The specific circuit is shown in the figure. Among them, the AC power transformer is 9Vac/6W, the four rectifier diodes are 1N400 1 (the maximum rectifier current is 1A, and the reverse withstand voltage is 30V), and the two filter capacitors are 2000μF/ 16V and100μ f/. The above components are the most commonly used, and they are easily available in the electronic market. The total cost is about 10 yuan (calculated by retail price).

The effective output voltage of AC power transformer is 9V AC, and the peak voltage is12.7V. After rectification and filtering, it becomes DC voltage of10.7V ~11.3v, with a small amount of AC ripple. Considering that the grid voltage will fluctuate by 10% according to the standard, the DC voltage is 9.4V ~ 65433.