tutorials:learn:powersupply:index.html
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tutorials:learn:powersupply:index.html [2010/10/25 21:40] ladyada |
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| Here is the power supply that is used in many apple products: | Here is the power supply that is used in many apple products: | ||
| - | {{:private:m8943.jpg|}} | + | {{ :tutorials:learn:powersupply:m8943.jpg?nolink |}} |
| Here is a classic 'wall wart' that comes with many consumer electronics: | Here is a classic 'wall wart' that comes with many consumer electronics: | ||
| - | {{http://www.ladyada.net/images/metertutorial/wart_t.jpg}} | + | {{ http://www.ladyada.net/images/metertutorial/wart_t.jpg?nolink }} |
| This is a massive power supply that's in a PC, usually you dont see this unless you open up the PC and look inside for the big metal box | This is a massive power supply that's in a PC, usually you dont see this unless you open up the PC and look inside for the big metal box | ||
| - | {{:private:pcsupply.jpg?500|}} | + | {{ :tutorials:learn:powersupply:pcsupply.jpg?nolink&500 |}} |
| All these power supplies have one thing in common - they take high voltage 120V or 220V AC power and **regulate** or **convert** it down to say 12V or 5V DC. This is important because the electronics inside of a computer, or cell phone, or video game console dont run at 120V and they don't run on AC power! | All these power supplies have one thing in common - they take high voltage 120V or 220V AC power and **regulate** or **convert** it down to say 12V or 5V DC. This is important because the electronics inside of a computer, or cell phone, or video game console dont run at 120V and they don't run on AC power! | ||
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| ====== AC/DC ===== | ====== AC/DC ===== | ||
| - | {{:tutorials:learn:powersupply:acdc.png?350|}} | + | {{ :tutorials:learn:powersupply:acdc.png?nolink&350 |}} |
| So the power coming out of your wall is high voltage AC but microcontrollers and servos and sensors all want low voltage DC. How shall we make it work? Converting between AC power and DC power requires different techniques depending on what the input and output is. We'll refer to this table | So the power coming out of your wall is high voltage AC but microcontrollers and servos and sensors all want low voltage DC. How shall we make it work? Converting between AC power and DC power requires different techniques depending on what the input and output is. We'll refer to this table | ||
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| | High Voltage AC (eg. 120V-220VAC) | Low voltage AC (eg. 12VAC) | Transformer | Really cheap, electrically isolated | Really big & heavy! | Small motors, in cheaper power supplies before the regulator | | | High Voltage AC (eg. 120V-220VAC) | Low voltage AC (eg. 12VAC) | Transformer | Really cheap, electrically isolated | Really big & heavy! | Small motors, in cheaper power supplies before the regulator | | ||
| | Low Voltage AC (eg. 20VAC) | High voltage AC (eg ~120VAC) | Transformer | Same as above, but the transformer is flipped around | Really big & heavy! | Some kinds of inverters, EL wire or flash bulb drivers | | | Low Voltage AC (eg. 20VAC) | High voltage AC (eg ~120VAC) | Transformer | Same as above, but the transformer is flipped around | Really big & heavy! | Some kinds of inverters, EL wire or flash bulb drivers | | ||
| - | | " | " | AC 'voltage doubler' | Uses some diodes and capacitors, very cheap | Not isolated! Low power output | | | ||
| | High Voltage AC (eg. 120V-220VAC) | High voltage DC (eg. 170VDC) | Half or full wave rectifier | Very inexpensive (just a diode or two) | Not isolated | We've seen these in tube amps | | | High Voltage AC (eg. 120V-220VAC) | High voltage DC (eg. 170VDC) | Half or full wave rectifier | Very inexpensive (just a diode or two) | Not isolated | We've seen these in tube amps | | ||
| | Low Voltage AC (eg. 20VAC) | Low voltage DC (eg 5VDC) | Half or full wave rectifier | Very inexpensive (just a diode or two) | Not isolated | Practically all consumer electronics that have transformer-based supplies | | | Low Voltage AC (eg. 20VAC) | Low voltage DC (eg 5VDC) | Half or full wave rectifier | Very inexpensive (just a diode or two) | Not isolated | Practically all consumer electronics that have transformer-based supplies | | ||
| | High Voltage AC (eg. 120V-220VAC) | Low voltage DC (eg 5VDC) | Transformer & rectifier \\ Combination of High->Low AC & Low AC->Low DC | Fairly inexpensive | Kinda heavy, output is not precise, efficiency is so-so | Every chunky wall-wart contains this | | | High Voltage AC (eg. 120V-220VAC) | Low voltage DC (eg 5VDC) | Transformer & rectifier \\ Combination of High->Low AC & Low AC->Low DC | Fairly inexpensive | Kinda heavy, output is not precise, efficiency is so-so | Every chunky wall-wart contains this | | ||
| - | | High Voltage AC (eg. 120V-220VAC) | Low voltage DC (eg 5VDC) | Switching supply | Light-weight, output is often precise | Expensive! | Every slimmer wall-wart contains this | | + | | High Voltage AC (eg. 120V-220VAC) | Low voltage DC (eg 5VDC) | Switching supply | Light-weight, output is often precise | Expensive! | Every slimmer wall-wart contains this | |
| Basically, to convert from AC to AC we tend to use a transformer. To convert from AC to DC we use a transformer + diodes (rectifier) or a switching supply. The former is inexpensive (but not very precise) and the later is expensive (but precise). Guess which one you're more likely to find in a cheaply-made device? :) | Basically, to convert from AC to AC we tend to use a transformer. To convert from AC to DC we use a transformer + diodes (rectifier) or a switching supply. The former is inexpensive (but not very precise) and the later is expensive (but precise). Guess which one you're more likely to find in a cheaply-made device? :) | ||
| - | ====== The good old days! ====== | + | We left a few types out of this table because they're a little more esoteric or complex, such as the AC voltage doubler. These are still used but you're a little less likely to see them and they don't get used in power supplies you're likely to encounter |
| - | {{:tutorials:learn:powersupply:xformtop_t.jpg}} | + | ====== Step by step converters ====== |
| - | Back a couple decades ago, the popular way to build a power supply was to get a big chunky 120VAC/12VAC transformer. We aren't going to get into the heavy detail of the electromagnetic theory behind transformers except to say that they are made of two coils of wire around a chunk of iron. If the number of coils are the same on both sides then the AC voltage is the same on both sides. If one side has twice the coils, it has twice the voltage. They can be used 'backwards' or 'forwards'! For more detailed information, check out the wikipedia page | + | To understand converters, its best to go through their design step by step. Let's start at the top with: |
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| - | {{:tutorials:learn:powersupply:xformpri_t.jpg|}} | + | |
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| - | To use it, one half would get wired up to the wall (the 'primary' 'high side') | + | |
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| - | {{:tutorials:learn:powersupply:xformsec_t.jpg|}} | + | |
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| - | and the other half would output 12V AC (the 'secondary' 'low side'). The transformer functioned in two ways: one it took the dangerous high voltage and **transformed** it to a much safer low voltage, second it **isolated** the two sides. That made it even safer because there was no way for the hot line to show up in your electronics and possibly electrocute you. | + | |
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| - | We'll use a schematic symbol to indicate a transformer, its two coils inside which are drawn out, the schematic symbol will have the same number of coils on either side so use common sense and any schematic indicators to help you out in figuring which is primary and which is secondary! | + | |
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| - | <schematic symbol> | + | |
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| - | Now that the voltage was at a non-electrocutey level of around 12VAC it could be converted into DC. The easiest and cheapest way to convert AC to DC is to use a single diode. A diode is a simple electronic 'valve' - it only lets current flow one way. Since AC voltage cycles from positive to negative and we only want positive, we can connect it up so that the circuit only receives the **positive half** of the AC cycle. | + | |
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| - | {{http://www.ladyada.net/images/parts/1n4001.jpg?350}} | + | |
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| - | The output is then chopped in half so that the voltage only goes positive | + | |
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| - | This will convert | + | |
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| - | {{:tutorials:learn:powersupply:ac.png?500|}} | + | |
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| - | {{:tutorials:learn:powersupply:halfwave.png?500|}} | + | |
| + | * [[http://www.ladyada.net/learn/powersupply/transformeracdc.html|Part 1. The Transformer-based AC/DC power supply]] | ||
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