Question
What does the Compliance Voltage specification in laser diode drivers mean?
Answer
All of our drivers are current sources. This means the current level is the focus of the control system. The voltage across the output device (laser diode, quantum cascade laser) will develop according to Ohm’s Law:
Voltage = Current * Impedance
The voltage varies with the resistance of the load. The current source does not force a particular voltage across the output device. The compliance voltage specification indicates the maximum voltage that can be provided to the output device at full current, not the voltage that will be delivered.
When using an OEM driver, the power supply is not included. The compliance voltage is also limited by what voltage the power supply is chosen.
For example, Wavelength’s PLD Series laser diode drivers have a maximum Compliance Voltage of 3 V with a 5 VDC power supply voltage and 28 V with a 30 VDC power supply voltage. This means that the PLD uses 2 V in the control electronics, so the load must require 2 V less than the input voltage to run. The 3 V or 28 V specification is the maximum voltage that can be provided to the output device, not the voltage that will be delivered.