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LED requirements to glow

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srija

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I am connecting a 5Volts from the battery to the Red LED. This LED actually needs 2.2V and 20mA. The battery is producing 1A current. does this LED bear that much amount of current??????
 

Add a 100Ohm or 220Ohm resistor in series with the LED so as to protect it. You can select the value of the resistor according to the LED's degree of intensity you wish.
 

thanking u very much

---------- Post added at 10:47 ---------- Previous post was at 10:37 ----------

I am trying for a simple circuit using a LED,Switch and power source(+5V & 1A). I need to glow the LED whenever the switch is pressed. I am using SPST push type switch. My circuit design is like I am connecting the +5V to one end of the SPST and the other diagonal end of SPST switch to the Anode terminal of the LED. The cathode terminal of the LED is Connected to the ground of the Power source. The LED needs 2.2volts and 20mA current.
My question is, is there any need of other components mainly resistor???
Because i don't know how much current and voltage the SPST switch passes when i press it. If it passes more than the Requirement of LED, then if i place resistor before the LED wont that resistor reduces the current??? because the supply is 1A, how that 1A is getting reduced?
My last question why the series connection of elements have same current throughout the closed loop?
I am very sorry if my question is confusing...........Thanking you in advance
 

The current is not being reduced, current is only drawn as needed. The purpose of the resistor is to limit the amount of current drawn from the power source, otherwise unlimited power will be drawn because it is effectively a short circuit between power and ground.

A series circuit has to have the same current throughout, it's only the voltage which changes.
 

The LED is just another diode. The voltage and current are exponentially related. That means even a small change in voltage might cause a drastic change in current. So you must limit the current flowing through it using an appropriate resistor. For more info refer the following link. Light Emitting Diodes (LEDs)
 

With that much current, your LED may burn out and battery will be drain more quickly and your circuit might get hot (waste of energy). Put a current limiting resistor of 120-160 ohms.
The 1 Ampere rating on your power supply is just shows on what is the maximum current that the power supply can provide.
 
Last edited:

srija said:
thanking u very much

---------- Post added at 10:47 ---------- Previous post was at 10:37 ----------

I am trying for a simple circuit using a LED,Switch and power source(+5V & 1A). I need to glow the LED whenever the switch is pressed. I am using SPST push type switch. My circuit design is like I am connecting the +5V to one end of the SPST and the other diagonal end of SPST switch to the Anode terminal of the LED. The cathode terminal of the LED is Connected to the ground of the Power source. The LED needs 2.2volts and 20mA current.
My question is, is there any need of other components mainly resistor???
Because i don't know how much current and voltage the SPST switch passes when i press it. If it passes more than the Requirement of LED, then if i place resistor before the LED wont that resistor reduces the current??? because the supply is 1A, how that 1A is getting reduced?
My last question why the series connection of elements have same current throughout the closed loop?
I am very sorry if my question is confusing...........Thanking you in advance
Click to expand...

A power supply (+5V & 1A) means that it delivers +5V but about the current it can supply from 0A up to 1A. The current will be determined by the load. For example if you connect 1K to the power supply the supply current will be 5V/1K = 5mA only, for 100 Ohm it will be 50mA ... and so on.
Now let us assume that we need just 20mA for the LED. Since the LED voltage is about 2.2V then the limiting resistor in series with the LED should be:
R = (5 - 2.2) / 20mA = 0.140 Kohm
So we can use 150 Ohm (the current will be a bit less than 20mA)
Please note that the contact of the SPST could be assumed having a resistance close to zero.
So your LED circuit branch will be formed by the supply +5V, red LED, 150R resistor, SPST contact and ground (supply negative terminal). Since all are in series, their places could be exchanged (that is, it doesn't matter if the resistor is before or after the LED for example).

Kerim
 

You can put a series capacitor of lower value (0.1ufd)so that switching ON the SPST gives a short current pulse for LED to flash.
The 5VDC/1Amp supply & contact can be checked out ..saving the LED too..
 

As every body said better to put resistor in series for current control and have your SPST switch in series....But to get the controlled intensity what you can do is use a POT configuration either in series or a voltage devide configuration where voltage accross the LED can be controlled will help you really better...to get the desired intensity...Kindly please note you need to chose the proper POT values for getting the current supply as you said your led is 2.2v and 20ma the resistance of LED become more than 1k thus you need probabaly more than 10k pot in cae to get controlled intensity
 

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