H-Bridge Transistor Current Limiting via Phased Shutdown
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Solution Overview
Problem
In 'H-bridge' circuits, the simultaneous turning off of all transistors during overcurrent events leads to substrate injection and increased supply voltage, necessitating costly semiconductor processes and larger decoupling capacitances.
Innovation Solution
A method that detects failures in individual transistors, turns off the affected transistor, and waits for discharge of accumulated output power before turning off the others, thereby reducing freewheeling diode injection and overshoot in supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all transistors are turned off simultaneously during overcurrent events, then protection against overcurrent is achieved, but substrate injection and increased supply voltage occur
Solution Approach 1:
The patent divides the transistor shutdown process into two distinct phases: first shutting off the affected transistor immediately for protection, then shutting off opposite transistors only after the inductive discharge phase completes. This segmentation in time prevents simultaneous shutdown of all transistors, thereby eliminating substrate injection while maintaining overcurrent protection.
Solution Approach 2:
The patent implements preliminary detection of the inductive discharge phase completion before shutting off the opposite transistors. By detecting when the freewheeling current has decayed to a safe level, the system prepares the shutdown sequence in advance to avoid substrate injection and supply voltage spikes.
2Reliability
If all transistors are turned off simultaneously during overcurrent events, then protection against overcurrent is achieved, but decoupling capacitances must be increased
Solution Approach 1:
The patent segments the transistor shutdown into sequential phases rather than simultaneous action. By delaying the shutdown of opposite transistors until after the inductive discharge phase, the method prevents supply voltage overshoot that would otherwise require larger decoupling capacitances to compensate.
Solution Approach 2:
The patent changes the timing parameter of transistor shutdown from simultaneous to sequential. This parameter change in the shutdown sequence eliminates the need for increased decoupling capacitance values, as the supply voltage remains stable throughout the phased shutdown process.
3Reliability
If freewheeling diodes are used for inductive discharge, then overcurrent protection is achieved, but freewheeling diode injection occurs
Solution Approach 1:
The patent implements preliminary detection of the inductive discharge phase completion before proceeding to the next shutdown step. This preliminary action allows the system to wait for the freewheeling current to naturally decay through the diode, preventing substrate injection while still utilizing the diode's protective function.
Solution Approach 2:
The patent converts the potentially harmful inductive discharge phase into a beneficial waiting period. By utilizing the natural decay of current through the freewheeling diode as a signal to delay the next shutdown action, the method transforms what could be a source of substrate injection into a protective timing mechanism.
Data Source
AI summary
A method for limiting the current in a device of “H-bridge” type having a plurality of transistors including the following steps: detection of a failure in a transistor from among the plurality of transistors; disabling of the transistor in which a failure has been detected; detection in the transistors opposite to the transistor, of the discharging of the energy accumulated at output; and disabling of the other transistors of the plurality of transistors. A system for limiting the current in a device of “H-bridge” type having a plurality of transistors is also disclosed.