Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

LED Test Jig...is this the cheapest/simplest way?

Status
Not open for further replies.
T

treez

Guest
Hello,
We are making a Test Jig which simply puts a small current (clamped to about 1mA) through a LED string so as to check that it has been connected up properly. If its properly connected, then the LEDs will be seen light up.
For safety reasons, the LEDs must only light up very dimly as we don’t want to blind people. Also, the LED string is >60V, so we hope that if someone accidentally touches the probes, they won’t be harmed. Also, the Test Jig must be simple to assemble.
Do you think that the attached Test Jig is the cheapest way to do this?

CLU038 LEDs:-
https://ce.citizen.co.jp/lighting_led/dl_data/datasheet/en/COB_5/CLU038-1208C4_P3706_0516.pdf

IK0524SA isolated DCDC module:-
https://www.farnell.com/datasheets/...MI07HlicK32AIVBbXtCh3g0QSWEAAYASAAEgKxdvD_BwE
 

Attachments

  • LED TESTER.pdf
    12.4 KB · Views: 99

The voltage is still >60 no matter how you generate it. You don't need D1, it serves no purpose at all.
As it is a constant current circuit (~5mA) it doesn't really matter whether the input voltage is precise or not. I think I would skip the intermediate 5V stage and use a conventional transformer to produce ~72V directly, it would be cheaper than 4 PSU modules.

Brian.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Thanks, i like the transformer idea, though i cant find anything on Farnell or anywhere else.
The three DCDC modules are about £3 each, and the 5V wall-wart is about £5, so its the cheapest way i've found so far.

I wonder what would happen if someone held the output probes in each hand? Its hard to see them being seriously harmed, but its so hard to tell?
It does need to be >60V for the LED voltage, but then we are stuck with this danger.

- - - Updated - - -

Also, for ESD resaons, do you agree that the 0V output of the entire system should be connected to earth ground?
(as in the amended schematic)
 

Attachments

  • LED TESTER.pdf
    14 KB · Views: 92

Hi,

I recommend to rearrange the constant current circuit in a way that the 100k voltage is independent of LED voltage.
This ensures more constant current vs LED voltage and decreases voltage drop.
If you use the three 24V sources, then you may use a 30k and single 24V only for the base circuit.

Klaus
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Thanks Klaus, but the actual LED string voltage could be as high as 62V and in fact, in some units it will be half that, just 31V, when only one COB is used.
To be honest, its just a test jig and as long as the led(s) light and are not blinding, then we dont care on the exact led current magnitude.
 

You do not want to have NOOBs touching 72V at 5mA. It might not electrocute them but they will jump so high or fall down that they certainly will be hurt and possibly killed. Wet your hands with salty water and try it yourself!
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Hi,

Thanks Klaus, but the actual LED string voltage could be as high as 62V a
Click to expand...
I don't want to reduce LED voltage, I just want to reduce the voltage for the resistor.

Klaus
 

Thanks, we have added an Earth connection via a 1MEG resistor so that the LEDs-under-test will not get ESD damage when the probes are connected to them.
Do you think this is a good idea?...as attached. We had to include the 1MEG resistor because the testers may accidentally apply the probes when the circuit is powered. -The led driver is an offline, non-isolated product.
 

Attachments

  • LED TESTER_1.pdf
    14.5 KB · Views: 96

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top