Sample and hold method and apparatus for sensing inductive load current
AssigneeDelco Electronics Corporation
InventorsJames C. Bach, John L. Kastura
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Abstract
An inductive load energized by a variable duty cycle pulse signal contains ripple at steady state conditions, and the average current is used as feedback to a controller. The average current is obtained without filtering by synchronously sampling the local maxima and minima of the current and averaging the last two samples. The maxima and minima are detected by sampling at the falling and rising edges of the pulse signal. The method is implemented by software in a microprocessor or by hardware comprising a pulse generator, sample and hold circuits, and an averager. The resulting average value is then asynchronously sampled by a microprocessor.
Claims10
Apparatus for sensing average current in an inductive load energized by a pulsed voltage causing a current waveform exhibiting local maxima and minima comprising:
- means for synchronously sampling the current at local current maxima and minima and for storing values representing the most recent of each of the current maxima and minima samples;
- means for averaging the stored values to yield an average value which is a measure of the average current;
- and
- a microprocessor for asynchronously sampling the average value, whereby the sensed current has no ripple during steady state conditions.
In a circuit including a microprocessor for controlling current to an inductive load by pulse modulation of applied load voltage wherein the current exhibits ripple, a method of measuring the average current independently of the effects of ripple comprising the steps of:
- sampling the current at local maxima and minima of current values;
- storing values representing the currents for the two most recent current samples;
- and
- averaging the stored values to determine the average load current.
Dependencies are inferred from the claim text.