AC to DC adapters
AC to DC adapters accept AC input voltage directly from a wall outlet, and output DC voltage. The primary configurations are wall-mount, where the adapter unit plugs directly into a wall and the DC lead then goes to the DC device, and desk mount, where the adapter unit is in-line between the AC plug and the DC output. Many DC devices use this type of adapter or power supply such as household items, printers, low-voltage DC boards, etc.
How does an AC/DC adapter work?
An AC/DC adapter is made up of a central unit which draws power from an AC outlet, it then converts the power to DC that is used to charge the device. Each AC adapter has a specific power rating, measured in volts or watts that it can handle and the output of a device. Because of the power rating and the type of plug on the end, an AC adapter is not universal and can only be used with devices with the same requirements and connector.
Nominal AC Input Choices
Nominal AC input choices for AC/DC adapters include:
- 115 VAC
- 230 VAC
- 115/230 VAC selectable
- VAC wide-ranging or auto-select
- 220 VAC European
- 100 VAC Japan
Common DC output choices for AD/DC adapters include:
- +5V, -5V
- +12V, -12V
- +15V, -15V
- +24V, -24V
- +48V, –48V
AC/DC adapters may be capable of more than one output. Many AC/DC adapters have a rating of the nominal total DC power supplied. Input plug styles, or AC pin (blade) type for AC/DC adapters can be two conductors or three conductors.
Two-conductor types include two round pin style, American flat pins, German round pin, etc. Three-conductor types include three-pin UK style, American flat pin / grounded, three round pins, etc. The international pin or blade style for two and three conductor plug types. The shape, size and configuration vary.
Output connectors can be DIN plug type, Mini DIN type, bayonet nut coupling (BNC), and thread nut coupling connectors (TNC).
- DIN 41612is widely accepted as a standard for interconnect applications in the telecommunications and data markets worldwide.
- Mini DINtypes include three, four, five, six, seven and eight pin Mini-DIN styles.
- A Bayonet Nut Couplingis a connector with bayonet-style couplings used for jacks on instrument front panels.
- A Threaded Nut CouplingConnector is an input / output electronic interconnect device similar to a BNC connector but with threaded couplings.
Condition. When present, it is most usually found on the primary output.
Overcurrent protection is internal circuitry that limits or shuts down the current output in an overcurrent condition.
Short circuit protection includes techniques to protect the power supply in the event of a short circuit on the load may include electronic current limiting and thermal resets with automatic recovery. An important environmental parameter to consider when specifying AC/DC adapters includes operating temperature.
If the manufacturer was smart enough (or compelled by law) to include the DC output on the label, you are in luck. Look at the “brick” part of the adapter for the word OUTPUT. Here, you’ll see the volts followed by the direct current symbol and then the current.
The DC symbol looks like this:
To check the polarity, look for a + or – sign next to the voltage. Or, look for a diagram showing the polarity. It will usually consist of three circles, with a plus or minus on either side and a solid circle or C in the middle. If the + sign is on the right, then the adapter has positive polarity:
If there is a – sign on the right, then it has negative polarity:
Next, you want to look at your device for the DC input. You’ll usually see at least the voltage near the DC plug receptacle. But you also want to make sure the current matches, too.
You might find both the voltage and the current elsewhere on the device, on the bottom or inside a battery compartment cover or in the manual. Again, look for the polarity, by either noting a + or – symbol or the polarity diagram.
Remember: the input of the device should be the same as the output of the adapter. This includes polarity. If the device has a DC input of +12V / 5.4A, get an adapter that has a DC output of +12V / 5.4A. If you have a universal adapter, make sure it has the proper current rating and that you choose the correct voltage and polarity.
Fudging It: What Happens if You Use the Wrong Adapter?
Ideally, you’ll have the same voltage, current, and polarity on your adapter and device.
But what if you accidentally (or purposefully) use the wrong adapter? In some cases, the plug won’t fit. But there are many instances where an incompatible power adapter will plug into your device. Here’s what you can expect in each scenario:
Wrong polarity – If you reverse the polarity, a few things can happen. If you’re lucky, nothing will happen, and no damage will occur. If you are unlucky, your device will be damaged. There’s a middle ground, too. Some laptops and other devices include polarity protection, which is essentially a fuse that burns out if you use the wrong polarity. If this happens, you might hear a pop and see smoke. But the device may still work on battery power. However, your DC input will be toast. To fix this, either replace the polarity protection fuse or get it serviced. The good news is that the main circuitry wasn’t fried.
- Voltage too low – If the voltage on an adapter is lower than the device, but the current is the same, then the device may work, albeit erratically. If we think back to our analogy of voltage being water pressure, then it would mean that the device has “low blood pressure.” The effect of low voltage depends on the complexity of the device. A speaker, for example, may be okay, but it just won’t get as loud. More sophisticated devices will falter, and may even shut themselves off when they detect an under-voltage condition. Usually, an under-voltage condition won’t cause damage or shorten the life of your device.
- Voltage too high– If the adapter has a higher voltage, but the current is the same, then the device will likely shut itself off when it detects an overvoltage. If it doesn’t, then it may run hotter than normal, which can shorten the life of the device or cause immediate damage.
- Current too high – If the adapter has the correct voltage, but the current is greater than what the device input requires, then you shouldn’t see any problems. For example, if you have a laptop that calls for a 19V / 5A DC input, but you use a 19V / 8A DC adapter, your laptop will still get the 19V voltage it requires, but it will only draw 5A of current. As far as current goes, the device calls the shots, and the adapter will have to do less work.
- Current too Low – If the adapter has the correct voltage, but the adapter’s rated current is lower than what the device input, then a few things might happen. The device could power on, and just draw more current from the adapter than it’s designed for. This could cause the adapter to overheat or fail. Or, the device may power on, but the adapter may not be able to keep up, causing the voltage to drop (see voltage too lowabove). For laptops running on undercurrent adapters, you might see the battery charge, but the laptop is not powering on, or it may run on power, but the battery won’t charge. Bottom-line: it’s a bad idea to use a lower current rating adapter since it could cause excess heat.
AC–DC converters are used in computers, televisions, cell phone chargers, and other electronic consumer devices. They are also used in medical, military, and telecommunications equipment; kitchen appliances; industrial machinery; and commercial products that use DC motors.