Tips on monitoring current for the PCO-7125.

Current Monitoring Theory

We prefer to measure current going through the laser diode rather than the voltage across it. The voltage as measured across the diode is difficult to filter for the noise present in the signal.

Using the installed current monitoring circuit (J2)

The PCO-7125 contains a group of very low value resistors in series with the laser diode. The resistors convert the current to a small voltage that is easily viewed with an oscilloscope and this signal is connected to J2.

Ordinary oscilloscope probes have too much unshielded wire and thus pick up too much noise from the heavy switching currents. To overcome this we offer the PCA-9245 Current Monitor Cable. With the PCA-9245 you simply set your scope to 50 Ω termination or if your oscilloscope does not have this option, use a 50Ω terminator at the input of the oscilloscope and plug the current monitor into J2 on the PCO-7125. The PCO-7125 current monitor output is 50 ohms.

The Current pulse will be displayed on the oscilloscope at 500 mV per amp.