BestOfGeeks: One boost converter generates bias voltages for LCD panels  

One boost converter generates bias voltages for LCD panels

Youssef Elarabi
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2015-06-23 16:41:45

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One boost converter generates bias voltages for LCD panels

Numerous prejudice voltages are essential pertaining to delivering and managing a good LCD section. Generally, dedicated built-in circuits along with many charge-pumps are employed to create the several voltages. Because the insight these units is mostly available to voltages close to 5V, any pre-regulator is required, if it's to get employed in a good car program while using characteristically wide voltage variety.

For output voltages exceeding the actual ±5V variety, further circuitry is necessary, which usually ends up with any quite cumbersome and high-priced prejudice supply answer. Nevertheless, it is possible to generate economical LCD prejudice supply answer using only 1 built-in enhance converter to create most needed prejudice voltages.

This insight voltage just for this car program stages coming from 3V around 13. 2V. Desk 1 displays a standard prejudice supply spec for just a 12in show. This 6. 6V and +6. 6V track have got tolerances of ±1. 5%, so this means beneficial regulation is necessary. Both the various other voltages have got much bigger patience rings, along with no less than 20% deviation in the nominal voltage. In the meantime, the latest calls for are quite diverse along with close to 50mA for your snug patience components and lower than 1mA for your door travel voltages.


Initially, the latest and energy calls for come up with a charge-pump centered answer feasible, that's commonly in addition beautiful from the charge place. On nearer research, that will become distinct that built-in charge-pump units are limited by voltages close to ±5V for the insight likewise for the output and thus not necessarily applicable just for this design.

A fix according to standard swap setting topologies could also be thought to be, although this specific doesn't just end up being way too cumbersome, although also are too costly.

This damaging voltages could also be created through a good inverting buck-boost – the actual 14V with a enhance, as the 6. 6V track needs a topology that may function within buck and enhance setting for the reason that insight may be better and below the actual output. This would involve several converters and several inductors in whole.

An appropriate ways of generating the actual 6. 6V expected with this program is a Sepic converter, that may function within buck likewise within enhance setting. This Sepic converter uses a flyback topology, that the output rotating is usually clamped for the primary with a capacitor. This kind of reduces the actual overshoot and higher surges on the transferring node for which any flyback design is usually notorious.

Such as a flyback converter, the actual Sepic also can have got many output windings, if coupled inductors, in lieu of personal inductorsm are employed. This several voltages are both quite comparable even though damaging or perhaps a a number of of yet another voltage inside the program. Thus any coupled inductor along with many windings need to enable any designwhich requirements simply this inductor along with a one built-in enhance converter.


Wuerth's WE-FLEX flyback transformers provide 6-8 the same windings one core. By adding all of them within parallel or perhaps string and stacking all of them consequently, most voltages may be created through such a one permanent magnetic. Physique 1 displays the actual constructed and examined routine, which usually uses a transformer using a basic inductance of 21. 6µH along with a TPS61175 enhance converter operating with a transferring consistency of 350kHz.

This insight for the energy period, in addition to the output 6. 6V track, is designed such as a normal Sepic converter. Two windings within parallel for the insight give you the expected inductance along with the inductor for the output is usually connected in between soil along with the coupling capacitor for the transferring node. This output with this track is usually linked to the actual responses on the controller, which usually ends up with a good precision which usually complies with the actual spec of ±1. 5%. All windings are piled on this specific rotating, as can often be noticed about flyback converters with no strong connection to the actual coupling capacitor.

Than the 6. 6V output, absolutely no energy is usually shifted in the insight for the output via the actual coupling capacitor, although most energy has to be shifted through permanent magnetic coupling between your further windings. Once and for all mix regulation between your components, beneficial coupling is usually obligatory.

By dismantling the actual WE-FLEX transformer, it had been identified the actual part attributes about three inside windings and about three surface windings for the bobbin. Just for this power supply, it truly is connected to the extent how the 6. 6V and -6. 6V windings are on the inside, along with 1 primary inductor privately along with the subsequent 1 on top to achieve beneficial coupling and thus beneficial output voltage precision for your damaging track (see fig 2).

Both the leftover exterior windings are employed for your 14V and -12V components, which usually let higher tolerances. By selection of the actual rectifier diodes, the actual output voltage is fine tuned to satisfy the actual given prices.

However the output energy is pretty small with close to 750mW, higher proficiency is usually achieved over the entire insight voltage variety. Which has a 3V insight, the actual proficiency is usually 87%, with 6. 3V, it truly is 89% and on the optimum insight voltage of 13. 2V, proficiency is usually 85%.

Mix regulation
Greater important description may be the mix regulation in between all four components while using optimum fill.

Just about all output voltages are very well licensed and into their tolerances. As a result of top discovery on the flyback rectifier, this specific multiple output Sepic converter will not likely function effectively if a good output isn't filled in any way, particularly if yet another output is usually thoroughly filled. This is simply not critical with this program, must be selected fill is always linked to all four components. Throughout apps wherever this may not be the way it is, any resistor which usually simply forces somewhat recent needs to be connected about every single output to prevent the actual output voltage climbing too much, which could deterioration the actual parts or perhaps subsequent circuits. Once and for all mix regulation, the actual track while using best fill would be wise to end up being handled straight from the responses on the converter.

This transferring node on the Sepic converter along with piled flyback windings displays any clean waveform with no substantial surges due to the clamping capacitor (C2 for the schematic). This kind of reduces the complete EMI to a great extent and has in addition a positive effect on the actual proficiency as absolutely no further snubber network is required.

Some sort of Sepic converter may be simply expanded in order to a number of components through stacking further windings for the output inductance. This approach combines many benefits of any flyback such as multi-output capability and buck-boost procedure with no drawback of substantial surges for the transferring node a result of the actual loss inductance on the coupled inductor. A typical transformer coming from inventory along with 6-8 the same windings is usually connected to the extent in order to created several diverse output voltages, constructive along with damaging, along with merely one built-in enhance converter. This kind of ends up with a little and economical answer for just a LCD prejudice supply along with wide insight voltage variety.

Industrial automation set to drive efficiency and savings
Industrial automation set to drive efficiency and savings
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