If using a linear regulator (eg LM338K as recommended by Jay) , consider adding a series resistor in the regulator input. This can switch a significant part of the dissipation out of an active component into a passive one. This may achieve economies and also increased reliability. The following table will be compressed by email scrambling but should be readable. Columns are I Current - 1 to 5 amps Pr Power in a 3 ohm series resistor Vr Voltage across resistor Vregin Voltage at regulator input Preg Power dissipated in regulator Ptot Total Power dissipated (incl load) Pload Pwer in load Notice that regulator power peaks at about 30 watts while resistor power peaks at about 75 watts (!) Without the resistor the regulator would dissipate 5 x (24-5) = 95 watts at 5 amps. I Pr Vr Vregin Preg Ptot Pload 1 3 3 21 16 24 5 2 12 6 18 26 48 10 3 27 9 15 30 72 15 4 48 12 12 28 96 20 5 75 15 9 20 120 25 You could consider using a properly sized lightbulb(s) for the resistor (although this would probably not be an adequate commercial solution). Be aware that the lightbulb will have a much lower resistance when cold than when operating. Use of a switching regulator as recommended by others would very substantially reduce your power dissipation. Due to the transforming action your 24 volt current will be well below your output current. eg at say 75% efficiency and 5v out at 5A the input current would be under 1.5 amps. A very simple switcher could be followed by a linear regulator if desired. Russell McMahon -----Original Message----- From: Jay.R.Vijay-Indra To: PICLIST@MITVMA.MIT.EDU Date: Saturday, May 15, 1999 9:12 AM Subject: Re: [OT] High Power Voltage Regulator >Try LM338K, This three terminal device (TO3a package) output voltage is set >by resister and can be between +1.2V to 32V. The input voltage range is +3V >to +35V. Maximum output current is 5A with load regulation of 0.1% and >0.005%/v line regulation. > >Regards, > >Jay > > > >At 19:34 14/05/99 +0200, you wrote: >>Hello Everyone.. >> >>I have always been served well by the simple 78lxx regulators and if not >>that then the straight 78xx, but now have to regulate a bit of a larger >>current - Basically I need to supply a circuit drawing around 3 to 5 A at 5 >>V from a 24 V supply. I would not have a problem using a larger linear >>regulator with a larger heatsink (I don't have to conserve energy - got >>plenty), except I can't seem to find one offhand.. >> >>Do I have to start looking at a switching circuit or transistor driven >>circuit, or is there a simpler (like 1 chip?) approach? >> >>Thanks >> Roland >> >> >> >