Laser Diode Current Control Circuit with Split MOSFET Measurement Paths
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Solution Overview
Problem
Existing laser diode driver circuits require high operating voltages and complex configurations to achieve low voltage drops, limiting their applicability in low-power applications and experiencing high power consumption and interference issues due to separate switching elements and voltage drops across laser diodes and transistors.
Innovation Solution
A circuit arrangement with a paired path through a measuring path switching element, using an auxiliary regulator and voltage control elements to generate a measuring current proportional to the laser current, allowing for low voltage drop and efficient control of the laser diode current with a single series element, and complementary measurement paths to reduce modulation dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If separate switching elements are used to control laser current and switching state, then the laser can be controlled independently, but the voltage drop increases and power consumption rises
Solution Approach 1:
The patent combines the control of laser current and switching state into a single switching element (the first switching element), eliminating the need for separate switching elements. This merging reduces the total voltage drop from Vsum≥Vt+ΔV+VF to a lower value, thereby reducing power consumption while maintaining independent control capability through coordinated control signals
2Adaptability or versatility
If a DC-DC converter is used to generate higher operating voltage internally, then the circuit can operate at low external voltage, but the circuit complexity increases and interference issues arise
Solution Approach 1:
The patent extracts and eliminates the DC-DC converter from the circuit architecture. Instead of using internal voltage generation, the invention directly operates at the available external voltage level by optimizing the switching element configuration and control method, thereby reducing circuit complexity and avoiding interference issues while maintaining low external voltage operation capability
3Measurement precision
If measurement is performed at a series resistance, then the laser current can be measured, but an additional voltage drop occurs
Solution Approach 1:
The patent introduces a paired second switching element as an intermediary for current measurement. This second switching element is paired with the first switching element such that their combined on-resistance equals the original series resistance value, but the measurement is performed through the second element's voltage drop rather than adding a separate measurement resistor. This eliminates the additional voltage drop while maintaining measurement precision
Data Source
Figure 1~2
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Figure 5~6
AI summary
The invention relates to a circuit (100) and to a method for controlling and measuring a current (IL) in at least one charge element (101), in particular in at least one laser diode, which can be used at a low operating voltage with laser current control and/or at a low drop in voltage, also for so-called "low power" applications. According to the invention, three MOSFET's (102, 104, 108) are coupled in a split manner for a charge path (103) and for two measurement paths (106, 110) and are maintained by means of an auxiliary controller (107) at the same working point such that they deliver the modulation current and comparison currents (11, 12) which is fixed with respect to the modulation current. The comparison currents are used to determine the average modulation current and to feed a control device (123) which deliver these currents and also the average modulation current to a desired value in which an operational or control current (VA. VB) is varied on a circuit block (114) by the control device. Said circuit block delivers the output signals (S1.S2) when the amplitude depends on the operational or control voltage and which controls two or more circuit elements in the charge path and the measurement path.