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Part 1: High Voltage Regulation
Part 2: C-library driver
Part 3: 24 Neon Lamp clock

A typical power supply controller uses both input current and output voltage to regulate the output voltage, so whatever load connected to the output, its voltage level stays stable. This is passive or reactive type of control. With a MCU controlled power supply, something like that can be easily implemented, but a MCU is much smarter, it knows exactly what the load is connected, and can proactively change the input current based on the load. For a 24+1 neon lamp clock, the load is just that, and can be easily represented by an integer from 1-25. The output voltage is the most stable with this technique, if 24 neon lamps are blinking at the same time. Any other feedback loops are not as stable under this extreme situation. The 24 neon lamp's brightness can be controlled by the output voltage, and each set of 8 neon lamps can be individually controlled by 3 different PWM hardware channels. Using the load as feedback to control the output is a bit tiresome in this situation.

To sum up:
Using a peak voltage and fixed frequency and duty cycle is ideal for produce a stable output voltage under different load, but if the load is light, the inductor will be buzzing, even a uni-body high quality inductor is installed.

Using PFM or PWM is ideal if the load is stable, but its response time is much slower since MCU response time is not very fast. There are 2 delays: ADC input delay and stabilization output delay. Blinking 24 neon lamps works fine and is not dangerous, but the output voltage is not stable. Not a problem for this board, since it can handle up to 200v, and ADC limits its output voltage to 140v, adding triple level of over-voltage protection. All neon lamps light up with an output voltage of 80v, so 80-140v is the main brightness control range plus 256 steps on each set of neon lamps.

Using the switching load as a feedback to control the PWM is ideal both in voltage stabilization and efficiency, but this doesn't work that well if load is dimmable. 3x 256 steps on 24 neon lamps is equivalent to 3*256*24=18432 possible load. Although brightness control for neon lamps is best in 3-5 steps.

Power:
Maximum current is less than 500mA with all neon lamps ON at 110V. Main power component warm to the touch after 1 minute of run time. 0.5*5=2.5 Watts. The output voltage will be limited to less than 140v, for safety and efficiency. The board has been tested for 180v and is working fine.

Finally:
It's determined that combining 1 and 3 loop is the best for ease of control, high efficiency, and flickering and buzzing free.