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General => General Technical Chat => Topic started by: Milacron on October 15, 2011, 03:12:50 pm

Title: Any way to convert negative 18 VDC to positive 3.3 VDC ?
Post by: Milacron on October 15, 2011, 03:12:50 pm

Wierd question I know.... involves an older (1996) Hitachi 5.7" color LCD (Hitachi LMG9520RPCC-A, on a CNC router control) that for some reason used negative voltage (pin 7, VEE power supply for LC) but it's closest Hitachi replacement LCD uses positive voltage for VEE. 

Have already tried taking the positive voltage from another source on the control but still no data showing on the new monitor, and can't help but wonder if it's due to the negative voltage output on the control "doing nothing" not connected and throwing the data output into an error mode.

Title: Re: Any way to convert negative 18 VDC to positive 3.3 VDC ?
Post by: tinhead on October 15, 2011, 03:35:23 pm

i doubt that there is any logic detecting the VEE consumption (but of course you can easily check this, just connect a
4.7k resistor between VEE and VSS) - the reason why you didn't see anything is probably timing.
Check the display datasheet and compare with the one you using

http://www.mikrocontroller.net/attachment/96841/LMG9520RPCC.pdf (http://www.mikrocontroller.net/attachment/96841/LMG9520RPCC.pdf)

Title: Re: Any way to convert negative 18 VDC to positive 3.3 VDC ?
Post by: Zero999 on October 15, 2011, 04:59:25 pm

A buck-boost converter can convert one voltage to the opposite polarity.

Title: Re: Any way to convert negative 18 VDC to positive 3.3 VDC ?
Post by: FenderBender on October 15, 2011, 09:21:28 pm

I'd say an MC34063 could do it using the inverting mode...

Title: Re: Any way to convert negative 18 VDC to positive 3.3 VDC ?
Post by: Milacron on October 16, 2011, 05:39:30 pm

Quote from: tinhead on October 15, 2011, 03:35:23 pm

i doubt that there is any logic detecting the VEE consumption (but of course you can easily check this, just connect a
4.7k resistor between VEE and VSS) - the reason why you didn't see anything is probably timing.
Check the display datasheet and compare with the one you using

http://www.mikrocontroller.net/attachment/96841/LMG9520RPCC.pdf (http://www.mikrocontroller.net/attachment/96841/LMG9520RPCC.pdf)

You could be right about the timing but I couldn't see any significant differences in the timing of the old monitor with the new.  But then I'm no expert in such matters.  The new one is Hitachi SW14Q001....would you be so kind as to compare the timing graphs to see if you can find any difference that might matter  in this regard ?
 
http://www.datasheetarchive.com/SX14Q001-datasheet.html (http://www.datasheetarchive.com/SX14Q001-datasheet.html)