Modern power supplies for personalcomputers belong to high-power devices. Older ATX units remain unclaimed, despite the fact that their resource has not yet been developed. If you have such a device without a case, you can build a laboratory power supply from it. In this case, special attention should be given to the current limiting device, as well as the possibility of regulating its threshold. Most often this component is a chip type TL494, as this is the simplest solution for rework.
We make a laboratory power supply with our own hands
For the embodiment of what was planned for usAny device of the AT, ATX type, based on the TL494 chip, is required. The diagram of such a power supply unit is presented in the photo. The device provides the possibility of limiting the load current parameter by including an additional signal amplifier of a possible error of the chip, which is not used by the manufacturers of the PC element in question. The amplifier is included in the laboratory power supply by an inverted voltage amplification circuit (negative value). This connection scheme is used because it is possible to connect the common wire of the device to the housing, in addition, the practical use of such a device shows stable operation in the entire range of current and voltage of the power source. The third advantage is considered high sensitivity. This allows the use of a current sensor with a lower resistance, thereby reducing the value of the incident power, as a result, the working laboratory power supply is practically not heated.
Nodes to be deleted:
1. Power Good.
2. Rectifiers, filters, all elements of output circuits. Only leave the output circuit +12 V.
3. The output oxide condenser should be replaced with a high voltage with a voltage of 25 V.
4. The throttle must be rewound. First, all the windings are removed, then rewind the new ones (a bundle of wire with a diameter of 0.6-1 mm before filling).
Principle of operation of the device
On the basis of a comparator previously used forgeneration of the "Power" signal, a node is assembled which provides an indication of the load current parameter limiting mode. The voltage is applied to the non-inverted input of the comparator (this value is proportional to the input value). On the inverted input is an exemplary value. As long as our laboratory power supply operates in the stabilization mode, the voltage at the non-inverted input is higher than on the inverted input. At the output of the comparator we receive a high signal level, so the indicator is extinguished. When the device exits the stabilization mode due to current limitation, the potential difference at the input will drop and the output will be set to a low level. The LED lights up, which means that the device has left the stabilization mode.
Semiconductor chips are powered by the on-duty source, which is assembled on a transistor, so that changing the value of the output voltage does not affect the operation of the microcircuits.
Laboratory power supply from ATX: advantages and disadvantages
The advantages of such devices include theircheap, because used blocks can be found everywhere. They contain all the necessary components, the main one of which is a pulse transformer. In addition, the computer power supply has excellent weight and size characteristics. The disadvantages include a large range of high frequency interference, which limits use.
