Post by thread:[EE]: Rectifier Question

Hello all, For those of you who knew about my little I2C problem that I had, I have officially given up on it until I receive my new sensors from Microchip - in which case I will try again :-) Anyway, working on the other parts of my project, I started on getting my MAX787 5V SMPS regulator working. It's a very simple connection, so it seems, according to the data sheet on maxim's web site (http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1271). I am using their EXACT circuit, and getting a nice solid +5V output. The problem is at the input from the rectifier. Basically, I have a transformer that goes to a full wave rectifier, and then the positive part of the rectifier is fed into the input of the regulator. As soon as I connect the input of the regulator to the output of the rectifier, the voltage at the input jumps up to ~45V. Without the regulator connected, the voltage at the output of the rectifier holds at ~25V. Checking the negative side, with no regulator connected, it gives a - 25V - so it's symmetric, which it seems fine. But as soon as I connect the regulator, when the positive swings up to 45, the negative becomes about -5. How come the voltage swings like that? Is this normal? Is there anyway I can control it? Thank you, Jai ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

The behavior sounds like that of a clamper, which employs a diode, capacitor, and second voltage source to shift an AC source by a certain DC level, in this case about +20 volts. I suppose it's possible that the cap, diode and 5V output on the output side of the regulator are combining to clamp the input signal up 20V. I'm afraid I can't tell you how to fix this problem though. If this is what's going on, it might not be such a problem since I think you would still have 5VDC for the output. I could be wrong though. Daniel Imfeld {Original Message removed}

Quoting Daniel Imfeld <spam_OUTdimfeldTakeThisOuTSOFTHOME.NET>: > The behavior sounds like that of a clamper, which employs a diode, > capacitor, and second voltage source to shift an AC source by a certain DC > level, in this case about +20 volts. I suppose it's possible that the cap, > diode and 5V output on the output side of the regulator are combining to > clamp the input signal up 20V. I'm afraid I can't tell you how to fix this > problem though. If this is what's going on, it might not be such a problem > since I think you would still have 5VDC for the output. I could be wrong > though. > You are right - it wouldn't be a problem since I'm getting +5 anyway (although specs say 40 MAX on the input... so that might be pushing it a little). BUT.. I need to feed a +12 regulator ALSO, which is just a linear - and the max is only 30V on that. I tried hooking it up (just for fun since I had a lot), and it suddenly became a +15V regulator instead of a +12 :-) So that's why I need to maintain it around +25. If this isn't possible, I will have to drop the voltage a bit with a resistor - which is fine, I just want to know if there is another way around. > Daniel Imfeld > > {Original Message removed}

On 8 Feb 2003, at 23:45, Jai Dhar wrote: > I started on getting my MAX787 5V SMPS regulator working. It's a very > simple connection, so it seems, according to the data sheet on maxim's web > site (http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1271). I am using their > EXACT circuit, and getting a nice solid +5V output. The problem is at the > input from the rectifier. Basically, I have a transformer that goes to a full > wave rectifier, and then the positive part of the rectifier is fed into the > input of the regulator. As soon as I connect the input of the regulator to the > output of the rectifier, the voltage at the input jumps up to ~45V. Without > the regulator connected, the voltage at the output of the rectifier holds at > ~25V. My guess is that you don't have a reservoir (bulk) capacitor and when you say "connect the input of the regulator to the output of the rectifier" you are including the 220uF cap which is on the regulator input. George Smith -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Ok, I have composed a schematic in Paint :-) (if anyone can recommend any FREE, commonly-used schematic creators, please do). I will just re-iterate that I am measuring the voltage at the positive end of the rectifier (when it gets converted to DC). On a better note.. measuring the AC inputs to the rectifier (right from the transformer) don't change when I connect the regulator. If that means anything. And I will copy the link to maxim's site again below for reference (since I didn't stick the regulator circuit in there). http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1271 Thank you again for all your help, Jai Quoting Dave Dilatush <EraseMEdilatushspam_OUTTakeThisOuTCOMCAST.NET>: {Quote hidden}> Jai Dhar wrote... > > >Is this normal? > > No. > > What you describe indicates something is very, very wrong: you've > got a malfunctioning component, or a wiring error, or an > inappropriate circuit. > > If you could post a complete circuit diagram of your power > supply, it would be a lot easier to help you. > > Dave D. > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body > ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> Ok, I have composed a schematic in Paint :-) Um, OK, but I don't see it. > (if anyone can recommend any > FREE, commonly-used schematic creators, please do). I hear there are free and low cost versions of Eagle with various limitations. I think all of them can do at least one page of schematic capture. However Eagle, like any complicated software package, takes a little while to learn and won't help you immediately. You could sketch the schematic with pencil and paper, scan it, and attach the GIF file or put it on a web site if it's too big. That sounds a lot easier than trying to use Paint to draw a schematic. > And I will copy the link to maxim's site > again below for reference (since I didn't stick the regulator circuit in > there). I don't know about others, but I'm not going to go chasing several links just to answer a PIClist question. You will get a better response if you put everything we need to know in one place that is easy to get to. Remember, you are asking people to do you a favor, and everyone has something else to do other than answering PIClist questions. You want to make the hassle factor as low as possible. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

AutotraxEDA is free. http://www.autotraxeda.com It is still in development stages, but works. At 10:33 AM 2/9/2003, you wrote: {Quote hidden}>Ok, I have composed a schematic in Paint :-) (if anyone can recommend any >FREE, commonly-used schematic creators, please do). I will just re-iterate >that I am measuring the voltage at the positive end of the rectifier (when it >gets converted to DC). On a better note.. measuring the AC inputs to the >rectifier (right from the transformer) don't change when I connect the >regulator. If that means anything. And I will copy the link to maxim's site >again below for reference (since I didn't stick the regulator circuit in >there). > >http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1271 > >Thank you again for all your help, > >Jai > >Quoting Dave Dilatush <RemoveMEdilatushTakeThisOuTCOMCAST.NET>: > > > Jai Dhar wrote... > > > > >Is this normal? > > > > No. > > > > What you describe indicates something is very, very wrong: you've > > got a malfunctioning component, or a wiring error, or an > > inappropriate circuit. > > > > If you could post a complete circuit diagram of your power > > supply, it would be a lot easier to help you. > > > > Dave D. > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body > > > > > > >---------------------------------------- >This mail sent through http://www.mywaterloo.ca > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

part 1 2673 bytes content-type:text/plain; charset=ISO-8859-1 (unknown type 8bit not decoded) My apologies to all - I forgot the picture (my webmail works in an odd fashion). I did not expect anyone to chase links by any means, so my apologies again. Here it is. Quoting Gordon Niessen <gordonEraseME.....GNIESSEN.COM>: {Quote hidden}> AutotraxEDA is free. http://www.autotraxeda.com It is still in > development stages, but works. > > At 10:33 AM 2/9/2003, you wrote: > >Ok, I have composed a schematic in Paint :-) (if anyone can recommend any > >FREE, commonly-used schematic creators, please do). I will just re-iterate > >that I am measuring the voltage at the positive end of the rectifier (when > it > >gets converted to DC). On a better note.. measuring the AC inputs to the > >rectifier (right from the transformer) don't change when I connect the > >regulator. If that means anything. And I will copy the link to maxim's site > >again below for reference (since I didn't stick the regulator circuit in > >there). > > > >www.maxim-ic.com/quick_view2.cfm?qv_pk=1271 > > > >Thank you again for all your help, > > > >Jai > > > >Quoting Dave Dilatush <EraseMEdilatushCOMCAST.NET>: > > > > > Jai Dhar wrote... > > > > > > >Is this normal? > > > > > > No. > > > > > > What you describe indicates something is very, very wrong: you've > > > got a malfunctioning component, or a wiring error, or an > > > inappropriate circuit. > > > > > > If you could post a complete circuit diagram of your power > > > supply, it would be a lot easier to help you. > > > > > > Dave D. > > > > > > -- > > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > > email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > > > > > > >---------------------------------------- > >This mail sent through http://www.mywaterloo.ca > > > >-- > >http://www.piclist.com#nomail Going offline? Don't AutoReply us! > >email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body > ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspamspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body part 2 24771 bytes content-type:image/pjpeg; name="circuit.jpg" (decode) part 3 2 bytes -

You wrote... >My apologies to all - I forgot the picture (my webmail works in an odd >fashion). I did not expect anyone to chase links by any means, so my apologies >again. Here it is. I don't see any reservoir capacitor in your circuit. Are you relying entirely on the 220uF capacitor shown in the Maxim diagram? If so, I doubt that's enough to hold up the input voltage to your regulator adequately under load. Whether you are or not, that wouldn't explain why the rectifier output voltage is going **UP** when you connect the regulator; that just doesn't make any sense. You ARE measuring this voltage with respect to circuit ground, right? And circuit ground (i.e., the transformer center tap) IS connected to regulator circuit ground, right? I really can't make sense of this. Are you sure your voltmeter is working properly? DD -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservSTOPspamspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

I think I see what's going on, maybe... There's no smoothing capacitor in your diagram. I bet there's a reasonable smoothing cap on the input of the regulator circuit though. When you measure without the regulator you measure the average of the rectified waveform, which is still dipping down to zero between each half cycle so you measure a lot less than peak, possibly less than RMS even? When you connect the regulator there's a capacitor present so it peak-detects and reads >50% higher. This is the relevant reading. If this is too high you have the wrong transformer. {Original Message removed}

Oliver Broad wrote... >I think I see what's going on, maybe... > >There's no smoothing capacitor in your diagram. I bet there's a reasonable >smoothing cap on the input of the regulator circuit though. > >When you measure without the regulator you measure the average of the >rectified waveform, which is still dipping down to zero between each half >cycle so you measure a lot less than peak, possibly less than RMS even? > >When you connect the regulator there's a capacitor present so it >peak-detects and reads >50% higher. This is the relevant reading. If this is >too high you have the wrong transformer. Duh. Why didn't I think of that... That's exactly what's going on, I'm sure of it. Jai, if you are intending to get +5V and +12V out of this power supply, there is no need for you to be using a transformer which puts out so much voltage. Instead of 50 volts center-tapped, I think 28 volts center-tapped would suffice. That would give you around 18-20 VDC at the input to the regulators. DD -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservSTOPspamEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

Quoting Dave Dilatush <KILLspamdilatushspamBeGoneCOMCAST.NET>: > Oliver Broad wrote... > > >I think I see what's going on, maybe... > > > >There's no smoothing capacitor in your diagram. I bet there's a reasonable > >smoothing cap on the input of the regulator circuit though. > > I have only the smoothing cap that the maxim site recommends (220uf) {Quote hidden}> >When you measure without the regulator you measure the average of the > >rectified waveform, which is still dipping down to zero between each half > >cycle so you measure a lot less than peak, possibly less than RMS even? > > > >When you connect the regulator there's a capacitor present so it > >peak-detects and reads >50% higher. This is the relevant reading. If this > is > >too high you have the wrong transformer. > > Duh. Why didn't I think of that... > > That's exactly what's going on, I'm sure of it. > > Jai, if you are intending to get +5V and +12V out of this power > supply, there is no need for you to be using a transformer which > puts out so much voltage. Instead of 50 volts center-tapped, I > think 28 volts center-tapped would suffice. That would give you > around 18-20 VDC at the input to the regulators. > You are absolutely right - I don't need a xformer that powerful. The problem was the surplus store only carried that type at the time. this is used of course, new xformers are sooo expensive that I didn't want to fork out that much just for this. Obviously, the better solution would be to wait until they get more in (Which they will) and use a more appropriate xformer. But anyway, your explanation makes perfect sense to me, thank you sooo much!! I actually understand why now. I appreciate all your help! > DD > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email EraseMElistservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body > ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listserv@spam@spam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

For those of you who tend to be careless at times like me - do NOT play guitar and touch the hot wire from mains at the same time. I just enjoyed quite the spunky shock since my hands happened to be on the strings while I switched the power on to my transformer (hence touching the hot wire by accident). Didn't even think twice about it... just letting those of you know who already don't :-) Jai Quoting Dave Dilatush <.....dilatushspam_OUTCOMCAST.NET>: {Quote hidden}> Jai Dhar wrote... > > >I appreciate all your help! > > You're very welcome. Best of luck with your project. > > DD > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email TakeThisOuTlistserv.....TakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body

At 07:11 PM 2/9/03 -0500, you wrote: >For those of you who tend to be careless at times like me - do NOT play guitar >and touch the hot wire from mains at the same time. I just enjoyed quite the >spunky shock since my hands happened to be on the strings while I switched the >power on to my transformer (hence touching the hot wire by accident). Didn't >even think twice about it... just letting those of you know who already >don't :-) > >Jai > Jai, you are the first person ever to get me to type: ROTFLMAO! Not really... but it did just about make beer shoot out my nose. Hope you are ok. I have read about musicians actually being killed by this stunt falling into a swimming pool. It totally amazes me that the things are not transformer isolated. Maybe they are and it was just some leakage current? Well, be more careful in the future, Jai. We need all the 'pic-listers' we've got. It would be a shame for this to get around on the net: "Hey, over there on the pic-list, some guy fried himself playing guitar while booting some code on his pic gadget. Stick with Atmel AVR's or SX's and stay away from those PIC weirdos...". In jest, Tom M. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservRemoveMEmitvma.mit.edu with SET PICList DIGEST in the body

Oliver Broad <RemoveMEoabdelphispamBeGoneCOAXIALPOWER.COM> wrote: > When you measure without the regulator you measure the average of the > rectified waveform, which is still dipping down to zero between each half > cycle so you measure a lot less than peak, possibly less than RMS even? Yes. the average value of a half-sinewave is 2/pi, or 63.66% of the peak value. The RMS value is sqrt(2)/2, or 70.7% of the peak value. 40V (peak value, with regulator attached) * 63.66% = 25.46V (average value) -- Dave Tweed -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistserv@spam@spam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Jai Dhar wrote: > > >too high you have the wrong transformer. > > Instead of 50 volts center-tapped, I > > think 28 volts center-tapped would suffice. > > You are absolutely right - I don't need a xformer that powerful. The problem > was the surplus store only carried that type at the time. Find the point where the 2 wires exit the transformer and are soldered onto the centre tap pin. Then cut one wire, and re-solder it as 28v in PARALLEL so you get twice the current. Probably takes 10 minutes and saves you buying a new transformer. -Roman -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseMEmitvma.mit.edu>

> Find the point where the 2 wires exit the transformer > and are soldered onto the centre tap pin. Then cut one wire, > and re-solder it as 28v in PARALLEL so you get twice the > current. Probably takes 10 minutes and saves you buying a > new transformer. > -Roman Not 100% on this, good idea, but wouldn't the windings need to be in phase ? If so, how would you do that safely (temporary series resistor ?) or would you just measure the voltage - if in phase it would be 28V, if out of phase, 0V ? ( Been blathering out of one end all day, thought I'd give the other a go ;-) ) -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu>

For best effect try touching your lips to a grounded microphone when you are touching metal guitar strings that are connected to 700v DC via your tube amp. :o) -Roman Jai Dhar wrote: > > For those of you who tend to be careless at times like me - do NOT play guitar > and touch the hot wire from mains at the same time. I just enjoyed quite the > spunky shock since my hands happened to be on the strings while I switched the > power on to my transformer (hence touching the hot wire by accident). Didn't > even think twice about it... just letting those of you know who already > don't :-) -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestRemoveMEEraseMEmitvma.mit.edu>

Jinx wrote: > > > Find the point where the 2 wires exit the transformer > > and are soldered onto the centre tap pin. Then cut one wire, > > and re-solder it as 28v in PARALLEL so you get twice the > > current. Probably takes 10 minutes and saves you buying a > > new transformer. > > -Roman > > Not 100% on this, good idea, but wouldn't the windings need > to be in phase ? If so, how would you do that safely (temporary > series resistor ?) or would you just measure the voltage - if in > phase it would be 28V, if out of phase, 0V ? Ha ha! You're serious? When paralleling 2 transformers or 2 transformer windings, just connect 2 wires then stick an AC voltmeter across the remaining 2 wires. If it reads double AC volts you guessed it wrong, if it reads close to 0v you got it right. Or just put your tongue across the 2 remaining leads... Jinxian roulette. ;o) -Roman -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-request@spam@mitvma.mit.edu>

> Ha ha! You're serious? I didn't want to send that last mail and look a plonker but some bigger boys made me > When paralleling 2 transformers or 2 transformer windings, > just connect 2 wires then stick an AC voltmeter across the > remaining 2 wires. If it reads double AC volts you guessed it > wrong, if it reads close to 0v you got it right Obvious of course. I've even done it too ;-) O O | ___ U -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestspam_OUT.....mitvma.mit.edu>

Considering I am still not comfortable with the fact that I OBVIOUSLY don't know much about electrical safety (hence my jolt), I am not even going to attempt this. Thankfully, I found an old xformer lying around that HAPPENED to dish out 30V instead of ~50... and it works beautifully with the whole setup! The only thing I can't figure out is that it seems to have 2 centertaps: One for the primary, and one for the secondary. I just left the primary middle wire unconnected (actually just chopped it off incase I touched THAt by accident), and connected the secondary centertap. Quoting Roman Black <spamBeGonefastvidEraseMEEZY.NET.AU>: {Quote hidden}> Jinx wrote: > > > > > Find the point where the 2 wires exit the transformer > > > and are soldered onto the centre tap pin. Then cut one wire, > > > and re-solder it as 28v in PARALLEL so you get twice the > > > current. Probably takes 10 minutes and saves you buying a > > > new transformer. > > > -Roman > > > > Not 100% on this, good idea, but wouldn't the windings need > > to be in phase ? If so, how would you do that safely (temporary > > series resistor ?) or would you just measure the voltage - if in > > phase it would be 28V, if out of phase, 0V ? > > > Ha ha! You're serious? When paralleling 2 transformers > or 2 transformer windings, just connect 2 wires then stick > an AC voltmeter across the remaining 2 wires. If it reads > double AC volts you guessed it wrong, if it reads close > to 0v you got it right. Or just put your tongue across > the 2 remaining leads... Jinxian roulette. ;o) > -Roman > > -- > http://www.piclist.com hint: To leave the PICList > piclist-unsubscribe-requestspamBeGonemitvma.mit.edu > ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-request@spam@spamBeGonemitvma.mit.edu>

Roman wrote... >Find the point where the 2 wires exit the transformer >and are soldered onto the centre tap pin. Then cut one wire, >and re-solder it as 28v in PARALLEL so you get twice the >current. Probably takes 10 minutes and saves you buying a >new transformer. ...and will accomplish absolutely nothing. Remember from the diagram he posted, he's using the full-wave center-tapped configuration. If he cannibalizes his transformer and runs the paralleled windings through a full bridge, he'll get **EXACTLY** the same DC voltage he's getting right now. In case you missed the relevant post, Oliver figured out the source of the original confusion: Oliver Broad wrote: {Quote hidden}>I think I see what's going on, maybe... >There's no smoothing capacitor in your diagram. I bet there's >a reasonable smoothing cap on the input of the regulator >circuit though. >When you measure without the regulator you measure the average >of the rectified waveform, which is still dipping down to zero >between each half cycle so you measure a lot less than peak, >possibly less than RMS even? >When you connect the regulator there's a capacitor present so it >peak-detects and reads >50% higher. This is the relevant reading. >If this is too high you have the wrong transformer. Voila. Problem solved. DD -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-request@spam@EraseMEmitvma.mit.edu>

At 10:26 PM 2/10/2003 +0000, you wrote: >Roman wrote... > > >Find the point where the 2 wires exit the transformer > >and are soldered onto the centre tap pin. Then cut one wire, > >and re-solder it as 28v in PARALLEL so you get twice the > >current. Probably takes 10 minutes and saves you buying a > >new transformer. > >...and will accomplish absolutely nothing. Remember from the >diagram he posted, he's using the full-wave center-tapped >configuration. If he cannibalizes his transformer and runs the >paralleled windings through a full bridge, he'll get **EXACTLY** >the same DC voltage he's getting right now. A little bit less, because of the extra diode drop. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" .....speffRemoveMEinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestSTOPspam@spam@mitvma.mit.edu>