Parallel Semiconductor Switch Control for Current Bias and Offset Error
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Solution Overview
Problem
Conventional methods for controlling in-vehicle load circuits using semiconductor switches result in uneven heating among switches due to current biases and lack of over-current protection, leading to inefficiencies and potential overheating.
Innovation Solution
A controller is designed with current sensors and a control unit that manage the ON/OFF states of semiconductor switches in parallel, using operational amplifiers to detect currents and adjust switching times to equalize heat distribution and prevent overcurrents by shutting off the circuit when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a plurality of semiconductor switches are connected in parallel to handle large current, then the current capacity is improved, but current bias due to element variations causes uneven heat generation among switches
Solution Approach 1:
The control unit preliminarily sets different ON-time zones and OFF-time zones for each semiconductor switch before operation. This preliminary timing differentiation compensates for current bias caused by element variations, ensuring that switches with higher current tendency have shorter ON-times or longer OFF-times, thereby equalizing heat generation across all parallel switches while maintaining high current capacity
2Device complexity
If conventional current sensors are used without offset compensation, then the device complexity is reduced, but offset errors cause inaccurate current detection
Solution Approach 1:
The patent merges the offset compensation function into the existing current sensor circuit by utilizing the operational amplifier's inherent capabilities. The differential amplifier configuration naturally rejects common-mode offset voltages, achieving accurate current detection without adding separate offset compensation circuits. This maintains device simplicity while significantly improving measurement precision
3Ease of operation
If semiconductor switches are turned on and off simultaneously, then the control simplicity is improved, but overcurrent conditions cannot be detected and protected against
Solution Approach 1:
The patent segments the control of semiconductor switches by assigning different ON-time zones and OFF-time zones to each switch. This segmentation enables the control unit to individually monitor and respond to overcurrent conditions in each switch branch. When overcurrent is detected in a specific switch, the control unit can immediately shut off only that switch while maintaining operation of others, providing both protection and continued system functionality
Data Source
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AI summary
Two semiconductor switches (Q1, Q2) are arranged in parallel in a load circuit for connecting a power source with a load. Further, the semiconductor switches (Q1, Q2) are controlled so as to be alternately tuned on and off. As a result, since a current flows through only either of the semiconductor switches (Q1, Q2), an offset error detected by current sensors (12, 22) includes only an offset error of either of the semiconductor switches, the detection of current with high accuracy can be accomplished. Therefore, when performing the control of shutting off the circuit to cope with the occurrence of an overcurrent flowing through the load, the shutoff control with high accuracy can be accomplished.