Title: **SST01 R1 and LED Questions**

Post by:**westers** on **January 11, 2016, 09:24:30 PM**

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Hi

What is the purpose of R1 - is it for limiting current inrush?

I have an insulated LED that is rated for 1.7VDC, and a forward current of 20 ma; I am confused on what values to use to work out the resistor value of R2 to allow the LED to operate. (I know V=IR, but I don't know what value of V to use (1.7VDC, or 230 VAC), or what value of I to use.

Thanks

What is the purpose of R1 - is it for limiting current inrush?

I have an insulated LED that is rated for 1.7VDC, and a forward current of 20 ma; I am confused on what values to use to work out the resistor value of R2 to allow the LED to operate. (I know V=IR, but I don't know what value of V to use (1.7VDC, or 230 VAC), or what value of I to use.

Thanks

Title: **Re: SST01 R1 and LED Questions**

Post by:**peranders** on **January 11, 2016, 09:40:16 PM**

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R1, yes

You can estimate the resistor to 1.7V/20 mA = 85 ohm, 82 or 100 ohm maybe-

You can estimate the resistor to 1.7V/20 mA = 85 ohm, 82 or 100 ohm maybe-

Title: **Re: SST01 R1 and LED Questions**

Post by:**westers** on **January 12, 2016, 10:40:48 PM**

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Thanks.

Can you explain the theory behind that - why those values are chosen instead of the supply voltage of the circuit and the 47ma current that is on those rails (from a previous thread). Electronics is not my speciality, however I like to learn, and google doesn't provide answers (it says to use (Vs - Vd) /I, where Vs = supply voltage, Vd= voltage drop, and I = current required. That equation is obviously no use in this context)

Thanks

Can you explain the theory behind that - why those values are chosen instead of the supply voltage of the circuit and the 47ma current that is on those rails (from a previous thread). Electronics is not my speciality, however I like to learn, and google doesn't provide answers (it says to use (Vs - Vd) /I, where Vs = supply voltage, Vd= voltage drop, and I = current required. That equation is obviously no use in this context)

Thanks