The current can not use resistance step-down, the pressure difference is about 0.7V can use the rectifier diode, the current is large or the pressure difference is large, you can use the DC-DC conversion chip.
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The use of resistance buck is suitable for the current within 500mA, and the current is relatively stable occasions. The use of resistance buck, the circuit is simple, directly between the battery and the electrical appliance string a resistor can be, according to the current through and the required voltage drop, calculate the resistance wattage. It is not suitable for high-current circuits, because the resistance wattage will be larger, the volume will be increased, and the resistance heat dissipation needs to be considered.
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Diode step-down, if the battery voltage and the electrical appliance required to obtain the voltage is about 0.7V, you can directly between the battery and the electrical appliance string a rectifier diode, the current is within 1A, you can choose 1N400 series, greater than 1A, you can choose 1N540 series. The voltage drop of the diode itself is about 0.7V, which can meet the voltage needs of electrical appliances.
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Electrical appliances require large current, or require stable voltage, you need to use DC-DC voltage conversion chip. You can use the BL8505-3, the external only need an inductor, an output capacitor, and a Schottky diode, you can solve.