7805 is a linear voltage regulator chip, a characteristic of the linear voltage regulator circuit is that the greater the pressure difference, the lower the efficiency, the more serious the heat. 7805, for example, suppose that the output load current is 0.5 A, so when to 12 v power supply, the differential pressure of 7805 is 12-5 = 7 v, heating power for P = UI = 7 * 0.5 = 3.5 W; If it is powered by 8V, the pressure difference of 7805 becomes 8-5=3V, and the heating power is reduced to P=UI=3×0.5=1.5W. 78 series voltage regulator chip differential minimum value is 2 v, so for 7805, 7 v power supply is the best choice. Its upper input voltage should be 35V. Attached is the DataSheet of TI's LM7805.
7805 Typical circuit to solve the pressure difference too big heat problem there are the following ways:
1. Reduce the input voltage, reduce the pressure difference, thus reducing heat;
2. Increase radiator area to improve heat dissipation efficiency;
3. Use low-voltage differential linear regulators, such as LM317, to replace 7805. This allows for a smaller pressure difference and less heat. In addition, the pressure difference and heating can be reduced by reducing the load current and increasing the capacitor filter.