Guest marr Posted September 4, 2004 Report Share Posted September 4, 2004 Looking ahead, I'd like to build a more-complicated sequencer the next time around. (Almost done with the first stock one.) Mostly, I think of editing asm to allow for more displays and tactiles.With extra backlight displays and LEDs it seems like the 7805 would get much too hot even with a heatsink (?), so I was wondering what options there are for staying away from using an internal fan (noise).When they say something is a 'regulated' powersupply, does that mean that it's 5V will be rectified and bufferred (?), like the bridge/caps setup on the CORE, but in advance? So I could leave out 7805s from the internals completely?Any ideas?Mark Quote Link to comment Share on other sites More sharing options...
TK. Posted September 4, 2004 Report Share Posted September 4, 2004 yes, it's just like the rectifer/buffer/regulation circuit between J1 and J2 of the core modul + a transformer.Many electronic shops have such premade PSUs for cheap money - e.g. Pollin (http://www.pollin.de) has a regulated PSU with +5 V/1 A, +12 V/0,25 A and -12V/0.25A output which is an excellent solution for MIDIbox SID and MIDIbox CVAnd it costs only 1.95 EUR!So, just open your eyes when you go through an (online) electronic shop :)Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
Duggle Posted September 4, 2004 Report Share Posted September 4, 2004 one way of making of making the 7805 run *much* cooler is to feed it with a lower input supply voltage.The lower limit input supply of these 78xx voltage regulators is 1.2V above the output voltage. This means using 6.2V on input. Make sure the input voltage never falls below 6.2V during the AC cycle otherwise your 5V regulated output will dip causing possibly quite subtle problems. Feeding your midibox core with a regulated 6.5V plug pack would be perfect.cheers Quote Link to comment Share on other sites More sharing options...
Steven_C Posted September 4, 2004 Report Share Posted September 4, 2004 out of interest... you can get more current out of a 7805 or similar voltage regulator by adding additional circuitry... some kind of current boosting transistor... a work colleage built a PSU the other day that goes up to around 10A from a 7812! but I don't know how he wired up the extra circuitry, sorry!This makes me wonder if I'm pushing the limits of the 7805 on my midibox LC... it has 2 backlit 40x2 displays running off the same 7805 as the rest of the circuit... so I bought the extra components to add a separate 7805 just for the backlights today!...Steve Quote Link to comment Share on other sites More sharing options...
Guest den_Juin Posted September 5, 2004 Report Share Posted September 5, 2004 Wouldn't exchanging the 7805 for a 78S05 do the trick? Quote Link to comment Share on other sites More sharing options...
TK. Posted September 6, 2004 Report Share Posted September 6, 2004 Yes, but you need a good headsink, or you have to mount it directly on a metal case.Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
Duggle Posted September 6, 2004 Report Share Posted September 6, 2004 hi,just to add my earlier post:The heat dissipated in the voltage regulator (measured in Watts) is determined by Voltage multiplied by current. The voltage is the voltage drop from input to output of the regulator. The current is the load current being supplied.eg midibox current= 200mA =0.2Amp input voltage=12V power(heat)=0.2*(12V-5V)=1.4W now with lower input voltage midibox current= 200mA =0.2Amp input voltage=6.5V power(heat)=0.2*(6.5V-5V)=0.3W less than 1/4 heat produced! Quote Link to comment Share on other sites More sharing options...
uclaros Posted September 6, 2004 Report Share Posted September 6, 2004 Can one just use more 7805 in parallel to gain more amperage?? Quote Link to comment Share on other sites More sharing options...
smashtv Posted September 6, 2004 Report Share Posted September 6, 2004 Can one just use more 7805 in parallel to gain more amperage??short answer, no (the loads served by each 7805 would have to be exactly the same and you would still have floating ground issues)Long answer, yes. A diode on the output of each reg would keep one reg from seeing the output of another, but the diode would cause a slight voltage drop (no longer 5vdc). This can also be compensated for by using the same type of diode between the ground pin of the reg and ground. (Same amount of voltage drop to ground=higher ground ref=each regs output back up to 5vdc.)You could use many regulators this way in a circuit to get 5, 10, or 20 amps out of standard regulators (but the bridge rectifier and amount of AC current coming in would have to change to suit)Also since your regs are not at true ground anymore they would need to be isolated (tabs not on a grounded heatsink, etc.)Check out this PDF, Page 3 for one implementation of this concept. I don't really agree with his choices for capacitors, but I doubt he was driving moving faders or audio circuits with this. ;)Let me know what you think and Have Fun!SmashTV Quote Link to comment Share on other sites More sharing options...
Duggle Posted September 7, 2004 Report Share Posted September 7, 2004 If you keep the 5V outputs from the two regulators separate, you can supply a different set of Vcc's on each.This will not reduce the total heat just spread it out between 2 devices which in most case wont be a real help. It also means you have to separate the Vcc (+5V) wires into 2 groups to split the load... Quote Link to comment Share on other sites More sharing options...
Steven_C Posted September 8, 2004 Report Share Posted September 8, 2004 The easiest way for more current...http://repairfaq.ece.drexel.edu/sam/samschem.htm#schslp2more discussion of current-boosting, and another diagram... http://wwwd.national.com/national/PowerMB.nsf/0/f17a1bcbe56e184288256ecc0065d4f8?OpenDocumentgood luck Quote Link to comment Share on other sites More sharing options...
Guest marr Posted September 9, 2004 Report Share Posted September 9, 2004 Thanks TK & all.. This clears up what I read on the CORE page in the comments about J1 and J2.For the record, I picked up a regulated 3-7.5V/2A powersupply at Radio Shack for US$22. It was named "Digital Camera Adapter" and had 5V as one of the switchable options...However, I did not end up using it for my SEQ because with a little heatsink the 7805 got almost hot enough to burn fingers, but not quite... I was satisfied with this for the time being. (I am using a non-regulated 9V/1.8A.)The next SEQ I build will use the regulated, or two, etc...Marr Quote Link to comment Share on other sites More sharing options...
Guest marr Posted September 13, 2004 Report Share Posted September 13, 2004 just a quick note.. I ended up switching to the regulated pws after all, left the buffer/rectifier components on the CORE, and so am running it at 7.5V.As expected, it is cooler, but I wasn't expecting it to be such a dramatic change. Thanks for the advice. Quote Link to comment Share on other sites More sharing options...
Duggle Posted September 14, 2004 Report Share Posted September 14, 2004 well done,indeed, the point Ive been trying to make in this thread is that the total current available from the 7805 is not the limiting factor (>1A!) but the heat produced when regulating down by a significant voltage.Remember the diodes in the recitifier will contribute a constant drop of about 1 to 1.2V total. This means that the regulator is seeing about 6.3 to 6.5V across it's input, which is about perfect as far as minimising the heat goes! cheers Quote Link to comment Share on other sites More sharing options...
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