Solar powered 2 pin RGB LED

Lucky-Luka

Joined Mar 28, 2019
101
Hi all
I have an RGB LED led that needs more or less 3 volts to perform correctly its light routine.
Can I use for my project a 3.3V zener diode?
Only using the rectifier diode and the cap as a buffer the voltage would be a rather constant 4.8V.
Cheers

Attachments

• 17.3 KB Views: 13

Tonyr1084

Joined Sep 24, 2015
5,990
Not fully confident I understand what you're looking for, but if I wanted to light an LED I'd start with a known - higher voltage than the LED's forward voltage (Vf). Then subtract the Vf from the higher voltage. Then I'd calculate the necessary resistance to achieve the current through the LED I wanted.

Example:
PS = 4.5V
Forward Voltage = 3.2Vf
Target current = 15mA (0.015A)

Solution:
(4.5V - 3.2Vf) ÷ 0.015 = 86.6•••Ω

Since I'm not going to find an 86 2/3Ω resistor I'd opt for using a 47Ω resistor in series with a 33Ω resistor for a total of 80Ω. That would give me a slightly higher current of 16mA.

Now, if I've gone in the wrong direction - sorry. Part of the reason for my confusion is your statement that you have an RGB LED. That type of diode typically has four leads. Bi-Color LED's have just two leads. One color when current travels in one direction and the other color when current travels in the opposite.

Last edited:

BobTPH

Joined Jun 5, 2013
3,316

Bob

Tonyr1084

Joined Sep 24, 2015
5,990
Just noticed you said a power source of 4.8 volts. In that case a 100Ω resistor would be required as opposed to my original suggestion of two resistors for a total of 80Ω. You still get 16mA.

Lucky-Luka

Joined Mar 28, 2019
101
I have a NiMH battery and a 6V 60mA solar panel.
I think that QX5252 IC even takes care of the current to the LED. No need for a resistor here.
These RGB LEDs have 2 pins and they aren't properly documented. Maybe in some chinese websites but I don't know that language... I've found some infos from the ebay seller but nothing more:

White: 6.500 k, 20.000 mcd, 3-3,2V
Blue: 455-465 nm, 15.000 mcd, 3-3,2V
Green:: 515-520 nm, 18.000 mcd, 3-3,2V
Yellow: 588-592 nm, 7.000 mcd, 2-2,2V
Red: 625 nm, 7.500 mcd, 2-2,2V

Nominal current: 20 mA;
Max current: 50 mA;
Max voltage: 5V;

I have updated the circuit: right now it works just fine and the LED draws more or less 10mA giving a nice luminosity.
Where would you place the ON/OFF switch?

Attachments

• 16.8 KB Views: 7

Tonyr1084

Joined Sep 24, 2015
5,990
These RGB LEDs have 2 pins and they aren't properly documented.
Well, if you say so. Nevertheless, I still believe an RGB Light Emitting Diode, which has three colors to it - Red; Green; Blue - should have four wires. Besides, noting in your circuit diagram shows an RGB type LED. IF your LED is white then it's likely approximately 3 to 3.2 Vf. MY white LED's are an average of 2.97Vf. I did some measurements and calculations on the LED's I got; since they came without any data sheets.
Where would you place the ON/OFF switch?
Didn't know we were talking about inserting a switch. But if you wanted to put it anywhere, I think I would have chosen on the LX line between L1 and D1. But where you have it should be OK. At least I can't see a reason for it being wrong. Just that L1 may want to draw current all the time. I'm just not sure.

Lucky-Luka

Joined Mar 28, 2019
101
Nevertheless, I still believe an RGB Light Emitting Diode, which has three colors to it - Red; Green; Blue - should have four wires.
This is the kind of LED that I'm using.

Audioguru again

Joined Oct 21, 2019
3,199
You must look at the datasheet of anything like a QX5252 IC before blowing it up. You said your solar panel is 6V!!
You did not say the voltage of your battery.
The datasheet of the QX5252 says its operating voltage is 0.9V to 1.5V from one Ni-MH battery cell as shown in the video.
The battery cell usually uses a 2.0V solar panel for charging.

The QX5252 uses a oscillator with an inductor to step-up the voltage. The current is limited and the Schottky diode and 0.1uF capacitor peak detect and filter the stepped up voltage pulses.

Why switch off the LED instead of switching off the battery? The QX5252 IC might be destroyed if you disconnect its load.

Lucky-Luka

Joined Mar 28, 2019
101
You must look at the datasheet of anything like a QX5252 IC before blowing it up. You said your solar panel is 6V!!
You did not say the voltage of your battery.
The datasheet of the QX5252 says its operating voltage is 0.9V to 1.5V from one Ni-MH battery cell as shown in the video.
The battery cell usually uses a 2.0V solar panel for charging.
I've read a couple of poorly written datasheets but I've also read several users experiences. I think it can handle 6V 60mA solar panel. I'm doing some experiments right now. btw the absolute max voltage it can handle (it is written in a datasheet that I've found) is 7V. Not always it's full sun so I think there will be no problems. 2V panels maybe are better for the longevity of the IC but right now I'm testing a 6V panel.

Why switch off the LED instead of switching off the battery? The QX5252 IC might be destroyed if you disconnect its load.
I've updated the schematic. Better now? I cannot understand how it can be ruined if the load is gone.

Attachments

• 21.7 KB Views: 8
Last edited:

Audioguru again

Joined Oct 21, 2019
3,199
If you disconnect the LED with a switch then the inductor has nothing to limit the amount of "flyback" boosted voltage each time it turns off. The high voltage might zap the IC.

You show a 0.1nF capacitor value that is too low. It should be 1000 times more at 0.1uF (usually marked 104).

Lucky-Luka

Joined Mar 28, 2019
101
If you disconnect the LED with a switch then the inductor has nothing to limit the amount of "flyback" boosted voltage each time it turns off. The high voltage might zap the IC.
I see... So even where I've placed the switch in the last version should be ok.

You show a 0.1nF capacitor value that is too low. It should be 1000 times more at 0.1uF (usually marked 104).
Yes, it's a typo.

Tonyr1084

Joined Sep 24, 2015
5,990
This is the kind of LED that I'm using.
OK. I've been schooled.

As stated in the video there's a chip inside the LED controlling the color changing. I had in mind something more primitive, where YOU select the color(s) you want. My RGB LED's all have four leads so I can pick the color(s) I want when I want.

Thank you.

BobaMosfet

Joined Jul 1, 2009
1,776
Hi all
I have an RGB LED led that needs more or less 3 volts to perform correctly its light routine.
Can I use for my project a 3.3V zener diode?
Only using the rectifier diode and the cap as a buffer the voltage would be a rather constant 4.8V.
Cheers

Attachments

• 386 KB Views: 6

Audioguru again

Joined Oct 21, 2019
3,199
I removed the switches from all my solar garden lights because they are poor quality and the contacts soon corrode and do not work anymore.
If you use a switch to disconnect LX then the IC is still connected to the battery and the battery might be discharged.
I recommend using a switch to disconnect the battery instead.

ElectricSpidey

Joined Dec 2, 2017
1,661
This is how I read that data sheet...

The maximum supply voltage is 7 Volts.

All devices will work with a battery voltage down to 1.5 volts but some will work down to .9 volts.

It is up to the designer to match the solar cell with the battery used.

Disclaimer...reading data sheets is not my expertise.

Lucky-Luka

Joined Mar 28, 2019
101
You are right. Even reading all the posts of a thread is a good practice: you would have noticed that I've already done my homework and what I was asking is not in those datasheets...

Audioguru again

Joined Oct 21, 2019
3,199
This is how I read that data sheet...
The maximum supply voltage is 7 Volts.
All devices will work with a battery voltage down to 1.5 volts but some will work down to .9 volts.
No. It is designed to use a single 0.9V (when almost discharged) to 1.5V (when fully charged) battery cell and it boosts the voltage to a maximum of 7V (usually 2V to 3.5V) for an LED.

Audioguru again

Joined Oct 21, 2019
3,199
A solar garden light uses a weak 2.0V/40mA solar panel and one 300mAh to 700mAh Ni-MH rechargeable battery.
In sunlight, the solar panel current is about an average of 30mA for 11 hours which is 330mAh. The garden light IC has a 0.3V Schottky diode in series with the battery, so the solar panel limits the charging current and the diode limits the maximum charging voltage.

Lucky-Luka

Joined Mar 28, 2019
101
A solar garden light uses a weak 2.0V/40mA solar panel and one 300mAh to 700mAh Ni-MH rechargeable battery.
In sunlight, the solar panel current is about an average of 30mA for 11 hours which is 330mAh. The garden light IC has a 0.3V Schottky diode in series with the battery, so the solar panel limits the charging current and the diode limits the maximum charging voltage.
Well my project is something like this:
It is not intended to be under direct sun all days so I've chosen an oversized panel. I will use a NiMH AA battery.

Audioguru again

Joined Oct 21, 2019
3,199
Another You Tube video from a kid in India.
His LED is extremely bright because he can't read the English datasheet showing an LED current is from 75mA to 150mA with the low value 47uH for his inductor. The maximum allowed current in an LED that size (5mm in diameter) is 30mA.
I use a 47uH inductor when I have five LEDs (30mA each).