Method for accurate current sensing in power converters
View Patent ↗A simple digital-to-analog converter (DAC) may be used to monitor a load current. The DAC may be configured to generate a voltage corresponding to an estimate of an average value of the load current. A comparator may be used to compare that voltage with a sense voltage corresponding to the actual load current. The estimate may then be adjusted based on a sample of the comparator output, allowing the estimate to track the load current over time, thus providing an average measurement capability without using a fast analog-to-digital converter. The DAC may additionally be configured to generate respective voltages corresponding to specified over-current (OC) and under-current (UC) values. The comparator may then be used to compare these respective voltages with the sense voltage to respectively detect OC and UC faults. Noise immunity may be increased by integrating a number of comparator samples instead of a single comparator sample before adjusting the estimate. Increased noise immunity may also provide a measure of the error between the estimate and the actual load current, improving the efficiency of monitoring the load current.
1. A method for monitoring load current, the method comprising:
(a) predetermining an estimated average value corresponding to a load current to be conducted by a load;
(b) generating a first signal corresponding to the estimated average value;
(c) generating a second signal corresponding to the load current;
(d) determining if the first signal is less than or greater than the second signal;
(e) adjusting the estimated average value based on whether the first signal is less than or greater than the second signal; and
performing (a)-(e) for a plurality of iterations, wherein the estimated average value tracks an actual average value of the load current conducted by the load over a specified period of time.
2. The method of claim 1 ,
wherein said determining if the first signal is less than or greater than the second signal comprises generating a count value based on a number of times the first signal is less than or greater than the second signal; and
wherein said adjusting the estimated average value based on whether the first signal is less than or greater than the second signal comprises adjusting the estimated average value based on the count value.
3. The method of claim 2 ,
wherein said generating the count value comprises:
incrementing a counter if the first signal is less than the second signal; and
decrementing the counter if the first signal is greater than the second signal.
4. The method of claim 3 , wherein said adjusting the estimated average value based on the count value comprises:
incrementing the estimated average value if the count value is negative; and
decrementing the estimated average value if the count value is positive.
5. The method of claim 2 , wherein said adjusting the estimated average value based on the count value comprises adjusting the estimated average value by a specified step size.
6. The method of claim 5 , further comprising adjusting the step size based on whether a sign of the count value at the end of any given iteration of the plurality of iterations is different than the sign of the count value at the end of an iteration of the plurality of iterations that immediately preceded the given iteration.
7. The method of claim 6 , wherein said adjusting the step size comprises:
incrementing the step size by a specified amount if the sign of the count value at the end of the given iteration is not different from the sign of the count value at the end of the iteration that immediately preceded the given iteration; and
setting the step size to a default value if the sign of the count value at the end of the given iteration is different from the sign of the count value at the end of the iteration that immediately preceded the given iteration.
8. The method of claim 7 , wherein the specified amount and the default value are both 1.
9. The method of claim 1 , wherein the first signal and the second signal are both analog voltage signals.
10. The method of claim 1 , wherein said adjusting the estimated average value based on whether the first signal is less than or greater than the second signal comprises:
incrementing the estimated average value if the first signal is less than the second signal; and
decrementing the estimated average value if the first signal is greater than the second signal.
11. The method of claim 1 , further comprising one or more of:
performing an over-current (OC) check comprising:
specifying an OC value;
generating a third signal corresponding to the OC value;
determining if the second signal is greater than the third signal; and
asserting a fault signal if the second signal is greater than the third signal;
performing an under-current (UC) check comprising:
specifying an UC value;
generating a fourth signal corresponding to the UC value;
determining if the second signal is less than the fourth signal; and
asserting the fault signal if the second signal is less than the fourth signal;
performing an average-OC check comprising:
specifying an average-OC value;
generating a fifth signal corresponding to the average-OC value;
determining if the first signal is greater than the fifth signal; and
asserting the fault signal if the first signal is greater than the fifth signal; and
performing an average-UC check comprising:
specifying an average-UC value;
generating a sixth signal corresponding to the average-UC value;
determining if the first signal is greater than the sixth signal; and
asserting the fault signal if the first signal is less than the sixth signal.
12. The method of claim 11 , wherein the first signal, the second signal, the third signal, the fourth signal, the fifth signal, and the sixth signal, are all analog voltage signals.
13. The method of claim 1 , further comprising automatically identifying a method used in said generating the second signal.
14. The method of claim 13 , wherein said automatically identifying the method used in said generating the second signal comprises:
measuring a first voltage at a first terminal of the load;
measuring a second voltage at second terminal of the load; and
determining the method used in said generating the second signal, based on said measuring the first voltage and said measuring the second voltage.
15. The method of claim 13 , further comprising selecting characteristics of an amplifier used in said generating the second signal, based on said automatically identifying the method used in said generating the second signal.
16. The method of claim 1 , wherein said generating the second signal is performed according to a user configurable method.