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walid

Is it bad design?

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jb13315632171.jpg

What is the function R3
If you know that the output voltage at both ends of the 220u capacitor is 9 volts DC, is not this resistance wastes 9mAh all of time
What is the point of that?
thanks

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If the transformer is low quality (cheap) then its output voltage is very high when there is no load. I have a cheap AC-DC wall wart with a rated output of 9V/100mA and its output is correct. But without a load its output is 19VDC.

The 1k resistor R3 provides a load when there is no other load to keep the output voltage from being too high.

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