Most modern appliances work due to the fact that is powered by a switch-mode power supplies (UPS). Analog devices (also referred to as "transformer") are not used, because the inferior pulse for a variety of indicators.
Before buying a particular sample feeding device is desirable closely to deal with the fact what is the difference between the two versions (pictured below).
Also need to consider why transformer PSU are found only in the old equipment.
Working principles of simple power supply and UPS
The analog power supply with a built-in transformer works on the classical principle of voltage conversion, which is reduced to its lowering and straightening.
That is to output constant 12 volts, for example, the following sequence of transformations performed in the device:
- First network 220 volt drop in the transformer to 15-17 volts AC.
- Then, via the diode bridge are rectified and converted to a ripple voltage amplitude of the order of 14-16 V (volts missing are lost on the diode junctions).
- Thereafter pulsations are smoothed high capacity electrolytic capacitor and provided to the stabilizer 12 volts.
Important! For normal operation of a typical stabilizer supplied to its input voltage should be 2-4 volts greater than the nominal output value.
One of the variants of the rectifier circuit BP is shown in the photo below.
In the present scheme is further incorporated security elements (fuse), and the display unit on and availability of the rectified voltage.
UPS operating principle
The principle of action of the UPS is not so simple and is as follows:
- First, the input voltage is also rectified, whereupon it is converted into pulses of relatively high frequency.
- Simultaneously, the circuit output is formed by the feedback signal, allowing them to stabilize the amplitude.
Then they re-straightened, which allows to obtain the output of the entire device the necessary voltage (photo below).
Described two-stage conversion is in many puzzling. Why AC to DC convert, and then make him a pulse signal (in fact - is also variable)? The answer is not so obvious, but it is quite clear from the technical point of view.
Due to the circuit used possible to:
- First, to simplify the process parameter control signal;
- and secondly - to reduce the size and weight of the entire device.
Note:This is explained by the smaller dimensions of the pulse transformer.
From this explanation easier to understand on what basis the advantages of using UPS.
In addition to reducing the size and weight, they are as follows:
- Low power consumption and small non-business losses.
- Easy to assemble.
- High efficiency and the ability to protect against overloads.
The disadvantages include the need to use UPS to protect against electromagnetic interference caused by the pulse of the circuit.