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I have a power supply that ranges from 12V-30V. I want to power a set of 4 (24V, 1A) solenoids in series. I also want to use a reduced hold current. So, I'm looking for an output of 96V for a time (~500ms) then reduce that to ~40V and hold there. There are some DC/DC switching controllers I see that we might be able to do this via the feedback resistor divider. Here is 1 possible part as a random example (https://www.digikey.com/en/products/detail/texas-instruments/LM3488MM-NOPB/367045) of a part that this might work for. Does anyone have any experience doing something like this? Can you forsee any any issues with this runtime adjustment of the feedback resistor network?

Alternatively, the solenoids could be in parallel and use a SEPIC with adjustable output and go from 24V to 10V, @ 4A if that would be better/easier. OR do a 2S2P configuration at 48V-20V and 2A.

EDIT: It doesn't particularly matter how quickly the output ramps down from peak to hold voltage. Could be over 1ms, or over 1000ms.

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  • \$\begingroup\$ There are already made ICs for that purpose. \$\endgroup\$
    – Marko Buršič
    Jul 21, 2021 at 21:34
  • \$\begingroup\$ @MarkoBuršič I've looked at the DRV110 from TI, but that doesn't do a boost. 12-30V in, need at least 24V out. Otherwise, it is exactly what I'd want. \$\endgroup\$
    – matth
    Jul 22, 2021 at 2:14
  • \$\begingroup\$ Your question demands buck, not boost. 96V / 4 = 24V per coil, then you reduce the voltage to 10V per coil - so buck. DRV110 is the exactly what I meant. Since those clutches are rather expensive and prof use, I would make a driver for each clutch, then you can power them with 24V and reduce to 10 /or/ 48V and reduce to 24, instead of boosting. \$\endgroup\$
    – Marko Buršič
    Jul 22, 2021 at 6:22
  • \$\begingroup\$ @MarkoBuršič I see, thank you for clarifying. My problem is, as you note, I need at least 24V if I am to drive them in parallel. But the input may range well below that, down to 12V. I was thinking of using a boost stage to a stable 36V rail for example, then use the DRV110 for current regulation. But that seemed overly complicated and I was wondering if there was a better solution. \$\endgroup\$
    – matth
    Jul 22, 2021 at 10:17
  • \$\begingroup\$ I see now. For a reliable operation of these clutches you do need also a reliable power source. It is somehow contradictory that a such fluctuating power source would deliver a stable operation. Why is not possible to have a stable source? \$\endgroup\$
    – Marko Buršič
    Jul 22, 2021 at 17:09

2 Answers 2

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Putting the solenoids in parallel would be the best solution. Not stated is what the solenoids do. Putting solenoids in series is not a good practice especially if they are not matched and the loads are not the same. The sepic converter would be your best solution. You can purchase them for a few bucks. You could use two of them, one for pull in and one for holding. There are parts called injection drivers that will do this function. One that comes to mind is the MC33812.

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  • \$\begingroup\$ The solenoids are electromagnetic power-off brakes (sepac.com/wp-content/uploads/protected/…). I assumed putting them in series would be good because then they all receive the same driving current. And when you say "purchase them for a few bucks" you mean buy the switching controller ICs for a few bucks? \$\endgroup\$
    – matth
    Jul 21, 2021 at 19:06
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schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I love this concept, and was trying to figure something out like this myself. I think the difficulty would be keeping the peak current for long enough. Since it would need to be at least for a few hundred ms, the peak would need to be much higher, and then we'd need another regulator. \$\endgroup\$
    – matth
    Jul 21, 2021 at 19:59
  • \$\begingroup\$ Could just increase C1 to 10,000µF (10mF) or even 100,000µF (100mF), depending on how current-hungry those brakes are. Of course the bigger C1 is, the slower it will recharge. \$\endgroup\$
    – rdtsc
    Jul 21, 2021 at 20:52

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