Half-Bridge Current Sensing With Shoot-Through Cancellation
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Solution Overview
Problem
Current detection in half-bridge circuits faces challenges such as power loss in shunt resistor methods and high costs associated with Hall effect sensors, particularly in applications requiring precise current limitation.
Innovation Solution
A current detection circuit that utilizes two current detection elements, one on the high-side and one on the low-side of a half-bridge circuit, to provide a summed signal indicative of the output current, thereby achieving reliable and cost-effective current measurement without significant power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used for current detection, then current measurement is achieved, but power loss increases
Solution Approach 1:
The current detection is segmented into two separate measurement points: one on the high-side and one on the low-side. By measuring currents at both ends and summing them, the system achieves accurate output current detection without requiring a high-power shunt resistor that would cause significant power loss.
Solution Approach 2:
The patent introduces an intermediary approach by using two smaller current detection elements instead of one large shunt resistor. The sum of currents through these two elements provides the output current measurement, avoiding the need for a single high-power lossy component.
2Measurement precision
If Hall effect sensors are used for current detection, then non-invasive measurement is achieved, but cost increases
Solution Approach 1:
The patent replaces expensive Hall effect sensors with inexpensive current detection elements (such as small resistors or sense FETs) that can be easily integrated into the circuit. These cheap detection elements provide sufficient measurement capability without the high cost of Hall sensors.
Solution Approach 2:
Instead of using a single expensive Hall sensor to directly measure the output current, the patent creates two copies of current detection at different points in the circuit (high-side and low-side). The sum of these two measurements replicates the output current information at a fraction of the cost.
3Measurement precision
If current detection is implemented in a half-bridge circuit, then current limitation control is achieved, but shoot-through current affects measurement accuracy
Solution Approach 1:
The patent converts the harmful shoot-through current into a beneficial cancellation effect. By summing the currents from both high-side and low-side detection elements, the shoot-through currents (which flow in opposite directions) naturally cancel each other out, leaving only the genuine output current for accurate measurement.
Solution Approach 2:
The patent segments the current measurement into two separate paths that can independently detect and subsequently cancel shoot-through currents. This segmentation allows the system to distinguish between legitimate output current and parasitic shoot-through current, improving measurement accuracy during current limitation events.
Data Source
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AI summary
A circuitry for detecting an output current of a half-bridge circuit, comprising a first current detection element arranged between the high-side switch and the high voltage rail, a second current detection element arranged between the low-side switch and the low voltage rail, and a summation point connected to provide an output signal equal to the sum of the currents detected by the first and second current detection elements. The output signal is indicative of the output current of the half-bridge circuit. With this approach, a reliable measurement of the output current is achieved at low cost, and without significant power loss. A further benefit is that any shot though current is cancelled out.