This will be a little post on how I modified an Acer monitor to work off a lower supply voltage.
I have an ACER G226HQL Monitor (22" LED, FHD) that I got for free - but no stand, power supply, etc. I'm looking to use this monitor in a "magic mirror" installation with a Raspberry Pi - the LCD will shine through the mirror and a program will display text and greetings on the mirror.
I don't have a suitable 19V supply, which the monitor is rated for. This would normally be provided by an external plug pack. The monitor will operate down to 15V on my bench PSU, and draws about 21 watts operating. But below 15V it just turns off and appears dead. The plan is to modify it to operate on 12V. I figure this should work fine - the display doesn't show any issues operating from 15V so I think it will cope with 12V just fine.
Additionally, I am planning to tap off the 5V supply to run a Raspberry Pi - older Model B+ which should draw around 1-2 watts.
So, I took it apart. Just clipped together and uses two screws. Easy. One PCB controls the monitor, and the T-con is bonded to the panel which is made by L&T Display China. I have never heard of this company before.
The first step is to try and understand what causes the monitor to stop working at 15V. The monitor doesn't show any sign of fault or defect - it turns off immediately when the voltage goes below a certain point. This indicates that there is likely some kind of under-voltage detection circuit.
I tested all the supplies on the monitor (+5V and +3V3) and found that they all stopped working when the supply voltage dropped below that critical 15V point. The +5V rail is supplied by a switching converter APW7080, a common part in Chinese electronics. The +3V3 is supplied via a linear regulator from the +5V rail so when the +5V rail goes, so will the +3V3.
Looking closer at the APW7080 I notice it has an enable pin (which turns the device on and off) and in the datasheet the enable pin threshold is specified as 2.3-2.7V. The device will turn on when the voltage rises above the threshold, and turn off when it falls. A small amount of hysteresis (10% or around 200mV) ensures the monitor does not turn on and off rapidly when the voltage is close to the threshold.
I tested this pin when the monitor was not working at 15V and it measures 2.44V - this is definitely in the UVLO window - and when operating at 19V it measures 3.09V, which is out of the UVLO window. So, this means, any time the voltage on the input falls between (2.7V*(19V/3.09V)) [16.6V] and (2.3V*(19V/3.09V)) [14.2V] it could shut off. It is guaranteed that it will be off at 14.2V but it may turn off as early as 16.6V. (The threshold isn't precise so the monitor could turn off anywhere within that range.) In my case it shuts down nearly precisely on 15V which is close to the nominal 2.5V threshold.
A simple mod will be to bridge the EN pin to VIN. The EN pin is rated to 20V, and since I am running the monitor on 12V this will be perfectly acceptable. Luckily, the pins are adjacent so it is even easier; a bridge with solder will work fine.
The result is... it works down to about 7V now. Below that the backlight starts flickering, but the monitor will still display something until about 5.5V though the image is very faint. No brightness difference operating from 12V.
I have an ACER G226HQL Monitor (22" LED, FHD) that I got for free - but no stand, power supply, etc. I'm looking to use this monitor in a "magic mirror" installation with a Raspberry Pi - the LCD will shine through the mirror and a program will display text and greetings on the mirror.
I don't have a suitable 19V supply, which the monitor is rated for. This would normally be provided by an external plug pack. The monitor will operate down to 15V on my bench PSU, and draws about 21 watts operating. But below 15V it just turns off and appears dead. The plan is to modify it to operate on 12V. I figure this should work fine - the display doesn't show any issues operating from 15V so I think it will cope with 12V just fine.
Additionally, I am planning to tap off the 5V supply to run a Raspberry Pi - older Model B+ which should draw around 1-2 watts.
So, I took it apart. Just clipped together and uses two screws. Easy. One PCB controls the monitor, and the T-con is bonded to the panel which is made by L&T Display China. I have never heard of this company before.
The first step is to try and understand what causes the monitor to stop working at 15V. The monitor doesn't show any sign of fault or defect - it turns off immediately when the voltage goes below a certain point. This indicates that there is likely some kind of under-voltage detection circuit.
I tested all the supplies on the monitor (+5V and +3V3) and found that they all stopped working when the supply voltage dropped below that critical 15V point. The +5V rail is supplied by a switching converter APW7080, a common part in Chinese electronics. The +3V3 is supplied via a linear regulator from the +5V rail so when the +5V rail goes, so will the +3V3.
Looking closer at the APW7080 I notice it has an enable pin (which turns the device on and off) and in the datasheet the enable pin threshold is specified as 2.3-2.7V. The device will turn on when the voltage rises above the threshold, and turn off when it falls. A small amount of hysteresis (10% or around 200mV) ensures the monitor does not turn on and off rapidly when the voltage is close to the threshold.
I tested this pin when the monitor was not working at 15V and it measures 2.44V - this is definitely in the UVLO window - and when operating at 19V it measures 3.09V, which is out of the UVLO window. So, this means, any time the voltage on the input falls between (2.7V*(19V/3.09V)) [16.6V] and (2.3V*(19V/3.09V)) [14.2V] it could shut off. It is guaranteed that it will be off at 14.2V but it may turn off as early as 16.6V. (The threshold isn't precise so the monitor could turn off anywhere within that range.) In my case it shuts down nearly precisely on 15V which is close to the nominal 2.5V threshold.
A simple mod will be to bridge the EN pin to VIN. The EN pin is rated to 20V, and since I am running the monitor on 12V this will be perfectly acceptable. Luckily, the pins are adjacent so it is even easier; a bridge with solder will work fine.
The result is... it works down to about 7V now. Below that the backlight starts flickering, but the monitor will still display something until about 5.5V though the image is very faint. No brightness difference operating from 12V.
Attached Files