eq lizer circuit - Page 2 - Electronic Circuits Projects Diagrams Free

audioguru · 28th April 2008, 04:57 PM

Quote:

Originally Posted by MrDEB

Maybe eliminate the transistors and the 4049 and using a uln2804?

It cannot be used in your circuit because you need to source current from the positive supply with PNP transistors. The ULN-series sink current to ground with NPN transistors which is the opposite.

MrDEB · 29th April 2008, 05:44 PM

see pic as I changed the buffer and transistor resistors.
contemplating a uln2074, t4hc4514
both used in an led display called ledtricks over at http://www.doityourselfchristmas.com/forums/

audioguru · 29th April 2008, 08:18 PM

Your circuit doesn't have anything to limit the current in the LEDs except the lottery called "transistor current gain".

The 3k base resistors limit the base current to about 3mA. Then depending on the current gain of the transistors, the LED current will be from 30mA to 2A. You must slam the transistors on hard then limit the current with a resistor in series with each LED. Then the amount of current will be predictable and all currents will be the same.

The LM3916 has regulated current in its outputs so a series resistor to the base is not needed but a resistor to the positive supply is needed to turn off each transistor.

The ULN2074 is NPN. You need PNP transistors.
The 74HC ICs have a max allowed output current of 25mA which is good enough to turn on nearly any PNP transistor.

MrDEB · 29th April 2008, 10:14 PM

I forgot a resistor in power supply transistor on 3916
but show a resistor in series from the row transistor/power supply to the led.
the 80 ohm resistor is for load of 150-200ma on the led row.
I hope your not meaning a seperate resistor per led? (100 resistors per display?)

audioguru · 30th April 2008, 01:23 AM

I think the ten current-limiting resistors for the LEDs should be at the collector of the pull-up columns driver transistors.

I don't know how you calculated 80 ohms.
The LM3916 plus the emitter-follower transistor use 1.0V. The LEDs use 2.5V at 180mA if they are red. The pullup transistor uses 0.2V which leaves 8.3V across the current-limiting resistors. Therefore its value is 8.3V/180mA= 46 ohms. Use 47 ohms.

MrDEB · 30th April 2008, 11:41 AM

just pulled 80 ohms from hat, inserted into TINA and come up with 90.9ma
the 47 ohm = 148.97 ma
put the 10 50 ohm resistors on the collectors of Q100 or Q200
we just might get this thing working

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

Similar Threads
Title	Starter	Forum	Replies	Latest
Circuit Help	skeeterb	Electronic Projects Design/Ideas/Reviews	7	5th May 2008 07:10 PM
High Voltage Power Pulse Circuit	Burnt	Electronic Projects Design/Ideas/Reviews	6	5th March 2008 05:21 AM
Help needed Temperature circuit	karenhornby	Electronic Projects Design/Ideas/Reviews	0	13th February 2008 10:19 PM
Circuit auto OFF feature after no events design	Uman	Electronic Projects Design/Ideas/Reviews	2	3rd May 2004 06:34 AM
Circuit functioning very strange. Why?	Cyclone	Electronic Projects Design/Ideas/Reviews	12	4th November 2003 01:31 AM

29th April 2008, 08:18 PM	(permalink)
audioguru	Your circuit doesn't have anything to limit the current in the LEDs except the lottery called "transistor current gain". The 3k base resistors limit the base current to about 3mA. Then depending on the current gain of the transistors, the LED current will be from 30mA to 2A. You must slam the transistors on hard then limit the current with a resistor in series with each LED. Then the amount of current will be predictable and all currents will be the same. The LM3916 has regulated current in its outputs so a series resistor to the base is not needed but a resistor to the positive supply is needed to turn off each transistor. The ULN2074 is NPN. You need PNP transistors. The 74HC ICs have a max allowed output current of 25mA which is good enough to turn on nearly any PNP transistor. __________________ Uncle $crooge

30th April 2008, 01:23 AM	(permalink)
audioguru	I think the ten current-limiting resistors for the LEDs should be at the collector of the pull-up columns driver transistors. I don't know how you calculated 80 ohms. The LM3916 plus the emitter-follower transistor use 1.0V. The LEDs use 2.5V at 180mA if they are red. The pullup transistor uses 0.2V which leaves 8.3V across the current-limiting resistors. Therefore its value is 8.3V/180mA= 46 ohms. Use 47 ohms. __________________ Uncle $crooge

30th April 2008, 11:41 AM	(permalink)
MrDEB	Resistor selection from hat just pulled 80 ohms from hat, inserted into TINA and come up with 90.9ma the 47 ohm = 148.97 ma put the 10 50 ohm resistors on the collectors of Q100 or Q200 we just might get this thing working