Electronics > Beginners
Help with circuit to drive LED lights
Firethelaser:
Hello,
(Please see attached schematic)
I have a set of 6 simple LED's that are each hooked to the single pole side of their own SPDT switch. The other poles are connected to a 5v source and 0-5v square wave signal source fed from a ZTX458 transistor. The switch selects between these two sources with the LED's activating when the square wave signal goes low (they blink).
My problem is that when the switch selects the square wave source, the fourth LED (from the left) fails to blink. The rest of them do. I checked the LED and it was not defective. When I measure the voltage drop on this LED I get 1.7v as compared the 0.4v I am getting with the other LED's.
When I remove this fourth LED, then the fifth one fails the blink. I used a 330 ohm resistor for this one because I ran out of 380 ohm resistors. I am wondering if this is the problem because the currents are not evenly distributed to the LED's? Any insight is greatly appreciated.
IanB:
I don't think you need to have your 117 ohm resistor on the collector of the transistor. What happens if you remove it?
bilko:
--- Quote from: IanB on May 01, 2012, 05:31:05 pm ---I don't think you need to have your 117 ohm resistor on the collector of the transistor. What happens if you remove it?
--- End quote ---
You will probably have to buy another transistor :(
T4P:
Eh ... where do i start?
Oh , did you only have the ZTX458 ? That's a pretty high voltage and high cost transistor ::)
Err ... i'm not entirely sure the transistor is happy driving 5 equal LED's then suddenly 1 unequal LED . LED's require constant current and i have never actually heard of somebody who placed a unequal LED before ....
But what staggers me is why would the 5th LED not blink? That i don't know .
TerminalJack505:
The 117 ohm resistor is way too small. It isn't going to allow the transistor's collector to get down near 0V. Use something like a 10k resistor.
Navigation
[0] Message Index
[#] Next page
Go to full version