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How does the internal circuit in the comparator work?

Latest Updated:03/01/2007

Question:

There is one channel that is not used when using the uPC393 comparator. I will design circuits with the recommended processing (using a 5 V single power supply, short circuit the - input pin and + input pin and connect them to GND (0 V), and keep the output pin open) for the unused pin of the unused channel. In this case, how does the internal circuit in the comparator work?

Answer:

When the input pins are short-circuited, output transistor Q8 turns either ON or OFF as a result of the offset state (amplification voltage is output from the input differential amplification circuit due to the VBE difference between the transistors connected to - input pin and + input pin) in the input differential operational amplification circuits (Q1 to Q6) in the equivalent circuit described in the data sheet.
Due to the fact that the output pin is open, the output current of the unused channel has no influence on the other channels.

[UPC393 equivalent circuit]

Related FAQ:Operational Amplifiers > Characteristics > What is offset voltage?

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Comparators