Hello,

There are two ways to make darlington transistors.
With two NPN transistors:
http://en.wikipedia.org/wiki/Darlington_transistor
Or with a NPN driver and PNP power transistor:
http://en.wikipedia.org/wiki/Sziklai_pair
The second one has less losses by the BE connections.

Bertus

 

okay, listen

i live in Norway, and it is very expensive to buy here components( 1,50 euro for 1 resistance)
and i have to drive about a 90 km 1 way.

is there a possibility to do something with just some pic chips, some bc547b and some 2n3055???

Are you sure you are buying from the correct store? It seems waaaay too pricy to pay 1.5euros per 1 1/4W resistance. Would you mind looking for another supplier?

A fellow Norwegian of yours states that he pays NOK 30 for 100 resistors (3.88 EUR for 100 resistors).

Credits to nerdegutta for the price inquiry.

 

Hello,

Did you ever look at Mouser or digikey for the components?
http://no.mouser.com/
http://www.digikey.no/?curr=NOK

Also you could take a look at the companies from this list:
http://www.list-of-companies.org/Norway/Electronic_Components_Supplies/

Bertus

 

I buy most of my stuff from elfa.se or from electradeshop.com.

Elfa send in the mail, usually I have the stuff after 2-3 workday. Electradeshop, is on my way home, so there I just stop by.

 

Hedalen, from the schematic you have posted, I don' t see any resistor on the base of your transistor. Well you told they are very expensive in your country, but nevertheless you will need them. Next be careful if your PNP have the collectors connected to the 12 volts rail then you will burn the pic port, so be carefull and use the 5 volts rail.

Cheers

Alberto

 

okay, okay, now i have many shops,

THANK YOU ALL, it will be much cheaper now to buy some components

 

... I don' t see any resistor on the base of your transistor...

They would not be needed in the emitter follower circuit he shows. However, the blue LED elements might not even turn on as there is better than 3v across the LED and another 1.4v across the 2 transistors. That does not leave much out of 5v. They might glow with R=60 ohms, but not at 1K.

 

Something like this would work if you really wanted to use bi-polar transistors. 2N3055's are huge overkill for the number of LEDs you are talking about. You could easily get away with something cheaper like a TIP31A, which would be more than enough.

Of course, this assumes the LEDs have 1K resistors on them.

 

okay, thanks, i will take a look how much i realy need.
i am talking about 82 leds (blue), and that is exclisive the RGB leds.
there are in total 42 RGB leds so in fact am i talking about 208 leds.
my question is now how to get the in and out fading (for the RGB leds) with pwm, in
PROTON IDE so that i get all the colors.

 

No Idea about the PROTON IDE, but it would be a cinch with most of the other development environments I've seen.

Basically, most will allow you to define the pin as a PWM output, then they give you commands to set the pulse width on that pin anywhere form 0% to 100%.

I just did a search on 'PWM with PROTON IDE' in google and found this.

BTW, 82 blue LEDs with 1K resistors should draw less than 750ma. You would need 4 channels. One for the blue only, and 3 for the RGB. The circuit I showed would be one channel. A TIP31A can handle 3 amps, so would be fine.

 

i have looked at the Microchip site and then the datasheets
but Microchip don't know the 16F1939 chip
so thats strange

 

Looking for this:

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en538148

 

I love these new enhanced midrange chips. Here is one that has exactly 4 hardware PWM's PIC16f1827 in a smaller package.