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  1. #1
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    Error amplifier's output is very low as it controls led driver (Op Amp output)

    Hi,
    We are designing a 6w LED driver using a HV9910B Driver IC, and an external error amplifier comprising a MCP6001 which drives the “LD” pin of the HV9910B. The control range for the LD pin of the HV9910B is from 0V to 0.25V…As such, the error amp’s output range for control will obviously be between 0v and 0.25V…this is very low, and even though the MCP6001 is said to be “Rail to rail input /output”, do you think this is too low?
    Should we put say two forward biased diodes between the MCP6001’s output and the LD pin, to raise up the voltage of the MCP6001 output as it controls the HV9910B?

    HV9910B datasheet:
    http://ww1.microchip.com/downloads/e.../20005344A.pdf

    MCP6001 datasheet:
    http://ww1.microchip.com/downloads/e...Doc/21733j.pdf

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  2. #2
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    Re: Error amplifier's output is very low as it controls led driver (Op Amp output)

    Adding diodes will degrade temperature stability. If you are concerned about near-ground response, why not use a potential divider at the output and increase the amplifier gain to compensate.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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  3. #3
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    Re: Error amplifier's output is very low as it controls led driver (Op Amp output)

    If the diodes are inside the feedback loop their variation should be irrelevant.

    So I don't think they harm anything but just check the specs, it says it goes to gnd+25mV. Unless you're really concerned about performance way down there it seems fine.


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