Difference between 1/4W and 1/2W resistors?
 

For a 5V input (USB - LED), should I use 1/4W or 1/2W?

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Difference between 1/4W and 1/2W resistors?
 

On 14/03/2011 09:58, Man-wai Chang wrote:

For a 5V input (USB - LED), should I use 1/4W or 1/2W?

It depends on how current is going to be drawn through them.

Jacquie.

Difference between 1/4W and 1/2W resistors?
 

On 14/03/2011 18:14, Jacquie wrote:
On 14/03/2011 09:58, Man-wai Chang wrote:

For a 5V input (USB - LED), should I use 1/4W or 1/2W?

It depends on how current is going to be drawn through them.

I only knew V=IR. How do I apply this principle to this W spec?

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Difference between 1/4W and 1/2W resistors?
 

For a 5V input (USB - LED), should I use 1/4W or 1/2W?

It depends on how current is going to be drawn through them.

I only knew V=IR. How do I apply this principle to this W spec?

And Power (W) =VI

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Difference between 1/4W and 1/2W resistors?
 

On Mon, 14 Mar 2011 18:34:25 +0800, Man-wai Chang rearranged some
electrons to say:

On 14/03/2011 18:14, Jacquie wrote:
On 14/03/2011 09:58, Man-wai Chang wrote:

For a 5V input (USB - LED), should I use 1/4W or 1/2W?

It depends on how current is going to be drawn through them.

I only knew V=IR. How do I apply this principle to this W spec?

P = VI

If the LED drops 2V (typical) then you have to size the resistor value to
also drop the same difference at the current you want to run the LED at.
Let's say, 20ma..

5V - 2V LED = 3V resistor.
3V/20ma = 150 ohms.

20ma * 3V = 60mW so a 250mW resistor is sufficient in this case. You
have to substitute the voltage drop and desired current for the LED that
you want to use.

Difference between 1/4W and 1/2W resistors?
 

20ma * 3V = 60mW so a 250mW resistor is sufficient in this case. You
have to substitute the voltage drop and desired current for the LED that
you want to use.

What if I used a 1/2W resistor instead of a 1/4W (250mW?)? Would it
reduce the current too much?

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Difference between 1/4W and 1/2W resistors?
 

On 14/03/2011 11:52, Man-wai Chang wrote:
20ma * 3V = 60mW so a 250mW resistor is sufficient in this case. You
have to substitute the voltage drop and desired current for the LED that
you want to use.

What if I used a 1/2W resistor instead of a 1/4W (250mW?)? Would it
reduce the current too much?


It's only the resistance value of the resistor and the load that
determines the current drawn, not the wattage of the resistor.

Jacquie.

Difference between 1/4W and 1/2W resistors?
 

It's only the resistance value of the resistor and the load that
determines the current drawn, not the wattage of the resistor.

Then why are resistors (in that shop at least) classified resistors by W?

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Difference between 1/4W and 1/2W resistors?
 

On 14/03/2011 16:06, Man-wai Chang wrote:
It's only the resistance value of the resistor and the load that
determines the current drawn, not the wattage of the resistor.

Then why are resistors (in that shop at least) classified resistors by W?


So you can choose the correct wattage for it's intended use.

Jacquie.

Difference between 1/4W and 1/2W resistors?
 

So you can choose the correct wattage for it's intended use.

Let me review your replies first. :)

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