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OPA54X - Current Limit LED

Richard Dzioba
Prodigy 60 points
Other Parts Discussed in Thread: OPA547, OPA569, OPA548

HI - is there a way to add an indication of when the OPA547/548/549 goes into current limit?  Thanks.

  • 0
    Guru 21975 points

    Richard,

    This might be possible but it's tricky and could be difficult. It would depend on the circuit configuration. An inverting amplifier configuration would be easiest and if the polarity of limiting is unipolar it would be easier. If you can provide some details on your application, I'll give it some thought.

    Have you considered the OPA569? It has this capability built in.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 60 points

    Hi Bruce - I am interested in using the OPA548 as a 0->50V, 0->2A linear power supply for lab/bench top use.  The OPA548 looks like it would be excellent for that purpose.  I was thinking of using the non-inverting configuration, similar to Figure 16 in the datasheet.  It would be "nice" to have some indication of current-limit.  I didn't consider the OPA569, but it has a package that would present some heatsink challenges.

    Thanks, Richard.

  • 0 in reply to Richard Dzioba
    Guru 21975 points

    Richard,

    Be aware that power op amps may not make the best general purpose lab supply. Supplies of this type are generally designed so that a load capacitor (bypass capacitor for the circuitry that is connected as a load) becomes part of the phase compensation of the regulator circuit. They are stable with very large load capacitance. A power op amp can become unstable with increasing capacitive load.

    The basic approach to detecting current limit is to determine when the two input terminals of the op amp are at different potentials. This is tricky because in the non-inverting circuit, the common-mode potential varies with input. You also must design a circuit that allows for a small differential input due to offset voltage and other errors. This requires an additional amplifier that does not significantly load the primary amplifier circuitry.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 60 points

    Bruce - thanks for that insight.  I thought the concept looked too easy - where there was almost everything I was looking for in one package!

    Regards, Richard.