Microcontroller control of switching power supply several control mode analysis
One is that the microcontroller outputs a voltage (via DA chip or PWM method), which is used as the reference voltage of the power supply. This way is just a microcontroller instead of the original reference voltage, you can use the key to input the output voltage value of the power supply, the microcontroller does not join the feedback loop of the power supply, the power supply circuit has not been changed. This way is the simplest.
The second is that the microcontroller extends the AD, constantly detecting the output voltage of the power supply, according to the difference between the output voltage of the power supply and the set value, adjusting the output of the DA, controlling the PWM chip, and indirectly controlling the power supply. This way the microcontroller has been added to the feedback loop of the power supply, instead of the original comparison of the amplification link, the microcontroller program to use a more complex PID algorithm.
The third is the microcontroller to extend the AD, constantly detect the output voltage of the power supply, according to the power supply output voltage and the difference between the set value, the output PWM wave, directly control the power supply. This way the microcontroller intervenes in the power supply work most.
The third way is the most thorough microcontroller control switching power supply, but the requirements of the microcontroller is also the highest. Requirements for microcontroller computing speed, and can output a high enough frequency PWM wave. Such a microcontroller is obviously also expensive.
DSP class microcontroller speed is high enough, but the current price is also very high, from the cost considerations, accounting for too large a proportion of the cost of the power supply, should not be used.
Cheap microcontroller, AVR series is the fastest, with PWM output, can be considered. However, the operating frequency of AVR microcontroller is still not high enough, can only be barely used. Here we specifically calculate the AVR microcontroller directly control switching power supply work can reach what level.
AVR microcontroller, the highest clock frequency of 16MHz, if the PWM resolution of 10-bit, then the frequency of the PWM wave is also the operating frequency of the switching power supply 16000000/1024 = 15625 (Hz), switching power supply work at this frequency is obviously not enough (in the audio range). Then take the PWM resolution of 9 bits, this time the operating frequency of the switching power supply is 16000000/512 = 32768 (Hz), which can be used outside the audio range, but there is still a certain distance from the operating frequency of modern switching power supplies.
It must be noted, however, that the 9-bit resolution means that the power tube conduction - off in this cycle, can be divided into 512 parts, on conduction alone, assuming a duty cycle of 0.5, can only be divided into 256 parts. Taking into account the pulse width and power supply output is not a linear relationship, the need for at least another discount, that is, the power supply output can only be controlled to a maximum of 1/128, whether the load changes or the network power supply voltage changes, the degree of control can only be up to this point.
Note also that there is only one PWM wave described above, which is single-ended. If you want to push-pull work (including half-bridge), then you need two PWM waves, the above control accuracy should be halved, can only be controlled to about 1/64 of the power supply does not require a high level of charging, such as batteries, can meet the requirements of use, but for the requirements of the power supply output accuracy is higher, this is not enough.
