Hello everyone i need a Mosfet having the lowest RDS(ON) perimeter.Kindly suggest me the one

 

What do you use for the MOSFET (V/I) ?

 

What voltage and current do you require? What maximum size is acceptable?

 

What voltage and current do you require? What maximum size is acceptable?

Helo Bro i have a power supply of 3 volts Battery/cell that is the requirement of design.My load is drawing a maximum current of 2.3 Amps but with 3 volt Power Supply Mosfet is only switching .097 Amps which is insufficient to run the load

 

Helo Bro i have a power supply of 3 volts Battery/cell that is the requirement of design.My load is drawing a maximum current of 2.3 Amps but with 3 volt Power Supply Mosfet is only switching .097 Amps which is insufficient to run the load

Do you have a schematic?

 

Helo Bro i have a power supply of 3 volts Battery/cell that is the requirement of design.My load is drawing a maximum current of 2.3 Amps but with 3 volt Power Supply Mosfet is only switching .097 Amps which is insufficient to run the load

So it sounds like the problem is the gate voltage not RDSon.
What FET are you using, and what voltage do you have between the gate and source?

 

Hello everyone i need a Mosfet having the lowest RDS(ON) perimeter.Kindly suggest me the one

That is not quite correct. What you actually need is a MOSFET with the lowest RDS(ON) that you can reasonably obtain. You should start by doing a parametric search on a site from which you can actually procure the part. Finding one that you can't buy for a price you cannot afford won't do you a bit of good.

 

So it sounds like the problem is the gate voltage not RDSon.
What FET are you using, and what voltage do you have between the gate and source?

Hi brother the 555 timer is giving the gate voltage which is approximatly 1.7 volts i have tried three types of Mosfets Attached are datasheets

 

So it sounds like the problem is the gate voltage not RDSon.
What FET are you using, and what voltage do you have between the gate and source?

i have connected my load between 3 volts supply and drain.The gate is triggered by 555 timer because i need a delay before switching.
The 555 timer is giving 1.7 volts approx do you have any idea whats wrong?

 

There are only a few MOSFETs which will be fully turned on (lowest RDS) at a gate voltage of 1.7V
When you look at the data, notice at what gate voltage RDS is specified. That needs to be 1.7V or less
https://www.mouser.co.uk/Semiconduc...zrZ1yiaumv&Rl=ax1sfZgjdhp5Z1y96qtkZ1yw8l6lSGT

 

You might be able to get better performance and/or make it easier to choose a suitable MOSFET if you cascade another transistor between the 555 and MOSFET. If you can get the gate voltage closer to the 3V supply voltage, it'll be much easier to find MOSFETs with suitable Rds on characteristics.

Of course, adding a stage in between will create a logic inversion. Depending on the rest of your circuit needs, it may or may not be easy to work around the inversion issue.

 

A MOSFET is not the correct choice for this application. Use a BJT instead.

 

A MOSFET is not the correct choice for this application. Use a BJT instead.

Why do you say that? It is quite common to use a mosfet to "turn on" (connect) a power supply to a circuit in either high or low (as described here) configuration.

 

Why do you say that? It is quite common to use a mosfet to "turn on" (connect) a power supply to a circuit -- in either high or low configuration. High with a P-mosfet might be a bit more common or simply a reflection of my experience.

MosFETS are field devices, state controlled by voltage. Their value is in being able to set a gate without having to maintain a gate charge, thus limiting their current consumption to maintain a state- which is why they are so prevalent in IC Logic. More importantly, most generally available FETs have a very high actual voltage requirement on the gate in order to fully saturate, and this fact is frequently obfuscated in the literatures as manufacturers jockey to make their product look the best.

BJTs are a better choice (and the math much easier to work out for gain factors) for most hobbyists if the 'gate state' benefit of FETs isn't something they require.

And finally, just because something is used in some ubiquitous fashion, doesn't mean that is right. It just means that people are not being properly educated in the proper use of the tools of the trade.

 

With low voltage sources, e.g., the 3.0 V the TS is using, the lower voltage drop of a logic-level mosfet can be an advantage. For example, an RDS(on) of 3 mΩ at Vgs = 2.5V will give only a 7 mV drop at 2.9A (25 mW). Moreover, the devices are small and don't generate as much heat as a BJT running at 2.9A.

 

MosFETS are field devices, state controlled by voltage. Their value is in being able to set a gate without having to maintain a gate charge, thus limiting their current consumption to maintain a state- which is why they are so prevalent in IC Logic. More importantly, most generally available FETs have a very high actual voltage requirement on the gate in order to fully saturate, and this fact is frequently obfuscated in the literatures as manufacturers jockey to make their product look the best.

BJTs are a better choice (and the math much easier to work out for gain factors) for most hobbyists if the 'gate state' benefit of FETs isn't something they require.

And finally, just because something is used in some ubiquitous fashion, doesn't mean that is right. It just means that people are not being properly educated in the proper use of the tools of the trade.

When minimal voltage drop is a priority, it's often easy to find a MOSFET with low enough Rds to outperform any BJT. For me at least, this comes up pretty often. It has nothing to do with fashion, popularity, or understanding what my options are. The gate properties aren't the only properties to consider when weighing options.

As for this particular project, it's challenging either way you go. If you want to go BJT, that's a lot of current, so you'll need a lot of base current... possibly so much that you'll need two stages (darlington, etc.) If you need a second stage anyway, might be better to use a mix of technologies, or two MOSFETs, one acting like a gate driver of sorts for the other.

*** EDIT:
While I was typing, @jpanhalt beat me to it with a more concise answer.

 

On the other website we told you that your ordinary NE555 or LM555 has a minimum supply voltage of 4.5V as shown on its datasheet. Most of them will not do anything if the supply is less than 4V. Since yours produced an output of only 1.7V then yours barely worked.

I recommended using a Cmos 555 (LMC555, TLC555 or ICM7555) that has a minimum supply of 2V and its output goes as high as its supply voltage. But if you cannot find a Mosfet that works properly with a gate-source voltage of only 3V (you might need to buy hundreds of logic level Mosfets then test them to find one) then use an ordinary 555 with a 12V supply to drive an ordinary Mosfet with its required 10V or gate-source voltage.

 

On the other website we told you that your ordinary NE555 or LM555 has a minimum supply voltage of 4.5V as shown on its datasheet. Most of them will not do anything if the supply is less than 4V. Since yours produced an output of only 1.7V then yours barely worked.

I recommended using a Cmos 555 (LMC555, TLC555 or ICM7555) that has a minimum supply of 2V and its output goes as high as its supply voltage. But if you cannot find a Mosfet that works properly with a gate-source voltage of only 3V (you might need to buy hundreds of logic level Mosfets then test them to find one) then use an ordinary 555 with a 12V supply to drive an ordinary Mosfet with its required 10V or gate-source voltage.

I agree that a 1.7V output is unreasonably low for working directly with a MOSFET - working options might be found, but it won't be fun.

However, once you get to 3V output, it shouldn't be that bad. Tons of 3.3V microcontrollers out in the world, and tons of products optimized to work with them. I don't remember specific part numbers right now, but I've looked for MOSFETs to use with 3V gate voltage in the past and never had any trouble finding them.

Anyway, I hadn't thought about minimum requirements for the 555. Sounds like you're on to something there. Switching to a CMOS 555 might make the rest of the project much easier.

 

I would use a TIP121 series darlington-transistor.

 

I would use a TIP121 series darlington-transistor.

Isn't the Vbe for that part (at high CE currents) dangerously close to the available 1.7V signal? Seems like that would leave little room for error when selecting a base resistor.