Load Driver Open Output Protection via Startup Current
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Solution Overview
Problem
Switched-mode drivers, such as those for LEDs, face issues with high voltage over the output buffer capacitor when an open circuit or no load is present, leading to potential damage and inefficiencies due to complex and costly protection circuits that cause 'burping' as they repeatedly start and stop.
Innovation Solution
A simplified driver design that provides a startup current via the load, using a coupling diode and a converter circuit with a startup terminal to prevent driver initiation without a load, thereby reducing component count and preventing overvoltage/open load protection 'burping'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complex protection circuit with numerous transistors, stabilivolt, and capacitors is used to sense voltage and prevent overvoltage, then overvoltage protection is achieved, but device complexity and cost increase significantly
Solution Approach 1:
The invention extracts the essential protection function from the complex circuit by removing unnecessary components. Instead of using numerous transistors, stabilivolt, and capacitors, the patent uses a simplified approach where the startup terminal naturally prevents driver initiation without a load by not receiving sufficient startup current, thereby achieving overvoltage protection with minimal components.
Solution Approach 2:
The startup terminal serves a dual function: it initiates the driver when a load is present and simultaneously provides overvoltage protection when no load is present. The circuit uses its own startup current mechanism for protection, eliminating the need for separate protection components. The converter circuit automatically detects the open load condition through the absence of startup current and prevents operation accordingly.
2Device complexity
If an IC-based solution is used to control the power switch, then driver control is simplified, but product cost increases
Solution Approach 1:
The converter circuit performs multiple functions using a unified structure: it converts input voltage to output voltage, generates startup current, and provides overvoltage protection. The startup terminal is integrated into the converter circuit, allowing the same circuitry to serve both driving and protection functions, thereby avoiding additional IC components and reducing cost.
Solution Approach 2:
The invention merges the startup current generation and overvoltage protection functions into the existing converter circuit. The startup terminal is coupled to the first output terminal, and the same converter circuit that drives the load also detects the load condition and prevents startup when no load is present, combining multiple functions into a single integrated solution.
3Ease of operation
If the driver is designed to start without load detection, then ease of operation is improved, but overvoltage damage risk increases
Solution Approach 1:
The circuit applies preliminary anti-action by preventing the driver from starting in the first place when no load is present. The startup terminal requires a certain voltage level to initiate the driver, and this voltage is only achieved when a load is connected to provide the necessary current path. By blocking startup before operation begins, the circuit prevents overvoltage damage before it can occur.
Solution Approach 2:
The startup terminal provides feedback about the load condition to the converter circuit. When a load is connected, current flows through the load to the startup terminal, indicating a valid operating condition. When no load is present, the startup terminal does not receive sufficient current, and the converter circuit detects this condition and prevents startup, thereby avoiding overvoltage damage.
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 high voltage buildup and eliminates 'burping' in switched-mode drivers, reducing component costs and ensuring safe operation by deriving the startup current from the load, thus providing reliable and efficient overvoltage/open load protection.
Implementation Method 1
a coupling diode coupled in forward connection from a first output terminal to a first terminal of the output buffer capacitor
Implementation Method 2
an output buffer capacitor; two output terminals coupled to the output buffer capacitor
Data Source
AI summary
Driver with open output protection Starting current for a load driver (200; 300) for driving a load (L) is provided via the load. In a load driver (200; 300) for driving a load (L), an operating current or an operating voltage at a reference point is derived from a power voltage bus (105; 305) by coupling said reference point to said power voltage bus via the load. A load driver (200; 300) for driving a load (L) comprises an output capacitor (125; 325) and two output terminals (128, 129; 328, 329) coupled to the output capacitor. A coupling diode (202; 325) is coupled in forward connection from one output terminal to a terminal of the output buffer capacitor. A startup terminal (111) of a converter circuit (110) is coupled to said one output terminal (129; 329) to receive a startup current (Is) via the driven load if the load is present to conduct this current.