Is there any way to turn on the LED in the below figure? You can apply different voltages at the diode input:



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It's not clear what the triangle with the circle is in detail, I suspect it's the output driver of a logic circuit (a microcontroller such as a PIC or AVR ?). If you can get the output of the driver to sink enough current and be at ground (0 Volts), the LED should light up.

If the circle of the output driver is meant to indicate negation, then you would have to set the input to logical 1 to switch the LED on.


The "triangle and circle" is an electronic component called an INVERTER. When an inverter input goes logic high, the output goes logic low, which would turn on the LED under certain conditions.

The inverter used to turn on the LED must have an output of the "open collector" type (see the data sheet), and must be able to SINK sufficient current in order to turn the LED on, typically in the range of 10 - 20 milliamperes.

  • \$\begingroup\$ Correct, except that there is no need for the inverter to be open collector (or open drain). \$\endgroup\$ – Spehro Pefhany Mar 3 '14 at 2:38

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