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One of the easiest ways of making a practical voltage converter is to use either readily available components or special purpose IC's such as the ICL7660 voltage convertor. A DC voltage can easily be converted to reversed polarity by using the DC supply to power a free-running square-wave generator.The schematic given below is an example of such a ckt which operates at 3KHz and drives a voltage-doubler output stage also.
i just tested the circuit and i had no luck, i used a 2.2k 10k, and 3 1microfared caps and 2 diodes and have no luck. I found some other sites with this type of negative voltage generator and i still have no luck. I'm using a 556 timer, (Dual 555)... this should work right?
ok, never mind, i got it working. But now i have a problem, my goal was to use the -5v to pull down a contrast line on my LCD. Everytime i hook up the contrast to the -5v, it becomes dark and then dimms to nothing. So the -5v is not strong enough. Is there anyways i can get a stable -5v able to pull down my contrast?
The easy way of getting (-) voltage is using the ICL7660 which is a dedicated voltage converter IC specially designed to generate an equal value negative supply from a positive source. If powered from a +5V supply it generates a -5V output. It can be used with any +1.5 to 10V DC supply, and has a typical voltage conversion effciency of 99.9 per cent :!:
when its output is unloaded;when the output is loaded it acts like a voltage source with a 70 ohms output impedance, and can supply maximum currents of about 40mA. It is housed in an 8pin DIL package and also houses a very efficient square wave generator that operates (without the use of external components) at about 10KHz and has an output that switches fully between the supply rail values. It also houses an ultra-efficient set of logic-driven multiplier 'diodes' that, when used with two external capacitors, enables voltage-doubling to be achieved with near-perfect efficiency.
(I tried this chip and the infor. I've got is from various text books)
I Know this an old thread, but if anyone needs a beefier version of the ICL7660, the MAX660 is such a beast. With a 5V input, it will output -4.3V at 100mA load. The negative output will look like the inverse of the input supply sourced through 6.5 Ohms (the ICL7660 looks like about 80 Ohms) so you can figure the droop at smaller loads. And, yes, I work at Maxim.