I need a chip that will act like the following switch:
Let say it has 2 input for control, and it acts as a "relay" (but for low currents, so I dont want an actual relay)
It is quite hard for me to explain what I want and I hope this diagram helps.
btw, only one "switch" is needed to be "close" or "conductive" at a time.
yes & no - you can get 4 SPST switches tho and wire one side all together.
Look for DG406 type parts
http://datasheets.maximintegrated.com/en/ds/DG406-DG407.pdf
srusha:
btw, only one "switch" is needed to be "close" or "conductive" at a time.
Actually with that last part it seems like a 1-to-4 demultiplexer could work.
Something like this?
http://www.arduino.cc/playground/Learning/4051
The original post didn't mention what exactly was being switched; but that MUX/DEMUX should handle analog or digital signals, as well as low current DC.
Edit: Provided the voltage levels don't exceed ±5 V by too much, of course.
I think that the DG406 would do the job, what is the highest current this chip can transfer? (I am talking about Iin) (Is Iin equal to Iout?)
I need that Iin should be equal to Iout, the thing about mux is that Iin has nothing to do with Iout, right?
btw, I am using regulated 9V for the voltage,
thanks.
Actually I think the SPST is perfect, but I could only find 4 channel and 16 channel, do you happen to know the name of the 8 channel?
DG408
DG401, 403, 405
The correct term is "analog multiplexer", they can handle voltages limited to the supply voltage range only and on resistances are typically 10 to 200 ohms or so depending on type and supply voltage.
CrossRoads:
DG408
http://www.maximintegrated.com/datasheet/index.mvp/id/1003/t/al
DG401, 403, 405
http://www.maximintegrated.com/datasheet/index.mvp/id/1001/t/al
the DG408 seems good but the problem is that the peak current is only 100mA, I think I need something more like 500-600.
the thing about mux is that Iin has nothing to do with Iout, right?
Wrong, I in will always equal I out, how can it not, it is a seriese circuit.
What you want is a bunch of P type FETs.
What you rearly want is to come clean and explain exactly what you are trying to do, our guesses so far are useless no you say you need 600mA. It would have been good to know that at the start. What voltage are you switching?
srusha:
(but for low currents, so I dont want an actual relay)
600mA isn't exactly a "low current". You may want to look at "solid state" relays.
Well, how can it not? in every MOSFET there is no relation what so ever between the current that is charging the Vgate and the Vdrain-source that is conducting the current to the Vout - as in inverter or any OR or AND gate for that matter.
I know that 600ma isn't a low current, I need it for 2 different tasks, I should have been more clear on that.
for the first one (low current) the DG408 will work, and for the second one I want to latch solenoids (for irrigation).
Well, how can it not? in every MOSFET there is no relation what so ever between the current that is charging the Vgate and the Vdrain-source that is conducting the current to the Vout
Two things wrong with that.
So for the second application use N-channel FETs if you want to just switch the power.
- a FET does not use any gate current to speak of it uses only voltage.
How about gate charges?
in every MOSFET there is no relation what so ever between the current that is charging the Vgate and the Vdrain-source that is conducting the current to the Vout
Generally speaking, that statement is not true. Rds itself, thus Ids under a given Vds, bears no relationship to the current going into / out of the gate, as Rds is dependent on Vgs.
However, Vgs is a function how fast you can charge up / discharge the gate capacitance. One big reason that mosfets burn up is the switching losses, which is how fast you can charge up / discharge the gate.
Thus, the current going in / out of the gate can greatly determine how much current is going through d-s.
When you talk and design mosfet you dont usually care about the Iin that is charging the gate, although the current that is used to charge it does grow with the Vgate and the Vgate affects the current that flows in the channel itself, it depends on the Vds and the Vgs and it depends if the MOSFET is on saturation or active,
But lets not get into this right now, as this is not the main issue here,
You think that I can just use N channel mosfet connected to demux (so I'd use only 3 outputs to control 8 transistors) in order to pass this..
this is interesting and I haven't thought about that before.. that is actually a pretty good Idea..
thanks.
When you talk and design mosfet you dont usually care about the Iin that is charging the gate
That is patently untrue. Mosfet's gate for this purpose is really a capacitor, with typical capacitance of 2000pf - 3000pf. So the "current" required to charge up / down a gate, a must to minimize switching losses, is a function of that capacitance + frequency at which such charges should be added / removed.
Thus, there exists a fairly sizeable market for devices that specifically perform this duty: gate drivers. You will see that to drive a typical to220 mosfet (IRF540 for example), you may need a gate driver capable of delivering up to 9amp of current to / from the gate.
Obviously, that need goes down significantly at low speed or for low current applications.
I can just use N channel mosfet connected to demux (so I'd use only 3 outputs to control 8 transistors) in order to pass this..
Yes, you can use mosfet for this purposes - solid state relays are essentially a bunch of mosfets.
Yes, you can use N-channel mosfets. But it is likely that you will need a driver for that - to drive the gate above the potential on the source.
Generally, it is much easier to use a p-channel mosfet for this purposes: pulling the gate low turns on the mosfet. A pnp does the same job too.
I would take a look at your application first to see if you are dealing with AC or DC current.