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I see a lot current forward on datasheet, but I don´t know the difference from the "normal" current.

EDIT

On this datasheet (datasheet), I saw a If (current forward) of 100mA and then on page 3 it states about current of 20mA. So, my question was about the difference of this two current.

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    \$\begingroup\$ What do you exactly mean by "normal" current? \$\endgroup\$
    – Vladimir Cravero
    Commented Jul 12, 2014 at 9:14
  • \$\begingroup\$ At the datasheet there is the If current of 100mA, and another current of 20mA \$\endgroup\$
    – Renato Pereira
    Commented Jul 12, 2014 at 16:24
  • \$\begingroup\$ Well provide a link to the datasheet then! I suspect you are referring to average and peak current, but without a specific question or a datasheet answer properly is impossible. \$\endgroup\$
    – Vladimir Cravero
    Commented Jul 12, 2014 at 16:43
  • \$\begingroup\$ Sorry, here is the link: everlight.com/datasheets/IR333_H0_L10_datasheet.pdf \$\endgroup\$
    – Renato Pereira
    Commented Jul 12, 2014 at 16:55
  • \$\begingroup\$ Page 3 uses a specific If as a condition for specifications; it does not describe a required or expected amount. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jul 12, 2014 at 20:44

3 Answers 3

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Forward current (If) of a diode is the maximum safe current you can continuously pass through the device without causing it damage. The circuit is expected to limit the current through the device to this amount if there will be no pauses in the current (100% duty cycle). The parameter exists for IR LEDs, visible LEDs, and normal rectifiers, but the exact amount varies for each family as well as each specific model.

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Forward current is the manufacturers specifications of the maximum allowable current through the diode without damaging it by the use of a current limiting resistor if the voltage is above the diodes voltage rating. To calculate for the size of the current limiting resistor, subtract the diodes voltage (Vled) specification from the source voltage (Vcc) then divide by the forward current (If) or the value that is less than the forward current to get the required LED current limiting resistance value.

For example, for Vcc = 3V, Vled = 2V, If = 100mA = 0.1A, the resistance of the limiting resistor is (3V - 2V)/0.1A = 10 Ohms.

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  • \$\begingroup\$ for consistency with example by user49219 ... solution should read Vcc = 3V, Vled = 2V, and If led = 100mA (3V - 2V)/0.100A = 10Ω \$\endgroup\$
    – lobsterman
    Commented Jun 17, 2016 at 13:00
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I see a lot current forward on datasheet, but I don´t know the difference from the "normal" current.

Those are two terms for the same thing.

To get an LED to emit light, you need to pass forward current through it - the "normal" current as you call it. It is a forward current because it flows in the direction indicated by the "arrow" of the diode symbol.

schematic

simulate this circuit – Schematic created using CircuitLab

Diodes of all kinds can also pass a minuscule reverse current, but that's not the use case you have in mind. The reverse current is an imperfection, but is not useless. It can be used to measure the physical environment the diode is in (temperature, light/radiation levels, etc).

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