# Switching a very big current with a very small current?

**URL:** <https://boards.straightdope.com/t/switching-a-very-big-current-with-a-very-small-current/641886>\
**Category:** Factual Questions\
**Created:** [November 23, 2012, 11:58am UTC](https://boards.straightdope.com/t/switching-a-very-big-current-with-a-very-small-current/641886 "2012-11-23T11:58:26Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\
**Post date:** [November 24, 2012, 7:33pm UTC](https://boards.straightdope.com/t/switching-a-very-big-current-with-a-very-small-current/641886/21 "2012-11-24T19:33:08Z")

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> [@Crafter\_Man](#):
>
> What supply voltage will be using with the open collector output and pull-up resistor? 12 VDC?

The documentation is a bit unclear, but I believe it is 12VDC without a need for pull-up resistor.

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<div class="post-metadata">

**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\
**Post date:** [November 25, 2012, 2:10am UTC](https://boards.straightdope.com/t/switching-a-very-big-current-with-a-very-small-current/641886/22 "2012-11-25T02:10:48Z")

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I suppose the easiest way is to directly control the input to the SSR using your open collector output. Just connect the open collector to the negative input to the SSR, and the SSR’s positive input to 12 VDC. The ground side of the 12 VDC should be the same as the ground side of your open collector output.

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