Directed Energy, Inc.

            Current monitoring for the PCO-7120, PCO-7121, and PCO-7810

            There's an easy way to see an accurate rendition of the output pulse from a PCO-7120, PCO-7121, and PCO-7810 on your oscilloscope.

            These modules include a circuit that works with the optional PCA-9145 current monitor cable. For the PCO-7120 and PCO-7121, the scale factor is 20 A per V into 50 Ω, which means the input impedance of the scope should be set to 50 Ω (or a 50 Ω terminator should be used). The displayed waveform is scaled to 1 V of amplitude for every 20 A of output current.

            All models of the PCO-7810 series have a scale factor of 40 A per V into 50 Ω.

            How does the monitor work? The driver contains a resistance in series with the output that converts the laser diode current to a small voltage. The current monitoring resistors in the driver, combined with the scope's 50 Ω input impedance, yields the scale factor.

            Compared with a standard scope probe, you'll see much less noise with this low-impedance system. The combination of a standard probe's long ground lead and the scope's high input impedance results in significant noise pickup from the high currents being switched nearby.

            Updated: 31 Jan 2019 07:06 AM
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