Step-down Switching Regulator Undershoot Prevention
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Solution Overview
Problem
Existing step-down switching regulators face issues with voltage undershoot and component damage due to delayed voltage reduction after power supply termination, leading to potential malfunctions and failures.
Innovation Solution
A synchronous-rectification-type step-down switching regulator with a control circuit and short-circuiting unit that quickly discharges the inductor by connecting the output terminal to ground, utilizing a second switching element to manage voltage and prevent undershoot, and an inverse current detection circuit to manage inverse currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the synchronous rectification switching element is used to discharge the inductor after power supply turn-off, then the inductor energy can be dissipated, but a large negative voltage (undershoot) is produced at the power-supply-side terminal of the inductor that can destroy the parasitic diode
Solution Approach 1:
The control circuit is configured to turn on the synchronous rectification switching element before the main switching element is turned off. This preliminary action allows the synchronous rectification switching element to be already conductive when the inductor current reverses, preventing the large negative voltage from appearing across the parasitic diode and avoiding its destruction.
Solution Approach 2:
The synchronous rectification switching element acts as an intermediary component that provides a controlled path for the inductor current. By being turned on in advance, it mediates the energy dissipation process, allowing the inductor to discharge its energy through the controlled switching element rather than forcing current through the parasitic diode, thus preventing voltage undershoot damage.
2Reliability
If the output capacitor charge is discharged via the inductor and resistor after power supply turn-off, then the voltage across the inductor is managed, but it takes time for the output voltage to decrease, extending the application of low voltage outside guaranteed operation range
Solution Approach 1:
The control circuit turns on the synchronous rectification switching element before the main switching element is turned off, creating a pre-configured low-impedance discharge path for the inductor. This preliminary configuration enables immediate and rapid energy dissipation when needed, avoiding the slow discharge through resistor that would extend the low voltage period.
Solution Approach 2:
The system dynamically switches between different discharge paths by controlling the synchronous rectification switching element. During normal operation, the inductor charges through the main switching element. Upon power supply turn-off, the control circuit rapidly transitions the synchronous rectification switching element to conductive state, dynamically changing the energy dissipation path from slow (resistor) to fast (controlled switching path), thereby achieving rapid voltage reduction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents voltage undershoot and quickly lowers the output voltage after power supply termination, preventing component damage and ensuring stable operation.
Implementation Method 1
an inductor that is charged by the input voltage when the first switching element performs the switching
Implementation Method 2
a large negative voltage is produced at the power-supply-side terminal of the inductor immediately after turning off of power supply. Because the aforementioned negative voltage is applied across the synchronous rectification switching element, a current flows from the ground voltage to the inductor via a parasitic diode of the synchronous rectification switching element
Data Source
AI summary
A step-down switching regulator prevents an output voltage undershoot and enables a quick lowering of an output voltage immediately after turning off of power supply. The step-down switching regulator includes an NMOS transistor connected between an output terminal and a ground voltage and another NMOS transistor connected in parallel with a synchronous rectification transistor. Upon reception of an on/off signal for terminating the operation of the switching regulator, the NMOS transistors are turned on into an on-state.