6502.org Forum  Projects  Code  Documents  Tools  Forum
It is currently Tue Jul 02, 2024 11:57 pm

All times are UTC




Post new topic Reply to topic  [ 7 posts ] 
Author Message
PostPosted: Thu Dec 13, 2012 5:57 pm 
Offline

Joined: Sat Dec 08, 2012 8:29 pm
Posts: 62
hi
i've got two STN LCDs, the first is requiring Vee=-20V while the second wants Vee=-40V.
Negative voltage is needed for contrast.

So, i need a negative voltage generator of -20V, -40V, on a current of 5..6mA.

Any idea for the proper circuit ?


Last edited by legacy on Thu Dec 13, 2012 8:03 pm, edited 1 time in total.

Top
 Profile  
Reply with quote  
PostPosted: Thu Dec 13, 2012 7:04 pm 
Offline
User avatar

Joined: Fri Aug 30, 2002 1:09 am
Posts: 8462
Location: Southern California
What voltages do you have to start with, and how good does the regulation need to be? (I imagine that for that, the regulation does not need to be good at all.) What I've done sometimes is to make an oscillator with decent output drive, even if that means a relaxation oscillator using a 5V schmitt-trigger inverter followed by the other five inverter sections in the hex inverter IC in parallel to provide more drive (74AC is strong, and 74ABT is even stronger), then follow those with a voltage multiplier with capacitors and Schottky diodes. It is compact and the efficiency is not bad. You probably won't even need to regulate it for your application.

Unfortunately switched-capacitor voltage-multiplier ICs won't work for the high voltage you need, and switching regulators are hardly in the hobbyist's reach because good board layout is so extremely critical to good operation, and you can't do it on prototyping board of any kind.

I do plan to put some power supply designs in my circuit potpourri page of the 6502 primer, including this kind of thing. I also have a small module here that I made to start with anywhere from 7 to 17 volts (allowing a wide range of battery, wall-wart, and vehicle power) and put out +5V and ±12V that I wanted to supply to hobbyists but unfortunately it will be too labor-intensive for me to assemble it to sell without losing my shirt, and I know there won't be the sales volume to justify the expense of setting up for automated assembly.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?


Top
 Profile  
Reply with quote  
PostPosted: Thu Dec 13, 2012 7:49 pm 
Offline
User avatar

Joined: Fri Aug 30, 2002 9:02 pm
Posts: 1696
Location: Sacramento, CA
I found this at digikey.com

http://www.digikey.com/product-detail/e ... ND/1927144

5v in, -24,-48,-72vdc outputs - cost is $14.45

Daryl

_________________
Please visit my website -> https://sbc.rictor.org/


Top
 Profile  
Reply with quote  
PostPosted: Thu Dec 13, 2012 8:07 pm 
Offline

Joined: Sat Dec 08, 2012 8:29 pm
Posts: 62
@GARTHWILSON
the LCD power is 3.3V, the board power is 5V, so Vin may be 5V =D

@8bit
NMT0572SC module ? Wow, it is perfect for my goal, thank you a lot =D


Top
 Profile  
Reply with quote  
PostPosted: Thu Dec 13, 2012 8:46 pm 
Offline
User avatar

Joined: Thu May 28, 2009 9:46 pm
Posts: 8238
Location: Midwestern USA
8BIT wrote:
I found this at digikey.com

http://www.digikey.com/product-detail/e ... ND/1927144

5v in, -24,-48,-72vdc outputs - cost is $14.45

Daryl

Good find, Daryl. I think that device would work in this application. The regulation is pretty good as well.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!


Top
 Profile  
Reply with quote  
PostPosted: Thu Dec 13, 2012 8:59 pm 
Offline
User avatar

Joined: Fri Aug 30, 2002 9:02 pm
Posts: 1696
Location: Sacramento, CA
BigDumbDinosaur wrote:
8BIT wrote:
I found this at digikey.com

http://www.digikey.com/product-detail/e ... ND/1927144

5v in, -24,-48,-72vdc outputs - cost is $14.45

Daryl

Good find, Daryl. I think that device would work in this application. The regulation is pretty good as well.


Just be sure to follow the datasheet. There is a MINIMUM current draw requirement that you need to be aware of. If using just the -24v output, minimum is 4.2mA If using just the -48v output, minimum is 2.1mA

Cheers!

Daryl

_________________
Please visit my website -> https://sbc.rictor.org/


Top
 Profile  
Reply with quote  
PostPosted: Thu Dec 13, 2012 9:04 pm 
Offline

Joined: Sat Dec 08, 2012 8:29 pm
Posts: 62
and fortunately my STN LCD eats 5mA as Iee =D
here it is my STN LCD hitachi sp14q006-t 's data sheet.

Also i have an other STN LCD (i do not remember its part number now) that wants -40V, with 6mA as Iee =P


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 12 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to: