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Registered Member #610
Joined: Wed Mar 28 2007, 09:44PM
Location: Middletown, RI
Posts: 110
Does anyone know of any current-sense chips that measure the current magnitide in both directions?
If not: I want to measure the current in a full bridge. I have a whole bunch of Allegro hall effect sensors that output a voltage proportional to the current through them, but the Zero-Current output voltage is 2.5V. I want to compare the output voltage to a user-settable voltage through a comparator. Problem is that the output voltage is below 2.5V when current is flowing in one direction, and above 2.5V when flowing in the other.
I already have them and would like to use them if possible. Anyone know of simple circuits that can solve the problem, or should I just use two chips in the bridge?
Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
You just need two comparators, one that activates when the current is greater than 2.5V + v, and another that activates when the voltage is below 2.5V - v, where v is the user adjustable voltage. You could use op-amps to make the voltages (2.5 + v) and (2.5 - v), and then use two comparators to do the comparison, and OR their outputs to get the overcurrent detected output.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I interpret what you wrote to be a (peak ac current exceeded) signal.
If so you must remember to enable the signal after the initial inrush current.
If the rectifiers/diodes that form the bridge have negligible leakage, then the uni-polar signal on the dc side of the bridge can be monitored, requiring only one comparator.
Assuming that a small voltage drop is allowable, you could just use a current-sense resistor in either the positive or negative line, allowing a simple comparison between a (divided) reference voltage and the voltage across the current-sense resistor. Or of course, you can use a hall effect sensor etc.
Registered Member #610
Joined: Wed Mar 28 2007, 09:44PM
Location: Middletown, RI
Posts: 110
Thanks... the bandwidth of this circuit is much higher than the Allegro chip. Though, it still discriminates current direction and I would still need a window comparator. It is an improvement.
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Unidirectional current sense
