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Can you power an LED with 5 volts?
No, you cannot safely power an LED with 5V without a resistor. The resistor is absolutely 100% required. The resistor isn’t put there purely on a whim, it’s required to set the current based on the supply voltage minus the LED forward voltage and the resistance of the resistor.
Do LEDs have a threshold voltage?
When the voltage difference across the LED exceeds the threshold voltage of the LED , current flows through the LED and light is emitted. If the LED voltage is less than the threshold voltage, no current flows and no light is emitted.
What kind of current does a led need to turn on?
The LED goes from zero to fully on over a range of something like 80 mV. Zener diode D1 biases the input so that the turn on takes place at around 5V. Note that only about 150 microamps of current are required across R1 to develop 0.7V across Q2’s EB junction.
How do I make a transistor turn on at a certain voltage?
So, increasing the base resistor (R2) will make the transistor turn on at higher voltage than 1.5V). If you want the LED to turn on when the voltage is below 1.5V *that is, invert what it is now) then you can do it like this: Now when the transistor turns on, it shorts out the LED so the LED goes dark.
How to power a circuit of LEDs with maximum 5V?
If you make 20 mA flow at 13 V then at 5 V the LED will still work but at a lower brightness. For that 20 mA you need a 500 ohm resistor. 500 ohm resistors are hard to find so get some 560 ohm resistors (that’s close enough) and use one resistor in series with one LED. Simple but works flawlessly.
How does a meter turn on a led?
I do not require the input has the same power source as the meter. To narrow the voltage range over which the LED turns on, you can use a transistor in order to create voltage gain, to drive a second transistor which drives the current into the LED. Results from simulation, where the input ramps from 0V to 8V over the period of a second: