Steps to Convert the 230V AC to 5V DC using Step Down Converter Every electrical and electronic device that we use in our day-to-day life will require a power supply. In general, we use an AC supply of 230V 50Hz, but this power has to be changed into the required form with required values or voltage range for providing power supply to different types of devices. There are various types of power electronic converters such as step-down converter, step-up converter, voltage stabilizer, AC to DC converter, DC to DC converter, DC to AC converter, and so on. For example, consider the microcontrollers that are used frequently for developing many embedded systems’ based projects and kits used in real-time applications. These microcontrollers require a 5V DC supply, so the AC 230V needs to be converted into 5V DC using the step-down converter in their power supply circuit. Power Supply Circuit Step Down Converter Circuit Power supply circuit, the name itself indicates that this circuit is used to supply the power to other electrical and electronic circuits or devices. There are different types of power supply circuits based on the power they are used to provide for devices. For example, the micro-controller based circuits, usually the 5V DC regulated power supply circuits, are used, which can be designed using different techniques for converting the available 230V AC power to 5V DC power. Generally the converters with output voltage less than the input voltage are called as step-down converters. 4 Steps to Convert 230V AC to 5V DC 1. Step Down the Voltage Level The step-down converters are used for converting the high voltage into low voltage. The converter with output voltage less than the input voltage is called as a step-down converter, and the converter with output voltage greater than the input voltage is called as step-up converter. There are step-up and step-down transformers which are used to step up or step down the voltage levels. 230V AC is converted into 12V AC using a step-down transformer. 12V output of stepdown transformer is an RMS value and its peak value is given by the product of square root of two with RMS value, which is approximately 17V. Step-down Transformer Step-down transformer consists of two windings, namely primary and secondary windings where primary can be designed using a less-gauge wire with more number of turns as it is used for carrying low-current high-voltage power, and the secondary winding using a high-gauge wire with less number of turns as it is used for carrying high-current low-voltage power. Transformers works on the principle of Faraday’s laws of electromagnetic induction. 2. Convert AC to DC 230V AC power is converted into 12V AC (12V RMS value wherein the peak value is around 17V), but the required power is 5V DC; for this purpose, 17V AC power must be primarily converted into DC power then it can be stepped down to the 5V DC. But first and foremost, we must know how to convert AC to DC? AC power can be converted into DC using one of the power electronic converters called as Rectifier. There are different types of rectifiers, such as half-wave rectifier, full-wave rectifier and bridge rectifier. Due to the advantages of the bridge rectifier over the half and full wave rectifier, the bridge rectifier is frequently used for converting AC to DC. Bridge Rectifier Bridge rectifier consists of four diodes which are connected in the form a bridge. We know that the diode is an uncontrolled rectifier which will conduct only forward bias and will not conduct during the reverse bias. If the diode anode voltage is greater than the cathode voltage then the diode is said to be in forward bias. During positive half cycle, diodes D2 and D4 will conduct and during negative half cycle diodes D1 and D3 will conduct. Thus, AC is converted into DC; here the obtained is not a pure DC as it consists of pulses. Hence, it is called as pulsating DC power. But voltage drop across the diodes is (2*0.7V) 1.4V; therefore, the peak voltage at the output of this retifier circuit is 15V (17-1.4) approx. 3. Smoothing the Ripples using Filter 15V DC can be regulated into 5V DC using a step-down converter, but before this, it is required to obtain pure DC power. The output of the diode bridge is a DC consisting of ripples also called as pulsating DC. This pulsating DC can be filtered using an inductor filter or a capacitor filter or a resistor-capacitor-coupled filter for removing the ripples. Consider a capacitor filter which is frequently used in most cases for smoothing. Filter We know that a capacitor is an energy storing element. In the circuit, capacitor stores energy while the input increases from zero to a peak value and, while the supply voltage decreases from peak value to zero, capacitor starts discharging. This charging and discharging of the capacitor will make the pulsating DC into pure DC, as shown in figure. 4. Regulating 12V DC into 5V DC using Voltage Regulator 15V DC voltage can be stepped down to 5V DC voltage using a DC step-down converter called as voltage regulator IC7805. The first two digits ‘78’ of IC7805 voltage regulator represent positive series voltage regulators and the last two digits ‘05’ represents the output voltage of the voltage regulator. IC7805 Voltage Regulator Internal Block Diagram The block diagram of IC7805 voltage regulator is shown in the figure consists of an operating amplifier acting as error amplifier, zener diode used for providing voltage reference, as shown in the figure. Zener Diode as Voltage Reference Transistor as a series pass element used for dissipating extra energy as heat; SOA protection (Safe Operating Area) and heat sink are used for thermal protection in case of excessive supply voltages. In general, an IC7805 regulator can withstand voltage ranging from 7.2V to 35V and gives maximum efficiency of 7.2V voltage and if the voltage exceeds 7.2V, then there is loss of energy in the form of heat. To protect the regulator from over heat, thermal protection is provided using a heat sink. Thus, a 5V DC is obtained from 230V AC power. We can directly convert 230V AC into 5V DC without using transformer, but we may require high-rating diodes and other components that give less efficiency. If we have 230V DC power supply, then we can convert the 230V DC into 5V DC using a DC-DC buck converter. 230v to 5v DC-DC Buck Converter: Let us start with the DC regulated power supply circuit designed using a DC-DC buck converter. If we have 230V DC power supply, then we can use a DC-DC buck converter for converting the 230V DC into 5V DC power supply. The DC-DC buck converter consists of Capacitor, MOSFET, PWM control, Diodes and Inductors. The basic topology of a DC-DC buck converter is shown in the below figure. DC to DC Buck Converter Voltage drop across the inductor and the changes in electric current flowing through the device are proportional to each other. Hence, the buck converter works on the principle of energy stored in an inductor. The power semiconductor MOSFET or IGBT used as switching element can be used to alternate the buck converter circuit between two different states by closing or opening and off or on using the switching element. If the switch is in on state, then a potential is created across the inductor due to in-rush current which will oppose the supply voltage, thereby reducing the resultant output voltage. As diode is reverse biased, no current will flow through the diode. If the switch is open, then current through the inductor interrupts suddenly and the diode starts conduction, thus a return path is provided to the inductor current. The voltage drop across the energized inductor gets reversed, which can be considered as primary source of output power during this switching cycle and this is due to the this quick change in the current flow. The stored energy of the inductor is continuously delivered to the load and thus inductor current will start to drop until the current rises to its previous value or the next on state. The continuation of delivering energy to the load leads to drop in the inductor current until the current rises to its previous value. This phenomenon is called as output ripple which can be reduced to an acceptable value using a smoothing capacitor in parallel with the output. Thus, DC-DC converter acts as step-down converter. DC to DC Step-down Converter using PWM Cotrol The figure shows the working principle of the DC to DC step-down converter controlled using a PWM oscillator for high-frequency switching and a feedback is connected with an error amplifier. All the embedded system based electronics projects require a fixed or an adjustable voltage regulator which is used for providing the required supply to the electrical and electronic circuits or kits. There are many advanced automatic voltage regulators capable of adjusting the output voltage automatically based on the criteria of application. For more technical help regarding the power supply circuit and step down converter, please post your queries as comments in the below comment section. 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