Load Driving Circuit Gate Hold-Off During Power Activation
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Solution Overview
Problem
Existing load driving circuits face malfunctions due to unstable main power supply voltage during activation, leading to erroneous operations and increased power consumption when attempting to prevent self-turn-on of output transistors.
Innovation Solution
A load driving circuit design incorporating a malfunction prevention circuit with a simplified power supply circuit, activated before the sub-power supply voltage rises, sets the control terminal of the output transistor to a predetermined voltage to prevent erroneous operations and reduces power consumption by ensuring the output transistor remains off until the sub-power supply voltage stabilizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pull-down resistor is continuously connected to the gate of the output transistor to prevent self-turn-on, then the output transistor can be prevented from malfunctioning during power activation, but the output signal waveform becomes distorted and quality inspection is impeded
Solution Approach 1:
The patent applies periodic action by controlling the pull-down resistor to operate only during the power activation period when voltage instability occurs. The resistor is activated at power-on and deactivated when the power supply voltage stabilizes, preventing continuous operation that would distort output waveforms. This time-limited activation resolves the contradiction by providing protection only when necessary.
2Reliability
If a separate logic circuit is used to initialize the load driving circuit at activation time, then malfunction can be prevented, but the sub-power supply circuit operates erroneously until the sub-power supply voltage rises sufficiently
Solution Approach 1:
The patent applies preliminary action by detecting the power supply voltage in advance and activating the pull-down resistor before the sub-power supply circuit becomes operational. This early activation prevents self-turn-on during the critical period when main power is applied but sub-power supply voltage has not yet stabilized, resolving the timing contradiction between protection and operational readiness.
3Reliability
If a differential circuit with a capacitor is used to prevent malfunction, then the output transistor can be protected from self-turn-on, but the capacitor requires large capacitance and is not suitable for semiconductor integrated circuit incorporation
Solution Approach 1:
The patent extracts the capacitor from the circuit by replacing the differential circuit with a direct voltage detection mechanism. Instead of using a capacitor to detect voltage changes, the invention directly monitors the power supply voltage level and activates the pull-down resistor accordingly. This eliminates the need for large-capacitance components while maintaining the protection function, making the circuit suitable for semiconductor integration.
4Reliability
If current is continuously supplied to a resistor to maintain pull-down function, then the output transistor remains protected from self-turn-on, but current consumption increases
Solution Approach 1:
The patent applies periodic action by controlling the pull-down resistor to operate only during the power activation period when voltage instability occurs. The resistor is activated at power-on and deactivated when the power supply voltage stabilizes, preventing continuous operation that would consume excessive current. This time-limited activation resolves the contradiction by providing protection only when necessary.
Data Source
AI summary
When a battery power supply voltage is applied to a drain of an output transistor at activation time, a drain-gate path of the output transistor is coupled and the output transistor tends to turn on by itself. A simplified power supply circuit operates in response to current conduction of a drain-source path of the output transistor. The simplified power supply circuit is activated at earlier time than activation of a power supply voltage Vcc of a logic power supply circuit, when the simplified power supply circuit operates with a main power supply voltage. The malfunction prevention circuit thus sets a gate voltage of the output transistor to a ground voltage by using an output generated by the simplified power supply circuit. As a result, malfunction of the output transistor is prevented at earlier time in comparison to malfunction prevention by initialization.