Author Topic: Switching an unknown DC voltage with a LVTTL signal  (Read 982 times)

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Offline hamster_nzTopic starter

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Switching an unknown DC voltage with a LVTTL signal
« on: June 24, 2020, 10:07:23 pm »
What is a good way to switch an known DC voltage (between 2.4V and 24V) with unknown polarity using a 3.3V CMOS logic signal?  The controlled signal will usually be driving low voltage DC motors. If the polarity was known I would just use a logic level MOSFET.

A relay would be the ideal, but energizing it uses too much power - I want to drive it for many hours from a CR2032 cell.
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Offline langwadt

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Re: Switching an unknown DC voltage with a LVTTL signal
« Reply #1 on: June 24, 2020, 10:29:50 pm »
What is a good way to switch an known DC voltage (between 2.4V and 24V) with unknown polarity using a 3.3V CMOS logic signal?  The controlled signal will usually be driving low voltage DC motors. If the polarity was known I would just use a logic level MOSFET.

A relay would be the ideal, but energizing it uses too much power - I want to drive it for many hours from a CR2032 cell.

if you supply is isolated, back-to-back mosfets? 
or maybe a latching relay?




 

Offline hamster_nzTopic starter

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Re: Switching an unknown DC voltage with a LVTTL signal
« Reply #2 on: June 24, 2020, 10:57:52 pm »
if you supply is isolated, back-to-back mosfets? 

Supply is definitely isolated (battery powered device). So something like this attached schematic?

Hummm - can't see how I would reference the 'smart switch' to the load being switched...


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Offline langwadt

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Re: Switching an unknown DC voltage with a LVTTL signal
« Reply #3 on: June 25, 2020, 02:34:58 pm »
if you supply is isolated, back-to-back mosfets? 

Supply is definitely isolated (battery powered device). So something like this attached schematic?

Hummm - can't see how I would reference the 'smart switch' to the load being switched...

basically this: https://www.homemade-circuits.com/wp-content/uploads/2020/01/SSR-concept.png

the two sources are "ground" for your control circuitry


 

Offline hamster_nzTopic starter

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Re: Switching an unknown DC voltage with a LVTTL signal
« Reply #4 on: June 25, 2020, 09:43:35 pm »
if you supply is isolated, back-to-back mosfets? 

Supply is definitely isolated (battery powered device). So something like this attached schematic?

Hummm - can't see how I would reference the 'smart switch' to the load being switched...

basically this: https://www.homemade-circuits.com/wp-content/uploads/2020/01/SSR-concept.png

the two sources are "ground" for your control circuitry

Perfect. Thanks for your help.
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