A single-phase alternating voltage of 220 V is supplied to private houses and apartments. It is ideal for incandescent light bulbs that illuminate a home. However, household appliances require DC power and a much lower voltage.
- 1 General network concepts
- 2 What is a power supply?
- 3 Types of power supplies
- 4 DIY Power Supply
- 5 Power supply advantages
- 6 Check in work
General network concepts
Everyone knows that to make a TV or computer you need to connect it to an electrical outlet. However, not everyone knows that TV units can not be connected directly from the mains 220V.
And there are two reasons for this:
- The AC outlet, and the components of the TV need a constant;
- Various nodes and TV circuits for their work use voltages of various sizes. And for this we need several lines with different indicators.
For example, for a radio to work, a constant voltage of 9V is required. And for a computer 5B and 12 V.
In order to obtain the voltage of the required size, there are power supply units that are located in the housing of household appliances.
What is a power supply?
The power supply is called electronic devicethat converts AC voltage to DC. It provides the individual components with current and voltage of the required rating.
The power supply is a source of electricity for all components of the device.
Can I do without a power supply? It is possible, but not always.
Instead of BP, you can use batteries or batteries.
This principle is acceptable in laptops, receivers or players, where the power consumption is not too large.
For a stationary computer or TV such inclusion is not appropriate.
Types of power supplies
In household appliances use two types:
Each of these units is ideally suited for various electronic devices, according to specified specifications.
Select the best or worst type is impossible. They have their advantages and disadvantages and successfully solve their task.
Transformer power supply unit consists of a step-down transformer with the primary winding under the mains voltage. And the secondary winding of the calculation of the required voltage and current.
AC voltage conversion in constant is carried out using a rectifier. The pulsating voltage is then smoothed with large capacitors. The transformer unit circuit may include high-frequency noise filters, short-circuit protection, current and voltage stabilizers.
Transformer power supplies are characterized by simplicity of design, high reliability, availability of the element base and low level of own interference. Gather according to simple schemes.
However, such power supplies have a large weight and size, low efficiency.
Pulsed power supplies are based on the principle of initial rectification of the input voltage, followed by conversion to higher frequency pulses.
In impulse blocks with galvanic isolation, the network is supplied to the transformer (with much smaller dimensions than in the transformer power supply).
If galvanic isolation from the mains is not needed, then the pulses are immediately fed to the low-frequency output filter.
Through the use of negative feedback, pulsed power supplies provide stable performance regardless of fluctuations in the input voltage and the magnitude of the load.
Pulsed power supply units have relatively small dimensions and weight. They cover a wide range of incoming voltage and frequency, they are distinguished by a high indicator of efficiency.
The disadvantages include high-frequency noise level caused by the principle of operation of pulsed power supplies.
As a rule, power supplies already built into the hardwareand there is no need to change this. However, in some cases it is necessary to have a separate power supply for a certain voltage.
For example: the radio receiver is designed to operate on batteries and does not have an integrated control device. It is reasonable to use a stand alone power supply unit. This will eliminate the hassle associated with frequent replacement of batteries.
In the case when the radio amateur is engaged in the manufacture or repair of electronic devices, he has to work with equipment using different supply voltages. Then a power supply with adjustable output voltage will be useful.
Of course, such a device can purchase at an electronics store. However, a creative person is much nicer to make such a device with his own hands. Especially as there may not be a power supply with the characteristics required by the master.
DIY Power Supply
In radio magazines and on the Internet, you can find a huge number of various schemes of adjustable power supplies.
But in amateur radio practice, it is enough to have a simple adjustable power supply from 0 to 12V. Such a device under the power to make their own hands, both experienced and novice radio amateurs.
Power supply advantages
- Ease of assembly;
- Lack of expensive radio elements;
- Adjustment range 0-12V;
- High stability.
The scheme is simple but reliable power supply with continuously adjustable consists of two parts:
- The main part (the power supply itself);
- Transistor output voltage regulator circuit.
The main part includes:
- Step-down transformer power up to 30W. A transformer with a primary winding, designed for alternating current 220V and a secondary winding with an output voltage of 15V and a current of 2-3 amperes is required;
- Rectifier assembled on four diodes KD202 (or similar) to convert a DC voltage from AC;
- Electrolytic capacitor with a capacity of at least 1000 microfarads. Due to its ability to accumulate and release stress, it performs the function of a smoothing filter. The higher the capacitor rating, the smaller the voltage spikes.
The transistor circuit includes:
- Parametric stabilizer consisting of a resistor and a zener diode. At the Zener diode, a constant value is formed with a small deflection coefficient;
- Variable resistor performing a smooth change in output voltage;
- Emitter follower consisting of two transistors operating in current amplification mode.
With proper installation, the device starts working immediately, without any settings in the scheme.
Check in work
Connect the voltmeter to the output of the PSU. Turn the voltage regulator to the minimum. The voltmeter reading should be zero. Smoothly translate the regulator in the right position. The readings of the voltmeter should gradually increase up to a maximum of + 12V.
In parallel, turn on the voltmeter load in half ampere. The drawdown of the output voltage should be minimal.
With all the simplicity of the design, the PSU produces good characteristics and parameters.
Small improvements with their own hands will improve the design. For example, you can install an overload protection node, or install an internal voltmeter.