can i use LED on collector? - Electronic Circuits Projects Diagrams Free

Hesam Kamalan · 4th July 2008, 01:34 PM

Hi,
i want to build a dancing light with micro, LED and transistor. is this schematic correct?

i want to increase the LEDs. is this schematic correct, too?

bananasiong · 4th July 2008, 01:44 PM

Hi,
Both the schematics are correct. The first one turns the LEDs on when the base is driven low while the second one turns the LEDs on when the base is driven high, i.e. when the transistor is turned on. You can increase the number of LED, provided that the voltage drop of the LEDs are not higher or equal than the supply voltage. The supply voltage must be higher than the total series voltage drop of the LED.
What color of LED are you using? Different color LED has different voltage drop.
You can put them in parallel too. Something like, a few parallel of series pairs.

*EDIT: The load is on the collector usually, so the answer is yes

Hesam Kamalan · 4th July 2008, 02:35 PM

thank you bananasiong,
i tested that schematics. but when i used two LEDs (serial or parallel), the intensity of LEDs was low. so i can't use some LEDs in serial or parallel.

another question:
in my project, i have used PIC16F84 and 12 LEDs. colors of LEDs are various such as blue, green or red (for example 6 blue, 4 red, 2 green). for estability of voltag i've used regulator 7805.
my question is, what do you prefer about connecting LEDs to forward of regulator (12LED * 30mA = 360mA) or backward of regulator (that i have 14V)?

bananasiong · 4th July 2008, 02:41 PM

Hi,
For series connection, assume the voltage drop for each LED is 1.8 V. So 3.6 V for 2 LEDs. If the supply voltage is 5 V, the voltage across the resistor is 1.4 V. Ohms law, 1.4 V/330

hm: = 4.24 mA. The LEDs are not expected to be very bright with this current. Try reducing the resistance, but do calculation for not higher than 30 mA. Also, remember to include the base resistor while driving the transistor via the PIC.

I don't get these:

Quote:

another question:
in my project, i have used PIC16F84 and 12 LEDs. colors of LEDs are various such as blue, green or red (for example 6 blue, 4 red, 2 green). for estability of voltag i've used regulator 7805.
my question is, what do you prefer about connecting LEDs to forward of regulator (12LED * 30mA = 360mA) or backward of regulator (that i have 14V)?

Hesam Kamalan · 4th July 2008, 04:13 PM

schematic of my project is:

i have used 12 LEDs that connects to each pin of PIC seperatly.
you think that wich of thees is better?
1) as you see in the schematic picture i connect anode of LEDs to VCC (5 volt) or node2.

2) or i connect anode of LEDs to 12 volt (node1)
if i connect anode of each LEDs to 12 volt and voltag drop of 1.8v, the voltage across the resistor is 10.2v. so 10.2/330=30mA

i think if i connect each colector to 12v the intensity and brightnes are higer. what you think so?

bananasiong · 4th July 2008, 04:17 PM

Hi,
For driving only the LED, transistor is not needed. The PIC is capable of sourcing 25 mA on each output pin. Just connect the LED directly via a resistor.

Hesam Kamalan · 4th July 2008, 05:03 PM

if i eliminate transistors and driving LEDs with PIC, won't Regulator overhit ?

matk95 · 4th July 2008, 05:15 PM

No Becuse the transistors are still coneted to the regulator output and this will use the same if not more curent than directly powering them from the pic. and the regulator will not get hot

audioguru · 4th July 2008, 11:50 PM

The PIC will burn out in your original circuit because the max allowed current from a PIC output is 25mA but without current-limiting resistors the current into the base of each transistor will try to be 60mA and the PIC will overheat.

With an output current into an LED of 25mA an output from a PIC will have about a 1V loss.

bananasiong · 5th July 2008, 01:17 AM

Hi,
The maximum allowed current for each pin of the PIC is 25 mA, but according to the datasheet, if the whole PORT is used for sourcing or sinking, 200 mA is shared by 2 PORTs, so average each pin sources or sinks around 12.5 mA. That is still enough for the LED.

Hesam Kamalan · 5th July 2008, 09:42 PM

Thanks,
i designed this cirduit:

what about this cercuit?

Mikebits · 5th July 2008, 10:08 PM

I thought AudioGuru suggested you put current limit resistors on the bases of your transistors. Maybe I was wrong.

audioguru · 5th July 2008, 10:34 PM

If you don't use current-limiting resistors in series with the base of each transistor (the transistors are not needed) then the micro-controller will burn up and die.

gramo · 6th July 2008, 11:21 AM

What about using a couple of ULN2803's?

**Nigel Goodwin** · 6th July 2008, 03:28 PM

Quote:

Originally Posted by Mikebits

I thought AudioGuru suggested you put current limit resistors on the bases of your transistors. Maybe I was wrong.

It's not a 'suggestion' it's a necessity

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Latest
collector output	sreeram_kasyapa	General Electronics Chat	5	2nd May 2006 11:56 AM
Open collector concept.	tkvenki	Electronic Projects Design/Ideas/Reviews	2	3rd April 2006 09:44 AM
Commom-Collector saturation	patroclus	General Electronics Chat	8	3rd February 2006 08:27 AM
open collector	jcaluma	General Electronics Chat	1	6th May 2004 10:16 PM
open collector	blibala	General Electronics Chat	9	4th December 2003 10:23 PM

4th July 2008, 01:34 PM	(permalink)
Hesam Kamalan	can i use LED on collector? Hi, i want to build a dancing light with micro, LED and transistor. is this schematic correct? i want to increase the LEDs. is this schematic correct, too? __________________ http://www.kamalan.com/default.aspx?lang=En http://www.kamalan.com/forums

4th July 2008, 01:44 PM	(permalink)
bananasiong	Hi, Both the schematics are correct. The first one turns the LEDs on when the base is driven low while the second one turns the LEDs on when the base is driven high, i.e. when the transistor is turned on. You can increase the number of LED, provided that the voltage drop of the LEDs are not higher or equal than the supply voltage. The supply voltage must be higher than the total series voltage drop of the LED. What color of LED are you using? Different color LED has different voltage drop. You can put them in parallel too. Something like, a few parallel of series pairs. EDIT: The load is on the collector usually, so the answer is yes __________________ Superman returns.. Last edited by bananasiong; 4th July 2008 at 01:54 PM.*

4th July 2008, 02:35 PM	(permalink)
Hesam Kamalan	thank you bananasiong, i tested that schematics. but when i used two LEDs (serial or parallel), the intensity of LEDs was low. so i can't use some LEDs in serial or parallel. another question: in my project, i have used PIC16F84 and 12 LEDs. colors of LEDs are various such as blue, green or red (for example 6 blue, 4 red, 2 green). for estability of voltag i've used regulator 7805. my question is, what do you prefer about connecting LEDs to forward of regulator (12LED * 30mA = 360mA) or backward of regulator (that i have 14V)? __________________ http://www.kamalan.com/default.aspx?lang=En http://www.kamalan.com/forums

4th July 2008, 04:13 PM	(permalink)
Hesam Kamalan	schematic of my project is: i have used 12 LEDs that connects to each pin of PIC seperatly. you think that wich of thees is better? 1) as you see in the schematic picture i connect anode of LEDs to VCC (5 volt) or node2. 2) or i connect anode of LEDs to 12 volt (node1) if i connect anode of each LEDs to 12 volt and voltag drop of 1.8v, the voltage across the resistor is 10.2v. so 10.2/330=30mA i think if i connect each colector to 12v the intensity and brightnes are higer. what you think so? __________________ http://www.kamalan.com/default.aspx?lang=En http://www.kamalan.com/forums

4th July 2008, 04:17 PM	(permalink)
bananasiong	Hi, For driving only the LED, transistor is not needed. The PIC is capable of sourcing 25 mA on each output pin. Just connect the LED directly via a resistor. __________________ Superman returns..

4th July 2008, 05:03 PM	(permalink)
Hesam Kamalan	if i eliminate transistors and driving LEDs with PIC, won't Regulator overhit ? __________________ http://www.kamalan.com/default.aspx?lang=En http://www.kamalan.com/forums

4th July 2008, 05:15 PM	(permalink)
matk95	No Becuse the transistors are still coneted to the regulator output and this will use the same if not more curent than directly powering them from the pic. and the regulator will not get hot __________________ Check Out My Website www.freewebs.com/electronicsmainia Last edited by matk95; 4th July 2008 at 05:16 PM.

4th July 2008, 11:50 PM	(permalink)
audioguru	The PIC will burn out in your original circuit because the max allowed current from a PIC output is 25mA but without current-limiting resistors the current into the base of each transistor will try to be 60mA and the PIC will overheat. With an output current into an LED of 25mA an output from a PIC will have about a 1V loss. __________________ Uncle $crooge Last edited by audioguru; 4th July 2008 at 11:50 PM.

5th July 2008, 01:17 AM	(permalink)
bananasiong	Hi, The maximum allowed current for each pin of the PIC is 25 mA, but according to the datasheet, if the whole PORT is used for sourcing or sinking, 200 mA is shared by 2 PORTs, so average each pin sources or sinks around 12.5 mA. That is still enough for the LED. __________________ Superman returns..

5th July 2008, 09:42 PM	(permalink)
Hesam Kamalan	Thanks, i designed this cirduit: what about this cercuit? __________________ http://www.kamalan.com/default.aspx?lang=En http://www.kamalan.com/forums

5th July 2008, 10:08 PM	(permalink)
Mikebits	I thought AudioGuru suggested you put current limit resistors on the bases of your transistors. Maybe I was wrong.

5th July 2008, 10:34 PM	(permalink)
audioguru	If you don't use current-limiting resistors in series with the base of each transistor (the transistors are not needed) then the micro-controller will burn up and die. __________________ Uncle $crooge

6th July 2008, 11:21 AM	(permalink)
gramo	What about using a couple of ULN2803's? __________________ Spency. PIC Micro's - Your mind is the limit PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net