What Wattage Rating Is Needed for a 33Ohm Resistor in a 9V, 1A Circuit?

[jack476]

that.

The 1A capability of the supply must not be exceeded.

But doesn't the Arduino's board have its own voltage regulators and resistors to keep that from happening?

 

[HeyAwesomePeopl]

But doesn't the Arduino's board have its own voltage regulators and resistors to keep that from happening?

Yeah, it only uses what it needs and it has a maximum. The power supply I ended up using is a 1.5 amp, 12volt power supply, more than enough for everything.

 

[NascentOxygen]

 

[HeyAwesomePeopl]

You just posted the same thing I posted...

 

[NascentOxygen]

You just posted the same thing I posted...

An exact copy. I couldn't improve on perfection.

 

[HeyAwesomePeopl]

An exact copy. I couldn't improve on perfection.

;)
Thanks for all your help guys!

 

[NascentOxygen]

I just noticed your 4.7k base resistors should be lower resistance. They set a base current of less than 1mA.

Consider the yellow LEDs. You have two strings in parallel, each 30 mA, making 60 mA collector current. If the transistor is to function as a switch, you are requiring it to have a current gain (β) of at least 60. It is safest to bank on no more than a β of 10. So each 4.7k should be replaced by 560 Ω.

 

[HeyAwesomePeopl]

I just noticed your 4.7k base resistors should be lower resistance. They set a base current of less than 1mA.

Consider the yellow LEDs. You have two strings in parallel, each 30 mA, making 60 mA collector current. If the transistor is to function as a switch, you are requiring it to have a current gain (β) of at least 60. It is safest to bank on no more than a β of 10. So each 4.7k should be replaced by 560 Ω.

How did you come up with 560 ohms? Why no more than a β of 10? Is there some sort of calculation that says how much current must be put into the base to close the transistor?

Explain what would happen if I used a 4.7K vs if I used a 560 Ohm resistor?

 

[NascentOxygen]

β is not a well-controlled parameter. Typically, a manufacturer may quote a wide range, such as 20 <β< 300. So if you design the base drive for β less than 20, you can be confident of switching any transistor properly. If there is not enough base current, the LEDs won't get the current you intended, and the transistor may overheat.

So, if you need a collector current of 60 mA, I suggest aiming for a base current of around 6 or 7 mA.

base resistor = 4.3v / 6mA