Newhaven Display Forum

Newhaven Products => Character LCDs => Topic started by: perky on January 28, 2016, 03:48:12 PM

Title: NHD-0108CZ-FSW-GBW-33V3 contrast voltage
Post by: perky on January 28, 2016, 03:48:12 PM
Hi,
I'm trying to design a temperature compensation circuit for the 3.3V NHD-0108CZ-FSW-GBW-33V3 module to be used in a commercial product. This is a 'wide' temperature range module, so I presume I have to generate a negative VEE voltage and use your app note using an NTC resistor and PNP transistor in order to temperature compensate across the full range (-20 to +70 deg C).

What would be a good VEE voltage to use for this? Do you have any recommended compensation circuits for this 3.3V module? Your application notes all appear to be for 5V modules, and this module has a VO pin instead of VL, so I'm unsure exactly how to proceed.

Thanks,
Mark.
Title: Re: NHD-0108CZ-FSW-GBW-33V3 contrast voltage
Post by: perky on February 07, 2016, 04:49:37 PM
Anyone?
Title: Re: NHD-0108CZ-FSW-GBW-33V3 contrast voltage
Post by: Saurabh_B on February 11, 2016, 08:05:02 AM
Mark,

You should not need to use a negative voltage input.
You would tie one end of the Temp comp circuit to the +3.3V, and the other end to 0V.

The V0 will be the same pin as VL.
Title: Re: NHD-0108CZ-FSW-GBW-33V3 contrast voltage
Post by: perky on February 12, 2016, 04:01:29 PM
Thanks, but I'm a little confused as there is a base-emitter diode drop between VO and VEE of the PNP transistor (about 0.65V) in the temperature compensation circuits. Also VDD-VO is specified as 3.3V typical (no minimum or maximum given), presumably typical is at typical temperature and VDD voltage, so VO would be typically 0V and we need at least -0.65V for VEE just for that case. Lowering the temperature to -20degC is going to require a more negative voltage than 0V on VO so this requires even more negative voltage on VEE. Or have I misunderstood something?

Mark.