Choosing the right AC/DC adaptor

When you buy a new piece of electronic equipment such as a cordless telephone, digital camera, camcorder, laptop or other household appliances, they often come supplied with an AC/DC adaptor to power them. These adaptors have generally been designed for use with the piece of equipment often with the manufacturers name on it. These adaptors are often manufactured directly for the product so once manufacture of the product ceases the adaptor will also become unavailable.

The majority of electronic devices run using similar voltage and current ratings meaning that it is often the case that Universal adaptors can be used as a replacement adaptor in the event of failure. This page has been produced to highlight what you need to know in order to select the right adaptor for your product.

There are four things you need to know to replace your AC/DC Adaptor:

1 - Input Voltage
2 - Output Voltage and Current
3 – Adaptor Type
4 - Output Polarity and Output plug size

1 – Input Voltage

The input voltage of the adaptor will indicate if it is suitable for Worldwide or UK use only.

Input Voltage rated at:
240V AC – Indicates UK use only
100-240V AC – Indicates worldwide use possible; a number of the power supplies we stock come with a range of primary input plugs so you do not need to buy separate plug socket adaptors.

2 – Output voltage and current

Probably the most important specifications of an adaptor are the Output Voltage and Output Current.

The Output voltage of the power supply must match that of the input voltage of you appliance; it cannot be under as the power supply will not be able to provide enough power to the device. If it is over then the appliance could be damaged by due to the excess power being forced into the appliance. There is however a tolerance on the output voltage of power supplies, generally in the region of 10% either way of the rated voltage; this means that the voltage settings on the power supply may not have to exactly match that of the input voltage of the equipment.

E.g.          Input voltage of device – 3.3V, use 3V setting as this will give up to 3.3V
                Input voltage of device – 11V, use 12V setting and this will give down to                 10.8V

NOTE: If you are going to set the adaptor to a higher voltage than that specified on the device ensure that you are using a regulated adaptor (see section 3) and that you are only setting the voltage at 10% or less than the specified input voltage.

The Output Current rating if the power supply must be equal or greater than the input current rating of the appliance to be powered. The appliance needs to be able to draw the amount of current rated in order to run so the output current must be at least equal to that. If the adaptor has a greater output current is not a problem, the device will run fine as long as it is a regulated power supply (see section 3 below), the device will only draw the current it needs from the power supply and the extra output will not be forced into the application.

3 – Adaptor Type

There are many different types of adaptor available but they can be categorised into three main types:

• Linear Unregulated, features include:
  • These are the cheapest form of adaptor.
  • They convert the AC mains power into DC output via a transformer, the output voltage is unregulated which means that the output may not match up completely to that rated on the supply so these adaptors can only be used on appliances whose input are not sensitive or have regulated circuitry fitted to them.
  • Low EMF (Electromagnetic Field) radiation and so do not effect other sensitive electrical equipment and can be used in environments where low EMFs is needed.
  • Quite large and heavy construction.
  • Can only be used in the UK (or one specified voltage region).

• Linear Regulated, features include:
  • More expensive than the unregulated type.
  • Same technology as the unregulated type but with regulated circuitry fitted so the output voltage is stable and will be that rated on the supply. This is the best type of power supply for sensitive applications.
  • Low EMF (Electromagnetic Field) radiation as with Linear Unregulated.
  • Same size and weight as unregulated type.
  • Can only be used in the UK (or one specified voltage region).

• Switch Mode features include:
  • Generally the most expensive of the three types of power supply.
  • Converts AC mains power to DC regulated power using a high frequency switch with a varying duty cycle to maintain the output voltage. This type of technology is improving but us not yet as stable as linear power supplies, and voltage spikes can appear at the output so care needs to be taken when using sensitive equipment.
  • High EMF (Electromagnetic Field) radiation compared with linear power supplies.
  • Much smaller and lighter than linear power supplies.
  • Only technology which enables the power supply to function world-wide (i.e. input voltage of 100-240V AC).

4 - Output Polarity and Output plug size

Output Polarity relates to the area of the output plug which is positive and which is negative, the way to determine the polarity of your adaptor is to look for a symbol like the one below:

This symbol indicates that the centre of the plug is positive and the outside of the plug is negative. The position of these symbols indicates the polarity so if they are reversed then the position of the positive and negative are also reversed. It is important to get the polarity of your equipment and that of the adaptor to match otherwise your equipment will not work and may be damaged. Many Universal Adaptors come with output plugs with polarity changeover, so you can adjust the polarity to match your equipment.

The range of output plugs that come supplied with Universal adaptors will depend on the manufacturer of the adaptor. Most come with 6 or 8 plugs which are designed to fit most household applications. We supply power supplies manufactured by Ansmann and Uniross, the list below indicates the plug sizes that come supplied with their adaptors.

Ansmann products

Adaptors with the product code beginning with AP are Ansmann product and come supplied with 8 output connectors:

S: Hollowplug - 0.75mm x 2.35mm x 10mm
J: Hollowplug - 1.75mm x 4.75mm x10mm
H: Hollowplug - 1.35mm x3.5mm x10mm
I: Hollowplug - 1.7mm x 4mm x10mm
D: Hollowplug - 2.1mm x 5mm x 12mm
G: Hollowplug - 2.5mm x 5mm x 12mm
A: Jackplug - 2.5mm x 13mm
B: Jack plug - 3.5mm x 15mm

Uniross Products

Uniross products come with different sets of output connectors for the different adaptors in their range, the various connectors available are summarised below.

UNI303RCS and UNI505RCS,
Measurements: Internal Diameter x External Diameter x Length
Black: Male plug - 3.5mm x 13mm
Yellow: 0.75mm x 2.35mm x 11mm
Black: 1.35mm x 3.5mm x 10.5mm
Yellow: 1.7mm x 4.0mm x 9.5mm
Blue: 2.1mm x 5.0mm x 11.5mm
Black: 2.5mm x 5.5mm x 11.5mm

AD101704, AD100942, AD101708
Measurements: Internal Diameter x External Diameter x Length
Red: 2.5mm 5.5mm x 12.0mm
Yellow: 2.1mm x 5.5mm x 12.0mm
Yellow: 0.7mm x 2.35mm x 10.0mm
Blue: 1.4mm x 3.5mm x 10.0mm
Yellow: 1.7mm x 4.0mm 9.5mm
Yellow: 1.75mm x 4.75mm x 9.5mm

If you need help with a product, application or using our web:
Call us on: 0191 427 4577 we are always please to help you.