Power Supplies

In choosing a power supply, you may be faced with choosing between a wall mount and desktop power supply. Each one has its share of pros and cons and choosing the right power supply will depend on your needs and preferences.

 

Wall Mount Power Supply

power supplies

 

A Few Basics

Wall mount power supplies have many names including AC adapters, wall bumps, wall adapters, wall warts, wall plug transformers, linear wall mount, power cubes.  Regardless of the name, these power supplies are the most common source of low voltage power. They consist of small plastic boxes that plug directly into the wall but they come in a variety of performance and quality levels.

 

The wall mount power supply is a space-saving option because you only need to plug one end into the wall and the other into your device. It also saves time and energy.

 

These PS can be either:

  • AC or DC
  • Regulated or unregulated
    • Regulated power supplies have voltage regulators on their output. The regulator ensures the output voltage will always stay at the rated value of the power supply, regardless of the current that the device is consuming.
    • Unregulated power supplies produce a certain voltage at a particular current. That is, unregulated power supplies provide a constant amount of power (voltage x current). The output voltage will decrease as the output current increases, and vice versa requiring that one match as closely as possible the voltage and current requirements of the device the power supply is powering.
  • Linear or switching Power Supplies
    • The Linear power supply converts high voltage AC into the low voltage using a transformer and then converts it into DC voltage.  It has low efficiency, is bulkier more reliable and faster than switching mode power supply (SMPS), there is no RF interference and is immune to noise and electromagnetic interference. This type of power supply is used in audio frequency applications and RF applications.
    • The SMPS converts the input signal into DC first then it steps down the voltage up to the desired level. It has high efficiency, voltage regulation is done by the feedback circuit, is less bulky in comparison to a linear power supply, has a slower response time, RF shielding is required as switching produces more RF interference, EMI filters are required since noise and electromagnetic interference is significant.  This type of power supply is used in chargers of mobile phones, DC motors etc.

 

Voltage

In choosing the correct wall mounted power supply you need to know what type of voltage your device needs: AC or DC. You should also look for a recommended charging current listed on the device you are powering. A further choice is whether the power supply is regulated or unregulated and whether it is a linear power supply or switching mode power supply.

 

The particular voltage requirements of the device are usually found written on the device itself.  It is important to know the correct voltage requirement since providing either lower or higher voltages than required could have significant, deleterious effects

 

In the best of circumstance, if one uses a device with a lower voltage than specified, the device will not operate correctly in an obvious and immediate way. At other times the device might seem to be working correctly only to later fail under a particular circumstance.  In other words, when you stray from the required specs, unexpected bad things may occur.  Some devices can be damaged by too low a voltage for extended periods of time. If, for example, the device has a motor, it may not be able to develop enough torque to turn and just idles generating heat.  It is also possible the device draws more current to compensate for the lower voltage.  This higher than the intended current can cause damage to the device.

 

Using higher than specified voltage also can have significant consequences since electrical components all have voltages above which they fail.

 

 

Current Rating

The load is determined by the device. That is, a device that uses 2 A of current will draw 2 A of current whether the power supply can only provide the 2 A, or whether it could supply 3, 5, or any other A. The current rating of a supply is what it can deliver, not what it will always force through the load. As opposed to a voltage where higher than or lower voltage than needed can damage the device, the current rating of power supply must be at least what the device wants but there is no harm in it being higher.

 

Replacing Existing Supply

When replacing a previous power supply, consider that power supply’s rating to be the device’s requirements. For example, if the device does not have a visible label but the device was powered from a 9 V and 1 A supply, you can replace it with a 9 V- and 1 or more-amp power supply.

 

Matching output connector and device’s plug socket

Choosing the right wall-mount power supply requires that the DC output connector matches your device’s plug socket This is a difficult specification to find on many of these power supplies since often the inner diameter of the plug/connector differs by only .4 mm. One can try calipers but this can be tricky to do accurately. You can buy one of a given diameter and then purchase an Adapter (2.1 to 2.5, or 2.5 to 2.1) 797 in case you buy the wrong one:

power supply - socket

 

Desktop Power Supply

When one needs a power supply that provides more power than a wall adapter, the desktop power supply is the choice.

 

Desktop power supplies are very similar to wall adapters in that they both plug directly into the wall outlet and into the device. Desktop power supplies are able to provide more power than wall adapters, and also typically have a wider range of features and also more agency approvals. Desktop power supplies usually have 2 components: the actual supply with a DC cord attached, and the AC power cord. A desktop power supply may or may not come with an AC power cord. It is available in three standard sizes—2-prong standard cord, 3-prong standard cord, and a 3 Prong Mickey Mouse style cord (flat or round cord).

 

As with wall mount power supplies, the most important thing to assess is what type of DC connector the device will need. DC output connectors include 2.1mm or 2.5 mm inner diameter x 5.5mm outer diameter female, 3.5mm male, 4-pin, 5-pin, and 6-pin DIN male; and also, stripped and tinned wires.

 

Having chosen the correct connector one needs to choose the corresponding voltage and current outputs that match the specs of the device just as one did in choosing the wall adapter. The specifications should be listed on the actual device for which you are providing a power supply.

 

Applications of Power Supplies:

Power supplies are an elemental component of most electronic devices and are used in widespread applications.

 

Here are some of the applications:

  • Medical:  Power supplies for medical devices require multiple levels of certification depending on the proximity of the power supply and the patient. Examples of medical devices are ventilators, infusion pumps, surgical and dental instruments, imaging, intraarterial scopes, and devices.
  • Computers:  The power supply converts the alternating current (AC) line from the home to the direct current (DC) needed by the personal computer
  • Electric Vehicles: A power supply unit is part of the necessary design to convert high voltage vehicle battery power.
  • Machining: 
  • Industrial Automation/Robotics:  refers to conveyors, assembly lines, bar code readers, cameras, motors, pumps, semi fab manufacturing
  • Power supplies for Railway Signals
  • Security power supplies
  • Traffic Light Control Systems

 

Jasper Electronics (located in Anaheim, CA) provides a multitude of power supplies from wall mount to traffic control to medical devices. Please visit their website at www.jasperelectronics.com for further details on the many power supplies they provide.  We invite you to call us at Peninsula Technical Sales where our highly technical staff can answer all your questions on how to choose the correct power supply. By phone reach us at 650-965-2233, by E-mail reach us at  sales@pentech.com or visit our website at www.pentech.com.

 

 

 


Peninsula Technical Sales represents electronic equipment manufacturers and is proud to offer our services online and to the following cities and their surrounding areas: San Francisco, Santa Clara, San Jose, Fremont, Sacramento, Milpitas, and Santa Rosa.