How to change DC 5V voltage to 3V voltage?
1?? From your description, turning 5V DC into 3V I guessed that your 5V DC is an old phone charger, and you want to turn this output 5V into 3V for the purpose of using it as two 1.5V batteries. This method is good, I have used this method to do a lot of power supplies, you can use the following methods to get:
* Open the charger box, find the output end has a 0, 5X0, 3Cm large black rectangular part called optocoupler, as long as you find a place on the two feet of the output end with a welding line in parallel with a resistance of tens of ohm, immediately become from 5V output to 3V, too simple,
* In order to adjust to 3V, you can use the potentiometer in parallel, adjust the twist exactly to 3V, and then measure the resistance, change a fixed resistance is good.
* Your bold attempt, the optocoupler output of one or two pins such as short circuit, the output is zero volts, I did not fail in many tests, and I changed to 1.5V ~ 12V to fine tune the selection voltage!
* Because you want the output current of the battery, when the charger is reduced to 3V, the current is not lower than the operating current of the 3V battery.
2?? If you do not have the above hands-on ability, it is simple to find three diodes in series on the positive line, that can get 2.9V voltage, you and an electrolytic capacitor, and can get 3V DC.
3?? If you have the hands-on ability and a small transformer, you can subtract the secondary coil from the number of thick turns of the output, stop and plug in 220V measurement, when the low-voltage output AC is 2.8V, and then use bridge rectification and filter, so that you will get 3.2V DC, more than 0.2V as a voltage drop consumption, exactly 3V DC.
4?? If the voltage of the transformer is 6 ~ 12V, you can not reduce the number of coils, but also after rectification and filtering, find a triode that can be installed with heat sink, and step-down into 3V. Its disadvantages are high voltage, low voltage, current overload heat, to install heat sink!
[Figure 1 is the schematic diagram of the mobile phone charger], [Figure 2 is the optocoupler diagram, R is the resistance you want to combine], [Figure 3 is the transformer output drop to 3.2V], [Figure 4 is the black arrow on the board is the optocoupler], [Figure 5 is the voltage regulator power supply I modified with the mobile phone charger], [Figure 6 is the old lithium lamp I assembled, it is charged with this voltage regulator power supply, which is always normal]
Thank you for reading?? !
First, the two resistors are connected in series.
< br >
The resistance leads to a line.
< br >
The [2K resistor] end is connected to the [positive electrode] of the power supply, and the [3K resistor] end is connected to the [negative electrode] of the power supply.
< br >
After power-on, the resistance [series central point to ground voltage] is [3V].
< br >
Summary: 1. First put two [resistors in series].
< br >
2, resistance [series center point] leads to a line.
< br >
3. One end of the [2K resistor] is connected to the power supply [positive electrode], and one end of the [3K resistor] is connected to the power supply [negative electrode].
< br >
4. After power-on, the resistance [series central point to ground voltage] is [3V].
The simplest way is to use the LM1117 3.3V voltage regulator module with 5V input and 3.3V output
The simplest is 3 1N4007 diodes in series at the 5V output, but it is less efficient! For high efficiency, you must use a 5V to 3V DC-DC converter!!