Sorry for the triviality of my question.
1. Is it correct that a circuit or device can take any power input as long as the voltage matches? For example, say a flashlight takes one AAA battery at 1.5v. Can I theoretically wire up four D size batteries that are in parallel? This still yields 1.5v yet will last many times longer.
2. If Yes to the first question, does that dictate the title of the device as being "passive" or is that the incorrect term?

I'm a beginner hence again apologize for such a beginner question. I thank so who contribute preemptively.

 

Most circuits are designed to operate at a specific voltage. When given that voltage they will draw the current (and hence power) they need and no more.

That is why the can plug an LED night light that takes maybe 1 Watt into the same outlet as a toaster takes that takes 1000 Watts or more.

Supplying a larger battery to such a circuit does not supply more power to the device. It supplies more capacity, i.e. it lasts longer.

There are circuits that need a specific current rather than a voltage. An LED is an example. But LEDs are generally built in to a circuit that delivers that current at a specific voltage or range of voltages.

A counter example to this is some cheap LED flashlights that rely on the fact that the battery can only supply so much current. A larger battery at the same voltage might very well blow them out.

 

Sorry for the triviality of my question.
1. Is it correct that a circuit or device can take any power input as long as the voltage matches? For example, say a flashlight takes one AAA battery at 1.5v. Can I theoretically wire up four D size batteries that are in parallel? This still yields 1.5v yet will last many times longer.
2. If Yes to the first question, does that dictate the title of the device as being "passive" or is that the incorrect term?

I'm a beginner hence again apologize for such a beginner question. I thank so who contribute preemptively.

You need to be careful about talking about "circuit" as a generic catchall. There are actually relatively few things that can be said that apply to each and every circuit.

For your example circuit, you are correct, but even here a caveat applies. There are flashlight circuits, such as the really-cheap giveaway button flashlights you might find on a key ring, that rely on the internal resistance of the battery, typically a coin cell, to limit the current to the LED. If you were to replace that with a "better" battery of the same voltage, it could destroy the LED in very short order.

Passive is a very different meaning in electronics. The general distinction between active and passive components is whether or not the component can use an external power source to amplify or modify a signal, while passive components modify signals without any external power (only the power present in the signal itself).

 

Welcome to AAC.

In a nutshell, the amount of power (measured in Watts (W)) that will be dissipated but a load is described by Ohm‘s Law.

Ohm’s Law as three terms:

• Voltage (V or E, measured in volts (V))
• Current (I, measured in amps or amperes (A))
• Resistance (R, measured in ohms (Ω))

The formula states: \( \mathsf{I = {V\over R}} \), that is, I (current in amps) is directly proportional to V (voltage in volts), and inversely proportional to R (resistance in ohms). When a load (something being powered) behaves according to this formula it is called “ohmic”. Most loads being fed direct current (DC) fall into this category—but not all.

The load is the primary source of resistance in the circuit. The power source and wires will have some resistance but it is safe to ignore for this discussion. Assuming your power source is not current limited, that is, it can produce sufficient current to satisfy Ohm’s Law for a given set of known values, then the resistance of the load and the voltage applied will determine the current that flows in the circuit.

This is why devices have a rated voltage. That voltage will provide enough, but not too much current to power the device safely. When current flows through a resistance it generates heat. If the voltage is excessive, the heat of the excess current will destroy the device.

Power, in Watts is simple to calculate. The formula is \( \mathsf{P = {V\times A}} \), where P is power in Watts (W), while V and A are the voltage and current as above. As you can see power is directly proportional to either term, and W is directly interchangeable with heat and work being done.

A device powered with the correct voltage will only draw as much current as it “needs”. So you can safely use as many cells in parallel to make your battery since the voltage will remain the same, and the current will not change. Only the capacity of the battery will increase.

Concerning “passive”, no—it is unrelated to this topic. Passive components are things like resistors, capacitiors, and the like while active components are things like transistors. The distinction being that such components amplify or switch, and can increase the energy at their outputs.

 

I have to mention this because I'm anal.

Batteries do not actually supply "power" they supply "energy"

Energy is defined as "the ability to do work"

Power is always a local thing produced where the work is being done.

When a battery has no load, it has no "power" power cannot be stored, but energy can be.

You can ignore everything I just said because there is no way anybody is going to start referring to power supplies as "energy" supplies.

 

there is no way anybody is going to start referring to power supplies as "energy" supplies

True, because there is nothing wrong with the term "power supply", as they do supply power to a load, and do not store any significant "energy".

 

Power supplies do not supply power...power never comes out of a "power supply".

 

Power supplies do not supply power...power never comes out of a "power supply".

Did I say it did?

 

Yes, you did say it.

" they do supply power to a load "

Power is always produced at the load, it doesn't come from the supply.

 

Power supplies do not supply power...power never comes out of a "power supply".

Yeah. That is why they are rated in Watts.

 

The wattage rating of a supply is the amount of power in can produce...not how much can come out of the supply.

 

Sorry for the triviality of my question.

No problem. We do newbs here.

As you can see, you have kicked off a small pedantic flurry. Don't worry about it, they just pop up from time to time. I suggest you check the thread in another 10-15 posts to see if anyone actually answered your questions.

ak

 

Yes, you did say it.

" they do supply power to a load "

Okay to continue this little exercise in pedanticry:
So what is incorrect about that statement?
Are you saying they don't provide power to a load?

 

Okay to continue this little exercise in pedanticry:
So what is incorrect about that statement?
Are you saying they don't provide power to a load?

Yes, that is exactly what I'm trying to say.

Power is always "produced" in the load, it does not come from the supply.

Power is defined as "work over time", work is always done where it is done...it doesn't come from somewhere else.

Energy does work at the load and "produces" power at the load.

 

Power is always "produced" in the load, it does not come from the supply.

That is a distinction without a difference.
It the power generated in the load does not come from the supply then where does it come from?

 

1. Is it correct that a circuit or device can take any power input as long as the voltage matches? For example, say a flashlight takes one AAA battery at 1.5v. Can I theoretically wire up four D size batteries that are in parallel? This still yields 1.5v yet will last many times longer.

You picked one of the cases where it could matter. Flashlights don't usually take 1 AAA battery. They're more likely to use 2 or 3 because 1.5V isn't a high enough voltage for white LEDs.

In the case of cheap LED flashlights, it could matter because most don't follow conservative design practices and put LEDs in parallel without resistors for each parallel string. They don't care if LEDs burn out. They're hoping you'll buy another. I have half a dozen with more than half of the LEDs not working. Most of them were free and, while I would like them to work longer, they didn't cost me much. Some of the newer ones only have 1 LED. Haven't had any long enough to know how long they'll last.

Take the case of LEDs connected directly to CR2032 batteries. Those batteries can't burn out LEDs because they have so little capacity. If you took the same LEDs and connected them to a 3V source that could supply amps of current, the LEDs would likely burn out.

For your AAA replaced with D, the lower internal resistance of D could be a problem.

 

That is a distinction without a difference.
It the power generated in the load does not come from the supply then where does it come from?

/ Starts banging head on table.

What part of power is "produced" at the load do you not understand? That is where the power comes from.

The supply provides the energy to do work and that work becomes "power" at the load.

 

Starts banging head on table.

Really?
Please don't hurt yourself.

What part of power is "produced" at the load do you not understand? That is where the power comes from.

Continuing with the pedantics:
No, that's now were the power "comes from".
Power isn't "produced" at the load, it is dissipated by the load.
That's not where the power comes from.
The source that provides the power that is dissipated is the supply, hence its name.

 

Power is produced and the resulting heat is dissipated.

 

Here... I will give you the chance to have the last word, all you have to do is explain exactly how the power gets from the supply to the load.