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searching for analog switch - help needed

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cruix

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Analog switch

Hello,

I'm searching for analog switch, preferably in small package like SO8, which is>

- controled from 5V (system supply)
- has 3 output pins : NO, NC, common
- can drive 35V, 1A, (low Ron)

It would be best if input is isolated from output.
Is there any such part? interesting is PI5A124, but its low power.

Help needed,
regards, cruix
 

flatulent

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use discrete parts

I do not know of any switches like you want. You can make your own from two power MOSFETs. Connect their sources together for the common point and pull one gate high and the other low to do the switching.

In effect you are making two high side or low side swithes and operating them one on and one off.
 

gnihgnahgnap

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Re: Analog switch

Ofcourse you can buy opto-isolated switch modules, but that's more expensive than DIY.
Another option: take an N channel MOSFET, and use it as a low-side switch.

This assumes a few things about your supply voltage and the type of load you
want to switch. Perhaps you could help us out here, and provide a more
detailed description of what you want. I assume it's 35 volt DC supply? Inductive?

How about something like this. Quicky values:
R1 = 220
R2 = 2.2k
R3 = 1k

For the opto-coupler, use anyone you have lying around. The BUZ11 is a cheapo
N-channel mosfet. Rds_on = 40 milli-ohm, max 50 V, 33 A.

Note: the R2, R3 voltage divider is to make sure the Gate-Drain voltage does not
exceed the maximum of 20V for this particular MOSFET. And the diode should be a fast one. This is included in case you want to drive inductive loads, as protection for the MOSFET.

Another quick remark: I just noticed I goofed up. The point that's connected to +5V should
in fact be connected to a logic gate, so you can toggle between +5V and 0V, and turn the MOSFET on and off. Will also work with 3.3V logic, BTW.
 

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