# Does the current in adjustable voltage regulators changes?

I'm looking for voltage regulator which gives an output voltage of 3.5V and output current of 3A. I found one adjustable voltage regulator MIC69301/2/3 which says, it gives 3A output current and support currents of 1A, 1.5A, 3A, 5A with an input voltage range of 1.65V - 5.5V.
Does it mean that giving any current value as input at specified voltage to the voltage regulator, give the fixed output current of 3A and desired output voltage based on the voltage divider circuit at the output.
Does the voltage divider circuit has no affect on the output current?

• Only effect on current is self heating from v drop* I Commented Aug 2, 2017 at 6:33
• You can't control both current and voltage at the same time. That's not how physics works. So, if it's a voltage regulator, it will control the voltage. It will draw as much current as it needs from the input, and it will offer, up to its maximum current, as much current as whatever you connect to its output draws. Commented Aug 2, 2017 at 6:44

This shows a common misconception about regulators. You can't control the current, and voltage at the same time, and this is why:

Think about your regulator like a water valve. The water flow is current, and the pressure is voltage. You can buy a regulator that controls current, or voltage; but either way it's just a "valve" and the most it can do is go all the way open, or all the way closed.

Switching regulators are more complicated, but we won't get into that now. Suffice to say, you can't control output current and voltage with those either.

So back to the "valve". From this analogy, you can see there's a few things your regulator simply cannot do.

• If there's not enough pressure or flow available at the input, the regulator will open up as far as it can, but the target flow or pressure will not be reached. It'll just pass through whatever's available (with some losses due to the valve itself).
• The pressure, and flow at the output are related directly to each other. If you force x gpm of liquid to flow, then the "push back" will by y psi. Your regulator can't do anything about that. It can try to control the flow into the output, or the pressure; but if it's controlling one, the other is being forced to a corresponding value.

Side note: A voltage regulator will also have a current rating. This doesn't mean it controls the current, it just means that if more than that current flows trough it, it will be damaged. You have to make sure that doesn't happen.

• Although it has to be said that voltage regulators usually do control the current, i.e. they have a built-in current-limiting circuit, and they have a thermal shutdown circuit, and thus they don't normally get damaged by a short circuit on the output. Commented Apr 9, 2021 at 21:41

Does it mean that giving any current value as input at specified voltage to the voltage regulator, give the fixed output current of 3A and desired output voltage based on the voltage divider circuit at the output.

No. The regulator will try to keep the output voltage constant at 3.5V, but the output current depends on the load.

The regulator specifies a maximum drop-out voltage of 0.5V, so you have to supply at least 4V at the input.

Remember that you also have to consider the power consumption. Lets assume that you supply the regulator from Vin = 5V:

With Poutmax = 3.5V * 3A = 10.5W

you would require a source that can supply at least

I = 10.5W / 5V = 2.1A

assuming 100% efficiency to get the max rated output power. In reality you would probably require at least 10-20% more.

• Thanks for your time. Can I know what is the use of flag pin. If it is not that to be concerned can I keep it as unconnected ?
– Ari
Commented Aug 2, 2017 at 7:10
• @Mounika: The "error flag" pin is an open collector output. You can leave it unconnected if you do not intend to use it. Otherwise connect a pull-up to Vout, "low" indicates a fault condition.
– Rev
Commented Aug 2, 2017 at 8:04
• Whether the APC pin of MIC69301/2/3 should be given Analog or DC supply?
– Ari
Commented Aug 7, 2017 at 14:24