LED Driver Circuit Inaccessible Current Calculation
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Solution Overview
Problem
Existing power converter technologies face challenges in measuring and controlling currents that are inaccessible due to physical separation, high power dissipation, or complex and costly measurement circuits, particularly in high current applications where resistive shunts result in significant power loss.
Innovation Solution
A simple, cost-effective circuit using analog multiplication and division techniques leveraging pulse width modulation (PWM) signals to calculate and control currents, employing minimal components such as switches, resistors, capacitors, and operational amplifiers to derive accessible currents for measurement and control, thereby overcoming the limitations of traditional methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistive shunt is used to measure current in a high current power converter, then the current measurement becomes accessible, but high power dissipation occurs due to high current passing through the shunt
Solution Approach 1:
The patent uses an intermediary approach by measuring a different current (switch node current) that is accessible and then using mathematical relationships to derive the inaccessible load current. This avoids placing a measurement element directly in the high-current path, thereby eliminating the power dissipation issue while still obtaining the desired current information for control purposes
2Measurement precision
If analog multiplication and division circuits are used to calculate inaccessible currents, then the measurement accuracy improves, but the circuit complexity, cost, and power consumption increase significantly
Solution Approach 1:
The patent extracts the essential functional relationship from complex analog multiplication/division circuits by utilizing the inherent PWM duty cycle information and simple analog relationships. By taking out only the necessary computational elements (using the duty cycle ratio directly in current calculations), the system achieves accurate current derivation without implementing full analog math circuits, thus reducing complexity while maintaining precision
Solution Approach 2:
The patent changes the approach from direct analog multiplication/division to using parameter relationships based on PWM duty cycles. By expressing current relationships in terms of duty cycle ratios (which are already available in the control system), the patent achieves the same computational goal with simpler parameters that require no additional complex circuitry
Data Source
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AI summary
In described examples, for operating a dimmable LED (1112), an LED driver circuit (1100) is coupled to a rectified output of AC dimmer (1102). A current (Iref) is related to an input voltage (Vin) of the LED driver circuit (1100). The value of the current (Iref) is multiplied by the input voltage (Vin) and a duty cycle of the LED driver circuit (1100) to generate a first voltage. The first voltage is compared with a voltage representative of current through a switch (1116) in the LED driver circuit (1100) to generate a comparison signal (PWM COMP). The comparison signal (PWM COMP) is used to generate a pulse width modulation (PWM) signal (D) for controlling the switch (1116) and the multiplication to drive the LED (1112).