emmo@moncam.co.uk (Dave Emmerson) (02/06/90)
In article <111700197@uxa.cso.uiuc.edu>, mms00786@uxa.cso.uiuc.edu writes: > > Hey! We just learnt about the Max232 in class; so how does it manage to turn > a DC +5 into +- 12? The only way I can think of is to make an oscillator, feed > it to a transformer, and convert it back to DC. But how do you do it within a > chip? > > Milan. > . You don't - quite. The chip has sets of mosfets acting like switches. First you charge up the 22uF tant straighht across the power rails, then you unhook it, connect it's 'negative' lead to +5volts, et voila- the positive side is at +10 volts, compared to ground. Do this repeatedly at high frequency, add a bit of smoothing, and stack 2 more like it to get the -10 volts, this time connecting the tant's positive side to ground, and that's a crude 232 chip. The idea had been around for years, the technology to put those super fet's all on one small chip only got here a couple of years back. There's a new one out now which doesn't need any external tants! I haven't got a data sheet yet, but I'm told it works fine. Dave E.