At least he supplied a schematic, which made the answer immediately obvious.Of course the LM339 data sheet will also show that the output is open collector (but who looks at a data sheet? ).
The LM339 comparators have an "open collector" output. They require a pull up resistor (R6). Google "open collector" for more info.
Of course the LM339 data sheet will also show that the output is open collector (but who looks at a data sheet? ).
Thank you very muchThis comparator with an open collector. Additional resistor gives current sourcing. The scheme can be simplified. Make R6 = 10kOhm. Remove the resistor R4. The base of the transistor connect to the output of the comparator.
View attachment 91900
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