# Simple LED circuit as current checker

Discussion in 'The Projects Forum' started by GrandElf, Oct 8, 2015.

1. ### GrandElf Thread Starter New Member

Oct 8, 2015
4
0
Greetings to all,

I need some help regarding my latest project.....I'll need to build a simple LED circuit as a current checker. Details as below:

Voltage in : 5V
Current in : 2.1A/1A
Total LED : 2

Condition :
1) When Iin=2.1A, both LED will be turn ON.
2) When Iin=1A, only 1 LED will be turn ON.

This project is to check the current inside a powerbank.

I try with current divider circuit but still can't achieve this results using only resistors. Any1 can share if you do have better idea for this simple circuit?

Thanks......

2. ### dannyf Well-Known Member

Sep 13, 2015
2,196
421
1. use current sensors, followed by comparators;
2. use transistors, if you don't mind excessive power dissipation.

3. ### GrandElf Thread Starter New Member

Oct 8, 2015
4
0
Hello dannyf, 1st of thanks for your reply.....the 1st option I think is not possible for me because I can only build the circuit from simple component.

Mind to enlighten me how it'll work with your 2nd method? As my Vin=5V is a constant.....The LED lighting will be depends on the total current supply in......

As 1st, I thought by changing the value of the resistors for 1 of the LED will work but somehow it's not working......

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,444
1,073
Since it takes a minimum of 2V to turn on a LED, the simple approach like this is not useful because of the voltage drop across the sense resistor.

I have a way of doing it, but it requires two specialized parts you will have to purchase.

5. ### DickCappels Moderator

Aug 21, 2008
5,319
1,638
You can probably do it with resistors only -I had designed a circuit that turns on zero to three LEDs as the applied voltage rises, but at those currents, you would be burning a lot of watts in the divider resistors.

Nov 5, 2010
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Wait a minute... how are you measuring "current inside" a powerbank? Do you mean the "current flowing into a powerbank?" Or do you mean you want to display the charge level of a powerbank; the amount of charge or percentage of its total capacity?

If you want an indication of the capacity, how is measuring 1A or 2A input to the powerbank going to give you any indication of its capacity?

7. ### dannyf Well-Known Member

Sep 13, 2015
2,196
421
1. Put a high-side current sense resistor. 0.6ohm for 1amp trigger. 0.3ohm for a 2amp trigger point.
2. emitter of a pnp transistor on the high-side of the sense resistor, base of the pnp to the low-side of the sense resistor, through a small resistor (like 1k).
3. collector of the pnp goes to ground through a current limiting resistor + led: the led will start to light up as the current through the sense resistor goes above 1amp.

The led's brightness will continue to increase with the current. For a sharper cut-off, you can insert a npn on the collector.

8. ### GrandElf Thread Starter New Member

Oct 8, 2015
4
0
I'm sorry that some of you still confuse with my project....Let me explain it more briefly......

I'd successfully build a circuit that can be power ON using powerbank only.....But as everyone know there're so many variation of powerbank in the market currently with 5V as constant Vout but with variable current value at Iout=1.0A, 2.1A, or 3.6A.....

My circuit can only be power ON if using a powerbank which can supply Iout=2.1A......So, in order to select the correct powerbank which give the correct Iout=2.1A, I'll need to build a simple ciruit with LED as indicator to determine the powerbank Iout value.....

Which bring me into this idea to build a simple circuit with 2 LED as an indicator to determine if the powerbank did supply Iout=2.1A or Iout=1.0A......

So, my concern for this is more on total current supply by the powerbank rather than the voltage as some of the powerbank even though indicate supply at 2.1A but actually didn't reach it.....

Thank you

9. ### GrandElf Thread Starter New Member

Oct 8, 2015
4
0
Dear all,

Sry for the constant question....Well, finally I have a new idea to design this using Op-Amp I-to-V Converter........

Means that if Iin= 1A/2A, using Op-Amp to convert I'll get Vout=5V/10V as my Vin to the LED circuit checker.......

The problem still remain how can I design to turn on 2 LED using Vin=5V/10V........I'm thinking of using transistor but not sure how to placement the LED......Could anybody guide me for this? (below are my rough idea using Vin=10V

10. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
1,535
412
I think there is some confusion here over how to measure current.

Do you want a circuit that will determine whether a Powerbank can deliver 2.1A at 5V? Then you must connect a load to the output that will draw 2.1A (2.38Ω in this case) and you then check the voltage is maintained at 5V. You can't test it meets its claimed current capability without attempting to draw maximum rated current.

Last edited: Oct 12, 2015