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OA47

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Joined: 11/04/2012
Location: Australia
Posts: 986

Posted: 09:36am 23 Apr 2020

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I currently have a solar powered project that is using a MCP1703 5v surface mount 3 terminal regulator. This reg is fed by a 12V SLA battery and was chosen for its low quiescent current due to the solar configuration. Unfortunately the MCP1703 is failing when I operate a solenoid due to exceeding its 250mA max rating. I have tried a LM2940T in its place and things seem to be stable as the 2940 can handle 1A current but as it does not have a low quiescent current nor will it fit the SOT pads on the PCB, I need a suitable upgrade regulator but I haven't found one that has the right pin out or specifications.

Has anyone got any ideas or recommendations?

Thankyou in advance

OA47

Quazee137

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Joined: 07/08/2016
Location: United States
Posts: 593

Posted: 10:17pm 23 Apr 2020

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Is there any chance of powering the solenoid off of the 12v? Then the MCP1705
will not have to deal with the current.

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6283

Posted: 10:45pm 23 Apr 2020

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A large capacitor on the 5V provided it has low leakage.
You might need a current limiting resistor on the charging side.

VK7JH
MMedit

OA47

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Joined: 11/04/2012
Location: Australia
Posts: 986

Posted: 11:12pm 23 Apr 2020

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Thanks for the comments.

The 5V reg is feeding a 1500u cap then a buck boost module that is wound up to 18V (these units self destructed when fed with 12V) The boost module feeds a 4700u cap via a limiting resistor and the cap is switched to the solenoid via a relay operated by the MMITE for 150mS through a UA2803 driver chip. I have tried giving the circuit more cap but beefing up the 3T reg seems to be the only answer.

OA47

Quazee137

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Joined: 07/08/2016
Location: United States
Posts: 593

Posted: 06:26am 24 Apr 2020

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One of my mite projects was using these powered by 12V and I had a problem
with them going into a thermal oscillation at times. My fix was to use 9V
and a small glued on heat sink. The 9V made them run much cooler.

OA47

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Joined: 11/04/2012
Location: Australia
Posts: 986

Posted: 06:54am 24 Apr 2020

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I have made some modifications which dont compromise the PCB's too much and limits the entry current to the buck boost module and this has seemed to circumvent the problem. Undergoing long term testing now so fingers crossed.

OA47

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