AC to DC Converters
AC to DC Converters are one of the most important elements in power electronics. This is because there are a lot of real-life applications that are based on these conversions. The electrical circuits that transform alternating current (AC) input into direct current (DC) output are known as AC-DC converters. They are used in power electronic applications where the power input a 50 Hz or 60 Hz sine-wave AC voltage that requires power conversion for a DC output.
The process of conversion of AC current to dc current is known as rectification. The rectifier converts the AC supply into the DC supply at the load end connection. Similarly, transformers are normally used to adjust the AC source to reduce the voltage level to have a better operation range for DC supply.
Concept of Alternating current (AC) & Direct current (DC)
Alternating Current
In alternating current, the current changes direction and flows forward and backward. The current whose direction changes periodically is called an alternating current (AC). It has non-zero frequency. It is produced by AC generator, dynamo, etc.
Direct Current
In direct current, the current doesn’t change its magnitude and polarity. If the current always flows in the same direction in a conductor then it is called direct current. It has zero frequency. It is produced by cells, battery, DC generator etc.
Simple Steps to change AC into DC
Now us discuss about AC to DC converter. Let us consider frequently used converter in the power supply circuit, 230V AC to 5V DC converter.
1. Stepping down the Voltage Levels
Sometimes voltages need to be increased while sending power to long distances. Similarly, voltages need to be decreased for equipment that uses the lower power. The step-up transformers are being used for stepping up the voltage levels and step-down transformers are being used for stepping down the voltage levels.
Consider a transformer with 12V Output. The 230V AC power supply is converted into 12V AC by using step down transformer. RMS value and its peak value can be given by the product of the square root of two and RMS value and is approximately equal to 17V which is the output of the step-down transformer.
2. AC to DC Power Converter Circuit
The rectifier converts the AC supply into the DC supply at the load end connection. There are different types of rectifiers, such as half-wave, full-wave, and bridge rectifiers.
Full Bridge rectifier which consists of four diodes are connected in the form of a bridge. The diode conducts only in one direction, i.e during forward bias. It remains in an off state in another direction, i.e. during reverse bias.
In the above circuit, during the positive half cycle, the diodes D2 & D4 conducts. And during the negative half cycle of the power supply, diodes D1 & D3 conducts. Thus, in this way input AC power is rectified into output DC power. But the problem is DC output power consists of pulses and is not pure DC.
3. Obtaining Pure DC Waveform
We need to convert the pulsating DC to pure DC. To do that, most of the circuit uses a Capacitors. The capacitor is used to store energy while the input voltage is increasing from zero to its peak value. The energy from the capacitor can be discharged while the input voltage is decreasing from its peak value to zero.
Thus, In this way, we can convert the pulsating DC into pure DC using this charging & discharging process of the capacitor.
4. Regulating Fixed DC Voltage
In order to fix the output voltage to the fixed desired value, we finally use the voltage regulator IC. The DC voltage regulators IC comes with the name 78XX. The last two digits XX-represents the output voltage value. For example, to limit the output voltage to 5V, we use the 7805 Voltage Regulator IC. And to limit the voltage to 9V, we use a 7809 Voltage regulator IC.
Applications
The AC to DC Converters are used in almost all electronics and electrical devices. They are used as power supply circuits for Household applications like vacuum cleaners, washing machines, refrigerators, electric rice cookers. For daily life, usable products like computers, televisions, cell phone chargers, etc AC-to-DC Converters play a very important role.
Most of the electronics sensors and modules only operate on DC supply and hence they use AC to DC Converters. They are also used in medical equipment, factory automation, building automation, process control systems, signage displays & telecommunication.
The other applications of AC to DC Converters are in renewable energy management, test & measuring equipment, defense, aerospace, and transportation systems.
