XPost: 24hoursupport.helpdesk   
   From: ianREMOVETHISjackson@g3ohx.demon.co.uk   
      
   In message , ian field   
    writes   
   >   
   >"Ian Jackson"  wrote in message   
   >news:RK8$DzIdHMcKFwRq@g3ohx.demon.co.uk...   
   >> In message , rf   
   >>  writes   
   >>>Roger Dewhurst wrote:   
   >>>>> You can get simple to use regulator chips that drop the voltage   
   >>>>> down, you only need a couple of components to make a working voltage   
   >>>>> regulator. Ask on News:sci.electronics.basic - the folk on there are   
   >>>>> usually very helpful and should explain all you need.   
   >>>>>   
   >>>>>   
   >>>> Why not just drop the voltage through a few diodes?  Very simple. Very   
   >>>> cheap.   
   >>>   
   >>>A *few* diodes at a couple of ten cents per each. A single 7809 for less   
   >>>that a $.   
   >>>   
   >> More like "a *few* diodes at a couple of cents per each".   
   >>   
   >> 3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required. More   
   >> than good enough for the job.   
   >> --   
   >> Ian   
   >   
   >The forward conduction knee curve on diodes isn't *that* sharp, depending on   
   >current draw and rating of the diode the drop can be as low as 0.55V and as   
   >high as 1.1V.   
   >   
   For most 'normal' Si diodes, that isn't really the case. The actual   
   voltage drop does, of course, increase with current, but at 'sensible'   
   currents, you can reckon on around 0.65V per diode. How much current is   
   the Tardis toy going to take? 1A max? 4 or 5 1N4000-series diodes should   
   work fine in this application. I've used this non-elegant 'KISS'   
   technique on several occasions, and haven't found any problems.   
   --   
   Ian   
      
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