The technique I described is particularly suitable for building test fixtures, one off hobby or tool projects, prototypes and so forth. I would have to carefully evaluate a number of factors before deploying the concept for a production type product. Those considerations would include:

1) Cost effectiveness of providing the extra regulator and added input head voltage from the power source to support it. Often this turns out to be a no brainer because the product already needs 5V for other things in addition to the 3.3V. Many products already have 12V for analog, relays and/or displays or are powered from something like a USB power source at 5V. If it is only the LCD that requires 5V the current requirements can be very low so the regulator can be a very small one.

2) Consider the ability of the microcontroller on the product to handle 5V tolerance on its inputs. LCDs powered from 5V will be driving the readback signals to 5V levels if reading is used. Often a write-only LCD approach can be used and no concern for 5V tolerance would be needed.

3) Evaluate the V_IH, V_IL, V_OH and V_OL requirements for the display and the microcontroller to see if they are compatible when the LCD is at 5V supply operation. The controller ICs on some LCDs provide TTL compatible signalling levels and so are inherently compatible with 3.3V drive from the MCU. And if they are not TTL and require CMOS type levels then is can be a good solution to add pullups to the LCD interface lines so that they rise up to near 5V. 8051/52 style MCUs with the quasi bi-directional type I/O pins and 5V tolerant inputs are an elegant solution for use with pullup resistors in a way that cannot be achieved with some other MCU types that offer only CMOS push-pull outputs.

Michael Karas