25 LED Chaser Transistor Outputs.

[Digital Electronics]

Hello,

I have made a 25 LED Chaser, However I want to have more current for my LED displays. Which transistor will give good current I was thinking of BC547's Or the 2N3904. Also could anyone tell me If this Is correct but on a schematic I saw that a 2N3904 collector was put on a positive supply the base was to the outputs from the IC's and then the emitter went to the LED's, Is that correct ?

Thanks,

Digital.

 

[MAAC0]

Which transistor will give good current

How much current do you need ? mA / KiloAmpere ?
Please post a schematic if You want some help.
A BC547 has 100mA collector current.
A 2N3904 can do 200 mA.
A usual 5mm led handles 20mA max. To be safe calculate the resistor for 10mA.

 

[Enzo]

When I switch stuff like that I like to use MPSA13 - a little darlington. it is rated at 500ma. and 30v. If you don't want darlingtons, my go-to part is MPSA06, 500ma, 80v.

Oh foo, MPSA13 is no longer available. I have a large inventory of them, but that does you little good. But MPSA06, I see Mouser has 35,000 of them at 25 cents each in lots of ten.

 

[Digital Electronics]

Hello MAAC0,

I'm only after mA I'm after a good bright display. What about BC184L's ?

Hello Enzo,

What displays have you made ? I've never actually used a darlington before. What do you think of the MPSA06 ?

Schematic Of The Chaser :

 

[Mooly]

Hello,

I have made a 25 LED Chaser, However I want to have more current for my LED displays. Which transistor will give good current I was thinking of BC547's Or the 2N3904. Also could anyone tell me If this Is correct but on a schematic I saw that a 2N3904 collector was put on a positive supply the base was to the outputs from the IC's and then the emitter went to the LED's, Is that correct ?

Thanks,

Digital.

What you describe is an 'emitter follower', however the base should have some form of limiting resistor. The emitter should also have a resistor to limit LED current. The LED would light when the input went 'high'. Any common small signal transistors are fine for this.

You could also use CMOS buffer packages to drive the LED's. Look at the CD4050. There is also the CD4049 invertor which would drive the LED's from the positive supply instead of to ground. Input goes high, output goes low and pulls current through the LED (and resistor) through the invertor to light it.

2N7000 FET's are a great interface for logic. Drive the gate direct from the 4017 chip and connect the FET as a common source configuration.

 

[Digital Electronics]

Hello Mooly,

What resistor would you recommend for my base of my transistor ?

Thanks.

 

[MAAC0]

Hope this helps.

Check the 10 led version.
They use the 2N3904 & 120 Ohm for 5V so for 12V 220 Ohm would be OK.

LED Sequencers, Flashers, Clocks, Faders

 

[Mooly]

Hello Mooly,

What resistor would you recommend for my base of my transistor ?

Thanks.

For an emitter follower as you describe and all running on 12 volts then something like a 10k or 22k.

The base current (current supplied by the chip) will be only a few tens of microamps in normal use.

Thinking a bit more about it and for that configuration it is not absolutely essential to use resistors but they do isolate the chip driving the transistor from any issues with the load connected to the transistor.