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TLV9061: Driving the load with constant current

yrgat
Prodigy 20 points
Part Number: TLV9061
Other Parts Discussed in Thread: TLV9062

Hi everyone,

I'm trying to drive a load (it can be vary between 5k and 10k) with constant current. I want to adjust current value between 0 - 200mA. I'm using TLV9061. My design is like that;

As expected I can't get 100mA across the load resistor (5k). If 100mA passes between 5k load resistor, 500v voltage drop occurs and it is impossible in this design. How can I overcome this problem? Is it possible such a design with TLV9062 or I need something else? Do you have any suggestion?

Thank you for your help.

tlv9062_design.TSC

  • Former Member
    0 Former Member

    Hi,

    Thanks for your question and welcome to the forum!

    Your analysis is correct in that, if we try to drive 100mA through the 5k load, then we are also trying to drop 500V across the R4 component and this can clearly not be done with the 300V V3 source.

    Can you please explain your design requirements/desires more clearly?  Where is this 300V source coming from?

    The combination of the TLV9062 with a FET should be able to provide you with 100mA, but it all depends on the characteristics of the FET.  If you need even more current, you may consider a Darlington-pair arrangement.

    300V is very high and it seems like the FET you've chosen can only handle 60V across the Drain-Source.  Furthermore, the amplifier is a 6V amplifier.  Exposing it to higher voltages will damage it.  Another thing I'd point out is that you can have up to an entire Watt of power flowing through the R2 resistor under 200mA conditions.

    Again, if you could explain why the 300V source is there, what has to be in the design, what does not have to be in the design, etc. it would help me a lot.

    Regards,

    Daniel

  • 0 in reply to Former Member
    Prodigy 20 points

    Hi Daniel,

    Thank you for your detailed answer and interest.

    300V coming from a flyback converter. Actually I expect that voltage dramatically drops when after drawing current from the source but it doesn't important for this application. I'm trying to stimulate the human muscle with this current. So load is actually human tissue not a resistor or something else.

    Also I stimulate the tissue with pulse. So there is no need to draw current constantly. I don't know it is acceptable because I'm working only on simulation, but I realize that when I put a capacitor parallel to load, then I'm able to draw 100mA from the source for a short time. Because I don't need to draw current for a long time maybe It will be enough.

    Do you have any suggestion? I can change the design completely.

    Thank you for your answer.

    Best regards.

  • Former Member
    0 Former Member in reply to yrgat

    Hello yrgat,

    Thank you for the further information.  It helps to clarify things.

    The issue here is going to be that the 5k to 10k load is too large and will create issues for you as the voltage drop across them will be very large.  You can use the resource below to get a detailed explanation of how to design such circuits.

    High-Side Voltage-to-Current (V-I) Converter

    I can't speak to whether the 5k to 10k load considered here is accurate.  It may not be correct for what is being modeled.  I would also advise that these types of current levels are definitely dangerous for humans.  Though this is not a safety forum, I believe it should be pointed out.  Have you checked that this current is ok?

    You mentioned that adding a load capacitor in parallel helped deliver pulses as needed.  This may well be the case as the capacitor can act as a "charge bucket."  It can store up the charge in its electrical field and then deliver it when the voltage changes.  This may, however, have secondary effects on your transient response that are not desirable.

    To summarize, my suggestion would be to verify that the load model is accurate and what type of voltage source you're planning on putting across the load.  This will determine whether this approach can be used or another is needed.  Also, please verify the safety of your application.

    Regards,

    Daniel