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Timer Queries

Anuraj nk
Intellectual 330 points
Other Parts Discussed in Thread: TLV9064

Hi Sir,

In my current deign of Ground Fault Circuit, I have a requirement to detect the fault only if the fault exists there for more than 0.4ms. If it is less than 0.4ms , no need to detect.

Please see the below diagram for better understanding.

 

 

Please suggest a part which meets this requirement.

Regards

Anuraj NK

  • 0
    TI__Guru 71526 points

    Hello Anuraj, 

    From your description, it seems you already have the Fault Detector designed, and you are asking for a timer to generate a 400usec signal to activate the Fault Detect circuit, is this correct? 

    You can choose from a number of Timers, such as the http://www.ti.com/product/NA555 .  

    If my understanding of your inquiry is not correct, please provide additional information, and perhaps a block diagram of this design.  ALso note that TI has several Reference Designs that incorporate Fault Detection, such as: 

    TIDA-01598    - Low Side, High Bandwidth Current Amp and Fault Detection for Solar Inverters Reference Design 

    TIDA-00807   - Fault Monitoring for Overhead Fault Indicators using Ultra Low Power Reference Design

    T

    TIDA-00442  - Shunt based Ground Fault Protection for Inverters Powered from 220Vac Supply Reference Design 

     

    Regards,

    ~Leonard 

     

  • 0 in reply to LeonardEllis
    Intellectual 330 points
    Hi Sir,

    I have the fault detection circuit designed. My system dont want to respond for fault current if it exists for less than 0.4ms. System should respond only if the current stays there for more than 04.ms. I am expecting the high current in less 0.4ms is due to the coil winding imbalance or the initial surge current.

    I have a comparator which gives high signal when ever the Ground Fault current is reached. But I need a timer circuit which neglect this high signal if the time is less than 0.4ms and the timer should respond if the comparator output stays for more than 0.4ms.


    Regards
    Anuraj NK
  • 0 in reply to Anuraj nk
    TI__Guru 71526 points

    Hi Anaruj,

      You can use the suggested timer to generate a pulse to disable the Fault Detection circuit for the 400uS.  When the 400uS times-out, enable the Fault Detector, keep it enabled until the next event.

    ~Leonard 

  • 0 in reply to LeonardEllis
    Intellectual 330 points

    Hi Leonard,

    Thanks for quick response. Can you suggest a timer part with below requirement. I am looking for the part other than the 555 since  555 is Re trigger-able.

    1. Single package

    2. Non-Retriggerable

    3. Should have a clear or reset pin.

    Regards

    Anuraj NK

        

  • 0 in reply to Anuraj nk
    TI__Guru**** 168946 points

    Anuraj,

    All of the 555 timers are non retriggerable. Timing (out high) starts on trigger low  and ends of threshold high. However, if trigger is still low when threshold is high the timing pulse won't end until trigger goes high. All 555 input are level sensitive (not edge sensitive). Reset input is the most powerful.

    I played with a few 555 circuits but I believe I need a 556 dual instead. Nevertheless I wasn't happy with my first attempt.

    I do like some aspects of this lightly tested TLV9064 solution. It really depends on the input "noisy" signal.

    TLV9064 400us.TSC

  • 0 in reply to Ron Michallick
    TI__Guru**** 168946 points

    Anuraj NK,

    This TLV9064 circuit could be reset by NPN collector(s) shorting out one or both capacitors.

    It also doesn't latch high. However the 4th amp in TLV9064 could be a latch.

  • 0 in reply to Ron Michallick
    TI__Guru**** 168946 points
    Anuraj,

    Let me know if you need more assistance. One thing that makes this solution difficult is that the input signal is not static high.
    It is easy to time 0.4ms, but then what? If input is high at that time then set output high, easy. If input is not high but goes high shortly after; that is harder. How long to wait for that high input before forgetting the first initial high input signal? So the task could stated as as input is high for more than 0.4ms but can be low for less than 'x' during the input "high" time.