Car LED Headlights dimmer?

[budm]

Re: Car LED Headlights dimmer?

If it is boost/buck type circuit inside to maintain constant current then I do not expect it to dim down when placing resistor (or MOSFET) in series to cause it to dim down, and if you lower the input Voltage to the regulated circuit then input current will go higher to maintain the same output power.
His second picture shows dimmer lights and lower current draw.

[redwire]

Re: Car LED Headlights dimmer?

A picture of the pcb inside the LED lamp would help.
BigClive did a teardown of one with a fan on the end and datasheets of QX9920 IC and sch.
https://www.youtube.com/watch?v=CX_uFs5vKc0

[capwizard]

Re: Car LED Headlights dimmer?

I think we're assuming the LED headlamp is like a light bulb, a linear load.
But inside is most likely a boost/buck converter.

So supplying the LED lamp with 10V or 15V should give the same (constant) power to the LED's and not really dim it.

The led light dimmer worked very good wild range adjustment, the very good linear adjustment from very dark to maximum brightness.

When I pulled the led light out, no heat dissipation, led overheat right away, not enough time for meter to read. Pic1, 2, 3

[redwire]

Re: Car LED Headlights dimmer?

You can lower the buck-converter output current by removing one or two of the three sense resistors R2, R3, R4 that are 0.25R each.
If the 6-pin IC is QX9920, roughly... all three = 3A, two = 2A, one =1A current to the LED's. The fan is 9V so it might be a 9V LED array.
I'm guessing:
9V 3A to the LED's is 12V 2.25A input
9V 2A to the LED's is 12V 1.5A input
9V 1A to the LED's is 12V 0.75A input

[capwizard]

Re: Car LED Headlights dimmer?

Your inference is very correct.

BigClive, He explained very well. I can add a little bit more here.

COB LEDs are 3 in each row and 10 in each line. Total 30 in my case. If leds are 3.3v then driver voltage will be 9.9v.

This is like putting all the LEDs of a 50-inch TV on two sides of one stick. That's why the stick is so hot. I have been using it for half a year, so far so good maybe is because of the fan.

One thing I don't understand is why they don't use 12 volts directly.

[stj]

Re: Car LED Headlights dimmer?

because a car is not 12v, it's as low as 11 when stopped with a low battery and as high as 14.8 when charging (or worse if the alternator is shit)

[capwizard]

Re: Car LED Headlights dimmer?

The Voltage reading of 12.17V @.177A, is it the Voltage reading on the LED terminal or on the input feeding Voltage to the circuit. What is the Voltage between S and D pin of the MOSFET? Once you know that then you can calculate the Power dissipation of the MOSFET.

The Voltage reading of 12.17V @.177A is it the input feeding Voltage to the circuit.

What is the Voltage between S and D pin of the MOSFET?

Sorry took a long time to answer this question because of pic1. As sti predicted, the breadboard is melted.
So I added a heat sink. Circuits are too simple to be true. Let's test for 3 days.

Next, I gonna put two led headlights to one MOSFET see what's going on?

[budm]

Re: Car LED Headlights dimmer?

I cannot tell from the pictures as to what Voltage you have between the S & D pin of the MOSFET.

[capwizard]

Re: Car LED Headlights dimmer?

I soldered Fluke test leads on S and D pins of mosfet already.

Full lightness is 11.9v at 2.478A.
12.4v at 0.178A
12.18v at 0.102A

[budm]

Re: Car LED Headlights dimmer?

https://www.badcaps.net/forum/attach...1&d=1549771216
That cannot be right since the MOSFET is in series with the load, so if you have 11.9 V at full brightness between S and D then the load will barely has any Voltage on it.
And at 11.9V @ 2.478A that will be lots of Wattage.

[capwizard]

Re: Car LED Headlights dimmer?

I connected two led lights together, reading is from a 12v power input at full brightness. Pic 1

[capwizard]

Re: Car LED Headlights dimmer?

I connected two led lights together, reading is from a 12v power input at full brightness. Pic 1

12.24v @ 4.825A for two lights. Mosfet is 50A that means OK.

[budm]

Re: Car LED Headlights dimmer?

But as you know in series circuit, if you have 12V between S and D pin then how can you have any Voltage left for the LED?
BTW, it is not just the current rating, you have to consider the power dissipation also to keep the junction temperature at the safe level so proper heatsink is required.
Right now you are operating the MOSFET in linear region.
https://cdn.badcaps-static.com/pdfs/...f668f60e6d.pdf
https://www.powerelectronics.com/dis...mode-operation

[capwizard]

Re: Car LED Headlights dimmer?

My bad, I am so Inteligente, series the meter leads to S and D, it should be parallel.

I used a more simple circuit and in the future only use one resistor.

[capwizard]

Re: Car LED Headlights dimmer?

My bad, I am so Inteligente, series the meter leads to S and D, it should be parallel.

I used a more simple circuit and in the future only use one resistor. Because potentiometer is not easy to find in Africa.

My idea is car has dim lights during the day. At night auto turn on and switch with full or half full light.

Pic 4 is at full brightness.
I double posted again...cellphone.

I have a dream......can we use this idea applies to the tv led backlight, forced to the people who refuse to reduce their brightness.

[budm]

Re: Car LED Headlights dimmer?

Well, when Data does not make any sense then you know something is not done right. Data is important to me.

[capwizard]

Re: Car LED Headlights dimmer?

MOSFETs Withstand Stress of Linear-Mode Operation....in this article I can't find fig. 1 ,2, 3, 4, 5 ?

an extended forward-bias safe operating area (FBSOA).

MOSFET is subjected to high thermal stress due to the simultaneous occurrence of high drain voltage and current resulting in high power dissipation. When the thermo-electrical stress exceeds some critical limit, thermal hot spots occur in the silicon causing the device to fail.

[stj]

Re: Car LED Headlights dimmer?

yes, so use PWM like it already does.

[capwizard]

Re: Car LED Headlights dimmer?

Or, a big heat sink? PWM IC is not easy to find in Africa.

I used half brightness, mosfet is not hot at all.
When I used full brightness, mosfet is getting hot, still touchable, the way to solve this problem is full brightness just bypass it.

No needs mosfet just use a coil from a hairdryer make 2.5A x 12v=30w current limit resistor.

[stj]

Re: Car LED Headlights dimmer?

you think africa cant get arduino nano's??