Dynamic current limit apparatus and method

1. A dynamic current limiter comprising:

an input node configured to be coupled with a test and measurement instrument;

an output node configured to be coupled with a device under test;

a current control valve coupled between the input and output nodes, the current control valve being configured to limit current flow received from the test and measurement instrument based on a control input; and

a current change detector coupled with the current control valve and the output node, the current change detector configured to:

detect a change in current provided by the test and measurement instrument, and

in response to the detected change in current, generate a control signal configured to drive the control input of the current control valve, the current change detector including a source resistor in parallel with a DC shorting element and a timing element configured to control the timing of the control signal in accordance with a time constant, the time constant configured to allow time for current limiting circuitry of the test and measurement instrument to establish current control, wherein the source resistor and the DC shorting element are coupled to the control input via the timing element.

2. The dynamic current limiter of claim 1 wherein the current control valve is a field effect transistor (FET).

3. The dynamic current limiter of claim 2 wherein the FET is a depletion type metal-oxide-semiconductor FET (MOSFET).

4. The dynamic current limiter of claim 2 , wherein the current carrying capacity of the FET is the maximum current that flows through the FET with a gate voltage of zero (0).

5. The dynamic current limiter of claim 1 wherein the DC shorting element is a diode.

6. The dynamic current limiter of claim 1 wherein the DC shorting element is an inductor.

7. The dynamic current limiter of claim 1 wherein the timing element includes a resistor and a capacitor.

8. The dynamic current limiter of claim 1 , further comprising a bi-directional current control valve and bi-directional current change detector.

9. The dynamic current limiter of claim 8 wherein the bi-directional current control valve includes two field effect transistors (FETs).

10. The dynamic current limiter of claim 8 wherein the bi-directional current change detector includes one source resistor in parallel with two DC shorting elements.

11. The dynamic current limiter of claim 8 wherein the bi-directional current change detector includes two source resistors, each source resistor being in parallel with a DC shorting element.

12. The dynamic current limiter of claim 1 , wherein the dynamic current limiter is in a two-wire configuration.

13. The dynamic current limiter of claim 12 , wherein the dynamic current limiter is configured to be retrofitted between the test and measurement instrument and the device under test.

14. A method of dynamically limiting a current provided to a device under test, the method comprising:

detecting, by a current change detector of a dynamic current limiter, an increase in current received from a test and measurement instrument;

in response to detecting the increase in current, generating, by the current change detector, a control signal that drives a control input of a current control valve of the dynamic current limiter to cause the current control valve to limit the current provided to the device under test; and

transitioning, in accordance with a timing element of the current change detector, the current control signal to cause the dynamic current limiter to enter a quiescent state over a period of time that enables current limiting circuitry of the test and measurement instrument to establish current control.

15. The method of claim 14 , wherein the the current control valve is a field effect transistor (FET).

16. The method of claim 15 , wherein the FET is a depletion type metal-oxide-semiconductor FET (MOSFET).

17. The method of claim 14 , wherein the timing element includes a resistor and a capacitor.

18. The method of claim 14 , wherein the current control valve is a bi-directional current control valve and the current change detector is a bi-directional current change detector.

19. The method of claim 18 , wherein the bi-directional current control valve includes two field effect transistors (FETs).

20. The method of claim 18 , wherein the bi-directional current change detector includes one source resistor in parallel with two DC shorting elements.

21. The method of claim 18 , wherein the bi-directional current change detector includes two source resistors, each source resistor being in parallel with a DC shorting element.

22. The dynamic current limiter of claim 14 , wherein a current limit of the quiescent state is based on a current carrying capacity of the current control valve.

23. The dynamic current limiter of claim 22 , wherein to drive the control input of the current control valve causes the current control valve to:

reduce the current provided to the device under test, and

transition, in accordance with the timing element, the current provided to the device under test to a steady state, wherein the current provided to the device under test at the steady state is limited based on a current carrying capacity of the current control valve.

24. The dynamic current limiter of claim 23 , wherein the timing element includes a gate resistor coupled with a gate capacitor, the gate resistor coupled with an input of the source resistor and an input of the DC shorting element, and the capacitor coupled with an output of the source resistor and an output of the DC shorting element.