PIC18F4520, IrLED want to get high Amps - help with capacitor value

Hi guys,

I am trying here with a project which is more or less an optical smoke detector working with IrLeds. My problem is that I need to send pulse current to the IrLED in order to get a peak pulse of almost 1 Amp and I cannot figure out which capacitor to choose for that case - as a matter of fact I am really confused how one chooses a capacitor at all. I know the formulas and all the theory around but in practice .... Please, give me a hint or share your knowledge with me as I am stuck with that for almost a month.

I am using PIC 18F4520, got a 5V voltage regulator, the IrLED is HE1-220AC, the phototransistor is BPW96. I am also not sure about the 2N2222 transistor that I am using. I would be VERY VERY Grateful for any suggestions!

View attachment 64368

The R9 resistor is just for simulating the IR light. Here I am attaching also the datasheet of the IrLED from Harvatek View attachment 64369

Firstly, to get 1 amp through D1, the resistor R1 will have to be 3R (or less).
The transistor Q8 will have to be a transistor such as BD 679.
The electrolytic C1 will have to be 470u.
The pulse from the micro will have to be just a few milliseconds.

Further to Colins comment you might want to use a low esr 470u cap, a standard one would be ok for a while butyou might find it'll start to get hot due to internal resistance.

You could rob one out of a dead switching supply, they are the tall thin ones.

but you might find it'll start to get hot due to internal resistance.

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How on earth do you work that out when the duty cycle will be only a few percent. The IR LED is about 100mW!!!!!

Check out my PIC IR tutorial, the hardware of which does exactly what you need (your circuit above is completely wrong on various points).