Pulsed Laser Diode Driver Parasitic Inductance Management
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Solution Overview
Problem
Existing pulsed laser diode drivers face challenges in generating very short, high-current pulses efficiently due to parasitic inductance, which leads to slow discharge and energy wastage, and existing solutions do not effectively manage the fall time or protect against reverse damage to laser diodes.
Innovation Solution
A pulsed current driver utilizing a high-speed switch like a Gallium Nitride FET, connected in series with the load, allows for rapid charging and discharging of the parasitic inductance, managing voltage to prevent ringing and reverse damage, while an energy recovery circuit recovers energy back to the power source, enabling short pulse widths and high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shunt protective diode is used to protect laser diodes from reverse voltage, then the laser diode is protected from damage, but the discharge time is prolonged due to parasitic inductance dissipating energy at low voltage
Solution Approach 1:
The patent changes the voltage parameter during discharge by using a two-stage approach: first discharging at high voltage through the laser diode, then switching to low voltage discharge through the shunt diode only after the main energy is depleted. This parameter change allows short discharge time while maintaining protection.
Solution Approach 2:
The patent employs periodic action by using a fast switch to control the discharge process in stages: initially connecting the laser diode to the capacitor for high-voltage discharge, then periodically switching to connect the shunt diode for low-voltage discharge of remaining energy. This periodic switching resolves the contradiction between protection and discharge speed.
2Duration of action of moving object
If high current is delivered to achieve short pulse width, then the pulse duration is reduced, but the inductance opposes the rapid current change
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to high voltage before the pulse is needed. When the pulse is required, the pre-charged capacitor can immediately deliver high current to the laser diode, overcoming the inductance opposition and achieving very short pulse widths with fast current rise.
3Loss of energy
If energy is dissipated through parasitic inductance at low voltage, then the inductance is discharged, but the process takes a long time interval
Solution Approach 1:
The patent uses periodic action with a fast switch to first discharge energy at high voltage through the laser diode (quick energy release), then periodically switch to discharge remaining energy at low voltage through the shunt diode. This time-separated approach minimizes total discharge time while ensuring complete energy dissipation.
Solution Approach 2:
The patent changes the discharge voltage parameter from high to low in sequence. Initially, high voltage discharge rapidly removes the majority of energy from the parasitic inductance. Then, the voltage parameter is changed to low voltage for completing the discharge through the shunt diode, significantly reducing the overall discharge time interval.
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 enables the generation of very short high-current pulses with fast rise and fall times, reduces energy wastage, and protects the laser diode from reverse damage, improving overall efficiency and pulse definition for applications like LIDAR.
Implementation Method 1
A pulsed current driver utilizes a high-speed switch like a Gallium Nitride FET, connected in series with the load, allows for rapid charging and discharging of the parasitic inductance
Implementation Method 2
When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, described by Faraday's law of induction
Implementation Method 3
According to Lenz's law, the direction of induced electromotive force (emf) opposes the change in current that created it
Data Source
AI summary
A current driver is disclosed which allows very short pulses at high currents to be generated for high power laser diodes. The parasitic inductance of the laser diode limits the speed at which the laser diode may be turned on and off. A high voltage is used to charge this inductance rapidly and maximize the rise time. The fall time is shortened by allowing a similar high voltage to be generated at turnoff without damage to the laser diode or switching components. A portion of the energy stored in the parasitic inductance may recovered to reduce drain on the power source, and to improve overall efficiency. The anode of the laser may be switched to ground at the end of a pulse.