DIYAPASON-L Digest #692 - Sunday, November 24, 2002
 
Loading power supply
  by "Pieter Smit" <pieter@cadence-engineering.co.za>
Re: [Residence Organs]  Loading power supply
  by "Jane and Dave Whitmore" <JDWhitmore@worldnet.att.net>
 

(back) Subject: Loading power supply From: "Pieter Smit" <pieter@cadence-engineering.co.za> Date: Sun, 24 Nov 2002 09:31:16 +0200   Unless a switch mode regulator is used, all other methods do indeed waste power.   A voltage regulator will dissipate Watts according to the voltage differential across it times the current drawn. But it will only happen while current is drawn. It has another nasty in the sense that there is always a voltage drop across it. It will lower the lowest output of the rectifier by another 1.2 to 2 volts even at full current when voltage is most needed.   The resistor is not a bad idea, but the power can be used to power lamps (rated at say 24 volts to increase their lifespan). The lamps can be utilised where light is needed (in the organchambers - lighting the pedalboard - lighting the music stand - register action, keyboards). In this way good use is made of the 'wasted' power.   Pieter Smit pieter@cadence-engineering.co.za    
(back) Subject: Re: [Residence Organs] Loading power supply From: "Jane and Dave Whitmore" <JDWhitmore@worldnet.att.net> Date: Sun, 24 Nov 2002 10:58:39 -0500   At 09:31 AM 11/24/02 +0200, you wrote: >Unless a switch mode regulator is used, all other methods do indeed waste >power. > >A voltage regulator will dissipate Watts according to the voltage >differential across it times the current drawn. But it will only happen >while current is drawn. It has another nasty in the sense that there is >always a voltage drop across it. It will lower the lowest output of the >rectifier by another 1.2 to 2 volts even at full current when voltage is >most needed.   Just right! The reason this happens is that real power supplies (as = opposed to ideal voltage sources) have an internal resistance. If you draw more current then the voltage drop across the internal resistance goes up and the output voltage falls. Really big power supplies have a lower internal resistance than wimpy ones so the voltage drop is less noticeable. Regulators get around this problem by sensing the voltage drop and compensating. There's usually a small IC adjustable voltage regulator that =   does the sensing and the output of this little regulator drives the = base(s) of the output transistor(s). This is the approach that Astron uses.   Just a small bit of EE101!   Dave in Vermont