How does a switching power supply reduce its power output? For example, suppose a CPU ends some task, reducing its power consumption. What happens internal to the computer's power supply to cause it to put out less power?
Electronic – How does a switching power supply reduce its power output
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Related Solutions
It seems I have misinterpreted your question, what you are asking is if you can use only one of the two outputs or if you have to use them simultaneously.
The answer is that you can use any one of the two, or both at the same time without any problem as long as you are withing current specs (up to the max allowed current).
A small voltage drop is normal, can be cause by several factors like the wire resistance or internal psu implementation.
(my original reply below doesn't seem to relate to what was asked)
I would suggest to follow the specifications given without the assumption that when using a single output you can source more current that the manufacturer has specified.
The only place I've seen a combined output consumption effect the maximum current ability is with pc supplies but for the worse.
Here is what I mean, this is the specification of a random pc psu
The 12v secs are:
- 12v1 35A
- 12v2 35A
The total is 12v * 70A = 840W but as you can see the manufactures allows only 648 combined.
Here is another example
The Max specs for:
- 5v/3v are 130W
- 12v1/12v2 are 360W
- -12v/+5v (vsb) are 22W
If you add these you get 512W But the watts given for all of the above combined is just 450W, even the allowed peak consumption is lower than that to just 500W.
The answer to which one you use depends on the application, and the efficiency needs.
For example, you're asked to make a phone charging dock. The dock is powered via a 12 V wallwart, and powers the phone with 5V of power at 500mA. Using a linear regulator, 3.5W is dissipated.That's quite a bit of waste, but you're connected to the mains, and a charging dock is a big enough device, where a properly heat sunk regulator wouldn't cause a lot of heating issues.
On the flip side, suppose you're building a wearable device that operates on a small Li-Po battery, even if you designed a LDO circuit that only wastes about 1W of power, a switching circuit would be more desirable as if designed properly, you could reduce your wastage to <10% that of the linear regulator
Note: Pay attention to the efficiency curves of switching regulators. They normally only have high efficiency for small ranges of current usage, and it helps to understand what current usage your application operates on in different condition to design the most efficient power circuit. Also - laying out swtiching regulators on a PCB can be hit/miss - I've seen a lot of incidents where tiny layout issues can mess with the desired voltage out.
Best Answer
The power supply's job is to maintain a constant voltage. When the CPU "switches off logic", less current is required from the power supply to maintain that voltage. The current demand from the CPU is constantly changing under normal operation, so switching power supplies have feedback mechanisms to adjust the current they produce such that they maintain the correct output voltage. Thus, if the CPU enters a special low power mode, the power supply need not do anything extraordinary. It just does what it always does: maintains the output voltage.