LM321: Schematic check

Jim Tsai

Part Number: LM321

Hi,

Please refer to the schematic, can I add 1000pF to -IN (pin3)?

0 Ron Michallick over 3 years ago

Hello Jim,

Is the purpose of R15 and R16 to control the VOH of the LM321. An open drain comparator would do this more efficiently.

The non-inverting input voltage is above the common mode input range. The correct range is 0V < IN < VCC - 2V

Is the capacitor the only connection to inverting input? If true then input bias current will charge the capacitor.

0 Jim Tsai over 3 years ago in reply to Ron Michallick

Hi Micha,

I’ll modify design to meet 0V < IN < VCC - 2V.

The capacitor is only connect to inverting input, so is that ok?

0 Ron Michallick over 3 years ago in reply to Jim Tsai

Jim,

If the circuit is supposed to be an "high temperature" detector then the capacitor won't work.

If the circuit is supposed to be an "one and done monostable timer" then time will vary with the input current so the time won't be consistent.

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