3V LED Pulse Circuit

Question

I am trying to make a very compact and lightweight circuit that will cause an IR LED to blink on and off at a constant rate, preferably at least once per second but the flashes can be more spaced out. Due to weight constraints, I would like to use a 3V coin battery to power the circuit. The battery doesn't need to last a long time because it can be easily replaced. I have looked online at LED pulse circuits but I haven't been able to find any that work at 3V. Does anyone know of a way to either reduce the voltage of some pulse circuits by reducing the resistance or a way to make a low resistance pulse circuit? Thank you very much in advance!

Here's a link to one design I have looked at http://www.instructables.com/id/How-to-Make-an-Led-Pulse-Circuit/

Answer 1

Not boost converter nor Op Amps, but low RdsOn CMOS Logic Relaxation Oscillator with a Schmitt Trigger.

but DON'T use a HC14 , it has too high an output ESR @3V and use 10M 0.1uF for 0.5s ramp ( due to 1/3Vdd= Va=1V not ~60%=T)

BOM

• Single inverter CMOS SMD https://www.fairchildsemi.com/datasheets/NC/NC7SV14.pdf < 3.3V >20mA

• 10MOhm feedback R and >0.1 uF low leakage cap to ground on input for <1Hz

• Panasonic 2032 Coil cell Lithium 300mAh 3.0V http://ca.mouser.com/ProductDetail/Panasonic-Battery/BR-2032-F2N/?qs=sGAEpiMZZMtEV04R3uo8FkXjBlacmoUJ1qGWoW%2fSZ8M%3d

• Series Cap to IR LED Pair 330uF low ESR,45 mOhms, 4V Tanatlaum http://ca.mouser.com/ProductDetail/AVX/TPSD337K004R0045/?qs=sGAEpiMZZMtZ1n0r9vR22dzXiwOw%252bhWCeYXuhE8EaaA%3d

• 2032 Coin cell holder

• AWG30 magnet wire for hookup (burn thru insulation with solder)

• IR LEDs ( your choice ) mine is Vishay Sharp types 5mm.

• Kapton tape for insulation.

This should last a few days.

Answer 2

Here's another answer. Same type of oscillator as Tony Stewart's but I assume you want very short ON pulses (like a flash) every second or so.

This is accomplished by using steering diodes D1 and D2 to route the charge and discharge current through different resistors so that the duty-cycle can be easily adjusted by the value of R1 and R2. Because R2 is 100x R1, the on time is 1/100 or 1% of the period.

You can use a chip like TI SN74LVC2G14. It can run as low as 1.65 Volts. At 3 Volts, it can drive 24 mA per inverter. By using two in parallel, you can drive 48 mA. You would, of course, need to add a series resistor to the out pin and then your IR LED.

http://www.ti.com/product/SN74LVC2G14

Answer 3

An astable multivibrator like this should work.

^{simulate this circuit – Schematic created using CircuitLab}

Note R2 parallel with the LED this makes the voltage swing on Q4 collector sufficient to drive Q3

Answer 4

The circuit link used by you is purely resistive and very much power hungry. You can use a low power version of 555 timer in astable mode to make 3v or lower voltage LED pulse circuit. TLC555, LMC55, TPL5010 are low power version of timer IC. Apart from being low power you'll be able to get power efficiency and longer battery life.

Refer this circuit for operating the circuit in astable (square wave) mode. Only difference will be using low power version of 555 time IC. You can change the pulse period by changing the value of R1.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 5

You can use this circuit below. Take note your allowable current is 50mA, IR LED must be low forward voltage type since you're only using 3V. The mosfet must also be low signal voltage type: https://www.vishay.com/docs/71172/si1032r.pdf

^{simulate this circuit – Schematic created using CircuitLab}

In the beginning when 3V supply is not available, both M1 and M2 gate are 0V. When 3V3 is available, M2 will turn on first as surge current flow is higher in R3 as compare to R6. D2 will then light up. (DC current will not go thru C2, instantaneous current will.)

M2 close will discharge C1 and the R1 + R2 circuit have to start charge up to 1.5V again (at M1 gate). When the voltage reaches suitable VGS of M1, M1 will close and causes M2 VGS to go low; causing M2 to open. D1 will then light up and D2 off.

You may play around R1, R2, C1, R4, R5 and C2 for the timings. If only 1 LED is needed, replace them (R3 + D1) with a suitable bigger resistor.