Controller Detecting Input Power Failures for Load Protection
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Solution Overview
Problem
Existing power converters fail to immediately activate a power-fault signal during brownouts or AC power shutdowns, potentially damaging loads like television apparatuses or portable computers, and require additional components increasing manufacturing costs.
Innovation Solution
A controller with a high voltage start-up pin, sample-and-hold circuit, brownout detector, AC-off detector, and OR gate to generate a protection signal using existing components, ensuring timely activation of the power-fault signal during brownouts and AC power shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate circuit with additional components is used to generate the power-fault signal, then the power-fault signal can be generated, but the manufacturing cost increases and the device complexity increases
Solution Approach 1:
The patent merges the power-fault signal generation function into the existing PWM controller by utilizing the HV pin and its internal sample-and-hold circuit. This eliminates the need for separate external circuits and components, thereby reducing device complexity while maintaining the reliability of power-fault detection. The controller integrates multiple functions (powering, sampling, threshold detection, and signal generation) into a single device.
Solution Approach 2:
The HV pin and its associated sample-and-hold circuit are designed to serve multiple purposes: providing start-up power to the controller, sampling the input voltage, detecting brownout conditions, and generating the power-fault signal. This multi-functionality reduces the overall component count and simplifies the circuit design while ensuring reliable power-fault protection.
2Duration of action of stationary object
If the X capacitor holds charges for a long time after AC power is switched off, then the capacitor maintains voltage, but the power-fault signal fails to be active timely causing load damage
Solution Approach 1:
The sample-and-hold circuit continuously samples and holds the input voltage on a capacitor during normal operation, maintaining an updated voltage representation ready for immediate comparison. When AC power is switched off or a brownout occurs, the held voltage is immediately compared against the threshold, enabling timely power-fault signal activation without waiting for the X capacitor to discharge. This preliminary sampling ensures rapid detection and response.
Solution Approach 2:
The circuit implements feedback by continuously monitoring the held voltage from the sample-and-hold circuit and comparing it with the threshold voltage. This feedback mechanism ensures that any drop in input voltage (brownout or power-off) is immediately detected and triggers the power-fault signal, overriding the delayed effect of the X capacitor discharge and ensuring timely load protection.
3Duration of action of stationary object
If the DC output voltage remains at an operable level for a while after brownout or AC power shutdown, then the output voltage sustains, but the load may still be damaged if power-fault signal is not active immediately
Solution Approach 1:
The circuit performs preliminary detection of input power failures using the sample-and-hold circuit and threshold comparison before the DC output voltage drops to dangerous levels. By detecting brownout or power-off conditions immediately and activating the power-fault signal in advance, the system provides timely warning to the load, allowing protective measures to be taken before the sustained DC output voltage causes damage.
Data Source
AI summary
A controller capable of detecting input power and generating a protection signal for a power converter, including: a high voltage start-up pin for connecting with an output terminal of an external start-up circuit; a sample-and-hold circuit for periodically sampling a voltage signal at the high voltage start-up pin to generate a detected signal; a brownout detector for generating a first power-fault signal according to the detected signal; an AC-off detector for generating a second power-fault signal according to the detected signal; and an OR gate having a first input end coupled with the first power-fault signal, a second input end coupled with the second power-fault signal, and an output end providing a third power-fault signal.