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I want to make a tiny led glow for 10 minutes once charged by induction. I want the entire PCB not greater than 20x20x5mm. Is it possible? I have come up with the following circuit, I don't know if it works are not but my idea is to store energy in capacitor and inductor when the switch is closed and make them discharge through LED when the switch is open. You see, LEDs of electronic devices glow for a while after they are turned off. I have not put accurate values as I don't know what capacity of components are available in the market. I don't want to use a battery as I want a very long lifetime. I am sorry if anyone gets offended for asking this without practicing electronics.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ "charged by induction". How? \$\endgroup\$ – winny Aug 14 '18 at 12:45
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    \$\begingroup\$ 1) is it possible? I never like questions like that as that can only be answered properly by either showing that such a product already exists or by actually making the product. 2) your schematic isn't going to work, period. It just makes no sense. You just can't design a circuit without the proper knowledge and experience. So trying to design "something" is a futile exercise. \$\endgroup\$ – Bimpelrekkie Aug 14 '18 at 12:48
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    \$\begingroup\$ I don't want to use a battery as I want very long life time. That assumes that a long lifetime is impossible when using a battery. Some batteries last 10 years. If you properly use a rechargeable battery it can easily last many years. Without a battery, what will then store the energy? A supercapacitor could be used, but even these don't last forever. Define what "very long lifetime" means. Also cost can be an issue, components with a guaranteed long lifetime can be expensive. What if that 10 years guaranteed battery or supercap costs $ 50, would you still want it? \$\endgroup\$ – Bimpelrekkie Aug 14 '18 at 12:53
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    \$\begingroup\$ Welcome to EE.SE, @neckTwi. Please edit your question to explain the theory of operation of your circuit. We suspect that there are large gaps in your understanding of electronics and may be able to point out some of these to you. \$\endgroup\$ – Transistor Aug 14 '18 at 13:01
  • \$\begingroup\$ @Bimpelrekkie I think batteries are bulky. I want the device to be as tiny as possible. Of course, there are apple air pods that are small. But I am more interested in not using a chemical storage. \$\endgroup\$ – Necktwi Aug 14 '18 at 13:03
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I have a feeling you want something similar to the way that mobile phone wireless charging works. but instead of it charging a battery in your mobile phone you want to charge a capacitor which can then be used to power your LED.

The following reference is useful to what I believe that you are looking for: WIRELESS LED CIRCUIT

enter image description here

A notable difference would be, instead of just the inductive coupling powering the led, you wish to store that energy to power the LED for 10 minutes.

You will then find the following question useful for calculation the discharge time of the capacitor: CAPACITOR DISCHARGE CALCULATIONS

However, after the above being said it wasn't made clear why there is a reason to use a capacitor and rely on keep charging it. some batteries are designed to last years especially at such low current draw.

EDIT: The following link regarding capacitors being used to power and LED may be of some use to you: CAPACITOR LED

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  • \$\begingroup\$ Thank you! U got me. I don't want the led glowing continuously to use a battery. And I don't want to use a switch. I want the LED to glow for 10 minutes with constant brightness once removed it from the induction charging plate. \$\endgroup\$ – Necktwi Aug 14 '18 at 13:24
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I want to make a tiny led glow for 10 minutes once charged by induction. I want the entire PCB not greater than 20x20x5mm. Is it possible?

No.

Putting the inductive charging aside, your non-battery energy storage requirements cannot be met in a volumetric space of 20 x 20 x 5 mm.
The 5 mm height constraint is very problematic.

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