High-power flyback design with ultra-wide input voltage range

There are a variety of power supply voltages in the field of industrial applications and factory automation. You will usually find a 24 volt AC (VAC) voltage, a 24 volt DC (VDC) voltage, 110VAC voltage, 230VAC voltage, and sometimes the voltage between them is also found. Due to cost reasons, electronic equipment manufacturers are often unwilling to develop different power supplies for each input voltage. So let's take a look at how to design a small power (from 19 to 265VAC and 19 to 375VDC) of the flyback converter. This small power reverse reference design (the author will use an example in which it as this blog) needs two outputs. An output rail provides a microcontroller and an analog circuit (a current is 5.0V); another output rail provides a voltage of 12.0V at a current of 40 mA to control the relay. Because the input and two outputs require 2.5 kV isolation voltage, the author first thought that the structure is simple and widely known inverse converter. Figure 1 shows such a converter - a controller linear regulator including an input filter, a rectifier, a startup circuit, and a secondary side. Figure 1: Box chart of flyback converter The wide input voltage range is not only a challenge to the controller, but also a big problem for the design of the transformer. For small power applications, the flyback converter is designed to operate under a non-continuous conduction mode (DCCM) to achieve a small solution size because the inductance of the coupled inductor is relatively small. The peak current in this mode of operation is larger than the peak current under the continuous conduction mode (CCM) - but they are still relatively small, because the power is small. For larger power applications, the flyback converter is usually working in CCM mode. At first glance, DCCM seems to be a model suitable for the flyback design, and the output power is approximately 500 mW. To avoid large switching losses in the upper limit range of the input voltage, the switching frequency should be relatively low. In this design, it is set to 130 kHz to allow the base wave below 150 kHz of the lower limit of electromagnetic interference (EMI). If it is assumed that the converter works only in DCCM mode, the duty cycle is within a range: from 70% until 4% (initial inductance of turns ratio of 3.58: 1,750μH). In order to reduce component stress, you should increase the minimum duty cycle by allowing the number of turns to remain unchanged and turning primary inductance to 4MH. Now, for low input voltages, the converter runs in CCM mode; for high input voltages, the converter runs in DCCM mode. Figure 2: Small power anti-excitement Ti Designs reference design with ultra-wide input voltage range, reading

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