Initial exchange - DC power supply
The birth of AC
At the end of the 19th century, Thomas Edison successfully used the method of direct current transmission to light the light bulb. However, due to the huge energy loss, the efficiency of the DC transmission was very low. Later, Nigulatas invented the AC transmission instead of DC transmission.
In the case of AC transmission, the voltage can be easily boosted or stepped down by the transformer, and the power can be transmitted over long distances.
Today, although the voltage and frequency used are different, AC transmission has been widely used throughout the world. The power supply frequency is 50Hz or 60Hz, and the power supply voltage is 100V to 240V.
Initial exchange - DC power supply
Invented vacuum tubes and radio receivers in the same era when AC emerged, but they needed to use DC power to work, so they also produced devices that convert AC power into DC power. This is what we call AC/DC power today.
The above diagram is the rectifier circuit diagram of the initial AC/DC power supply. Since it is an AC power supply at the industrial power frequency, bulky bulky step-down transformers and filter capacitors are used.
Now, explain the working principle of this circuit through the above picture. The industrial alternating current is input from the left side of the figure, and the alternating current voltage is converted into the voltage required by various devices through the transformer in the middle of the figure, and then the stepped down alternating current is converted into direct current through the filter capacitor. However, because the voltage is only converted by the transformer, the generated DC voltage may fluctuate due to the load state of the device.
The emergence of switching power supply
Since the power supply requirements of equipment in recent years are high accuracy and can provide a stable voltage, the switching power supply circuit is mainly used.
The circuit diagram above is an example of a power supply used today. A typical example of such a power supply is the self-oscillating RCC (Ringing Choke Converter) shown here. In this circuit, the DC voltage obtained by rectifying the AC voltage is converted into a high-frequency rectangular wave of several tens of kilohertz. The transformer then converts the voltage to a desired value and rectifies it again.
We will explain the operating principle of this switching power supply circuit through the above figure. In the same way as in the initial AC/DC circuit, AC power will be input from the left side of the circuit diagram, common-mode noise will be eliminated by the EMI filter, and AC voltage will be converted to DC voltage by the bridge rectifier and filter capacitor. Then, the synthesized voltage is converted into a high-frequency rectangular pulse wave through a Q1 high-speed switch of several kilohertz. Subsequently, the pulse wave will be supplied to the high-frequency transformer, the secondary-side output will be rectified by the diode and the filter capacitor, and the generated DC power will be supplied to the load.
Initial AC - Comparison of DC Power Supply and Switching Power Supply
The following figure shows the comparison between the initial AC/DC power supply circuit and today's AC/DC power supply circuit. The advantages of the current switching power supply circuit are that the transformer has small size, stable output, and high efficiency.
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