Digital Backup Signal Circuit for Load Control
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Solution Overview
Problem
Existing load-control backup signal generation circuits face challenges in quickly outputting a backup control signal due to variations in component characteristics, particularly capacitance, and are prone to malfunctions from instantaneous power interruptions, leading to delayed recovery and incorrect activation.
Innovation Solution
A load-control backup signal generation circuit that includes a watchdog input terminal, a pulse count unit, and a signal selection unit, which uses a clock pulse generator and a digital comparator to generate a backup control signal based on count output signals, allowing for automatic adjustment and reduced design margins, enabling rapid output of the backup signal even during power interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an analog circuit with capacitor and resistor is used to generate backup control signal, then the circuit can detect malfunction, but the response time is delayed due to component characteristic variations
Solution Approach 1:
The patent replaces the analog RC circuit with a digital circuit comprising a pulse counting unit and comparator. The digital circuit counts clock pulses during the malfunction detection period and compares the count value against a reference, eliminating dependence on capacitor charging characteristics and component variations, thereby achieving rapid and reliable malfunction detection without time delays.
2Reliability
If large design margins are used to accommodate component variations, then reliability is improved, but the response time increases
Solution Approach 1:
The patent changes the detection parameter from analog voltage threshold (dependent on component characteristics) to digital pulse count (independent of component variations). The pulse counting unit counts clock pulses during the malfunction period, and the comparator checks if the count exceeds a reference value. This parameter transformation eliminates the need for large design margins while maintaining reliability and reducing response time.
3Reliability
If the circuit is designed to be insensitive to power interruptions, then false activation is prevented, but the ability to detect actual malfunctions is reduced
Solution Approach 1:
The patent applies preliminary action by resetting the pulse counting unit at the start of each watchdog period. This ensures that the counting begins from zero each time, allowing the circuit to accurately measure the duration of malfunction regardless of power interruption history. The systematic reset mechanism enables reliable distinction between temporary power issues and actual malfunctions.
Solution Approach 2:
The circuit incorporates feedback through the watchdog signal that periodically resets the pulse counting unit. This feedback mechanism allows the system to adapt to normal operation conditions (including brief power interruptions) while maintaining the ability to detect sustained malfunctions. The feedback loop provides context about system state, enabling accurate malfunction detection without false activation.
Data Source
AI summary
In a case in which a malfunction occurs in a control processor which operates according to a predetermined program, a load-control backup signal generation circuit supplies a backup control signal to a switch of a load connected to an output of the control processor. The load-control backup signal generation circuit includes: a watchdog input terminal to which a watchdog signal periodically output from the control processor is input; a pulse count unit which counts a clock pulse generated with a constant period and which controls a count state of the clock pulse according to a signal input to the watchdog input terminal; and a signal selection unit which selects, from a plurality of options, a predetermined condition for causing a backup signal output unit to generate the backup control signal, based on a count output signal of a plurality of bits output from the pulse count unit.