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TINA/Spice/OPA551: Output current question

Part Number: OPA551
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hi team,

The customer use OPA551 to build up a current source whose current can be changed by changing the voltage of the V+. See the simulation in TINA.

And the simulation in TINA shows when the schematic is correct.

But when I test the current output in the circuit without connecting the load, the current range is (-60mA 20mA).

After I connect the load, the current range becomes (-41.68mA 41.68mA) which is the same as the simulation.

Could you explain the cause?

There is about 0.3V gap between the positive and negative input of the amplifier and the temperature of the amplifier is high.

Does it make sense?

Thanks a lot!

Lacey

  • There are several key concerns with power op amp V to I circuits like yours. Refer to the link below for some detailed explanation of how to design with these circuits. Pay close attention to the thermal design. I will perform and post a stability analysis for you but I need both the resistive and inductive part of your load. Also I need exact input voltage waveform you are trying to command current through the inductive load. Frequency, rise/fall times, and amplitudes. There will be small signal bandwidth limitations, large signal bandwidth limitations (slew rate), and physics limitations (V=L*dI/dt).
    Link:
    e2e.ti.com/.../3600.high-current-v-i-circuits
  • Hi Tim,
    Thanks for your reply.
    The customer mentions that if he doesn't connect the load, the output current range of the his circuit is not in accord with the simulation in TINA.
    Does it make sense?

    Thanks a lot!
    Lacey
  • It does not make sense to discuss current out of the voltage to current converter with no load. The op amp will saturate and input bias currents can go up. If customer has not used power op amp circuit in a voltage to current mode like he shows it is VERY important to have him review the collateral I recommended in the previous post.
  • At this point TI thinks this is resolved. Post again if you need additional help.