Answer is in manufacturer datasheet for particular LED product.
Voltage for white LED is usually in range 3,4V-4V but this means nothing in comparison with manufacturer datasheet.
Each LED have product ID with lots of parameters including max forward voltage, max current, angle,....
Make tests. Try to test diode on 3,4V at two currents 25mA and 35mA. If you notice that led heating then apply lower current ratings for that LED.
Every manufacturer specifies related technical details on the pack or pouch of every LED. In case you have an unknown LED, you may test it with the tester posted in other thread of yours. Hope you are opening multiple threads with same topics..
LED test explanation :
1. Set power source to 3,4V
2. Connect LED
3. Measure current with ampermeter
1. Set power source to 5V
2. Use resistor to limit current for LED forward voltage 3,4V first try 25mA then 35mA
3. Monitor heating of LED body and legs. If LED heats up then use lower current ratings for that LED.
1)25 mA=5 V/(R_led+R)
2)35 mA=5 V/(R_led+R)The value of resistance that is chosen to limit the current supplied to the LED is dependent on the resistance of the LED that you are using which is determined by using the Ohms Law(V=I*R).You know the values of V(drop in the LED ) and the current drawn (from measurement).Apply the law, and you can arrive at the value of the resistance of the LED.Now to limit the current to say 25 mA,the resistor R(for denoting this unknown resistance) is added along with the resistance of the LED(R_led) as they are connected in series and the formula now is,
Then proceed with the steps 2 and 3 to determine the correct rating suitable for the LED.Code:1)25 mA=5 V/(R_led+R) 2)35 mA=5 V/(R_led+R)
You should NEVER apply a voltage source to an LED (3.4V and 5V were said) since nothing will limit the current.
An LED does not have a resistance since it is a diode. The value of the resistor is determined by (V-power supply - VLED (that you do not know) / the current that you also do not know.
Most 3mm and 5mm diameter LEDs are spec'd with a current of 20mA. Many LEDs have a maximum allowed current of 30mA.ok got it but why we are assuming 25mA ? It could be more or less depending on type i guess ?
To measure the forward voltage connect a 330 ohm resistor in series with an LED then measure the voltage across the LED. Red LEDs are about 2.0V, dim old green LEDs are about 2.2V, new very bright green LEDs, blue and white LEDs are about 3.3V.Too sir would you please tell me the very practical step say where to connect & to measure quantities by meter etc etc ??
Simply buy name-brand parts that have a detailed datasheet.then how to know that unknown quantities as per your idea ?
Most 3mm and 5mm diameter LEDs are spec'd with a current of 20mA. Many LEDs have a maximum allowed current of 30mA.
To measure the forward voltage connect a 330 ohm resistor in series with an LED then measure the voltage across the LED. Red LEDs are about 2.0V, dim old green LEDs are about 2.2V, new very bright green LEDs, blue and white LEDs are about 3.3V.
Simply buy name-brand parts that have a detailed datasheet.
Sorry, I forgot to say to use a new 9V alkaline battery. The 330 ohm resistor in series with an LED will limit the current to about 21mA for a red one and to about 17mA for a bright green, blue or white one.you said 330 ohms resistor in series but with what voltage level ?????????
Sorry, I forgot to say to use a new 9V alkaline battery. The 330 ohm resistor in series with an LED will limit the current to about 21mA for a red one and to about 17mA for a bright green, blue or white one.
A red LED could have a voltage from 1.7V to about 2.3V and the other colors can be from 3V to 4V.
When you know the actual voltage of your LEDs then you can calculate a certain current and resistor value.
Because a 9V alkaline battery is modern, has a long shelf life and has fairly good capacity.okk well why you said alkaline battery ?
Because a 9V alkaline battery is modern, has a long shelf life and has fairly good capacity.
Maybe you want to use an old carbon-zinc or "Super Heavy Duty" 9V battery designed 60 years ago with a short shelf life and very low capacity?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?