Temperature Limited Current Driver Circuit Design
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Solution Overview
Problem
Conventional driver circuits in integrated circuits are overly conservative in their self-protection features, limiting average load current delivery and requiring fixed duty cycling to prevent excessive operating temperatures during short circuits or overcurrent conditions, which can lead to inefficient operation.
Innovation Solution
A driver circuit with a temperature sensing circuit and a voltage-controlled current source that generates a control signal to regulate load current based on the operating temperature, allowing continuous current delivery while maintaining safe operating temperatures by adjusting current magnitude as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed safe duty cycle is imposed on the output stage during short circuit or overcurrent situations, then the integrated circuit is protected from exceeding safe operating temperatures, but the average load current is lower than it could be
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed duty cycle to a dynamically adjustable duty cycle that varies based on real-time temperature conditions. The control circuit continuously monitors temperature and adjusts the duty cycle accordingly, allowing the system to operate at higher currents when cool and reduce current when hot, thus resolving the contradiction between protection and productivity
Solution Approach 2:
The patent changes the parameter of duty cycle from a fixed value to a variable value that depends on temperature. By making the duty cycle a temperature-dependent parameter, the system can optimize current delivery at different operating temperatures, achieving both thermal protection and maximum possible load current delivery
2Reliability
If the current limit is reduced in short circuit or overcurrent conditions, then the integrated circuit is protected from damage, but the average load current is lower than it could be
Solution Approach 1:
The patent makes the current limit dynamic by adjusting it based on temperature feedback. Instead of a static current reduction, the system continuously adapts the current limit to match thermal conditions, allowing higher current delivery when the device is cool and providing protection when hot, thus resolving the contradiction between reliability and productivity
3Temperature
If duty cycle control is used to maintain safe operating temperatures, then temperature protection is achieved, but continuous current delivery is interrupted
Solution Approach 1:
The patent uses preliminary action by anticipating temperature rise and proactively adjusting the duty cycle before excessive heating occurs. The control circuit monitors temperature trends and preemptively reduces current delivery when necessary, maintaining continuous operation while preventing thermal damage, thus resolving the contradiction between temperature control and continuous current delivery
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 maximum possible current delivery while ensuring safe operating temperatures, eliminating the need for duty cycle control and providing continuous load current, thus optimizing driver performance and adapting to temperature and voltage variations.
Implementation Method 1
The temperature sensing circuit may include a bipolar junction transistor having a collector coupled to a first supply voltage, a base coupled to a bandgap voltage, and an emitter coupled to the voltage controlled current source. A resistor may be coupled between the emitter of the bipolar junction transistor and ground, with the first voltage being generated across the resistor.
Implementation Method 2
The voltage controlled current source may be an operational transconductance amplifier having a non-inverting terminal coupled to the second voltage and an inverting terminal coupled to the first voltage.
Implementation Method 3
The current source may include a first current mirror receiving the control signal as input and generating a second control signal as output, and a second current mirror receiving the second control signal as input and generating the load current as output.
Data Source
AI summary
A driver circuit includes a temperature sensor generating a first voltage representative of current operating temperature. An amplifier compares the first voltage to a second voltage representative of an upper threshold operating temperature, and generates a control signal based thereupon. A variable current source generates a load current from the control signal. The amplifier generates the control signal to cause the variable current source to generate the load current as having a magnitude equal to an upper threshold when the first voltage is less than the second voltage. The amplifier generates the control signal to cause the variable current source to generate the load current as having a magnitude that is decreasing until the first and second voltages are equal, and then generates the control signal to cause the variable current source to maintain the load current magnitude at a level at which the first and second voltages are equal.