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I'm driving an LC load using ULN2003AN IC. The input pulses are 5V at 25 KHz with 50% duty cycle.

I connected an oscilloscope (VM1) to the coil. I was hoping to see some kickback a voltage levels, but there wasn't any. All I got was an alternating square signal between 0 and 11V.

How do I see the kickback voltage? Should I be changing the frequency/duty cycle or is it the ULN2003 not suitable for this task?

schematic

simulate this circuit – Schematic created using CircuitLab

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Install a TEN OHM resistor in the output, from the Driver to the Inductor. That will let you see the inductor voltage move (briefly) beyond the rails.

You will also be able to determine how quickly a (10 ohm) dampening R dissipates the stored energy.

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Diode D2 is protection against kickback.
If you remove D2, you will see 1 kickback. After that darlington transistor Q2 will be probably dead.
ULN2003 is not suitable for you, because it is protected against kickbacks as you can see from your diagram.

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  • \$\begingroup\$ Well, looks like it is so. I will add a bigger BJT transistor to this curcuit, or create a cascade instead using ULN2003. Thanks. \$\endgroup\$ Feb 10 '17 at 9:21

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