Hi all,
I have a power supply of 12V-7.0A(max)-84W(max). I want to power a circuit which uses a CMOS 4000 IC and I want to limit the current up to 500mA.
Could someone help me on how to do this.
I have already plenty of BC547 npn transistors and resistors if those could be used....

Thank you for help guys!!

 

Hello,

When a circuit is well configured, it will not take more current than it needs.
If the 4000 circuit takes 10 mA, it will take just this 10 mA and not more,
even when the powersupply is capable of much more.

Bertus

 

I wrote this for a somewhat different situation, but it might help you. Please, you can laugh at me, but don't curse.

 

Now why would I believe a poodle that says

'trust me'

But a cool document all the same Bychon

 

Thank you. This is the first time I have allowed that document to go out in public and was quite afraid ppl would think me crazy.

 

Oh, your definitely crazy. But it is a good document for the n00bz!.

I would throw an LED sample formula worked out. For the "I have a 9v battery connected to a LED. Why do they always explode?"
You can use that line if you want, its all yours.

 

I have 2 pages on Watt's Law and 2 pages of examples. I'll see what I can do with "The exploding LED trick".

 

So aris, the answer to your question is, regardless of the AVAILABLE amperage of the power supply, you want a resistor to be sure nothing in the circuit pulls more amps throught the part.

In these cases, you use a 'current limiting resistor'.
Ohms law will tell you how many ohms you need to limit the amperage.

So you want 10mA at 12v.

resistance = voltage divided by amps


12 / .01 = 1200 OHMS
So you want a 1200 ohm resistor or a few resistors in series that equal 1200 ohms to limit the current to 10ma (.01A)

 

So aris, the answer to your question is, regardless of the AVAILABLE amperage of the power supply, you want a resistor to be sure nothing in the circuit pulls more amps throught the part.

In these cases, you use a 'current limiting resistor'.
Ohms law will tell you how many ohms you need to limit the amperage.

So you want 10mA at 12v.

resistance = voltage divided by amps


12 / .01 = 1200 OHMS
So you want a 1200 ohm resistor or a few resistors in series that equal 1200 ohms to limit the current to 10ma (.01A)

Not if you still want 12V when the load is, say, 5mA. You will then need something more sophisticated than a resistor.

 

Not if you still want 12V when the load is, say, 5mA. You will then need something more sophisticated than a resistor.

Ahh, very true, my friend.

You will need a current regulator that will adapt to the changing load and "regulate" the current.

Maybe thats why they named them that.

 

thank you all for you response!!
in my case a simple resistor as retched describes would do for me!!!

Thank all of you once more for your time!!!!!

 

thank you all for you response!!
in my case a simple resistor as retched describes would do for me!!!

Thank all of you once more for your time!!!!!

You may be disappointed.

 

Listen to Ron H. You will probably end up like most of my dates, dissapointed.

Remember, your voltage will sag more when you have a load connected to the resistor. All depending on what your circuit is, it mat be ok. But as voltage changes, so does the resulting current. Ohms law continues regarless of what you want.