How to run 120 leds using mosfet with 4017ic

[japanjot]

hello my frndz, am new to this forum.......seeking for urgent help,
i am making led flasher for my car, am using a typical ic 555 and decade counter 4017 for this.for many weeks m not able to solve the problem to derive 120 leds from ic 4017 output........i have used transistor 2n2222a earlier, but after searching google i came to knw dat i must use power mosfet....so i purchased STP55NF06 power mosfet...........i dont know how to get around 1-1.5 amps of current from it........my power supply would be 12volt car battry....would be glad if you frndz would help me out.


please specify me how to connect mosfet to this, how mush resistance should be connected to gate or source.
sorry to ask but i dont know y we connect resistance to gate or sorce, would appreciate if u would help a dumb like me.
thank you

 

[IanP]

Re: How to run 120 leds each using mosfet

Take a look at this example:
http://picprojects.org.uk/projects/bigmosfetrgb/
I'd even decrease the value of the gate resistors to, say, 100Ω ..

Also, connecting LEDs in parallel is not the brightest idea ..
You should consider an array being a combination of serial and parallel connections (incl. resistors for equilazation) ..
See this website:
**broken link removed**

Rgds,
IanP

 

[dick_freebird]

How to run 120 leds each using mosfet

You might take this even further and make longer series
strings, and run them off a current-mode controlled boost
converter. There are LED driver ICs from most of the major
semiconductor companies for exactly this purpose (and you
have the benefit of their app notes).

 

[japanjot]

Re: How to run 120 leds each using mosfet

Take a look at this example:
http://picprojects.org.uk/projects/bigmosfetrgb/
I'd even decrease the value of the gate resistors to, say, 100Ω ..

Also, connecting LEDs in parallel is not the brightest idea ..
You should consider an array being a combination of serial and parallel connections (incl. resistors for equilazation) ..
See this website:
**broken link removed**

Rgds,
IanP

so should i connect 100Ω resistance at gate???? sorry to ask , but y do we connect resistance at gate???
and as you specified in the diagram which helpd me alot for led arrangement, one thing i didnt got------->>>>


Vin<<< why +vin at gate?
sorry m lil confused

Added after 6 minutes:

You might take this even further and make longer series
strings, and run them off a current-mode controlled boost
converter. There are LED driver ICs from most of the major
semiconductor companies for exactly this purpose (and you
have the benefit of their app notes).

thnk you frnd, can you give me some part numbers or links to them??

 

[erikl]

Re: How to run 120 leds each using mosfet

Vin<<< why +vin at gate? sorry m lil confused

Misunderstanding: Not connected to +vin, but to the outputs of your 4017 counter/decoder! This only means the active output level is (nearly) equal to +vin.

A series resistor between the 4017 outputs and the MOSFET gate limits the load current to the high input cap of the MOSFET. It's sort of a safety feature for the 4017, also against the (unlikely) case of drain-gate shortage of the MOSFET, i.e. not absolutely necessary, however recommended. Any value between 100Ω and 10kΩ is ok; for your LED application I'd suggest 1kΩ.

 

[japanjot]

Re: How to run 120 leds each using mosfet

Vin<<< why +vin at gate? sorry m lil confused

Misunderstanding: Not connected to +vin, but to the outputs of your 4017 counter/decoder! This only means the active output level is (nearly) equal to +vin.

A series resistor between the 4017 outputs and the MOSFET gate limits the load current to the high input cap of the MOSFET. It's sort of a safety feature for the 4017, also against the (unlikely) case of drain-gate shortage of the MOSFET, i.e. not absolutely necessary, however recommended. Any value between 100Ω and 10kΩ is ok; for your LED application I'd suggest 1kΩ.

okies thnx budy

 

[Audioguru]

The 100 ohm resistor should be attached very close to the gate pin of the Mosfet. Another function for it is to prevent the Mosfet from oscillating at a VHF frequency.