12v step-down 5v power step-down resistor.
In DC circuits, step-down resistors are generally used to step-down in the case of small current (power). If the load current (power) is large, the resistance is generally not used to buck, because a load current (power) is large, then the power of the buck resistance used will be very large, not only the heat dissipation is not good to deal with, but also a waste of energy.
If 12v is reduced to 5v, and the current is 1 amp hour, then,
Step-down resistance R= (12-5) \/1=7 ohms, and the minimum power of the resistance is 7 watts.
First, use a 7Ω10 watt resistor. Porcelain uranium or wire winding and cement resistors are available (load is resistive).
Second, this is when the load current is assumed to be 1 amp
Third, 12v to 5v requires a 7v step-down on the resistance. 7Ω at 1 amp (theoretical value 7Ω, the actual resistance series does not have, can only choose 6.9Ω. The resistance step-down is 7v (6.9v). 1 amp 7v power is 7 watts (6.9 watts). Leave room for 10 watts.
Therefore, the actual final voltage obtained is 5.1v.
Use a 7Ω10 watt resistor
The 12V DC output power supply wants to become about 5 V, which is only suitable for small current situations. The series resistance needs to be reduced by about 7 volts, the size of the resistance depends on the size of the load current of 5 volts, the specific size of the resistance can be divided by the voltage of 7 volts by this current, and the resistance value is obtained. For example, 5 volts of current is 7 mA, then the resistance is 1K ohms. If the current to be stepped down is relatively large, a 7805 three-terminal regulator block can be used.