On the LM317T microassembly , the power supply circuit (PSU) is simplified many times. Firstly, it is possible to make an adjustment. Secondly, power stabilization is performed. Moreover, according to the reviews of many radio enthusiasts, this microassembly is many times superior to domestic counterparts. In particular, its resource is very large, can not be compared with any other element.
The basis of the power supply is a transformer
It is necessary to use a step-down transformer as a voltage converter. It can be taken from almost any household appliances - tape recorders, televisions, etc. You can also use TVK-110 transformers, which were installed in the vertical scan unit of black and white TVs. True, they have an output voltage of only 9 V, and the current is quite small. And if you need to power a powerful consumer, it is clearly not enough.
But if you want to make a powerful PSU, it is more reasonable to use power transformers. Their power should be at least 40 watts. To make the power supply for the DAC on the LM317T microassembly, you need an output voltage of 3.5-5 V. This is the value you need to maintain in the power circuit of the microcontroller. It is possible that the secondary winding will need to be slightly modified. In this case, the primary one is not rewound, only its isolation is carried out (if necessary).
Rectifier Cascade
A rectifier block is an assembly of semiconductor diodes. There is nothing complicated in it, only you need to decide what type of straightening you need to use. The rectifier circuit may be:
- half-wave;
- half-wave;
- pavement;
- with doubling, tripling, tension.
It is reasonable to use the latter if, for example, you have 24 V at the output of the transformer, but you need to get 48 or 72. At the same time, the output current will inevitably decrease, this should be taken into account. For a simple power supply, the bridge rectifier is most suitable. The used micro-assembly LM317T power supply unit will not allow to do so. The reason for this is that the power of the chip itself is only 2 watts. The bridge circuit allows you to get rid of the ripple, and its efficiency is an order of magnitude higher (when compared with a half-wave circuit). It is allowed to use both diode assemblies and individual elements in the rectifier cascade.
Housing for power supply
It is more reasonable to use plastic as the material for the case. It is convenient to handle, can be deformed during heating. In other words, you can easily give the blanks any shape. And for drilling holes do not require much time. But you can work hard and make a beautiful, reliable case made of sheet aluminum. Of course, there will be more trouble with him, but the appearance will be amazing. After manufacturing the case from sheet aluminum, it can be thoroughly cleaned, primed and applied in several layers of paint and varnish.
In addition, you will immediately kill two birds with one stone - you will get a beautiful case and provide additional cooling to the microassembly. On the LM317T, the power supply is built on the principle that stabilization is carried out with the release of a large amount of heat. For example, you have 12 V at the output of the rectifier, and stabilization should give out 5 V. This difference, 7 Volts, is spent on heating the microassembly body. Therefore, it needs good cooling. And the aluminum case will contribute to this. However, itโs possible to do something more advanced - mount a thermal switch on the radiator that will control the cooler.
Voltage stabilization circuit
So, you have the LM317T microassembly, the power supply circuit on it before your eyes, now you need to determine the purpose of its conclusions. She has only three of them - input (2), output (3) and mass (1). Turn the case face towards you, the numbering is from left to right. That's all, now it remains to carry out voltage stabilization. And it is not difficult to do this if the rectifier unit and the transformer are already ready. As you know, the minus from the rectifier is fed to the first output of the assembly. With the plus of the rectifier, voltage is applied to the second terminal. The stabilized voltage is removed from the third. Moreover, at the input and output, it is necessary to install electrolytic capacitors with a capacitance of 100 ฮผF and 1000 ฮผF, respectively. That's all, only at the output it is desirable to put a constant resistance (of the order of 2 kOhm), which will allow electrolytes to discharge faster after shutdown.
Power supply circuit with voltage regulation
To make an adjustable power supply on the LM317T is simple, it does not require special knowledge and skills. So, you already have a power supply with a stabilizer. Now you can slightly upgrade it to change the output voltage, depending on what you need. To do this, it is enough to disconnect the first output of the microassembly from the power supply minus. On the output, turn on two resistors in series - constant (nominal 240 Ohm) and variable (5 kOhm). In the place of their connection, the first output of the microassembly is connected . Such simple manipulations allow you to make an adjustable power supply. Moreover, the maximum voltage supplied to the input of the LM317T can be 25 volts.
Additional features
With the use of the LM317T microassembly, the power supply circuit becomes more functional. Of course, during the operation of the power supply, you will need to monitor the main parameters. For example, current consumption or output voltage (this is especially true for a regulated circuit). Therefore, you need to mount indicators on the front panel. In addition, you need to know if the power supply is plugged in. The duty to notify you of the inclusion in the power supply is best left to the LED. This design is quite reliable, only the power for it needs to be taken from the output of the rectifier, and not microassemblies.
To control current and voltage, you can use arrow indicators with a graduated scale. But in case you want to make a power supply that will not be inferior to a laboratory one, you can also use LCD displays. True, to measure the current and voltage on the LM317T, the power supply circuit is complicated, since it is necessary to use a microcontroller and a special driver - a buffer element. It allows you to connect an LCD display to the controller's I / O ports.