Power Supply Unit Soft Start Circuit Reducing Terminal Count
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Solution Overview
Problem
Conventional power supply units consume current in standby mode to charge capacitors, which reduces battery life in portable devices, and require additional terminals for control, making them less desirable for soft start functionality.
Innovation Solution
A power supply unit with an output circuit, error amplification circuit, and reference voltage generation circuit that uses a voltage level detector and level shift circuit to enable soft start without increasing consumption current, allowing control based on an operation command input voltage, reducing the number of external terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is connected in series with a constant current source and a power switch to enable soft start, then the power supply unit can undergo slow start, but the number of external terminals increases
Solution Approach 1:
The patent merges the power switch control function with the existing operation command input terminal. The operation command input voltage itself serves as the control signal for the power switch, eliminating the need for a separate control terminal. This integration reduces the number of external terminals while maintaining soft start capability through the capacitor charging mechanism.
2Reliability
If a predetermined current flows through the power switch in standby condition to charge the capacitor, then soft start can be ensured, but the consumption current increases
Solution Approach 1:
The patent implements periodic action by only charging the capacitor when the power switch is turned off. In standby condition (power switch on), no current flows through the capacitor. The constant current source charges the capacitor only during the brief period when the power switch is off, which occurs periodically during normal operation but not during continuous standby. This eliminates continuous current consumption while maintaining soft start capability.
3Reliability
If the power switch is turned off to charge the capacitor, then soft start is achieved, but the power supply unit cannot operate continuously
Solution Approach 1:
The patent applies preliminary action by charging the capacitor in advance during standby condition before the power switch is turned off. The operation command input voltage gradually rises with a predetermined time constant,预先 charging the capacitor through the constant current source. When the power switch is subsequently turned off, the capacitor is already charged and can immediately provide the necessary current for soft start, enabling continuous operation without requiring the power switch to remain off for charging.
Data Source
AI summary
A step-like operation command signal is inputted into a time-constant circuit to generate a gradually rising operation command input voltage, which is supplied to a power supply unit. Enablement and disablement of the power supply unit is controlled on the basis of the operational command input voltage. When the operation command input voltage exceeds a first predetermined voltage level, a detection signal and a reference voltage are generated, and at the same time an error amplification circuit is enabled. On the other hand, when the operation command input voltage exceeds a second predetermined voltage level, a level shift voltage for initiating a soft start is generated, which enables execution of a soft start of the power supply unit without increasing its consumption current and reduction of the number of its terminals.