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Step 5Create a Voltage Divider Circuit
Unfortunately, most manufacturers refuse to release any information regarding their inverters. Some fiddling and testing is usually necessary to determine the input voltages on the inverter before it can be wired up for use. If you are using a complete LCD monitor, simply reassemble it, plug it in and turn it on and skip the rest of this instructable.
From my experimenting I've discovered that many inverters expect 12V+ input to drive the inverter and and around 5V+ to "enable" and set the "dimming" level. Check this generic spec sheet for some guidance: http://www.lcdinverter.co.uk/MH-1405A04-spec.htm. From my testing, the circuits are quite robust and can accept between 4.5 and 7 volts on the enable and dim pins and work properly. Above 7 volts a suspicious whining tends to be emitted.
A 12V DC power source can be easily adapted to power the inverter by using a voltage divider circuit. In a voltage divider circuit, use two resistors to drop the voltage as needed. In this circuit R1 drops the voltage 7V then R2 an additional 5V. Notice that 7V+5V=12V. The schematic below shows the circuit I used to create the voltages I needed to drive my inverter.
In this circuit, C is Ground, A is 12V+, B is 5V+. For an inverter that has enable and and dim pins, connect those to 5V+ to turn the screen on.
Prototype your circuit using a breadboard. Measure the voltage between C and A; it should be 12V+. Measure the Voltage between C and B and it should be 5V+. If you get values within 10-20%, you should be OK.
If you need assistance in choosing resistors for your particular voltage source, check out the Circuit Design Tutor.
Some tips to keep in mind:
A: 12V+
B: 5V+
C: 12V-
R1: 70K Ohm Resistor
R2: 50K Ohm Resistor
K1: SPST switch
From my experimenting I've discovered that many inverters expect 12V+ input to drive the inverter and and around 5V+ to "enable" and set the "dimming" level. Check this generic spec sheet for some guidance: http://www.lcdinverter.co.uk/MH-1405A04-spec.htm. From my testing, the circuits are quite robust and can accept between 4.5 and 7 volts on the enable and dim pins and work properly. Above 7 volts a suspicious whining tends to be emitted.
A 12V DC power source can be easily adapted to power the inverter by using a voltage divider circuit. In a voltage divider circuit, use two resistors to drop the voltage as needed. In this circuit R1 drops the voltage 7V then R2 an additional 5V. Notice that 7V+5V=12V. The schematic below shows the circuit I used to create the voltages I needed to drive my inverter.
In this circuit, C is Ground, A is 12V+, B is 5V+. For an inverter that has enable and and dim pins, connect those to 5V+ to turn the screen on.
Prototype your circuit using a breadboard. Measure the voltage between C and A; it should be 12V+. Measure the Voltage between C and B and it should be 5V+. If you get values within 10-20%, you should be OK.
If you need assistance in choosing resistors for your particular voltage source, check out the Circuit Design Tutor.
Some tips to keep in mind:
- If the sum of the ratio of the resistors equals the input voltage, your design will be much simpler. For example Vin=12V, ratio of resistors is 50:70 or 5:7 - 5+7=12.
- Remember you can simply add resistors together in series to create a single resistor (read up on Ohms Law for help here.
- If your input voltage is 18V, R1 should be 130K Ohm, R2 should be 50K Ohm.
A: 12V+
B: 5V+
C: 12V-
R1: 70K Ohm Resistor
R2: 50K Ohm Resistor
K1: SPST switch
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