high side switch selection

[conmanxx]

Hello,

i need some sort of high side switch to switch voltage on/off to an output load.

the switch needs to be controlled by a TTL logic input.
The max voltage on this device is 50V with a current up to 0.5 of an amp.

I've tried using a BC141 NPN BJT. This looks like it should work as the spec meets my requirements... but so far no joy.

Is there a power mosfet that'll do this job? would I need some sort of mosfet Driver to get the circuit to work? ... i'm looking for a low part count solution!

Any help given is very much appreciated.

 

[chuckey]

You don't say what voltage you are working with. With a high side driver, the control element will be near the + rail and with TTL its ouput will be near the 0V rail. So I would have thought you need two transistors. First to change 0->TTL to 0 - supply volts, second to supply the current at supply rail voltage.
Frank

 

[conmanxx]

You don't say what voltage you are working with. With a high side driver, the control element will be near the + rail and with TTL its ouput will be near the 0V rail. So I would have thought you need two transistors. First to change 0->TTL to 0 - supply volts, second to supply the current at supply rail voltage.
Frank

Hi Frank,

The max switching voltage is 50V DC. Maybe a relay would do this job just as good?

 

[alexan_e]

A Pmosfet would work fine assuming that you use this to switch on/off something in a very low rate.
In that case you can get away without a driver but you still need to use a transistor as a level translator because
the mosfet turns off when the gate has the positive voltage and turns on when the gate voltage gets lower compared to the source.

You either need two transistors or a transistor and a mosfet or with the relay you would probably need a transistor to drive the coil too so the component count would be the same in any case.
Using the output transistor solution you would have a lower voltage to the load because of the Vce voltage drop.
The moasfet and relay have very low output resistance so they don't have such problems.

Also the transistor and relay have higher consumption because the driver has to provide the base or coil current constantly while they are turned on,
a mosfet only needs some gate current while it is switching and then the gate pulls no current.

Alex

 

[conmanxx]

Hi Alex,

Thanks for your information, very helpful,

I continued searching for a low cost/part count solution and
came across this profet from infenion,
It's max input voltage is 45V, I think I could live with this.

INFINEON|ITS4142N|IC, PROFET, PG-SOT223-4 | Farnell Ireland

I think i can drive this directly from a ttl input as the onstate input current is 110uA.

I'll order some in for test.

Thanks for your help

 

[FvM]

Infineon also has an ITS 4140N which is capable of 60V/1A. "Intelligent" MOSFET switches are generally a good idea, they provide logic level drive, short circuit and overload protection, and load diagnosis. Other manufaturers, e.g. IRF have similar devices.