NorthernLightX Posted March 4, 2006 Report Share Posted March 4, 2006 Hi,I'm using this schematic for my PSU:a short question:- Is it wise to connect the ground lines of the 5v and 9v branches, to create a common ground?If not then please also answer the following question:- I'm going to wire up 4 Core boards and 4 SID boards. On the SID both 2 voltages are used. Should I use the ground from the 9v branch, or the 5v branch?And another one:The MIDI and audio jacks, where should I ground them to? Is star-topology grounding an issue here?Thanks in advance!More pics of my PSU design will follow shortly ;) Quote Link to comment Share on other sites More sharing options...
moebius Posted March 4, 2006 Report Share Posted March 4, 2006 Hi.a short question:- Is it wise to connect the ground lines of the 5v and 9v branches, to create a common ground?Short answer: Yes. (Long answer: the ground is the ground is the ground... ect.)It's reference voltage where everything is referenced - Your 5v might not be anything like 5v when referenced to the 9V ground.Moebius Quote Link to comment Share on other sites More sharing options...
NorthernLightX Posted March 4, 2006 Author Report Share Posted March 4, 2006 Great! Thanks Moebius!I still don't understand how the common ground could affect my 5v, my 7805 regulates that, doesn't it?With all my gathered knowledge here I can (and will probably) write a newbe howto on PSUs someday :)Might even become part of the fotoblog I'm planning.Cheers, Alex. Quote Link to comment Share on other sites More sharing options...
NorthernLightX Posted March 4, 2006 Author Report Share Posted March 4, 2006 Hi moebius,where would be the best place to connect the 5v ground to the 9v ground? At the end of the branches, or earlier, like before the regulators?thanks, Alex. Quote Link to comment Share on other sites More sharing options...
moebius Posted March 5, 2006 Report Share Posted March 5, 2006 At the beginning of the all Common Grounds. (Whoops - is this some sort of a Joke?!?)Let any "ground" be this point. Let any voltage be referenced to this point.Moebius Quote Link to comment Share on other sites More sharing options...
NorthernLightX Posted March 5, 2006 Author Report Share Posted March 5, 2006 OK, not really an answer I completely understand, but I gave it a shot and connected the branches just behind the 100nF caps, works fine!The only problem now is that since I rebuilt the PSU board, the 9v I measured erlier now measures 8v. Right before the 7809 I still measure 10,5v, so this has not changed since the rebuild. Has the 7809 been too hot perhaps, bacause of soldering and desoldering, or do I need to seek the cause in a different direction?Cheers, Alex.[edit]I'm going to post this question in the troubleshooting forum, as it isn't a design question.[/edit] Quote Link to comment Share on other sites More sharing options...
moebius Posted March 5, 2006 Report Share Posted March 5, 2006 ""Common Ground" is something that any decent Midibox should have. There might be some on the eBay and some on the "Request to sell".. Please - don't trust on these - If not approved by Thorsten -none of these have the "Common Ground" the Midibox has!"Do connect the grounds.M Quote Link to comment Share on other sites More sharing options...
NorthernLightX Posted March 5, 2006 Author Report Share Posted March 5, 2006 ""Common Ground" is something that any decent Midibox should have. There might be some on the eBay and some on the "Request to sell".. Please - don't trust on these - If not approved by Thorsten -none of these have the "Common Ground" the Midibox has!"Do connect the grounds.MDamn, I just bought myself a bucket of common ground and put it in the box.... Couldn't you have warned me earlier???No room for SID and Core modules now either... ;D Quote Link to comment Share on other sites More sharing options...
RadicalAns Posted March 21, 2006 Report Share Posted March 21, 2006 Hi moebius,where would be the best place to connect the 5v ground to the 9v ground? At the end of the branches, or earlier, like before the regulators?thanks, Alex.Is this taking into account the voltage drop across the rectifier? Quote Link to comment Share on other sites More sharing options...
NorthernLightX Posted March 21, 2006 Author Report Share Posted March 21, 2006 Is this taking into account the voltage drop across the rectifier?It's ground, it doesn't matter ;) And by the way, the rectifier ups the voltage by about 41% (minus about 0,7v), it doesn't drop it at all.(When I started understanding the concept of ground a few days ago, it felt to me like suddenly the light was turned on, now I can't imagine not undertanding it anymore :) ) Quote Link to comment Share on other sites More sharing options...
Mendelt Posted March 23, 2006 Report Share Posted March 23, 2006 The 0,7V is the rectifier dropping the voltage :)And the 41% isn't really the rectifier upping the voltage but that's due to the 12V at the input of the rectifier being 12V AC. That means that the average voltage is 12V but the peak voltage can get much higher. For a sine wave you can just multiply the average with the square root of 2 to get the peak voltage.The capacitors after the rectifiers will store the voltage you put in them. They will lift the voltage to the peak voltage they receive. That's where the 41% comes from.But I see everyone has fallen asleep so I'll stop the useless technical explanations ::) Quote Link to comment Share on other sites More sharing options...
drin Posted March 23, 2006 Report Share Posted March 23, 2006 But I see everyone has fallen asleep so I'll stop the useless technical explanations ::)Not useless at all! I'm enjoying the thread. :)And the 7805 and 7809 eliminate the ripple voltage from the caps, right? (As well as dropping the voltage appropriately)See, I'm not too old to learn a new trick! :)-drin Quote Link to comment Share on other sites More sharing options...
Mendelt Posted March 23, 2006 Report Share Posted March 23, 2006 Yup.The regulators need about 2 volts more than their output to regulate correctly. So If you put in a 7809 you need a capacitor big enough to store enough electrons to keep the input of the regulator above 11V. Quote Link to comment Share on other sites More sharing options...
NorthernLightX Posted March 23, 2006 Author Report Share Posted March 23, 2006 Yup.The regulators need about 2 volts more than their output to regulate correctly. So If you put in a 7809 you need a capacitor big enough to store enough electrons to keep the input of the regulator above 11V.So for the big capacitors to be able to do so, you'll need to supply them with at least 11Vdc. THat means, taking the 1,41 rule into account, that your Vac just before the rectifiers has to be at least 7,8 - plus the 0,7V the rectifier consumes, so 8,5Vac at least. 9,5 would be more comfortable, for example when your mains power is below average (which caused "unexplainable" readings on my box earlier :D )Just a post to check if I understand correctly now, correct me if I'm wrong about anything ;-) Quote Link to comment Share on other sites More sharing options...
Mendelt Posted March 23, 2006 Report Share Posted March 23, 2006 So for the big capacitors to be able to do so, you'll need to supply them with at least 11Vdc. THat means, taking the 1,41 rule into account, that your Vac just before the rectifiers has to be at least 7,8 - plus the 0,7V the rectifier consumes, so 8,5Vac at least. 9,5 would be more comfortable, for example when your mains power is below average (which caused "unexplainable" readings on my box earlier :D )Correct.Another thing you should take into account is that your capacitors get 100 peaks (120 in the US) every second but the voltage in between peaks drops to 0V. The trick is making sure you dont deplete them too much in between peaks. When your supply just supplies 100mA you can use small capacitors because you're not discharging them very fast. But when you're building a bigger supply you need bigger capacitors so they can hold more charge. Quote Link to comment Share on other sites More sharing options...
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