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I am powering a 1A bipolar hybrid stepper motor driven by a DRV8825 with a 12V 10A switching power supply. There is a 220uF capacitor placed at the motor power supply near the driver. The driver's current control is set to 0.5A.

When the driver is in sleep mode, it is woken up and there is a 2ms delay for wakeup time in the code (avr-gcc) before the direction is set, then 1us delay for setup time and then the step pulses are sent, starting pretty slow and accelerating with a linear profile.

All works just fine when powering the driver/motor with a linear 12V 2.5A power supply.

But when powered with the 12V 10A switching power supply (plugged in/switched on, idling), there sometimes is a short interruption shortly after the motor starts and the motor is losing steps. Looking at the voltage of the power supply, it actually breaks down some volts when this happens.

I am not aware of such behaviour, but I have the impression that the switching power supply needs a bit time to deliver power from idle state. Interestingly enough, if I let it continuously power another consumer drawing about 1.5A at the same time, it is stable and all runs fine.

Is my observation correct? Does a (switching) power supply need a short moment to stabilize? If yes, is this by design or some soft start or power saving feature?

I can easily change my code to wake up the driver and give the power supply some time to stabilize before the motor starts stepping.

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Yes, power suppplies need a little to time to stabilize its output voltage after turn on. Some need a minimum load to work fine. It depends on the specific powersupply. Try looking at the supply documentation to see if that is the case. You should try adding the delay you mention in the question to see if it improves.

Another thing to consider is that motors generally draw a big amount of current at start transient. If possible add a soft start to the motor, so it gradually increases its speed.

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  • \$\begingroup\$ It was probably not clear from my question (just edited it), but the power supply is powered on and idling. I am not turning it on and starting the motor immediately. And I do have an acceleration profile, but the motor draws the 0.5A already at stand still after waking up the driver, which is expected. \$\endgroup\$ – Torsten Römer Feb 28 '16 at 20:27
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    \$\begingroup\$ When checking the specification, look for "transient response", " step response", or possibly "load regulation", although the latter is usually used to characterize the regulation for different steady loads. \$\endgroup\$ – Michael Karcher Feb 28 '16 at 20:38

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