With the transformer why DC power supply, DC power supply is 220VAC input, output 24VDC; transformer is 220V / 24V. Is this not repeated?
The transformer output is AC, must be rectified into DC to use; In addition, the rectification is only the direction of the DC, the size will change over time, so some of the voltage fluctuations in the case of strict control but also after the rectification Filter circuit and voltage regulator circuit,
We usually refer to the "DC power supply", is also available from the mains power supply, through the transformer buck, full bridge rectifier, filter, regulator, and so on several steps.
But now the low-power power supply has been no use of transformer buck, but the direct use of PWM buck way buck. The advantage of this step-down is the small size and light weight. So our home TV, mobile phone charger, etc., has no traditional body of the transformer.
You'd better describe the problem in detail.
Normally, the transformer changes the voltage of the alternating current, that is, the input is alternating current, the output is also alternating current. But we usually need electrical equipment DC power supply, so the need for rectification after the transformer, filter, regulator and other processing circuit, to provide to the electrical equipment.
