Under voltage detection

Discussion in 'General Electronics Chat' started by mishra87, Feb 9, 2016.

  1. mishra87

    Thread Starter Member

    Jan 17, 2016
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    I have NCP300 with sft1341 mosfet. I want to monitor my battery at 3V. Does attached circuit work. I have a confusion how P channel MOSFET works with NCP300. Could anybody explain me working of this circuit.

    Thanks
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    A P-channel MOSFET will not work in your circuit as you have drawn it. Why have you added it, since the NCP301 is available with an open drain? If you want to invert the logic polarity of the output, use an N-channel 2N7000 or 7002 as an inverter.

    Page 1 of the datasheet shows the internal schematic, and pages 14-16 describe its operation.

    ak
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    When the battery voltage drops below 3V (assuming you have the 3V version of the NCP300), the IC output goes low, turning on the PFET.
    It looks as though your PFET is upside down.
    Your circuit output can pull down only as far as the Vgs(thr) threshold, not to zero.
     
  4. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    NCP30x for battery low voltage detection
    I have Li ion 3.7 V single cell battery and I want to prevent it by deep discharge. So by using NCP30x I can monitor threshold voltage at 3V. Since it has got active low output for reset so I want to drive a mosfet as switch in a such manner that when my input voltage is above 3V , the load deliver same as input and when input is below 3V it disconnect the load.

    What does it mean if you say open drain.
    What could be schematic to achieve above.
     
  5. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    NCP30x for battery low voltage detection

    I have Li ion 3.7 V single cell battery and I want to prevent it by deep discharge. So by using NCP30x I can monitor threshold voltage at 3V. Since it has got active low output for reset so I want to drive a mosfet as switch in a such manner that when my input voltage is above 3V , the load deliver same as input and when input is below 3V it disconnect the load.

    What does it mean if you say open drain.
    What could be schematic to achieve above.
     
  6. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    NCP30x for battery low voltage detection
    I have Li ion 3.7 V single cell battery and I want to prevent it by deep discharge. So by using NCP30x I can monitor threshold voltage at 3V. Since it has got active low output for reset so I want to drive a mosfet as switch in a such manner that when my input voltage is above 3V , the load deliver same as input and when input is below 3V it disconnect the load.

    What does it mean if you say open drain.
    What could be schematic to achieve above.
     
  7. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    Could you explain me what is open drain. So in open drain I need not to connect switch. I am not more technically sound so please explain me how to do in order to achieve my objective.
    My objective is if Input voltage above 3V i.e. 3-4.2 I should get same voltage and if less than 3V it disconnect the load.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Open drain means the drain of the output N-FET in the NCP301 isn't connected to anything.
    For your purpose, connect an inverting stage (as AnalogKid mentioned) between the IC output and the P-FET gate, and connect a pull-up resistor between the P-FET gate and V+.
     
  9. hp1729

    Well-Known Member

    Nov 23, 2015
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    (mot homework, right?)

    You want +V out when > 3 V and low when < 3 V? Or the opposite. Both options are shown for both types. Open Drain is shown in the NCP301. "Open collector" for a CMOS output.
    Most confusing ... if the output is on the P-MOSFET side the Source goes to +V and the Drain is still an "open drain" output.
     
    Last edited: Feb 10, 2016
  10. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
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    Thank you so much for your reply !!!
    Now i have some confidence by looking schematic diagram.
    My end application is Electronic Pipette Controller and i have to drive inductive load (stepper motor). My intention to implement this circuit is avoid deep discharge of battery as i told earlier as well. i have implemented the same by using some Battery protection IC like MM3280 and Mosfet but was unable to implement and deliver the result. As per i think the quiescent current of NCP30X is .5uA so its not enough to drain the battery fully if it is in active low state means when the load is disconnected. I do not that am i right.

    +3.7 when > 3 V
    Gnd when < 3 V Actually that is what i was looking for and have 2 options to do so.

    Before procuring the part number i want to know that i have few quarries.

    is NCP301 able to deliver the current of 1A peak. i have below test report of our instrument.

    Input Current of Instrument :
    Power On: 19.2Ma (Transient state)
    Standby mode: 4.2mA
    Switch is pressed: 56mA (Transient Current)
    Full Load : 132mA (Transient state Pump On)
    : 102mA (Steady state Pump On)
    Load Current :
    Current drawn by PUMP :
    DISPENSE MODE:
    A). Transient state: 125mA
    B). Steady state: 76mA
    ASPIRATE MODE:
    A). Transient state: 135mA
    B). Steady state: 77mA

    Please let me know whether it is worth implementing.
     
  11. hp1729

    Well-Known Member

    Nov 23, 2015
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    Re: "is NCP301 able to deliver the current of 1A peak."
    No 70 mA, thus the need for your transistor on the output.
     
  12. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    What is the best options for my application.
    BJT or MOSFET ( High or Low side switching)
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    70 mA is the absolute worst case under a test condition. At that current, either sourcing or sinking, the output voltage will be the opposite of the intended state. For example, the only way for the output to source 70 mA by pulling the load high is if it is shorted to ground. Even at 10 mA (datasheet page 6) the output voltage is sagging to 50% of the rail in some conditions. The plots on page 13 confirm this.

    The best way to drive a load with this part is to use an N-channel logic-level MOSFET for low-side switching. Note that without adding hysteresis the output might oscillate.

    ak
     
  14. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    Could you support me some schematic and part number of logic level mosfet. Does it suitable for my application.

    3.7 when >3V
    Gnd when < 3 V that is what I am looking for. Please have a look of attached schematic by hp1729 in 2nd coloumn figure. In either cases we are getting inverted output so that is not my requirement.

    So as far I think either we need to add High side switching in 1st coloumn schematic or need to add inverter in 2nd column schematic.

    Can it be done by P channel Mosfet. I am not more technically sound do please explain me by schematic so that it is easy to understand me as hp1729 done...

    Thank you so much for all your effort.
     
  15. hp1729

    Well-Known Member

    Nov 23, 2015
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    I am missing how you are getting from the NCP301 to a stepper motor.
     
  16. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    In a pipette controller I have to aspirate and dispense the liquid for that I need to drive motor. The motor has been directly driven by battery through mosfet configurations. So my actual load is not motor . Its pipette controller which has got many more peripherals like OLED, CONTROLLER, Buzzer and Keyboard , pump.

    This circuit I want to connect between battery and pipette controller. To stop deep discharge of battery . Since intsrument is in production so I do not want to do any further changes in circuit and i want to do so by externalcomponents.

    So that's why I asked that is NCP30x able to drive my load if not so how I can do . That's all.
     
  17. hp1729

    Well-Known Member

    Nov 23, 2015
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    Not a bad idea. So how did you intend to accomplish this connection? Monitoring the battery is no problem.
     
  18. mishra87

    Thread Starter Member

    Jan 17, 2016
    168
    2
    As per your schamtic , i.e for 1st coloum schematic can it be done by using some converter circuit something like MOSFET as a switch .

    And in 2nd column schematic , i can be done by adding Inverter before MOSFET.

    2nd option :
    NCP30x has also got Active High reset output so the all outputs of your combination will just opposite and by mosfet switching can get the results.

    If by doing that we are able to load then fine we can think of selection of Mosfet i. e. Either Power/logic .

    Please edit the schematic according to my requirement so that I can move further.
     
    Last edited: Feb 11, 2016
  19. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Expanding on hp1729's posts, here are the two options (A for high-side and B for low-side switching of the load). The NMOS FET should be a logic-level type with a Vgs(thr) < 1.5V.
    SwitchingLoad.PNG
     
  20. hp1729

    Well-Known Member

    Nov 23, 2015
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    This?
     
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