LCD monitor inverter alternatives

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The old CCFL inverter board is too FUBAR to repair. So I decided to use
a couple of cheap 12V dual ccfl inverters (like the kind used for
pc-mods, ect) to power the four backlights.

The power supply board inside the monitor provided the 12v for them to
work and everything works great except...THEY NEVER SWITCH OFF!!!! They
stay on even if the monitor is in standy mode! The only time they shut
off; is if I unplug the monitor from the power source, of coarse.

The connection to the original inverter:
1. VCC (constant 12V)
2. GND
3. ON/OFF (5V) < switches to 0V when on standby mode or off
4. DIMMING (2-5V)

The inverters are connected to 1 and 2.

Could someone please give me an idea what to do here. TIA

 

[[email protected]]

The old CCFL inverter board is too FUBAR to repair. So I decided to use
a couple of cheap 12V dual ccfl inverters (like the kind used for
pc-mods, ect) to power the four backlights.

The power supply board inside the monitor provided the 12v for them to
work and everything works great except...THEY NEVER SWITCH OFF!!!! They
stay on even if the monitor is in standy mode! The only time they shut
off; is if I unplug the monitor from the power source, of coarse.

The connection to the original inverter:
1. VCC (constant 12V)
2. GND
3. ON/OFF (5V) < switches to 0V when on standby mode or off
4. DIMMING (2-5V)

The inverters are connected to 1 and 2.

Could someone please give me an idea what to do here. TIA

So you need a transistor to switch them off when wanted.
View in nonproportional font.

| invertor 0v line
|
| o
| |
| 3 R1 | C
| o--[__]--+__/
| | \ npn tr
| R2 > | E
| > |
| | |
| ---------+---+----o 2


The npn tr must be rated for the current the invertor takes.
Collector goes to the invertors 0v line.
'2' goes to psu connector terminal 2
'3 goes to psu connector terminal 3

R1 and 2 depend on power and beta. Lets say CCFL is 12w max, ie 1A, and
beta min is 30, so we need 1A/30 = 33mA base i to power the tr.
5-0.6 = 4.4v, 33mA -> 133 ohms so use 100 ohms for R1.
R2 can be 1mA 0.6v -> anything from 560 ohms to 1k.

Adding dimming is a bit more work, but quite doable.


NT

 

[Mike]

well on the old inverter like you listed, there is a signal wire. the
processor in the LCD controller switches the inverter on and off via that
signal wire.


So like he suggested, take an NPN transistor tie the collector of the NPN
transistor to the ground of all the inverters. and tie the emitter to
ground. so when the transistor is turned off, the inverter circuit path is
broken, so they are off.

then take a 1k resistor from the base of the transistor to the signal pin
for the old inverter connection, make sure the transistor can handle the
current of the inverters.

Then, plug it in, the inverters should be off. turn on the monitor and feed
it a signal, the monitor will then send out 5V on the signal pin, which is
more than enough to saturate the transistor, turning on the inverters, as
the transistor is sinking the current to ground.

The old CCFL inverter board is too FUBAR to repair. So I decided to use
a couple of cheap 12V dual ccfl inverters (like the kind used for
pc-mods, ect) to power the four backlights.

The power supply board inside the monitor provided the 12v for them to
work and everything works great except...THEY NEVER SWITCH OFF!!!! They
stay on even if the monitor is in standy mode! The only time they shut
off; is if I unplug the monitor from the power source, of coarse.

The connection to the original inverter:
1. VCC (constant 12V)
2. GND
3. ON/OFF (5V) < switches to 0V when on standby mode or off
4. DIMMING (2-5V)

The inverters are connected to 1 and 2.

Could someone please give me an idea what to do here. TIA

So you need a transistor to switch them off when wanted.
View in nonproportional font.

| invertor 0v line
|
| o
| |
| 3 R1 | C
| o--[__]--+__/
| | \ npn tr
| R2 > | E
| > |
| | |
| ---------+---+----o 2


The npn tr must be rated for the current the invertor takes.
Collector goes to the invertors 0v line.
'2' goes to psu connector terminal 2
'3 goes to psu connector terminal 3

R1 and 2 depend on power and beta. Lets say CCFL is 12w max, ie 1A, and
beta min is 30, so we need 1A/30 = 33mA base i to power the tr.
5-0.6 = 4.4v, 33mA -> 133 ohms so use 100 ohms for R1.
R2 can be 1mA 0.6v -> anything from 560 ohms to 1k.

Adding dimming is a bit more work, but quite doable.


NT

 

[JW]

The old CCFL inverter board is too FUBAR to repair. So I decided to use
a couple of cheap 12V dual ccfl inverters (like the kind used for
pc-mods, ect) to power the four backlights.

The power supply board inside the monitor provided the 12v for them to
work and everything works great except...THEY NEVER SWITCH OFF!!!! They
stay on even if the monitor is in standy mode! The only time they shut
off; is if I unplug the monitor from the power source, of coarse.

The connection to the original inverter:
1. VCC (constant 12V)
2. GND
3. ON/OFF (5V) < switches to 0V when on standby mode or off
4. DIMMING (2-5V)

The inverters are connected to 1 and 2.

Could someone please give me an idea what to do here. TIA

Two things:

1. Can you see what chip is on these inverters?
2. What chip is on the original inverter?

You might be able to tap directly into the new inverters from your old
controller, if the chips have an enable pin.

 

[Mike]

if he is using PC CCFL invertsers like i says hes using, most likely its a
simple 2 transistor inverter.

 

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The old faulty inverter uses the BIT3105 CCFL controller chip FYI, I
tried to replace the four shorted mosfets (FDS8958A) but they still
keep frying...maybe a shorted primary winding on one (or more) HV
transformers?

The cheap "PC-mod" inverters seem to work great so far with the
transistor switch.

Thanks for the help everyone!