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how to generate infra red for a 100m range

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Re: how to generate infra red for 100m range

kkk sir following above discussions its better to make repeaters & boosters but actually what i want is simply transmission of IR beam from a low cost L.E.D to a low cost photodiode with a high gain sensitivity unit so as to grab rays from a long distant range . Well i succeded with a 15 m range & the transmitting L.E.D. uses a power of less than 1.2 volts from a button cell only not more than that & its able to trigger the sensor unit which costs only 30 /- approx , now i ve to move for 100 m , thanks to all
 

Re: how to generate infra red for 100m range

a button cell has too high an ESR to be lower than the ESR of the IR LED so you cannot use that effectively for driving the IR LED to its max of say 100mA or 150mA depending on device.
If the button battery had a superior cap or low ESR capacitor beside to sustain the voltage over the pulse interval with an 1 ohm load which approximate sthe ESR of the IR LED at 150mA.

If using 50kHz pulse carriers at 20uS. Normally RC time constant is taken as the 1/e asymptote or 63% of full scale > If you expect the decay amount to be low such as 5% of the battery voltage then the RC time constant must be 63/5=12.6 x T
If T of a single pulse is 20uS and R=1 Ohm the 63% decay value of C = T/R = 20uS/1ohm = 20 uF but for 5% regulation you need ~ 250uF then the voltage decays 5% after each successive pulse in acumulative fashion. the the T duration is the actual message duration * duty cycle.. So you can see the capacitor needs will get very large.

An Alkaline battery is required capable of producing >> 1A pulses on short circuit.or << 1 Ohm ESR. There is proof to support my statement that the power source ESR must be much less than the load ESR if regulation is required.

In the audio industry it is called dampening Factor. DF=Rl/Rs
In the power suplpy industry it is called "load regulation" of ESR of load / ESR of source for a given currrent step current.

Consider a simple case if the Battery ESR was 1 Ohm and the IR LED is a perfect Zener with a 1OHm resistor. then when the battery is applied the voltage will drop exactly 50% between the Battery and LED threshold voltage , which is 1.2 for IR LEDs
IR LEDs are often rated at 1.5V because the 0.3V additonal voltage is from a 150mA pulse or 0.3V/0.15A= 2 Ohm ESR ( ballpark range of ESR) for 5mm LEDs

side note.... White HB 5mm LEds are around 10~15 ohm ESR with a threshold of 2.6 and std rating 3.2 ~3.4 typ. +/- 0.2
 
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