Create a Voltage Bias Solution For Automotive LCD Panels


  • The design uses a Sepic converter to develop an efficient buck converting solution with different bias voltages.
  • This design is based on the working of WE-FLEX transformer circuit.

Several bias voltages are needed for operating an LCD panel. In most cases, specialised integrated circuits are used to generate different voltages. The input of these devices is mostly around five-volt. A pre-regulator circuit is needed to rectify the input voltages of the panel.

Additional circuitry is necessary for devices working above the five-volt operating range. This results in the development of a bulky and expensive bias supply solution. However, it is possible to create a low-cost LCD bias supply solution which only uses an integrated boost converter. This solution can generate all the different bias voltages required in an LCD panel.

Texas Instruments released a reference design for Automotive LCD panels. The PMP10051  based on using a Sepic converter for supply design. This converter can help in the generation of voltage lines ranging from 3.3 Volts of up to 12 Volts.

This design can eliminate the challenges of a flyback design


The Sepic converter can work in a buck as well as boost configuration. It uses a flyback topology. In this technology, the output winding of the transformer is clamped to the primary winding using a capacitor. This helps in reducing the overshoot and high spikes at the switching node. Thus, this design can eliminate the challenge of a flyback design.

Like a flyback converter, the Sepic can also have several output windings. Coupled inductors are used in the design in place of individual inductors. The four output voltages of the converter are similar. Hence, a circuit can be designed using a boost converter and a coupled inductor with several windings. This circuit can reduce the overall cost of the system developed for LCD panels.

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The design is based on working of a WE-FLEX transformer

LCD panel supply design
LCD panel supply design

This Sepic converter circuit is based on the working of WE-FLEX transformer. This transformer offers six equal windings on a single core. All the required voltages can be generated by stacking the different windings together.

It was discovered that the WE-FLEX transformer contains three inner windings and three outer windings. For making the power supply, it is connected in such a way that the 6.6 Volts and -6.6 Volt windings are inside the transformer. The inductors are placed on the side and on the top of the coils. This helps the transformer to achieve higher output voltage accuracy for the negative rail. This hence increases the overall efficiency of the circuit.

Offers efficiency of up to 85 per cent

The test result shows that the efficiency of the circuit can go up to 85 per cent in all working voltages. The switching node of the Sepic converter showed a smooth waveform without large spikes. This is due to the use of the clamping capacitor. This capacitor reduces the overall EMI heavily. It also reduces the need for an additional snubber network.

This results in a small and cost-effective solution for an LCD bias supply with a wide input voltage range.

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