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LM124AQML-SP: LM124A-SP: Voh, Vol at low supply voltage

Part Number: LM124AQML-SP
Other Parts Discussed in Thread: LM124A, TLV1704, LM139AQML-SP, LM339, LM139, LM124AQML, LM324, LM358, LM124

I am looking for an OPAMP working down to 3.3V, SP or SEP.

In the application=, it will be used as in a comparator mode with small output current level:  3 to 5ma max

don't need real sophisticated performance but my goal is to drive a NPN base transistor through a series resistor (Emitter to GND)

then Vol/Voh shall allow proper ON/OFF operation

Supply level can be adjusted from 3.3 to 4.5V

LM124A datasheet does not show much data about Vol and Voh performances at low supply level and low current. 

Q1 Can you provide some ?

Q2 Do you have another OPAMP that could be used as a superior or good substitute?

I was also trying to understand the difference between these 2 part numbers:

LM124AWGRQMLV        5962R9950402VZA       (more expensive  by 40$)

LM124AWGRLQMLV     5962R9950401VZA

From Octopart, 402VZA model seems to have better performance (slew  rate)...but I can not find this information on TI web site

Q3 Can you tell me where I can find this information ?


  • Hi Kai

    I was looking to the TLV1704 previously and the Vol guarantee  was very high: 1.1V

    LM139AQML-SP seems to have 250mV guarantee @ 4mA

    is it true for down to supply = 3.3V ?

    in the electrical characteristics,

    Isink min = 6mA @ Vo = 1.5V

    Vsat @ I sink=4mA   =  400mV  and 700mV (sub groups 2,3)

    at 700mV, a NPN transistor could be turned ON when it shouldn't in the application

    this is why I was not trusting it.....

    I could but a resistor divider between the LM339 op  and the NPN base. to reduce the voltage level.....

    Can we get data about the OPAMP and the LM339 to see which one could simplify the solution ....

    let me know what you think



  • Hi Yves,

    I cannot properly answer your question without knowing your base current.

    There are at least four options:

    1. A pull-up plus a voltage divider in front of the NPN.

    2. A pull-up (plus a single base resistor) in front of a NPN-Darlington.

    3. A voltage divider in combination with a PNP: 470R from the output of LM139 to the base of PNP and a 10k resistor across the base emitter juntion, with the emitter connected to the positive supply voltage.

    4. A pull-up (plus a single gate resistor) in front of a N-MOSFET.

    What load do you want to drive with the NPN? What NPN do you intend to use?


  • Hello Kai

    My goal is to simplified the circuit

    I already got a solution using PNP and Comparator with open-collector output

    I can not use NMOS

    this is why I would like to know more about the LM124A Vol at Vsupply=[3.3 - 4.5]V

    do you have this information ?



  • Hi Kai

    From Design Support LM124AQML: Output voltage swing  in  Amplifier Forum

    Making reference to Application Design Guidelines for LM324/LM358 Devices   SLOA277A – JANUARY 2019 – REVISED AUGUST 2021

    It seems that Voh-Vcc  is independent of VCC value for a certain load.

    The datasheet does not contain information @Vcc=3.3V

    Only this at Vcc=5V:    Voh will be 2.4V @ Vcc=5V, Isink=10mA  :  2.1V drop

    Is it possible to get information about Voh_min when current level is below 1mA, 100uA ?

    Voh-Vcc   shall be smaller than -2.5V to get enough current through NPN base. (estimated to 66-80uA minimum)

    For Vol, in my application, the current will be null (NPN base to gnd), then what could be the Vol_max level in that case (Vcc=3.3V)?

    Let me know



  • Hello Yves,

    For LM124, VOH with low current will be based on semiconductor physics and will always be similar to chart in application note.  VOH at higher current will vary more with device performance. VOL when no sinking current is required, will be close to ground.

    Cold will be the weakest NPN drive because VOH is least, VBE is greatest, and NPN beta is lowest. So check this carefully.

  • Hi Yves,

    I would definitely go for the solution with the PNP driven by a true comparator with open collector output. This combination looks optimal.


  • Hey Yves, 

    Was the issue resolved? I will mark Kai's answer as "TI Thinks Resolved," please confirm.
    If the issue isn't resolved, please let us know so we may further assist. 

    All the best,