. Yes? – Andy aka Feb 01 '22 at 16:58
  • ... or perhaps an [ideal diode](https://electronics.stackexchange.com/q/223935/11683) – Dave Tweed Feb 01 '22 at 16:58
  • Yes that's the one,. I'm sorry for the confusion i can't make a diagram right now because I'm currently using my phone. – Aezakmi123 Feb 01 '22 at 16:59
  • @user306443 who are you addressing in your last comment. I used `@user306443` to address you. – Andy aka Feb 01 '22 at 17:08
  • @Andyaka, yes sir,. that's the one sir. – Aezakmi123 Feb 01 '22 at 17:08
  • @Andyaka I'm really sorry. I'm having trouble using the comment function of the site, and I only manage to know how to mention ppl in the comments rn. I'm new here. Hehe – Aezakmi123 Feb 01 '22 at 17:11

2 Answers2

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It sounds like you "need" an under-voltage-lock-out circuit with hysteresis. So, as the supercap voltage is rising up to 10 volts, the UVLO+H circuit is disconnecting the supercaps from the MPPT stage until the voltage rises to 10 volts (and above) then, on the way down, as the voltage drops, it disconnects when the voltage has dropped to 5 volts. Yes?

@Andyaka, yes sir,. that's the one sir

Then you need to use a comparator with hysteresis like this: -

enter image description here

Image from here.

The comparator circuit will enable the device that connects your supercap to the MPPT circuit (maybe you are using a p channel MOSFET?).

To design it correctly you may have to find a comparator (an op-amp will do usually) that can work with the maximum voltage on the supercap. The Vin input will need to be potted down to maybe about 50% of the true supercap voltage and the two resistors chosen so that you have a rising threshold at say 6 volts (10 volts on the supercap) and a falling threshold at about 3 volts (5 volts on the supercap).

Andy aka
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A follow up for my question. Thanks to @Andyaka, I've able to make a design that works. Below is the circuit diagram that I've used. However I haven't tried it on actual yet. Only on simulation.

enter image description here

I'm not sure on the resistor values, although I've tested those on simulation and works well for 10 V to 5 V close circuit, and 5 V to 10 V open circuit.

Note: The super cap is rated for 5.5V, and had been setup in series to cater 10V.

There are also IC that does this function but is not readily available from where I live. Only using common components.

LM358 Pinout

enter image description here

74HC02 Pinout

enter image description here

Aezakmi123
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