Smart linear pulsed laser diode driver, and method
In a pulsed laser diode driver an energy storage capacitor is continuously being charged to a supply voltage Vr. When a pulse is initiated, energy stored in the capacitor is delivered to the laser diode load. The capacitor voltage Vd at the end of a pulse is used to control Vr to ensure that Vd is maintained above a minimum voltage Vm required to ensure operation of a current control device (such as FET) just above saturation. Test pulses (such as with attenuated currents or reduced pulsewidth) may be fired to determine an initial optimum value for Vr. After a test pulse, a slightly high estimate for Vr may be used and may be iterated (incremented) down to an optimum value Vm during a firing burst. A digital processor may be used to calculate and store data to optimize the performance. Various embodiments are disclosed.
1. Method of operating a load which is laser or light emitting diodes in a pulse mode with a diode driver comprising:
providing a storage capacitor;
providing a power supply receiving input power and providing output power for charging the storage capacitor to a capacitor bank voltage (Vr);
providing a current sense device, having an output providing a current sense signal indicative of a current flowing through the load;
providing a current control device for controlling the current flowing through the load in response to a current control signal;
providing a controller having inputs for capacitor bank voltage (Vr) and the current sense signal, and outputting the current control signal, and the controller further has a voltage set output for setting the bank voltage (Vr) output by the power supply;
with the controller, adjusting the power supply voltage to ensure minimum voltage across the current control device at the end of a pulse and minimize its dissipation; and
measuring temperature of the load and providing a signal to the controller to make a feed-forward adjustment to allow a more rapid setting of a correct voltage with lower instantaneous peak power in the current control device.
2. The method of claim 1 , further comprising:
generating at least one precursor pulse or pulses to determine a correct initial storage capacitor bank voltage (Vr).
3. The method of claim 1 , further comprising:
storing conditions of a last, prior, or test pulses to allow a rapid setting of the correct capacitor bank voltage (Vr).
4. The method of claim 1 , wherein the laser is a Q switched laser and further comprising:
detecting a single short pulse output of the laser with a photodiode, and feeding information about the pulse back to the controller.
5. The method of claim 4 , further comprising:
shutting down the current flowing through the load at the time of the short pulse.
6. The method of claim 4 , further comprising:
scaling back one or more of the power supply voltage and current and pulse width to optimize the overall efficiency.
7. The method of claim 1 , further comprising:
the diode driver is used to pump a non electro-optically Q switched laser and the current is increased at a predetermined time to enhance the probability of the laser firing within a predetermined desired time bracket.
8. A driver for providing pulsed power to a load comprising laser diodes or LEDs, the driver comprising:
a storage capacitor that provides the primary energy for the pulse;
a power supply receiving input power and providing output power for charging the storage capacitor to a predetermined capacitor bank voltage (Vr);
a current sense device, having an output providing a current sense signal indicative of a current flowing through the load;
a current control device for controlling the current flowing through the load in response to a current control signal (Control V); and
a controller having inputs for the capacitor bank voltage (Vr) and the current sense signal, and outputting the current control signal, and the controller further has an output (voltage set) for adjusting the power supply voltage to ensure minimum voltage across the current control device at the end of a pulse and minimize its dissipation;
further comprising:
a temperature sensor for measuring temperature and providing a signal to the controller to make a feed-forward adjustment to allow a more rapid setting of a correct voltage with lower instantaneous peak power in the current control device.
9. The driver of claim 8 , wherein:
the current sense device comprises a resistor connected between the load and ground.
10. The driver of claim 8 , wherein:
the controller includes a digital signal processor (DSP).
11. The driver of claim 8 , wherein:
the current control device comprises a FET.
12. The driver of claim 8 , wherein:
the load is connected to the storage capacitor;
the current sense device is connected to ground; and
the current control device is connected between the load and the current sense device.
13. The driver of claim 8 , wherein:
the power supply is a programmable power supply.
14. The driver of claim 8 , wherein:
the current sense device comprises a photodetector detecting light emitted by the load.
15. The driver of claim 8 , wherein the power supply comprises:
a boost converter for boosting input voltage to a voltage higher than input power;
a high voltage capacitor for storing the high voltage; and
a buck converter for charging the storage capacitor.
16. The driver of claim 8 , wherein:
the controller includes a digital signal processor (DSP);
the controller includes a boost converter and a buck converter; and
the DSP is used to control switching of the power supply, including the boost converter and the buck converter.
17. The driver of claim 8 , wherein:
the controller includes a digital signal processor (DSP); and
the DSP is used for setting current, pulse width and pulse repetition frequency for the load.