Zener and Transistor Power Supply
Considered below stabilized power supply is one of the first devices that are collected by novice radio amateurs. This is a very simple, but very useful device. Its assembly does not require expensive components that are easy enough for a beginner to pick up depending on the required characteristics of the power supply unit. The material will also be useful to those who want to understand in more detail the purpose and calculation of the simplest radio components. In particular, you will learn in detail about the components of the power supply, such as:Diagrams in radio electronics are generally disassembled in the direction in which current flows through them. In a power supply with voltage stabilization, everything starts with a transformer (TR1). It performs several functions at once. First, the transformer lowers the mains voltage. Secondly, it ensures the operation of the circuit. Third, it feeds the device that is connected to the unit. The diode bridge (BR1) - is designed to straighten the lowered mains voltage. Speaking in other words, an alternating voltage enters it, and the output is already constant.Without a diode bridge, neither the power supply unit itself nor the devices that will be connected to it will work. A smoothing electrolytic capacitor (C1) is needed in order to remove the pulsations present in the home network. In practice, they create interference that adversely affects the operation of electrical appliances. If, for example, take a sound amplifier powered from a power supply unit without a smoothing capacitor, then these same pulsations will be clearly heard in the columns in the form of extraneous noise. In other devices, interference can lead to malfunction, malfunction and other problems. Zener diode (D1) is a component of the power supply that stabilizes the voltage level. The fact is that the transformer will produce the desired 12 V (for example) only when there is exactly 230 V in the outlet. However, in practice there are no such conditions. Voltage can both subside and increase. The same transformer will give and output. Due to its properties, the zener diode balances the undervoltage regardless of the jumps in the network. For this component to work correctly, a current limiting resistor (R1) is needed.It is described in more detail below. Transistor (Q1) - needed to amplify current. The fact is that the Zener diode is not able to pass through itself all the current consumed by the device. Moreover, it will work correctly only in a certain range, for example, from 5 to 20 mA. To power any devices of this frankly little. This problem is handled by a powerful transistor, the opening and closing of which is controlled by a zener diode. Smoothing capacitor (C2) - designed for the same as the above-described C1. In typical circuits of stabilized power supplies, there is also a load resistor (R2). It is necessary for the circuit to remain operable when nothing is connected to the output terminals. Other components may be present in such circuits. This fuse, which is placed in front of the transformer, and the LED signaling the switching on of the unit, and additional smoothing capacitors, and another amplifying transistor, and a switch. All of them complicate the circuit, however, increase the functionality of the device.
- power transformer;
- diode bridge;
- smoothing capacitor;
- zener diode;
- resistor for Zener diode;
- load resistor;
- LED and a resistor for it.
A typical scheme of a stabilized power supplyThere are a lot of various schemes of power supplies with voltage stabilization today. But one of the simplest configurations, with which it is worth starting a newcomer, is built on only two key components - a stabilitron and a powerful transistor. Naturally, there are other details in the scheme, but they are auxiliary.
Calculation and selection of radio components for the simplest power supplyThe transformer is selected according to two main criteria - the secondary voltage and power.There are other parameters, but within the framework of the material they are not very important. If you need a power supply, say, 12 V, then you need to select a transformer so that you can remove a little more from its secondary winding. With the power all the same - we take with a small margin. The main parameter of the diode bridge is the maximum current that it can pass. On this feature and should be guided in the first place. Consider the examples. The unit will be used to power the device consuming a current of 1 A. This means that the diode bridge should be taken approximately by 1.5 A. Assume you plan to power any 12-volt device with a power of 30 watts. This means that the current consumption will be about 2.5 A. Accordingly, the diode bridge should be at least 3 A. Its other characteristics (maximum voltage, etc.) in such a simple circuit can be neglected.
Design and manufacture of a printed circuit boardNow briefly Consider a good example of the development and assembly of a stabilized power supply with your own hands. First of all, it is necessary to find all the components present in the circuit. If there are no capacitors, resistors or zener diodes of the required nominal values, we exit the situation in the ways described above.
Component Testing and Power Supply AssemblyAfter the board has been developed in the program, we transfer it to fiberglass laminate, etch, pave the paths and remove excess flux. br>
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