CAD Amps, voltage, no batteries?

[Prismseed]

I'm using an app on my phone, Every Circuit to learn about circuits. I'm able to set voltage and current sources but I can't find a battery option. Is this a lacking program, or is there a reasoning for it?

 

[Mikebits]

Try using the voltage source as shown on the website. https://everycircuit.com/

 

[Mikebits]

I started thinking that maybe I did not give enough info for you to understand. The voltage source I speak of should look similar to the symbol found in Spice programs such as LTSpice. See image below:

You should be able to use the voltage source, just like you would a battery. I just realized the app also works with IOS, so if your stuck I may give the app a download and should be able to assist you. Let me know if that helps. umkay?

 

[Prismseed]

I can set the voltage, but I can't adjust the amperage. If I add an amperage source in series it cuts the voltage.

 

[strantor]

I can set the voltage, but I can't adjust the amperage. If I add an amperage source in series it cuts the voltage.

the amperage will depend on what's in your circuit. Any circuit will only draw the amps it needs, no more. if you use a current source set for 1A and a load resistor of 10ohm, there will be 10V across it as ohm's law dictates. Even if you want it to have 100V across it, that won't happen, because that would be more than 1A.

 

[Prismseed]

Any circuit will only draw the amps it needs, no more.

LED is an exception to this isn't it?

 

[Mikebits]

LED is an exception to this isn't it?

I think I might see your confusion. When driving multiple LED's, it is often desirable to use a constant current source so you do not need individual current limit resistors for each LED. A constant current source can be used to supply the desired current for each LED, let us say in this case 5 mA per LED. Refer to attached figure below, which I just threw together to illustrate what I mean, in fact this would be a good circuit for you to build on your app to see what I am talking about. This is not the best type of current source, but it is a good one in learning about constant current sources. If you build this circuit in your app, you will notice that as you switch in and out the LEDS, that the current remains near 6.5 mA, also note that collector voltage is changing, as this is a constant current, so ohms law dictates, that for current to remain constant, then voltage must be changing.
So my challenge to you is to construct this circuit in your nifty little app, and see what you learn from it. Let us know. P.S. I did this circuit in Multisim Blue Premium edition.
Also use any transistor you like, the 2n2222 would be a good choice.

 

[strantor]

LED is an exception to this isn't it?

It's not an exception to the rule but it could arguably be an exception to the way I worded the rule. I said "Any circuit will only draw the amps it needs, no more."

Consider a circuit consisting of a car battery and a copper bar. The copper bar is a resistor, whose resistance is something like 0.00001 ohms. Ohms law says 12V across incredibly low resistance equals incredibly high current. And Ohms law is right; we place the copper bar across the battery terminals and scary noises, flying sparks, intense heat, and possibly flying shrapnel make the proof clear. This circuit consisting of only a copper bar, demands ("needs," as I put it earlier ) quite a lot of current, and the battery does its best to deliver only the 1.2 million amps demanded, and not one amp more..

Now replace that copper bar with a 1Mohm resistor. Ohms law says that only 12 micro amps will flow.

Now replace that resistor with an LED. LEDs don't have a fixed resistance; they have a fixed voltage drop. Lets say you have an LED rated 1.4V/20mA. You apply 12V, current flows and the LED drops 1.4v, and 10.6v is left over. The current of That 10.6v is not limited by any resistance except that of the wire. So the current will be like 10.6v/0.01 ohms =1,060A. So the circuit "demands" (earlier worded as "needs") over 1,000A, and that current will flow through the LED for a very brief moment until it burns out. This led should have a resistor in series with it so limit the current through it.

So the perfect voltage source will always supply however much current the circuit demands, up to infinity (direct short ), whether that is how much current you to flow or not (like as in "ah crap, I didn't want 1000A flowing thru my LED. I forgot the resistor.")

 

[Mikebits]

So the perfect voltage source will always supply however much current the circuit demands, up to infinity (direct short ), whether that is how much current you to flow or not (like as in "ah crap, I didn't want 1000A flowing thru my LED. I forgot the resistor.")

You discovered the governments secret weapon, a 1000A LED