Flyback Converter Multi-Function Pin Start-Up Control
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Solution Overview
Problem
Prior flyback power converter circuits require an extra dedicated pin to control the high-voltage start-up switch, leading to increased cost and circuit size.
Innovation Solution
A multi-function pin is used to control the high-voltage start-up switch for rapid power start-up, also providing functions like over temperature and overvoltage protection, reducing the total number of pins and thus cost and circuit size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated pin is used to control the HV start-up switch, then the start-up control function is reliable, but the total number of pins increases leading to higher cost and larger circuit size
Solution Approach 1:
The PROG pin is designed to perform multiple functions: during start-up it controls the HV start-up switch SSU, and during normal operation it provides protection functions (over-current, over-voltage, over-temperature protection). This multi-functionality eliminates the need for a dedicated start-up control pin, reducing the total pin count while maintaining reliable start-up control
2Device complexity
If a multi-function pin is used to control the HV start-up switch, then the total number of pins is reduced lowering cost and circuit size, but the pin must perform multiple functions increasing design complexity
Solution Approach 1:
The pin's function dynamically changes based on the operating stage: during start-up (when VDD < VSTART) the pin outputs a start-up signal to control SSU, and after start-up (when VDD ≥ VSTART) the pin switches to providing protection signals. The controller circuit adaptively changes the pin's output characteristics based on the system state, enabling one pin to serve multiple purposes without conflict
Data Source
AI summary
A flyback power converter includes a transformer having a primary winding for receiving an input power, a secondary winding for generating an output power, and an auxiliary winding for generating a supply voltage, a primary side switch coupled to the primary winding, a high voltage start-up switch coupled to the input voltage and the controller supply voltage, and a primary side controller powered by the controller supply voltage. The primary side controller includes a multi-function pin coupled to a control terminal of the high voltage start-up switch, a high voltage start-up circuit for controlling the high voltage start-up switch to be ON through the multi-function pin when the controller supply voltage is lower than a threshold, and a protection control circuit which is coupled to an protection sensing signal through the multi-function pin; the protection control circuit operates the flyback power converter according to the protection sensing signal.