How could I find a FET with specific specs?

[EasyGoing1]

Re: How could I find a FET with specific specs?

or use pwm.

PWM from a microcontroller would not have nearly enough current for this application, which is why I need to drive those LEDs through a transistor of some kind. I am going to use PWM to drive the transistor, however. An ATTINY85 to be exact.

[EasyGoing1]

Re: How could I find a FET with specific specs?

but i think you need to use darlington transistors.
maybe a ztx602

... so ... looking at the datasheet for that transistor ... am I reading this right? Would this not fully saturate long before it hits 3.3 Volts?

[stj]

Re: How could I find a FET with specific specs?

or use pwm.

[eccerr0r]

Re: How could I find a FET with specific specs?

But where's the transistorized portion, that's a huge part of the circuit missing!

Do also keep in mind that BJTs have a saturation voltage that may drop the voltage below 3.2 volts, and you may need to use MOSFETs with op amps, possibly with charge pumps, to get the gate drive high enough to fully turn on.

[EasyGoing1]

Re: How could I find a FET with specific specs?

well fets need variable voltage, and transistors need you dont say your led drive voltage, but i think you need to use darlington transistors.
maybe a ztx602

This is a screenshot from a website where I put in the parameters and this is what it kicked out. I was presuming that I would build the circuit like this ... I just need to drive it...

[eccerr0r]

Re: How could I find a FET with specific specs?

No transistor likes being part on (linear mode), they all get hot whether BJT or FET.
All depends on how the heat can and is being dissipated.

If you want (nearly) linear voltage (or current) to current translation, you have to use a BJT. MOSFETs are not linear to Vgs and... (broken record...) YOU NEED NEGATIVE FEEDBACK to get a linear response using a MOSFET. You can see people *do* use MOSFETs for audio amplifier final stages, and you do see they have negative feedback in order to get this to work.

[stj]

Re: How could I find a FET with specific specs?

well fets need variable voltage, and transistors need variable current.
most fets dont like being part-on(linear mode) and get hot.

you dont say your led drive voltage, but i think you need to use darlington transistors.
maybe a ztx602

[EasyGoing1]

I need a FET or a transistor ... don't care really, I'm going to use it to source current to three LEDs at three different levels of brightness (meaning I'm going to drive the transistor at three different voltage levels). It needs to be able to handle 850 milliamps and be fully saturated at around 3.3 volts ...

Is there a way to search for a FET or a transistor based on parameters like this?

Thank you,

Mike