Linear Power VS Switching Power Supplies

!: Linear Power VS Switching Power Supplies

Choosing a power supply is one of the most important steps when building a customized computer. Since the building of customized computers have risen in popularity due largely to the gaming community as well as computer enthusiasts, it is important to understand how to choose a power supply for the ensuing stroke of genius that is created as a portal to the Internet. Without the heartbeat of electricity, and a steady stream that can handle the power built into a custom computer, even the best designed customized computers fall into the land of permanent rest.

Linear and switching power supplies are options as well as the uninterrupted power supply variety. The choice comes down to what you need for your particular computer and the amount of voltage necessary to run your new source of pride and joy.

Linear power supply is seldom the answer for customized computer. These types of energy supply require very large transformers and are extremely heavy. Unless you are a body building champion with a need to prove yourself, linear power is probably not what you want at approximately one pound per ampere. Add to that the necessity of large heat sinks to dissipate energy loss and an efficiency of about 50%, linear power options are simply too cumbersome and inefficient to meet the needs of most home computer building purposes.

Most enthusiasts choose something in the switching power supplies category since they want a computer-not a weight lifting championship. There is higher production costs involved, but these options are lighter weight and smaller-meaning they will fit in your house. Another advantage is that these power supplies are about 70-90% efficient. Since the efficient running of your computer is generally the goal, this increase in efficiency has a big pull for power supply choice.

While this sounds confusing, it really isn't. Switching power supplies use AC voltage-120V or 220V-which is generally what a house is equipped to handle anyway. There isn't any sophisticated equipment that you have to have wired into your house for its use. The main difference in the power supply needed comes in choosing the power factor correction and not in changing your plugs and house wiring to be able to use a switching power supply.

You may, however, have to increase your breaker capacity if you already have too much depending upon them when you plug your newest creation in, but that is to be expected with anything you add that uses the electrical circuits available in the average home. Another necessity is protecting your computer from power surges with a properly designed surge protector. Otherwise, there isn't much you have to do to prepare for your power supply choice.

If you are still confused, simply call up your local computer store and ask. Many of the employees in the stores can help you decide and find what you need. Always consider asking a professional computer tech who has experiencing in networking and other hardware areas of computers for the added security of getting the correct information and helpful recommendations that can make your experience with powering your computer an enjoyable one.

Linear Power VS Switching Power Supplies

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Switching, Regulated, Or Transformers? Choosing the Right Power Supply

!: Switching, Regulated, Or Transformers? Choosing the Right Power Supply

I received another message from Dan, this time asking about power supplies:

Subject: Frustrated with power converters

So, the past month or 2 I've been trying to figure out how different types of AC to DC power supplies work, since i have a few audio/video receivers that im trying to install PC fans inside that require that type of power.

The problem is that I don't have any power converters that are less than 18 volt DC. I've been researching capacitors, different types of diodes and ways to hook them up but I cant seem to lower the voltage. I've tried a few different ways to hook a resistor up to it and sometimes the resistor starts smoking or doesn't change much of anything. im just really annoyed with spending many hours on this simple project. I'd hate to ask you to explain multiple electronic parts since you're probably very busy so instead could you give me a short answer to this?

I've been to over 50 Google websites and cant find anything on YouTube that I understand.

So it sounds like Dan has a situation where AC to DC has been converted, but he DC is too high to use with a 12V fan. The quickest solution is to find an AC fan (they do exist, but they can be noisy, and overkill for this kind of situation). So instead let's look at the alternatives.

Let's say that Dan has 18V coming from the power supply and he needs 12V to drive a quiet PC fan.

Voltage Regulators

Where you require a large amount of current, using a resistor/potential divider is not always the best idea, as the current levels causing heating/smoking - and that's usually a bad thing. An alternative is to use a voltage regulator - this does the same thing, dissipates the excess voltage as heat, but does it in a more controlled way and lets you attach a heat sink to it. You need to work out the current required by the motor driving the fan, then multiply this by the voltage drop. So if you are trying to drop 18v to 12v and your fan needs 1/4 amp - this would be (18-12) * 1/4 = 1.5 Watts. (Watts being power and equal to volts x amps). The hookup is simple - 3 legs: input voltage, gnd and output voltage.

So your regulator is going to operate like a 1.5Watt heater, and if you don't have enough heat sinking attached it will may overheat and go into thermal shutdown.

(Like the 5V regulator did on my original laser harp design)

So if the power dissipated is not that high, the cheapest solution would be to use the regulator.

Switching Convertors

A better, more efficient method is to use a "Switching" power supply. These take the input voltage (18V) and turn it on and off very quickly (thousands of times per second). The amount of time the voltage is on, compared to the amount of time it is off is called the "duty cycle". So if I wanted to convert 18V to 12V I would need a duty cycle of 2/3. This is then fed through a network to smooth it back out to DC. I recently built some efficient DC converters for a robotics project. It was important to make them switching as they would not drain the battery as much as a regulated power supply.

AC to DC

If Dan wants to tap just the AC power then this has to be regulated and stepped down first. The old school way of doing this is to use a transformer with windings that get you close (but slightly above) the voltage you want. Eg - 110V to 16V would be a good step down. Then the 16V AC is fed into a full wave rectifier array of diodes that do full wave rectification, and then finally through 2-3 large capacitors to smooth the voltage down to something usable.

It's worth pointing out that you can get switching power supply units that run off AC directly. The AC has to rectified and smoothed first, but then the full 110V is switched on and off to generate the voltage you require. The beauty of these units is that they can run on either 110V or 220V unmodified, the circuitry just monitors the output and adjusts the duty cycle of the switching to deal with whatever input voltage you pass in.

Probably the best thing for Dan to do is check out electronic surplus websites and pick up a 12V or 5V switching "wall wart" and then install this inside the case. They are small, efficient, and sometime go on sale for a dollar or two.

Switching, Regulated, Or Transformers? Choosing the Right Power Supply

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