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[SOLVED] Mosfet as switching circuit

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FvM said:
I agree, that MOSFET are preferable in terms of efficiency. But Linspire has been asking explicitely for a bipolar transistor circuit. In those cases, where the supply current doesn't vary too much, the additional base current can be almost neglected with a correctly dimensioned circuit.
Click to expand...

Yap, I have tried search logic level mosfet in my local online shopping which doesn't sell it or maybe (I really no idea these MOSFET stuff)
http://my.element14.com
RS Malaysia | World Leading Distributor of Electronics, Electromechanical and Industrial Components

What'd you mean by correctly dimensioned circuit ?

Linspire

---------- Post added at 18:41 ---------- Previous post was at 18:39 ----------

I have used multisim ver.10; I cant find anything regarding about logic level MOSFET, and your model (KMoffett) isnt at there at all.


Linspire
 

What'd you mean by correctly dimensioned circuit ?
Click to expand...
Setting the base current according to Ic and transistor B with some margin.

I have tried search logic level mosfet in my local online shopping
Click to expand...
I'm sure RS has a representative portfolio of logic level FETs. There may be a problem to find it in the rather confuse catalog.

I have used multisim ver.10; I cant find anything regarding about logic level MOSFET.
Click to expand...
Once you identified a suitable transistor, you can add SPICE models provided by the manufacturer.

P.S.: I checked the RS portfolio, and there's are in fact many logic-level MOSFETs. If you select e.g. Vds = 20 or 30 and SOT-23 package, you get a neat offer that can be reviewed one-by-one. As a first choice, how about ZXM61P02F and ZXM61N02F?

I see, that the RS catalog has been recently improved, but it's still missing a Vgs,th (or "logic-level") selection.
 
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FvM said:
I agree, that MOSFET are preferable in terms of efficiency. But Linspire has been asking explicitely for a bipolar transistor circuit. In those cases, where the supply current doesn't vary too much, the additional base current can be almost neglected with a correctly dimensioned circuit.
Click to expand...

Thread title: Mosfet as switching circuit

Ken
 

Thread title: Mosfet as switching circuit
Click to expand...
Right, but see post #2 and #3. It's been you mentioning bipolar transistors the first time. :smile:
 

@FvM
The components are surface mounted.
Prefer pcb leg.

Can you state clearly regarding the term "margin" ?

Linspire
 

Thanks KMoffett and FvM for helping me out.
The circuit's working properly as expected.

Thanks again. :)

Linspire
 

I have built the circuit as suggested by FvM.
For the load part, I use two 10k resistor as voltage divider to further reduce low level logic voltage(0.69V which still can turn on the hardware) from microcontroller.


Regards
Linspire
 

Dear,
To drive a MOSFET, you can use a specific drives like IR2110. you can also use some optocoupler compatible with logic inputs and can deliver up to 18V, pulse transformer can be used as well.
try this TC4469, it can help you.
 

Hello,

I have a similar problem.
Attached is a part of my drawing.







It is a low power design, with very limited board space.
The MSP430 Controller has to switch off the flash memory.
I want to save the normal driver transistor for the gate of the logical p-canal Mosfet.
It is not possible for me to test the circuit, because I have no logical p-canal Mosfet by hand and I am designing now the PCB board.
I am under big time pressure.

My design idea for switching is :

T1 is off, when Port P1.5 = INPUT
T1 is on, when Port P1.5 = OUTPUT and LOW

Is it possible, that the protection circuit inside the MSP430 ( diodes) will make problems ?
R11 will be more higher, like 470 k.

I hope that somebody can give me a qualified answer.

Best regards and a nice day to everybody

sigges
 


In the schematic above he has a Vgs of 3v and according to the following graphs from the datasheet he can easily get 50mA with negligible voltage drop

DMP3098.jpeg

Alex
 

Hi Ken
Hi Alex

Thanks soo much that you have spend time for me.
I think I have to test it, when I have the Mosfet in my hand.
I see maybe only a problem with the protection diodes of the MSP430 Input.
We will see ......... it is a prototype and for production I can change the design.
Again thanks and have a nice day
With best regards
sigges
 

FvM said:
I wasn't aware of so much ways to mess up a simple circuit.

Click to expand...

Hi FvM,
Can you show me the calculation how actually this circuit works as KMoffet explained above ?
Like why the resistance R1 : 100k and R3 : 2.2 K ?


Linspire
 

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