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Electronics => Beginners => Topic started by: davelectronic on January 17, 2017, 10:59:14 am

Title: Reverse a swtch.
Post by: davelectronic on January 17, 2017, 10:59:14 am
So i bought a couple of thermal swiches (bi metalic) unfortunately tired i ordered NC instead of NO relised when they turned up. So not wanting to reorder again, i thought relay to reverse the thermal switch state over when activated to NO, closing on temperature rise. My question is, does anyone know of a better arrangement to this problem  ? Thanks for reading.
Title: Re: Reverse a swtch.
Post by: danadak on January 17, 2017, 12:28:59 pm
If the switch was operating line operated loads, relay good idea.
If just a logic level signal you could use single gate logic to effect
the inversion.


http://www.ti.com/lit/sg/scyt129f/scyt129f.pdf (http://www.ti.com/lit/sg/scyt129f/scyt129f.pdf)


Regards, Dana.
Title: Re: Reverse a swtch.
Post by: davelectronic on January 17, 2017, 07:31:58 pm
Its only for 12 Volt loads at a few hundred mA, thanks, i will take a look at this idea.
Title: Re: Reverse a swtch.
Post by: eblc1388 on January 19, 2017, 12:28:44 am
Its only for 12 Volt loads at a few hundred mA, thanks, i will take a look at this idea.

On temperature rise, a NO thermal switch would operate and provide power to the load, if that's what you want.

In order to use a NC thermal switch to provide the same function, you can use either a relay or better still a PMOS to save on idle power lost.

Connects the S(source) pin of the PMOS to +12V, its D(drain) pin to the load. Connects the NC thermal switch between its G(gate) and S pin. Then connects the G via a 22K resistor to 0V. Because of the NC nature of the thermal switch, the PMOS is cut off so no power to the load. When temperaure rises, the thermal operates and becomes open circuited. PMOS is biased and power is then fed to the load. The idle power loss is the current through the 22K resistor only.
 
Title: Re: Reverse a swtch.
Post by: alanb on January 19, 2017, 01:43:16 pm
Is there a mechanical solution to this whereby you  disassemble the switch and re assemble with the bi-metallic strip the other way up?