transformed variable

импульсный источник электропитания с коммутацией тока на первичной стороне
-

In primary switch mode power supplies, the AC mains voltage is first rectified and smoothed and then chopped ("switched"). Chopping means that the DC voltage is switched periodically at a frequency of 40 to 200 kHz using a power transistor.
In contrast to linearly regulated power supplies, the power transistor does not act as a variable resistor but as a switch instead. This generates a square-wave AC voltage that is transformed to the secondary circuit using a high-frequency transformer. In the secondary circuit, the voltage is rectifi ed and smoothed. The quantity of energy transformed to the secondary circuit is controlled, depending on the load, by varying the chopping rate. The longer the transistor is conductive, the higher is the quantity of energy transformed to the secondary circuit ( pulse width modulation).
Due to the use of high-frequency AC voltage, primary switch mode power supplies have the decisive advantage that their transformer can be of much smaller size than required for the transformation of low frequencies. This reduces the weight and the dissipation inside the unit. The effi ciency of these units is between 85 and 95 %. Since the output voltage does not directly depend on the input voltage, these units can be used for a wide input voltage range and can even be supplied with DC voltage. Furthermore, it is possible to buffer short-time mains voltage breakdowns up to 200 ms. However, the power failure buffering time is limited by the size of capacitor C1 since a longer buffering time requires a higher capacity and thus a bigger size of the capacitor. Especially in case of small power supplies this is not desirable.
Therefore, a practicable compromise has to be made between the size of the power supply and the buffering time.
Primary switch mode power supplies can be used for all purposes. For example, they are suitable for the supply of all kind of electronics as well as for electromechanical applications.
[ABB]

Тематики

• источники и системы электропитания

EN

• primary switch mode power supply

линейный регулируемый источник электропитания
-

Рис. ABB

The AC mains voltage is transformed to a lower level, rectified and smoothed by capacitor C1. Then, voltage regulation is performed, typically using a power transistor. The power transistor acts as a variable resistor, controlled to keep the output voltage constant.
The efficiency of linearly regulated power supplies is only approx. 50 % due to the high losses inside the power transistor. The remaining energy is emitted in the form of heat. Due to this, sufficient ventilation is required to cool the power supply. Compared with unregulated power supplies, linearly regulated power supplies have a very small residual ripple of the output voltage (in the dimension of millivolts).
Linearly regulated power supplies are used for all applications that require a very exact output voltage, e.g. for highly precise medical devices.
[ABB]

Тематики

• источники и системы электропитания

EN

• linearly regulated power supply