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Please help with dimming control

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hooko

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Hello, can i ask anybody for a help with my 2 din car china dvd. It has an LCD display with the led backlight. The problem is that it didn't have a dimming option when it's turn on the illumination of the car, the display it's very bright when driving in the evening. Backlight is operate from the led driver MP3202 and datasheet shown that it can do the dimming. Please tell me what i must to soldering to have the dimming when turn on the illumination. Thank you! and sorry for my English.
 

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In the existing circuit, what resistor value is between Pin 3 (FB) and Gnd? Whatever that resistor value is, try doubling, tripling, or quadrupling it...
 
You could reduce the LED current by either (a) increasing the value of the resistor between pin 3 and ground, or (b) providing an added current path in parallel with the LEDs.
How much current does the LED backlight draw?
 
So try 2.2Ω, 3.3Ω, or 4.7Ω
 
Ш
You could reduce the LED current by either (a) increasing the value of the resistor between pin 3 and ground, or (b) providing an added current path in parallel with the LEDs.
How much current does the LED backlight draw?
I don't know, but it's a strip with leds (12-15 pcs) It's a 8 inch display
 
Thank you, i'll try it! But what is in the figure 6? Vdc - for what?
Vdc is an adjustable dimming voltage that comes from an external source.

If all you want to do is make the screen more dim while driving at night, then just increasing the single resistor from pin 3 to gnd will work.

If you would like to add an external dimming pot, then wire it like fig 6, so that Vdc goes from zero to 2V.
 
Using the component designations in Fig 6 of the datasheet, it seems you have R1 = 1 Ω. Do you also have resistors corresponding to R2 and R3? If not, then it seems the backlight current must total 104mV/1Ω = 104mA. To reduce that to, say, 20mA you would have to find an alternative source (R2, R3 and a voltage source) to drive 104mA-20mA = 84mA through R1 unless you can increase R1.
 
Using the component designations in Fig 6 of the datasheet, it seems you have R1 = 1 Ω. Do you also have resistors corresponding to R2 and R3? If not, then it seems the backlight current must total 104mV/1Ω = 104mA. To reduce that to, say, 20mA you would have to find an alternative source (R2, R3 and a voltage source) to drive 104mA-20mA = 84mA through R1 unless you can increase R1.

My circuit it's exactly like in fig.2, there is only R1 and R2 with the value in 1 Ω each. About the alternative source - how many volts it must to have? 5v?
 
My circuit it's exactly like in fig.2, there is only R1 and R2 with the value in 1 Ω each.
Ahh. So, we now know the LED current is ~180mA.
Simply removing R1 or R2 would halve the current (but that may still be too much).Can you remove both and replace with a single 2.2 Ohm or 3.3 Ohm or therabouts experimentally (as Mike suggested) to find the best night-time setting?
What is the input voltage to the 3202?
 
Yesterday i try to make everything what you tell me to do, i replace the R1 from 2Ω to 150Ω, but no change in backlight... :( I think the only solutions will be like in fig.6 , but how to get 0-2 volts from external power?
 
Ahh. So, we now know the LED current is ~180mA.
Simply removing R1 or R2 would halve the current (but that may still be too much).Can you remove both and replace with a single 2.2 Ohm or 3.3 Ohm or therabouts experimentally (as Mike suggested) to find the best night-time setting?
What is the input voltage to the 3202?

The input voltage for 3202 is 5V
 
Yesterday i try to make everything what you tell me to do, i replace the R1 from 2Ω to 150Ω, but no change in backlight...

Likely a step too far. If this approach is likely to work, R1 should have been changed to a value like 5Ω.


You will have to trace out the schematic diagram of how the driver chip is wired. Post it when you do...
 
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but how to get 0-2 volts from external power?
It doesn't have to be 0-2V. We now know you have 5V as the 3202 input, so you could use that plus a variable resistive divider to give control as in the Fig 6 arrangement.
 
This should do it (as per Fig 6). Your two existing 1Ω resistors would make up the 0.5Ω R1.
BacklightDimmer.PNG
 
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