5mW boost converter
- From: Adam S <not.valid@nosuchaddress>
- Date: Thu, 27 Apr 2006 10:57:59 +1000
Hi,
I am trying to run a LCD character module from a 3.3V supply in a battery powered instrument. The LCD module logic runs perfectly at 3.3V (tested it down to 1.8V), however the LCD display voltage needs about 4.5~5V negative to VDD (@ 1mA). Normally a simple charge pump would do, but I need to save every milliamp possible. This is where I thought up a simple boost converted like shown in the following schematic.
http://members.optusnet.com.au/~eseychell/pictures/boost_conv_01.png
Measured efficiency of this converter was about 60% with a 1mA load between +3.3V and VOUT as shown. I tried to find where most of the power is lost, and it seems due to the 74HC14. With 5V applied across the 74HC14, the current into the VDD pin is 0.8mA, and when I remove L1 it drops further to 0.6mA. Any ideas on reducing oscillator current while still keeping it fairly simple ?
Adam
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