Intelligent control switch design

There are several control methods for the power supply designed by intelligent control switch. One is that the microcontroller outputs a voltage (via DA chip or PWM mode) as the reference voltage of the power supply. This method only replaces the original reference voltage with the microcontroller, and the output voltage value of the power supply can be input by key. The microcontroller does not join the feedback loop of the power supply, and the power supply circuit has not been changed. This method is the simplest. The second is that the microcontroller expands AD, continuously detects the output voltage of the power supply, adjusts the output of DA according to the difference between the output voltage of the power supply and the set value, controls the PWM chip, and indirectly controls the work of the power supply. In this way, the microcontroller has been added to the feedback loop of the power supply, replacing the original comparison and amplification link, and the program of the microcontroller must adopt a more complex PID algorithm. The third is that the microcontroller expands AD, continuously detects the output voltage of the power supply, and outputs PWM waves according to the difference between the output voltage of the power supply and the set value, directly controlling the work of the power supply. In this way, the microcontroller intervenes in the work of the power supply the most. The third method is the most thorough microcontroller control of the intelligent control switch, but the requirements for the microcontroller are also the highest. The microcontroller is required to have a fast computing speed and be able to output a sufficiently high frequency PWM wave. Such a microcontroller is obviously expensive. DSP-type microcontrollers are fast enough, but the current price is also very high. Considering the cost, they account for too large a proportion of the power supply cost and are not suitable for use. Among the cheap microcontrollers, the AVR series is the fastest and has PWM output, so it can be considered for use. However, the operating frequency of the AVR microcontroller is still not high enough and can only be used reluctantly. Let's specifically calculate what level the AVR microcontroller can achieve by directly controlling the switching power supply. In the AVR microcontroller, the highest clock frequency is 16MHz. If the PWM resolution is 10 bits, then the frequency of the PWM wave, that is, the operating frequency of the switching power supply, is 16000000/1024=15625 (Hz). The switching power supply is obviously not enough to work at this frequency (within the audio range). Then take the PWM resolution as 9 bits, and the operating frequency of the switching power supply is 16000000/512=32768 (Hz). It can be used outside the audio range, but it is still a certain distance from the operating frequency of modern switching power supplies. However, it must be noted that the 9-bit resolution means that the power tube can be divided into 512 parts in the on-off cycle. As far as the on-state is concerned, assuming the duty cycle is 0.5, it can only be divided into 256 parts. Considering that the pulse width is not linearly related to the output of the power supply, it is necessary to at least halve it, that is, the power supply output can only be controlled to 1/128 at most. Regardless of the load change or the network power supply voltage change, the degree of control can only go so far. It should also be noted that there is only one PWM wave in the above description, which is single-ended operation. If push-pull operation (including half-bridge) is required, two PWM waves are required, and the above control accuracy is halved, which can only be controlled to about 1/64. For power supplies with low requirements, such as battery charging, it can meet the use requirements, but for power supplies with higher output accuracy, this is not enough. In summary, AVR microcontrollers can only be used in direct PWM control with great difficulty. However, the second intelligent control switch design control method listed above, that is, the single-chip microcomputer adjusts the output of DA, controls the PWM chip, and indirectly controls the work of the power supply, does not have such high requirements for the single-chip microcomputer, and the 51 series single-chip microcomputer is already competent. And the price of the 51 series single-chip microcomputer is still lower than that of AVR. The disadvantage of the intelligent control switch design is that the dynamic response is not enough, and the advantage is that the design is flexible, such as protection and communication, the combination of single-chip microcomputer and pwm chip. The frequency of the pwm output of the general single-chip microcomputer is generally not too high. If the frequency is too high, it is difficult to achieve single-cycle control. So I think the single-chip microcomputer can complete some flexible analog settings, and there are pwm chips to complete some work later. I have seen an article that uses CPLD and single-chip microcomputer for control. It is well known that the price and development difficulty of CPLD are by no means comparable to single-chip microcomputers, so why does he do this? The reason is as the author said, because the PWM width of the single-chip microcomputer is small, the accuracy is low and it cannot meet the requirements of the system. The author also said that in these cases, the application of off-chip PWM circuit is undoubtedly an ideal choice. He chose CPLD chip to implement PWM. I suggest: use the original control chip of the switching power supply. Not only is the price low, but it is also easy to implement protection functions such as single-cycle current detection. We don't need to control digitally just for the sake of digital control. The above is the design of the intelligent control switch. Please participate in the discussion and make corrections.