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4097 Views 3 Replies Latest reply: Mar 8, 2010 3:03 AM by enrico.migchels RSS
vips Level 1
vips
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Mar 2, 2010 7:29 PM

Voltage window detector/comparator

We have a chip used in the design which has certain voltage level restriction.

There are two voltages, one is 1.0V and other is 1.2V (independent supplies), the restriction is the difference between these two should never be more then 300mV

I have searched many but couldn't find one which would dinamically compare both supplies, all those I found has one supply as a reference.

Please help me out!!!

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  • enrico.migchels Level 4
    enrico.migchels
    Currently Being Moderated
    1. Mar 3, 2010 2:14 AM (in response to vips)
    Re: Voltage window detector/comparator

    Hi Vipul,

     

    You don't mention what should happen if the voltage difference is > 0.3V. Are you allowed to regulate 1 of the 2 voltage accordingly (to meet Vdif < 0.3V)? or do you want 1 or both supplies to switch off? I would recommend if your suppy voltages have a high tolerance or a high output impedance (far away located from the chip) to make a small reference suppy of 1V and 1.2V close to the chip. The current needed for the chip is small i guess?

     

    Best regards,

     

    Enrico Migchels

    Power Converseion Design Engineer

    Heliox B.V.

    Best - The Netherlands

  • vips Level 1
    vips
    Currently Being Moderated
    2. Mar 5, 2010 4:09 PM (in response to enrico.migchels)
    Re: Voltage window detector/comparator
    Hi Enrico,

    Many thanks for the prompt response.
    If the  difference goes over 300mV, then the circuit should give some high or  low out put which in turn will be use to shut down one of the power  supply (preferably 1.2V).
    Current is pretty high, on 1.0V it is about 16Amp and on 1.2V it is  about one Amp.
  • enrico.migchels Level 4
    enrico.migchels
    Currently Being Moderated
    3. Mar 8, 2010 3:03 AM (in response to vips)
    Re: Voltage window detector/comparator

    Hi Vipul,

     

    If you have a higher voltage to work from you might consider using a instrumentation amplifier (see link below). The opamp needs 5 - 15Vdc for the supply.

     

    http://en.wikipedia.org/wiki/Instrumentation_amplifier

     

    The instrumentation stage could be followed by a comparator stage (4th opamp from a quad-opamp, for example LM324). Tie one of the inputs to a stable reference voltage, for example a TL431 (2.495), the other input senses the voltages coming from the instrumentation amplifier. Don't forget to add a positive feedback from output to + input for hystereris.

     

    TL431 = 2.5V

    Max voltage difference = 300mV

     

    Gain instrumentation amplifier = 8.33 (resistor settings)

     

    With the output voltage of the comperator you can disable the 1V2 power source. Always remember that this circuit could cause troubles at start-up. You should look very carefull at the timing between the 1V and 1V2 power source.

     

    Best regards,

     

    Enrico Migchels

    Power Conversion Design Engineer

    Heliox B.V.

    Best - The Netherlands

    www.heliox.nl

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