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I'm designing a switching regulator for motor controlling, I have tried this circuit with spice but it does not work:

enter image description here

The problem is that the voltage on the load of the regulator never goes down, as is depicted in the picture:

enter image description here

Is there anyone to explain me why?

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  • \$\begingroup\$ In what way does it not work? What's the failure? \$\endgroup\$ – John Honniball Nov 17 '14 at 14:51
  • \$\begingroup\$ @JohnHonniball edited \$\endgroup\$ – Daniel Nov 17 '14 at 14:57
  • \$\begingroup\$ Which is load, can you please explain bit more. \$\endgroup\$ – AKR Nov 17 '14 at 16:30
  • \$\begingroup\$ The load is a dc motor, modeled in the picture @AKR \$\endgroup\$ – Daniel Nov 17 '14 at 18:21
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You are using a model of a P-channel FET, which is hooked upside down, so body diode conducts all the time. Source needs to connect to +12V and drain needs to connect to R1 C2 node. Also, D1 is in the wrong place, anode should go to ground while cathode goes to R1 C2 node.

Here is a related question concerning drive of brushed DC motors.

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