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i try to make a current 4.2v with the switching regulation methode as you can see in the attached picture.

The problem is that when i ajuste the voltage manualy from the ajustable resistance to 4.5v from a 12v power supply and i unplugged the power source, the voltage change completly in the output to 12v again when i plug the power supply. Did i miss something ? enter image description here

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  • \$\begingroup\$ You missed the part of the datasheet which describes how to set the output voltage. Your feedback with R4 is all wrong. \$\endgroup\$ – brhans Sep 21 at 23:20
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R4, will act like you connect Vout directly to FB, and reach the FB limit (0.950V Max), So Duty cycle of PWM (inside MP2307) will be max.

Solution:change VR R4 to 2 resistors to ground and connect middle of two res to FB pin. enter image description here

R1=26.1k, R2 = 10k (according datasheet)

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