I bought LEDs with a built-in chip which make them blink. The type of the LEDs are Kingbright L-56BSRD-B. The complete spec sheet is here.

After reading the spec sheet I do not know if this LED needs a series resistor.

The spec states:

  • With built-in blinking IC.
  • Operation voltage from 3.5V to 14V.

But then it has a row with the forward current:

IF Forward Current, Min:8mA, Typ:22mA, Min:VF=3.5V, Typ:VF=5V

Do I need a series resistor for this LED if I stay in the specified operating voltage range?

  • \$\begingroup\$ Didn't know this was a thing, thanks for enlightening me, so to speak! \$\endgroup\$ – Dan Aug 18 '15 at 18:15

No you don't need a series resistor. On page 3 you see that the current is only rising a little bit depending on the voltage. On normal leds the current almost doesn't depend on the voltage

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  • \$\begingroup\$ A perfect! I absolutely missed this diagram. \$\endgroup\$ – Flovdis Aug 18 '15 at 16:51
  • \$\begingroup\$ I wonder if the chip uses die temperature to control the blinking? Normally a chip with a built-in current-limiting device would have to dissipate more heat than one without, but if the device switches on until it reaches an upper temperature threshold, and then off until it reaches a lower one, the heat dissipation could actually be useful rather than posing a problem. \$\endgroup\$ – supercat Aug 18 '15 at 17:57
  • \$\begingroup\$ @supercat I don't believe they do. Evilmadscientist did some intersting analysis of a "random" flickering LED, and from previous spec sheets I think the regular flashing ones switch the current in a similar way. \$\endgroup\$ – Chris H Aug 18 '15 at 19:07
  • \$\begingroup\$ Temperature dependence would be too slow for switching also on small scale i think it's not enough fast. I think it's a pwm or a step down converter, which generates a smaller voltage (current limiting included of course) \$\endgroup\$ – Sider Aug 18 '15 at 19:35

No, no resistor is required, the chip takes its place.

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