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The key to power miniaturization is the miniaturization of the power supply, so the loss of the power supply circuit must be reduced as much as possible. When the switching power supply such as the industrial control equipment power supply is in the switching state, the switching loss of the switching power supply such as the industrial control equipment power supply inevitably exists, and the loss increases as the switching frequency increases. On the other hand, the loss of magnetic elements and capacitive elements such as transformers and reactors in a switching power supply increases as the frequency increases.

In the current market, the power transistors in the switching power supply such as industrial control equipment power supply are mostly bipolar transistors, the switching frequency can reach several tens of kHz, and the switching frequency of the MOSFET switching power supply can reach several hundred kHz. High speed switching devices must be used to increase the switching frequency. For power supplies with a switching frequency higher than MHz, a resonant circuit can be used, which is called a resonant switching mode. It can greatly increase the switching speed. In principle, the switching loss is zero and the noise is very small. This is a way to increase the operating frequency of a switching power supply. A megahertz converter using a resonant switching mode.

Switching power supplies such as industrial control equipment power supplies can solve this problem well by high-frequency switching mode. For high frequency switching power supplies, the AC input voltage can be boosted before entering the transformer (typically 50-60 KHz before boosting). As the input voltage increases, the components of transformers and capacitors do not have to be as large as linear power supplies. This high-frequency switching power supply is required for our personal PCs and devices like VCR recorders. It should be noted that the "switching power supply" we often refer to is actually the abbreviation of "high-frequency switching power supply", and has nothing to do with the power-off and opening type of the power supply itself.

Switching power supplies such as industrial equipment power supplies have a variety of circuit structures:

(1) According to the driving method, there is self-excitation. (2) According to the composition of the circuit, there are resonance and non-resonance

(3) According to the working mode of DC/DC converter: 1) single-ended forward and flyback, push-pull, half-bridge, full-bridge, etc.; 2) buck, boost and boost.

(4) According to the control method, it is divided into: pulse width modulation (PWM), pulse frequency modulation (PFM), PWM and PFM mixing. (5) According to the power isolation and feedback control signal coupling, there are problems such as isolation, non-isolation, transformer coupling, and optoelectronic coupling. These combinations can form a variety of switch mode power supplies. Therefore, designers need to effectively combine the characteristics of various modes to produce high-quality switching power supplies to meet the needs.

The PWM circuit has already shouldered the task of voltage rectification. The input voltage will be corrected again before passing through the switch, and the voltage entering the transformer has become a square wave. Therefore, the waveform of the transformer output is also a square wave, not a sine wave. Since the waveform is already a square wave at this time, the voltage can be easily converted into a DC DC voltage by the transformer. That is, after the voltage is recalibrated by the transformer, the output voltage has become a DC DC voltage. This is why switching power supplies are often referred to as DC-DC converters.

The loop feeding the PWM control circuit is responsible for all required adjustment functions. If the output voltage is wrong, the PWM control circuit changes the duty cycle control signal to accommodate the transformer and eventually corrects the output voltage. This situation often occurs when the power consumption of the PC rises. At this time, the output voltage tends to decrease, or when the power consumption of the PC decreases, the output voltage tends to rise.