Modern power supplies for a personal computer are devices of high power. Old ATX-type units remain unclaimed, despite the fact that their resource has not yet been exhausted. If you have such a device idle, then you can build a laboratory power supply from it. In this case, special attention should be paid to the current limiting device, as well as the possibility of regulating its threshold. Most often, such a component is a TL494 type chip, since this is the simplest solution for remodeling.
Do-it-yourself laboratory power supply
To implement our plan, we will need any device of the type AT, ATX, the basis of which is the TL494 chip. A diagram of such a power supply is shown in the photo. The device provides for the possibility of limiting the load current parameter by turning on an additional signal amplifier of a possible chip error, which is not used by the manufacturers of the PC element in question. The amplifier is included in the laboratory power supply according to an invertible voltage amplification circuit (negative value). This switching circuit is used because of the possibility of connecting 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 high sensitivity. This allows the use of a current sensor with a lower resistance, thereby decreasing the value of the incident power, as a result of which the working laboratory power supply practically does not heat up.
Nodes to be deleted:
1. Power Good Signal Generator.
2. Rectifiers, filters, all elements of the output circuits. Only the +12 V output circuit should be left.
3. The output oxide capacitor should be replaced by a high-voltage one with a voltage of 25 V.
4. The throttle must be rewound. First, all windings are removed, then new windings are wound (with a harness from a wire with a diameter of 0.6-1 mm to fill).
The principle of operation of the device
On the basis of the comparator, previously used to generate the “Power” signal, a node has been assembled that provides an indication of the load current parameter limiting mode. The voltage is supplied to the non-invertible input of the comparator (this value is proportional to the input value). At inverted input - exemplary value. As long as our laboratory power supply is in stabilization mode, the voltage at the non-inverted input is higher than at the inverted one. At the output of the comparator, we accept a high signal level, so the indicator is off. When the device exits the stabilization mode due to current limitation, the potential difference at the input will decrease, and the output will become low. The LED lights up, which means that the device has left the stabilization mode.
Semiconductor microcircuits receive power from a standby source, which is assembled on a transistor, so that a change in the value of the output voltage does not affect the operation of the microcircuits.
ATX Lab Power Supply: Benefits and Drawbacks
The advantages of such devices include their cheapness, as 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 the use.