Can I pulse an inductive load with a laser diode driver?

Laser diode drivers are current sources and can drive inductors. But, the driver may need to output a much higher voltage than expected if you want fast rise times.

Here's the formula to determine the voltage:

V = (L • di/dt) + (R • I)

The first term, (L • di/dt), calculates the voltage needed to force the given current through the inductor in the time allowed. The units are henrys (L) and amperes per second (di/dt).

The second term, (R • I), gives us the additional voltage needed to accommodate the drop across the inductor's DC resistance, cabling, connectors, etc.

For example, assume the inductor is 1 μH and the DC circuit resistance is 0.2 ohms. If we want 300 A to flow in 1  μs, then it takes:

V = (1 • 10-6) (3 • 102) / (1 • 10-6) + (2 • 10-1) (3 • 102) = 360 V

to do the job.

Speeding up the rise time to 500 ns requires 660 V.

On the other hand, reducing the inductance and/or the current, or slowing the rise time, reduces the the driver requirements.

Updated: 19 Feb 2019 12:42 AM