LED light MOD, opinions.

Thread Starter

Yami

Joined Jan 18, 2016
352
Hi guys,
Wanted your opinion about a simple circuit I'm thinking of MODing. Basically its one of those LED lights on a bicycle. When you turn it on and off and on again it changes the brightness. Its controlled by a unidentifiable IC RL001.
Anyway I want to change the button to a latching type button and when its on the LEDs are at full brightness. Take out the control IC altogether.
I've attached the original circuit and the two options I was thinking of

Option A:
When I place the switch at the position and when its in the off position the LEDs are completely off (obviously). But whats interesting to me is that if I touch the open end near the 1M resistor the LEDS come on. If I touch it with the DMM probe it lights as well. I'm wondering why that is? Its not a huge issue but my reservation is that if the light is assembled and if there is any sort of static it would turn the LEDs slightly on which would drain the battery.

Option B:
This is the simplest design I can think of. But wanted to ask if there would be any issues by placing the switch there. Do I need capacitors across the switch?

Also I'm thinking of changing the 5.6K resistor to a 10K resistor by doing so low current is drawn from the supply and I'm pretty happy with the illumination level.

Lastly I wanted to ask with this circuit how does the transistor used. Is it used for the purpose of a constant current source? Or is the only reason because the light was designed to illuminate at different brightness.
While experimenting I noticed that I can take down the input voltage(supposed to be 6V) all the way down to 3ish volts without seeing any difference in the illumination level.

Thanks in advance.
P.S: The transistor is 8550
 

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LowQCab

Joined Nov 6, 2012
1,605
Where are You getting 6-Volts from ?
Can You rewire the LEDs so that they are in Series ?
What is the Current Rating of the LEDs ?,
( if You don't know, You can safely assume that it's probably around ~20ma )

A better plan would be to completely replace the
internal Circuitry with a CL520 Current-Limiter, super easy, and only 1-cheap-part.
.
.
.
 

Thread Starter

Yami

Joined Jan 18, 2016
352
Where are You getting 6-Volts from ?
Can You rewire the LEDs so that they are in Series ?
What is the Current Rating of the LEDs ?,
( if You don't know, You can safely assume that it's probably around ~20ma )

A better plan would be to completely replace the
internal Circuitry with a CL520 Current-Limiter, super easy, and only 1-cheap-part.
.
.
.
The 6 Volts is from 4 x 1.5V batteries which are connected in series.Right now I'm using my bench power supply. Thanks for your suggestion about the CL520, I'll try to look for that.
I was hoping you could help me understand the purpose of the transistor in this circuit originally. Is it just because of the different illumination level only?
 

Dave Lowther

Joined Sep 8, 2016
123
I was hoping you could help me understand the purpose of the transistor in this circuit originally.
It looks like it's being used because the IC RL001 could not supply enough current to light the LEDs.
I guess that IC can select different illumination levels by switching the LEDs on and off so quickly that they don't appear to flash. The amount of time the LEDs are on vs off would alter the illumination level
 

Juhahoo

Joined Jun 3, 2019
257
Avoid using LEDS in parallel without resistors in series. You can adjust the brightness by altering resistors for PNP but it is very bad way. It's okay for switching light on/off. For brightness, use simple current loop like:
1628856026504.png
This will be a solution for very dim lights, high powered ones needs more sophisticated less power wasting methods. Q1 and R sense will dissipate the excessive power to heat.
 
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