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TS321: Amplifier suggestion

Part Number: TS321

Hi Guys

Customer asked:

I have a circuit design (see below) where I am injecting a PWM signal (from a microcontroller) into a Opamp to produce a 0-10V dc output (effectively a simplified DAC).

The circuit works fine (changing the PWM mark to space ration provides a good controllable linear 0 to 10V signal.

I was wondering if you had any ideas on either a different opamp or some additional circuitry to protect the amplifiers potential high output from someone shorting it to ground ?

At the moment I have put two 1k ohm resistors in parallel (for heat distribution) so that the opamps output current is not exceeded if a direct short is place on the unit.

This kind of works but I am concerned that the output  will always need to drive into a very high impedance input to avoid any voltage drops (i.e. potential divider made from the 500R output impedance and the load input)

 

I think some amplifiers are available with internal current limiting protection, or is there anything else that you may suggest?

Thanks

Rodney 

  • Rodney,

    You could move the 1k resistor pair to the left putting it inside the feedback loop. The op amp will try to compensate for the voltage lost on the resistors.

    This will support 0V to 10V output under a load (>500 ohms) provided the the load terminates to ground (current flows out of the circuit).

    If the load is terminated to a higher voltage then getting a 0V output may not be possible (with or without 1k resistor pair).

  • Hi Rodney,

    why is your supply voltage so high? A much lower supply voltage would be sufficient to allow the OPAmp to produce 10V at its output.

    Kai