Very low powered light help

Question

Hello again,
Here's a thing: I need to build something that takes generic 3V LEDs of (almost) any color, running at half+quarter (3/4) of its brightness, which uses generic components anyone can find in electronics components seller (like NPN transistor), takes 0.7V~1.5V, and lights LED until the sun comes up, which is about 6~10 hours.

It does not have to be using rechargeable batteries (it'll be great if they do however) but it must sense light so it turns off when the sun shines.

(Nobody likes to change batteries daily just to enjoy teeny tiny light)

It'll be almost mass-produced (~100 units, hand-assembled) so it needs to be very simple.

Its circuit will be based on matrix type breadboards (not Veroboard, which has strips of copper running along the rows) and it does not need to be very small.

Battery types will vary from generic AAA size cells to LR42/AG13 batteries.

Colors: Green / Blue / White / Warm White, 2.7V~3.3V <- This is not the voltage the boost converter should output! This is for reference only!

Since it will be running at half of its maximum brightness, the voltage could be lower.

More information:

The output of the boost converter ("joule thief") should be just enough to light a generic 3V LED just enough to be visible in a dark room (illuminating small area around it), as mentioned earlier.

It uses high intensity LEDs with clear lens (instead of diffused one). You know, those LEDs used in toys such as spinning tops.

The LEDs are running in limitless mode. (there are no current-limiting resistors)

The circuit could be very tiny in some cases. (1.3cm in diameter, excluding batteries)

It needs no smoothing. (30Hz~)

Manufacturing cost should be minimal as I can't order ready-made ICs now.

Updated: There were some misleading lines. They're fixed now. Sorry for the confusion!

clem57 · Answer

I give you this link for ideas only. But if you can understand the concepts, I feel certain a gem will be found in the discussion: low power - simple, energy efficient circuit to make single IR LED blink - Electrical Engineering Stack Exchange

D_Hersey · Answer

The web is full of designs intended to keep an led lit as the battery drains.

D_Hersey · Answer

LEDs are typically excited with currents rather than potentials

shabaz · Answer

You have an unclear (to me anyway) goal, and you've already specified a few tight technical requirements and restrictions.

This makes it hard to suggest any off-the-shelf design that will immediately suit all your requirements and restrictions, hence why people are suggesting you read around the subject of efficient LED lighting circuits, and low voltage lighting circuits.

Generally if you have tightly defined restrictions in some areas (e.g. that specific voltage range) then you're going to need to design and experiment yourself, but you could use some existing web resources for ideas (even if it helps eliminate some ideas or helps you relax some of the tighter restrictions).

By the way, no such thing as a generic 3V LED of almost any color, some colors (including some that you suggested) need a higher voltage than 3V. That difference matters significantly for voltage multiplying/boost type circuits if you're working with such low supply voltages as you suggest.

D_Hersey · Answer

cto http://www.edn.com/design/led/4369638/Light-an-LED-without-wasting-energy

dougw · Answer

The battery can be turned off during daylight with a cadmium sulfide sensor, resistor and a PFET. The LED can be driven from low voltage with an inductive relaxation oscillator, or any oscillator with an inductive flyback output. The circuit plus FET switch takes 2 or 3 transistors.

gihu · Answer

Hi There are many LED ic driver, for different currents, fixed or adjustable, with different topologies buck, boost... depending on input voltage, and how you connect LEDs in the output (single LEDs, or a string of several LEDs). If your power supply has lower voltage than the LEDs in the output, then chose a boost topology. Also, very important to know the current you want through the LED, as D_Hersey suggest, LED are typcally controlled by current. Hope that helps,

pathfider1998 · Answer

Thanks for the info! Below is a slightly more detailed explanation for this project. I need to make a boost converter which outputs high voltage (relative to input voltage, of course) but with low amperes. This circuit is commonly known as "Joule Thief". I need to somehow make it shut off during daytime and work under batteries, which may or may not be rechargeable. (The circuit I am trying to build will have no support for charging, though) Agendas: Make a high-V low-I boost converter, with minimal parts available basically anywhere Make the circuit shut off during daytime and turn on during night No microcontrollers allowed (due to its cost and possible hiccups during programming)

michaelkellett · Answer

Phil, you need to define the problem and then look for solutions that actually solve it. Never rule anything out until you have evidence. Your problem is not that you need an up converter - you want to get a constant current into your LED and that may need more or less volts than the battery. You can't do that with a relaxation oscillator (I can't bring myself to call it a J**** T**** !!). I doubt very much if you can do it starting from 0.7V without using some quite pricey parts (you'll need a bought in boost converter that can start from about 0.5V (to give a working margin from your spec of 0.7V) and then a second switcher to drive the LED efficiently. It may be that someone makes a chip that does all this in one part but I don't know of one. Often you start out with a spec and need to refine it because it has internal conflicts - I think that in your case the 0.7V and the constraints on the type of parts you want to use might be such a conflict - so you'll need to change soothing to get it any further. MK

michaelkellett · Answer

Start here: https://en.wikipedia.org/wiki/Joule_thief Then look at this: www.diodes.com/_files/datasheets/ZXLD381.pdf Not perfect but close to what you want. Here's another: White LED is Powered by One NiMH Cell - LED_and_Light_Circuit - Circuit Diagram - SeekIC.com Google searches used: 'single cell led driver chip' 'joule thief analysis' MK

michaelkellett · Answer

Read some of the articles about how it works - it'll be worth it. It has to be a transformer - otherwise the transistor would stay on all the time. Digikey part number: ZXLD381FHCT-ND Farnell don't sell it, RS do. MK

michaelkellett · Answer

This is not an efficient or cost effective way to light an LED ! But it might be fun to play with if you have the bits to hand. MK