DC Regulated Power Supply
Why we need DC Regulated Power Supply?
Everywhere in world an electric energy is available in houses and industries in the form of alternating voltage. The AC mains supply has a voltage rating of 230V or 120V (RMS) at a frequency of 50Hz/60 Hz. Nowadays almost all equipments used in houses and industries includes an electronic circuits. The electronics circuit uses semiconductor components and devices which requires stable dc voltage for their operation. The Batteries, cells cannot be used because they are costly and inconvenient to use. So it is necessary to convert the available AC voltage of mains supply into D.C. voltage and can be use for operation of electronic circuits. The equipment which converts AC voltage into pure and stable DC voltage is called as a DC Regulated power supply.
We are going to study all about DC regulated power supply. It includes the necessity, construction and working of all the circuits used inside DC Regulated power supply. Lets us discuss about general block diagram of the DC Regulated power supply. It consists of following blocks as shown in block diagram.
- Rectifier circuit.
- Filter circuit.
- Voltage Regulator circuit.
Before a detailed study about all above devices and circuits, let us see functions of each blocks used in brief.
what is the function of Transformer?
The main purpose of using transformer in DC Regulated power supply is that the transformer provides electrical isolation in between AC mains supply and secondary output voltage. (In turn we can say AC input current and DC output current) Because of this property it makes a DC regulated power supply as a shockproof. The types of the transformer according to obtained secondary voltage are
- Step-up transformer.
- Step down transformer.
- Isolation transformer.
The transformer used in DC regulated power supply is generally a step down transformer which provides less secondary output voltage. So therefore the secondary output voltage is easy for conversion in dc voltage as well as we can easily obtained required level of DC voltage.
The transformer primary winding is connected to AC mains supply and the secondary winding is connected to the rectifier circuit for conversion in DC voltage. We can select the required transformer voltage rating as per need of DC output voltage. Generally 9V, 12V, 15V or 18V with 500mA, 750mA, 1A, or 1.5A transformers are used for construction of laboratory purpose DC regulated power supply as per requirements.
The process of converting Bi-directional AC voltage into the Unidirectional DC voltage is called as Rectification. An electronic circuit consists of crystal diode/ PN junction Diode which coverts AC voltage into DC voltage is called as a Rectifier circuit. The rectifier is also called as “Battery Eliminator”. Generally three circuits are used for the rectification.
- Half wave rectifier
- Center tap full wave rectifier
- Bridge full wave rectifier.
Why Filter circuits are necessary?
The rectified output voltage of rectifier is applied to filter circuits the electronic circuit required constant DC voltage similar to the voltage from battery for their working. The rectifiers cannot provide ripple free DC voltage, they provide pulsating DC voltage. It means the output voltage of rectifier consists of AC voltage variations along with DC voltage so it is necessary to remove AC variations from the output of rectifier. Therefore to produce pure dc voltage filter circuits are necessary in DC Regulated power supply.
What is a Filter circuit?
The circuit used for filtering the AC voltage variations from rectifier output voltage of rectifier and produces smooth and pure DC voltage is called as Filter circuit. The filter circuit blocks the AC components and passes only DC components towards the load.
The commonly used filter circuits are
- Capacitor input filter
- Inductor filter
- L C filter
- CLC filter or π filter
- R C filter
The filter circuit provides output voltage s called as smooth or pure DC voltage.
The Power supply consists of Transformer, Rectifier and Filter circuits is called as unregulated or unstabilized power supply. It provides sufficient steady DC output voltage. But the output voltage across load resistor may be change due to change in Load current and change in Line voltage. So an unregulated power supply cannot provide constant or stable output voltage. It means it has poor voltage stabilization or regulation and most of all electronic circuit requires constant operating voltage.
Therefore to maintain a constant voltage across the load even when there are variations in an AC supply voltage or the load current or both the voltage regulation is necessary. The commonly used types of voltage regulators are
- Zener diode voltage regulator.
- Transistorized series voltage regulator.
- IC voltage regulators.
- SMPS or switch mode power supply.
A zener diode voltage regulator is basic type of voltage regulator can provide stable output voltage but its output voltage cannot be varied. Also zener diode available in limited voltage and power ratings so it has limited output voltage and load current.
The transistorized voltage regulator can provide good stability and its output voltage can be varied but it is discrete type of regulator and also it generates heat. So to remove generated heat it requires heavier heat sinks or fan which makes it bulky.
The various types of IC voltage regulators are use but the 3 pin IC voltage regulators are most commonly used. The IC voltage regulators are easy to use because need to make so less connections and also easily available with low cost.
The SMPS is a switch mode power supply in which regulation is done by switching of transistor at a very high rate so the transistor not consuming any power. The SMPS is used in many analog as well as digital equipments and instruments. Mostly the SMPS is used in Computers and Laptops.