120V to 12V Transformer Applications

Electricity is an essential service in every household, factory, and business premises. Today’s world depends so much on electrically powered devices that life seems to come to a standstill when an outage occurs. The power system starts with a generator and ends with a gadget that consumes electricity to function. Between generation and consumption is a complex power system. While you may not be interested in the generation, transmission, and distribution of power, you sure do need to know the power you are supplied with by a utility service provider. This will allow you to match supplied power and device power ratings. One of these key parameters is voltage and to convert alternating current voltage magnitude a transformer is used. The post will specifically dig deeper into 120v to 12v transformer.


There are two main single-phase voltage levels provided to consumers by utility companies worldwide. One is 120 volts that are commonly associated with the United States and 240 volts commonly associated with Britain. There are however many equipment manufactured to consume power at 12 volts ac or dc. To lower 120v to 12v a transformer is engaged, when dc power is needed a rectifier is further engaged. A single-phase step-down transformer with a turn’s ratio of primary versus secondary being 12:1 is used. It’s among low voltage transformers and power electronic equipment and computer-related devices.

Construction and Operation

Construction of the transformer comprise of 4 main parts;

  • Winding- there are two windings that are electrically not into contact. A winding is usually thinly insulated copper wires rolled into a specific number of turns on a core. The winding that receives input power is referred to as primary while the one that outputs power is referred to as secondary.
  • The core- this is a material that enhances magnetic linkage between the windings. It holds the windings in place and prevents any chance of them coming into contact. The core is made of laminated iron and is a poor conductor of electricity.
  • Primary terminal – this is a pair of connection points at the ends of the primary winding where input conductors are connected to the power supply.
  • Output terminals – the two ends of secondary winding form the terminal that is connected to supply power to the device.

The transformer may have an outer case that covers it depending on its insulation needs. The operation is based on Faraday’s electromagnetic induction. The energized primary winding induces an electromotive force on the secondary winding hence a voltage appears across the terminals. The voltage depends on the primary voltage and turns ratio. It’s prudent to point out at this juncture that there is a saturation point of magnetic flux that induces a secondary voltage. This serves as a safety and protection function as no matter the primary voltage, there is a fixed upper limit of secondary terminals. No machine is perfect like a transformer. There are eddy current losses in the core and a humming sound that accounts for losses. Care should be taken not to scratch or tear any part of the winding as the thin insulation will be destroyed and a short circuit faulty occur. This fault is fatal as it can cause the fire to ignite, for this reason, they ought to be protected against overcurrent.

Applications of 120v to 12v transformer

There is quite a wide range of application of 120v to 12v transformer in manufacturing of electrical gadgets. Some of them are highlighted below.

  • Power adapters- these are used to condition power from the utility supply before it gets to the device. A transformer is the first component to receive power, lowers it to 12V. This may then be supplied to load, rectified to direct current voltage, or further lowered using voltage divider circuits.
  • Electronics devises power supply inside most electronics devices sits a transformer that lowers the voltage to a level required by equipment parts. Most computer-based gadgets consume around 5-12 volts dc.
  • Battery chargers- most batteries are rated 12 volts, to charge it from a utility supply, the charger utilizes a transformer to step down the voltage before rectification is done.
  • Lighting- Led and halogen light bulbs use 12Volts, this requires a voltage transformer from 120V supply.


The uses and advantages of the device cannot be overestimated. The lower voltage the better for working with both end-user and service technicians. The electrical isolation of high voltage primary circuit and low voltage secondary circuit offers protection of delicate components from power surges not to mention the user’s and technician’s safety. A word of caution, never do anything you are in doubt or don’t have adequate knowledge of with electricity, it kills. Yes, even the 12 volts can kill. Always hire a licensed electrical worker. Bravo.

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