What is an AC Adapter?
AC adapter converts a higher-voltage AC to a lower-voltage DC. Many electronic appliances require constant DC voltage for their operation. The AC adapter is used for charging the batteries of various electronic equipment. There is extensive use of AC adapter for the following equipment.
- Cell phones
- Laptop PC
- and many more electronic appliances
There has been a revolution in AC adapter technology.
The older AC adapter was relatively bulky and the efficiency was quite low because of wastage of energy.
How does AC adapter Work?
The old technology ac adapter has the following parts.
- Rectifier unit
- Electronic Filter
The transformer in the AC adapter is a step-down type transformer that lowers the high voltage AC to low voltage The rectifier converts the step-down AC voltage to DC voltage. Thus, the transformer is used for stepping down the voltage in an adapter.
Types of AC Adapter
There are three types of rectifier units commonly used for ac adapter.
- Half wave Rectifier
- Full wave Rectifier
- SMPS Rectifier
Half-Wave Rectifier adapter
The half-wave rectifier allows the positive half of the ac cycle to pass through the diode and blocks the negative half of the ac cycle. Thus, current flows in the electric circuit are for 10 milliseconds, and for another 10 mill seconds, no current flows through the diode.
Only half of the ac waveform is utilized and the rest half cycle is wasted. As a result, the efficiency of the half-wave rectifier is very low. It is about 40.9 %. Because of ripples in the output voltage, the dc voltage is low. A filter circuit filters out the ac ripples to make the DC voltage more smooth.
Full-Wave Rectifier Adapter
There are two types of full-wave rectifiers.
- Full Wave Bridge Rectifier
- Centre-tap Full Wave Rectifier
In a full-wave rectifier, one diode conducts in a positive half-cycle and the other diode conducts in a negative half cycle. Thus, the DC voltage is available for the full cycle across the load. The power capacity of the full-wave rectifier is more than the half-wave rectifier. The efficiency of the full-wave rectifier is just double the efficiency of the half-wave rectifier. It is because of output DC voltage has fewer ripples. The efficiency of the full-wave rectifier is more than 82 %
The filter circuit filters out the ac components present in the DC components. Thus, by filtering of rectified DC voltage, we get more smooth DC voltage. The capacitor smoothes the DC voltage by providing a low impedance path to ac components. The capacitor has very less capacitive reactance for AC frequency, and the ac components easily pass through the capacitor. Hence, we get smooth DC voltage.
Modern AC adapters– SMPS Based
Switched Mode Power Supply(SMPS) is the latest state of the art technology in the field of rectifiers.
Advantages of AC Adapter
The followings are the advantages of the SMPS power supply.
- More Power delivering capacity
- More Efficient
- Lighter in weight
- Low cost
Applications of AC Adapter
The SMPS power supplies are most popular nowadays, and there is widespread use the SMPS for the following devices.
- Battery Charger
- ESP( Electrostatic precipitator) power supplies