Power Switch Circuit Prevents Backup Leakage
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Solution Overview
Problem
Existing power switch circuits experience current leakage from the backup power supply when the main power supply voltage drops below the backup power supply voltage, leading to insufficient voltage for operations like data backup, which can result in data loss and reduced backup power supply capacity.
Innovation Solution
A power switch circuit with a first and second switch transistor connected in series, each with a diode configuration that prevents leakage current when deactivated, and a switch control unit that activates and deactivates them in a complementary manner to selectively output either the main or backup power supply voltage, ensuring the backup supply capacity is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single MOS transistor is used to switch between main power supply and backup power supply, then the circuit structure is simple, but current leaks from the backup power supply when main power supply voltage drops below backup power supply voltage
Solution Approach 1:
The patent divides the single switching element into two MOS transistors (first MOS transistor for main power supply switching and second MOS transistor for backup power supply switching) that operate in a complementary manner. This segmentation allows each transistor to be optimized for its specific function while working together to prevent the current leakage problem that would occur with a single transistor.
Solution Approach 2:
The patent inverts the conventional approach by using two transistors instead of one, and by configuring their body diodes in opposite directions through complementary control. The first transistor is activated when main power supply voltage is sufficient, while the second transistor is activated when backup power supply voltage exceeds main power supply voltage, effectively preventing current leakage from the backup power supply.
2Reliability
If back-to-back MOS transistors are used to prevent current leakage, then current leakage is prevented, but the layout area and mounting complexity increase
Solution Approach 1:
The patent applies local quality by configuring the body diodes of the two MOS transistors in opposite directions based on their specific functional requirements. The first MOS transistor's body diode is oriented to conduct when main power supply voltage is high, while the second MOS transistor's body diode is oriented to conduct when backup power supply voltage is high. This localized optimization of diode orientation prevents current leakage while maintaining a compact layout.
3Ease of operation
If backup power supply voltage is set lower than main power supply voltage, then the main power supply can normally operate the device, but current leakage occurs when main power supply voltage drops below backup power supply voltage
Solution Approach 1:
The patent implements feedback control by continuously monitoring the voltages of both the main power supply and backup power supply, and using this information to control the activation states of the two MOS transistors. When the main power supply voltage drops below the backup power supply voltage, the control circuit detects this condition and activates the second MOS transistor to prevent current leakage from the backup power supply, thereby maintaining its capacity for data backup operations.
Data Source
AI summary
A power switch circuit includes a first switch transistor connected to a main power supply, which supplies a first voltage, a second switch transistor connected in series to the first switch transistor and to a backup power supply, which supplies a second voltage. A switch control unit controls activation and deactivation of the first and second switch transistors so that either one of a voltage corresponding to the first voltage and a voltage corresponding to the second voltage is selectively output to a connection node between the first and second transistors. The first switch transistor includes a first diode, which is formed so that a direction from the main power supply toward the connection node defines a forward direction, and a second diode, which is formed so that a direction from the connection node toward the backup power supply defines a forward direction.