i have a circuit using a 555 timer to fade leds, i use a bc-547 transistor my question what transistor should i use to fade a 5050 led strip. bc-547 is to small what would be a equal replacement? thanks bill

 

It is difficult to answer without knowing lengths. 5050 led strips draw lots of current. Are you using a capacitor to get the fade?

 

i have a circuit using a 555 timer to fade leds...

Is this a PWM circuit? Once you know the current you need, just choose a MOSFET rated to at least double that. Getting a higher current rating will add very little to the cost of the MOSFET, so be generous. I have IRF540 MOSFETs on hand and that's where I'd start, but there are many, many options.

 

Is this a PWM circuit? Once you know the current you need, just choose a MOSFET rated to at least double that. Getting a higher current rating will add very little to the cost of the MOSFET, so be generous. I have IRF540 MOSFETs on hand and that's where I'd start, but there are many, many options.

if i use a mosfet do i still need the transistor to drive it

 

try 2sc1061 It can handle up to 3A .

 

if i use a mosfet do i still need the transistor to drive it

No, but a schematic would be nice. I'm making assumptions about your circuit.

 

Hi,
i just google the 5050 led strip and it shown a lot of helpful ideas and solutions.
And also giving the right power supply for any number of LED per strips.
ok

 

First post your circuit, if your using pwm then an IRF510 /Irf540 fet will do it easily, otherwise use a bipolar like Tip41, Tip121

 

No, but a schematic would be nice. I'm making assumptions about your circuit.

i have a circuit using a 555 timer to fade leds, i use a bc-547 transistor my question what transistor should i use to fade a 5050 led strip. bc-547 is to small what would be a equal replacement? thanks bill

here is the schematic

 

I'm glad I asked for the schematic, because a MOSFET will not work as a direct replacement here. You need either a different circuit, which is what I would recommend, or just an appropriate transistor. How much current are we talking about?

A problem you may have is that the base current to the transistor is limited to the output capacity of the 555, which is ~200mA. That limits the current you can control with the transistor. And I think the size of that capacitor needs to increase as that base current increases. It starts becoming an impractical circuit for scaling to higher current.

 

I'm glad I asked for the schematic, because a MOSFET will not work as a direct replacement here. You need either a different circuit, which is what I would recommend, or just an appropriate transistor. How much current are we talking about?

A problem you may have is that the base current to the transistor is limited to the output capacity of the 555, which is ~200mA. That limits the current you can control with the transistor. And I think the size of that capacitor needs to increase as that base current increases. It starts becoming an impractical circuit for scaling to higher current.

we are looking at about 2 amps of current. any ideas ?

 

Well, that's borderline but you should be able to modify that circuit to make it work. What do you want that circuit to accomplish? I don't see a variable resistor for dimming.

If you want dimming, I really think you'd be better off with a 555-based PWM circuit. You could make your own or get one off e-bay very inexpensively.

 

Just adapt this one and use a 2n7000 Fet.
http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
Max.