An every Embedded system needs an RPS (regulated power supply), and the circuit of this power supply gives a changeable regulated supply and turns off in the no-load situation. During an arrangement of the voltage regulator, potentiometer and the o/p voltage is changed from 3.7volts to 8.7volts.This power supply has another feature that is, when there is no load then it automatically switches off. This process will be achieved by an arrangement of relay and transistors.
Self-Switching Power Supply
The hardware requirements of the self-switching power supply include a transformer, rectifier, filter, regulator, relay, a transistor (BC547, BC557), Resistor, Capacitor, 1N4007.
Step down Transformer
- Step down transformers secondary voltage is less than its primary voltage
- It is mainly designed to reduce the voltage from the primary winding to the secondary winding
- The transformer changes the high voltage, low current power into low voltage, high current power
Transistor (BC547, BC557)
- The BC547 transistor is an NPN Epitaxial Silicon Transistor.
- The BC547 transistor is a general-purpose transistor in small plastic packages.
- It is used in general-purpose switching and amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors.
- Whenever base is high, then current starts flowing through base and emitter and after that only current will pass from collector to emitter
- The BC557 transistor is a PNP Epitaxial Silicon Transistor
- The BC557 transistor is a general-purpose transistor in small plastic packages. It is used in general-purpose switching and amplification BC847/BC547 series 45 V, 100 mA PNP general-purpose transistors.
A bridge rectifier is an arrangement of four or more diodes arranged in the form of which gives the same output polarity for either i/p polarity. It is employed for altering an alternating current input into a direct current output.
A filter is a capacitor which filters out a certain frequency from a circuit. Generally, capacitors can be used to filter out very low-frequency signals. These signals are very near to 0Hz in the value of frequency, which is referred to as DC signals.
LM7805 Voltage Regulator
A voltage regulator 7805 is used to maintain the level of voltage automatically. It is a part of 78xx series of fixed linear voltage regulator ICs. The series xx in 78 indicates the fixed o/p voltage it is designed to provide. It provides +5V RPS (regulated power supply).
A relay is an electromagnetic switch operated by a small electric current. The main purpose of the relay is to control the movement of the gate. It is used to control the electrical devices. A relay is able to control an o/p circuit of higher power than i/p circuit.
The circuit of a regulated power supply (RPS through a fixed-voltage regulator provides features like a variable and switch off This is attained by connecting a potentiometer among common regulator IC terminal and GND. For every 100 ohm increase in the value of in-circuit the potentiometer resistance, the o/p voltage increases by 1 volt. Thus, the o/p changes from 3.7V-8.7V.Another significant feature of the supply is that it turns off itself when no load is connected to its o/p terminals.
This is attained with the help of transistors, diodes, and capacitor. When a load is connected to the o/p, the potential drop across diodes is enough for transistors to perform. As a result, the relay gets activated and remains in that state as long as the load remains connected. At the same time, capacitor gets charged to around 7-8 volt potential through the transistor. But when the load is detached, the transistor is cut off. But, the capacitor is still charged and it begins discharging through the base of the transistor.
After some time, the relay is de-energized, which turns off the mains input primary of the transformer.To restart the power again, switch Push button should be pushed momentarily. Upper the value of capacitor more will be the delay in turning off the supply on detachment of the load and vice versa.
A transformer with a secondary voltage (12V-0V, 250mA) was used, it can yet be changed as per requirement. For drawing more than 300mA current, the regulator IC should be built-in with a small heatsink above a mica insulator. When the secondary voltage of transformer increases beyond 12V (RMS), potentiometer must be re-dimensioned. Also, the voltage of relay rating should be prearranged.
Self-Switching Power Supply Advantages and Disadvantages
The advantages and disadvantages of self-switching power supply include the following
- It is used as a protector for electronic circuits
- It can get different voltages
- Perform as a protector for monitors
- Not expensive
- If once the supply breaks then it is powered manually
Self-Switching Power Supply Applications
- Self-switching power supply circuit can be used in different electronic types of equipment as the supply voltage.
- This circuit is used for damage fewer uses.
- By using this circuit we can generate various voltages
Almost all electronic equipment comprises a circuit that alters AC voltage of main supply into DC voltage. This portion of the equipment is termed as a power supply. Generally, at the power supply input, there is a power transformer. A diode circuit named rectifier follows it. The o/p of the rectifier goes to a smoothing filter and then to a voltage regulator circuit.
The rectifier is an essential component in the power supply. This is used a variable one and this circuit is useful in various electronic experimental applications. If you have any queries regarding this concept or to implement any electrical projects, please give your valuable suggestions by commenting in the comment section below. Here is a question for you,