Isolated Load Switch Driver IC With Current-Limited Input Power
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Solution Overview
Problem
Current load switch drivers for low voltage digital outputs face challenges in interfacing with high voltage loads, requiring additional components like relays or opto-couplers, which can degrade over time and generate electromagnetic interference, and often need separate power connections, complicating circuit design and increasing pin count.
Innovation Solution
The development of an isolated load switch driver IC that uses a current limiter circuit to charge a buffer capacitor, allowing controlled current flow and enabling a DC-DC converter to provide isolated switching without external power connections, reducing complexity and eliminating moving parts and optical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relays are used to drive isolated loads, then switching capability is achieved, but moving parts degrade over time and generate electromagnetic interference
Solution Approach 1:
The patent replaces mechanical relay contacts with solid-state switching elements (MOSFETs or IGBTs) that have no moving parts, eliminating mechanical wear and electromagnetic interference from contact arcing. The solid state relay uses electronic switching to achieve the same load isolation function without mechanical components.
2Reliability
If opto-couplers are used for isolation, then galvanic isolation is achieved, but optical components degrade and require precise alignment
Solution Approach 1:
The patent replaces optical isolation components with galvanic isolation achieved through transformer coupling or capacitive isolation. This substitution eliminates optical degradation issues, alignment requirements, and the need for precise optical component positioning while maintaining effective galvanic isolation between control and load circuits.
3Adaptability or versatility
If separate power connections are provided for load switch drivers, then power supply flexibility is improved, but pin count and circuit complexity increase
Solution Approach 1:
The patent combines the power supply function with the signal input function by allowing the same input pin to serve dual purposes: providing both the control signal and the power supply voltage. This merging eliminates the need for separate power connections, reducing pin count and simplifying the circuit while maintaining the ability to drive isolated loads effectively.
4Reliability
If current limiting is implemented to protect digital outputs, then digital output protection is improved, but current available to energize relay coils is reduced
Solution Approach 1:
The patent segments the current path by introducing a buffer capacitor that accumulates charge from the limited current provided by the digital output. This segmentation allows the digital output to safely provide a small continuous current for charging the capacitor while the capacitor subsequently provides the larger peak current needed to energize the relay coil or drive the isolated load, effectively resolving the power limitation.
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
This solution enables efficient, galvanically isolated switching of high-voltage loads using a single IC pin for both signal and power, reducing pin count and eliminating the need for external power supplies, while minimizing current consumption and avoiding electromagnetic interference.
Implementation Method 1
charge a buffer capacitor
Implementation Method 2
impedance circuit that receives a digital input voltage signal and selectively allows a current signal to flow
Data Source
AI summary
Disclosed examples include isolated load switch driver circuits to drive a load, including an impedance circuit that receives a digital input voltage signal from a signal source, and selectively allows a current signal to flow from the signal source to charge a buffer capacitor. An impedance control circuit controls the impedance circuit to limit the current signal in response to the buffer capacitor reaching a first threshold voltage, and an output circuit provides an output isolated from the digital input voltage signal to switch the load. A signaling circuit selectively enables the output circuit to draw power from the buffer capacitor in response to the voltage of the buffer capacitor reaching the first threshold voltage.