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Author Topic: opposite of transistor switch  (Read 1472 times)
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is there a way to use it so that current flows between the circuit when there is NO power given to the IC
No and that applies to FETs as well.
You always need power to maintain conduction in a semiconductor. Looks like you need a relay, look at reed relays.
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I thought for a P-FET the current passes through the drain and source until a positive voltage is applied to the gate which breaks the connection between the drain and source?

So technically, when no voltage is applied to the gate, it will act like an closed circuit and when the arduino's digital pin activates the gate, the circuit will be broken?

I was hoping to stay away from relays due to their size and power usage.
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I thought for a P-FET the current passes through the drain and source until a positive voltage is applied to the gate which breaks the connection between the drain and source?
No that is not how FETs work.

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So technically, when no voltage is applied to the gate, it will act like an closed circuit and when the arduino's digital pin activates the gate, the circuit will be broken?
No. Enhancement mode FETs work by lowering the resistance of drain to source due to the electric field applied.
You could use a depletion mode FET but I think these are rare nowadays, and anyway it will not do what you want.
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Sorry I meant P-JFET. Isnt that how a JFET works? and I want to use the P version rather than the N version for my purposes?

Is that correct or am more clueless than I think I am?
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You could use a depletion mode FET but I think these are rare nowadays, and anyway it will not do what you want.

I guess I don't agree.
What wrong with a depletion jfet with source and drain to pass high side signal? Gate down, audio passes.
« Last Edit: July 24, 2012, 12:33:22 am by db2db » Logged

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How about using a DIL reed relay?
www.rapidonline.com/Electronic-Components/SPNC-DIL-Reed-relay-71147#techSpecs

Pull-in Voltage 3.75   Dropout Voltage 0.8   Coil 140 ohms   179mW input power

Smallest relay there is (fits into an IC socket) at a reasonable price.
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im guessing that relay doenst latch so it would use current whenever activated?
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Latching realys are available in all types and kinds. It's true that they draw no current latched But it either takes an "Unlatch" coil or toe polarity of the coil voltage must be reversed to unlatch them. Years ago there was a rotary solenoid that would turn On with a pulse and then turn Off with the same pulse to the same coil. Potter and Brumfield made one type that I used frequently for a motor reversing switch. As to solid state devices for latching... All have a quiescent current drain of some kind and None are as durable as a relay... Relays can serve nicely as latching devices amnd one has the option of drawing current either in the On state or in the Off state... OIf course a CD4013 makes a Very Low current Latch too for 50 to 100 uA of current the device can remember it's state for quite a long time on a simple coin cell The main switched power can be turned on or off and the Flip-flop will remember it's state regardless.

Doc
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Have a battery status indicator?, use another ATtiny if needed to monitor the battery.

Have several coin cells connected in parallel, will still be small.


Here`s a wacky idea, have the audio input power the circuit...
Bridge rectifier/ smoothing cap etc
Relay = 4/140 = 28mA = 114mw

Hmm. smoothing could be an issue at audio frequency and it would maybe attenuate the input a bit... smiley
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