LED Glowing in OFF condition

[electronika.design]

I am making a Transistorised Relay Card in which LED plays an important role(indicate if I am getting an Input & if my board is providing an output to the load)
The circuit is powered by +5V. It is simple switching.
The load is a coil.
My input LEDs are working just fine, but...
I cant understand why my output LEDs still glows partially(30-40% of its capabilty) in OFF condition, though when in ON condition they glow at 100%.
I need to make them totally off in OFF condition.

Thanks

 

[KlausST]

Hi,

please show your circuit.

Klaus

 

[electronika.design]

Sorry one correction
My board runs on a supply +24Vdc

 

[KlausST]

Hi,

I need some additional informations:

* you say it is powerd with 5V. Is it the left side (optocoupler input side), is it the right side (marked with VCC) or both?
* When your LED glows: What is at the input? Shorted to GND (push pull driver, like HC logic output) or open circuit?
* what happens (LED glowing) when you short both inputs?
* what is your load?
* where is your load connected to? (I assume GND)
* I doubt the LED is glowing when the load properly is connected to GND. Am I right?

***
Schematic:
I personally don´t like how C1 is conected.
Now evertime you power ON the right side of your circuit, then Q11 automatically becomes conductive for a short time, forcing power to the load.
--> I´d connect C11 in parallel to R51.

R35 is useless.


Klaus

 

[c_mitra]

I cant understand why my output LEDs still glows partially(30-40% of its capabilty) in OFF condition, though when in ON condition they glow at 100%.
I need to make them totally off in OFF condition.

Obviously, the LED is getting current both when the TIP147 is ON or OFF. The max current the LED can get is about 1 mA (much less) with a 5V supply. Perhaps when the transistor is OFF, it is still getting perhaps 0.1 to 0.3 mA. I suspect that you are not turning off the TIP147 hard. The base is not getting anywhere near ground.

I guess you are not turning it ON hard (can't you reduce the 10K-- R51?

I suggest you give 1-5mA to the LED (if possible) and see that the emitter has a path to ground if the load is disconnected.