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TLV9061: Constant current sink for AC

Gary Kitten
Prodigy 130 points

Part Number: TLV9061

Hello all,

I'm trying to design a constant current sink for a photoelastic modulator (PEM).  This PEM returns current in an AC format, but it seems all the reference designs for constant current sinks target standard DC current.

I've been looking at this TLV9061 reference design:

http://www.ti.com/lit/an/slaa868/slaa868.pdf

The voltage across Rset is going to be fluctuating since it sees an AC current.  How can I program the DAC to focus on / track the positive peak of this AC current?

In essence, I want a constant AC current going through Rset.

Thank you!

  • 0
    TI__Guru**** 174826 points

    Hello Gary,

    I only learned about Photoelastic modulators just now after a couple minutes of reading. So I'm no expert.

    Is the goal to provide an AC current to the modulator? If so how much current, how much bandwidth, what is the the RCL (electrical equivalent) of this Photoelastic modulator?

    Also what supply voltages are available to use?

  • 0 in reply to Ron Michallick
    Prodigy 130 points

    Ron,

    The goal is to stabilize the feedback (return) current the modulator produces.  This will be in the 10 mA range, at 45 to 70 kHz.  I have multiple supply voltages at my disposal:   +/-5V, 3.3V, 24V.

    But I think the key question here is:  how can I create a constant current sink for an AC current?

  • 0 in reply to Gary Kitten
    TI__Guru**** 174826 points

    Gary,

    Constant and AC are contradictory concepts. Do you mean AC voltage to AC current convertor (Voltage controlled current source)?

    10mA is a current level that many op amps can do by themselves. The characteristics of the load driven will be a big factor. I just pick load characteristics arbitrarily and put this together. The circuit run near resonance which may be similar to your needs.

    Output current is VIN / 10 ohms

    TLV172 Resonance driver.TSC

      

  • 0 in reply to Ron Michallick
    TI__Guru**** 174826 points

    Gary,

    Just reply to this e2e thread if you need more assistance with this issue. I will be glad to help you further.