Laser Diode Driver User Manual

LDD CW Diode Driver Power Supplies

The LDD family of CW diode laser drivers are intended for OEM industrial and medical laser applications using high power diode lasers. They have been designed to be integrated into systems for maximum performance at a cost far below traditional laboratory and scientific diode laser drivers.

LDD power supplies utilize a proprietary low loss, high frequency power factor correction circuit which keeps power factor above 0.98. Power factor corrected power supplies use up to 30% less input current and meet stringent IEC harmonic requirements. The output inverter is a state-of-the-art zero voltage switching (ZVS) inverter with permits very high frequency power conversion with minimum losses.

As a diode laser driver, the LDD power supply acts as a current source and delivers constant current based on the input program signal, Iprogram(+), which is normally 0-10V. All units are configured with a maximum current and maximum voltage capability, depending on the user's requirements. LDD power supplies will deliver current, as programmed, into any load, providing the voltage requirements of that load do not exceed the maximum rated voltage of the unit. When the required compliance voltage is higher then the maximum rated output voltage of the unit, the unit will limit output current.

LDD Diode Drivers - Theory of Operation

(Refer to Figure 1)

The LDD laser diode drivers were designed specifically for the OEM high power CW laser diode systems. OEM power supplies for the laser diode industry have the following requirements:

Safe laser diode operation
Broad range of control of output current
Safe rise/fall times
Small size
Auxiliary power supplies to simplify overall laser system
Power factor correction to conform with CE requirements
Low conducted electromagnetic emissions
Low leakage for medical applications

Referring to the "LDD Laser Diode Power Supply" block diagram, the following is a brief description of operation.

AC Input Power Circuitry

AC input power is processed through a line filter to reduce the conducted EMI to an acceptable level. The LDD line filter has minimum capacitance to ground to minimize leakage currents. Earth Ground stud is provided near the AC input terminals and should be connected to the system ground.

Power Factor Correction Boost Inverter

The rectified input power is next applied to power factor boost inverter. This boost inverter boosts the input power to 400VDC. In the process of boosting the input AC voltage, the input AC current is adjusted so that is in phase with the input AC voltage. Without this power factor correction circuit, the AC input current would be delivered to the power supply in high amplitude, narrow spikes, which have a high harmonic content. With power factor correction, the non-50/60 Hz harmonics are reduced to near zero. Since only the fundamental frequency is now used to deliver power, the efficiency of the power supply is improved considerable.

One problem with standard input power factor correction circuits is that a high frequency switching circuit is placed across the line in the input side of the traditional input capacitor filter. This results in substantial switching noise conducted to the line. Lumina Power employs a proprietary soft-switching boost inverter which produces minimum switching noise, reduces switching losses, and results in a smaller heat sink associated with the power factor circuit.

Zero Voltage Switching (ZVS) Inverter

The ZVS inverter and the output transformer are used to step the 400VDC bus to the appropriate output value. The ZVS inverter is the most modern high frequency/low loss/low noise topology utilized in power electronics today. Instead of running the inverter in a traditional PWM mode, the inverter is run in a phase shift mode. With the appropriate output inductor and the appropriate capacitance across each switching device, in this case MOSFETS, there are virtually no switching losses in the inverter. The only losses in the devices are I2R losses associated with the Drain/Source resistance of the MOSFETS. Therefore, the ZVS inverter also contributes to reduced losses, reduce EMI noise and a reduction in overall system heatsink requirements.

Output Circuit

The output filter is a two stage RC filter designed to keep ripple and output noise very low. For lower power units, such as the LDD-250, a single stage filter is used.

Control Circuit

The control circuit handles all the responsibilities associated with safe operation of the laser diode. Controlled rise and fall times, as well as tight current regulation, overvoltage and over power protection are controlled and monitored in the control circuit.

Auxiliary Power

All internal power supply requirements as well as the external +/-15V and +5V power supplies are derived from the power factor control boost inductor. All auxiliary power supplies are regulated by standard linear regulators.

Figure 1

Enlarge