Any cons with using integrated fw bridge rectifier?

[SILVERGUN]

Just wondering if there is anything wrong, or questionable, with using an integrated bridge rectifier in the power supply of a fresh build?... I have seen a lot of people just use the diodes in series technique, and was wondering if there is any proven benefit/drawback to this method?

I prefer overrated components, especially in the ps
This is the type I use everyday in welding equipment- 50 amp/1000 volt:

[phsyconoodler]

Nope.Will work fine.That one must be pretty large!

[jojokeo]

what's up SG!? I prefer the individual diodes mainly because I like the UF400x diodes because of their faster and quieter operation (due to switching noise) over 1N400x types which you don't get with the FW types. It's not a huge difference but every little bit you do in this regard to noise reduction proactiveness counts.

[SILVERGUN]

Thanks guys...I just wasn't sure if there is a spec I didn't know about that would rule these out....I like the idea of something I will never need to look at again, and would just mount it right to the chassis next to the power xfmr, instead of on a board.....footprint is about 1" square

not sure I understood your answer jojo (but thanks for the quick response)...I assume you're saying this type would consist of the slower diodes?

would that increase ripple?......first cap stage will be 100uf/100uf followed by a power resistor, for that manufactured "sag" action:

[Willabe]

Hi SG,

I agree with jojokeo on the ultra fast diodes and that it all adds up in reducing noise sources.

It's not about ripple it's about the switching noise when the diodes turn on/off. KOC talks about them in his TUT books. Merlin talks about them too in his book on PSU.

Although it is nice to have a small package like that and with those ratings. I would think that sooner or later they will start making those bridge packages in an ultra fast verson.  

Your drawing won't open up to full size.


                   Brad        

[SILVERGUN]

Thanks Brad, I'll see if I can find a spec sheet on these....and you've sparked my curiosity about the availability of a faster version

If you have trouble opening the .gif picture, save it, and then right click it to open it with your default picture viewer (Microsoft picture manager, if you have it) or just open in paint, (it's nothing special, just standard issue ps)

[SILVERGUN]

Is that it??...or could one of the bigger brains weigh in on this.....even just a link to an explanation
I tried searching the forum, with MANY mixed results
Here's a general video on the subject, which doesn't really get too in depth:
Diode Tutorial & How to build an AC to DC power supply

Are there specs to consider/compare when choosing integrated bridge vs. series diodes?
I am aware of TRR, but is that ever an issue to consider when designing a tube amp PS?

I guess another way to word my question is, "do I need to worry about high speed diodes in a 60 hz PS?"

[Willabe]

no one addressed that the P/T may have a center tap on the secondary.  Therefore select your PT to match up to a full wave rectifier.  (Bridge). 

Yep.

Most guitar amps use a PT with a CT and use a Full Wave/half bridge. A PT with no CT uses a Full Wave/full bridge, like the unit you've posted a pic of. (Or a half wave/half bridge)

If you use a FWFB with a PT that has a CT and ground the CT and the FWFB you'll kill the PT.

You can not ground both.

And even if you don't ground the CT you can not just swap a FWFB for FWhb because the B+dcv will be way higher.


                    Brad       

   

[SILVERGUN]

P/T will be Hammond 290fx---640 VCT

[Willabe]

Then you can't use the FWFB.


                Brad     

[SILVERGUN]

Thank you Brad,
I knew there was a good reason I had to ask that question.....you promted me to read more and get a deeper explanation, and I should've known that!!

I wonder how many guys have tried that and wound up with 900 vdc?? B+
I'll be using the series diode method as pictured...thanks for straightening that out for me.
I hope someone else reads this before they make that mistake!!

[SILVERGUN]

And thank you ,drgonzonm, for bringing up the CT issue......priceless.....whew, that was a close one

And for anyone who is curious, go here:
http://www.valvewizard.co.uk/bridge.html

[Willabe]

Rome wasn't built in a day. Lot to learn in life.

Your doing fine. You ever see some of the dumb stuff I post here?     

         
                  Brad     

[PRR]

> I wonder how many guys have tried that and wound up with 900 vdc??

 

BTW: your little GIF _is_ little.... I bet you uploaded a thumbnail instead of the full-size.

[bigugly]

P/T will be Hammond 290fx---640 VCT

If you use the bridge do not ground the neg(-) terminal. Just put a bit of shrink wrap on it or cut it off and epoxy over the stub. Then you can ground the CT as normally done and all will be okay. Also, you can put a UF4007 in series immediately after the bridge and before the first reservoir cap to get the benefits of reduced switching noise. (see page 29 of Merlin's wonderful book on PSU design)

[SILVERGUN]

P/T will be Hammond 290fx---640 VCT

If you use the bridge do not ground the neg(-) terminal. Just put a bit of shrink wrap on it or cut it off and epoxy over the stub. Then you can ground the CT as normally done and all will be okay. Also, you can put a UF4007 in series immediately after the bridge and before the first reservoir cap to get the benefits of reduced switching noise. (see page 29 of Merlin's wonderful book on PSU design)

I assume that would reduce the power handling rating of my bridge by 50% because I would only be going through 2 of the 4 diodes at that point?

Just for the record, I talked to one of my techs here and he gave me one of these to use ....they're not cheap, but man does it fill my need for overkill
(dual independant fast recovery rectifier--- 1000 volt, 60 amp, 35ns trr):

[HotBluePlates]

I assume that would reduce the power handling rating of my bridge by 50% because I would only be going through 2 of the 4 diodes at that point?

Fortunately, no. Each diode within the package is rated for the voltage and current of the total package.

Terminology check: The gif you posted before of a power supply shows a full-wave rectifier, with 2 legs of 3 diodes each (the 3 diodes arrangement is only to get the needed voltage rating for the series set of diodes). Your integrated rectifier is a full-wave bridge rectifier, and uses 4 diodes.

However, in the full-wave bridge, the arrangement of diodes and secondary winding taps is such that at any instant, only 2 of the 4 diodes are conducting. The other 2 are in a cut-off condition. When the polarity of the secondary voltage reverses as the primary a.c. voltage transitions from positive to negative (and vice versa), the original 2 diodes of the bridge go into cutoff, and the previously cut off diodes begin conducting.

The arrangement is such that the output d.c. voltage maintains the same polarity regardless of the polarity of the secondary voltage.

Such bridge packages usually have a ~ to mark the two terminals to which you attach the PT secondary a.c. Then, you'll note a terminal with a + and a terminal with a -. If you have a center-tapped secondary, use the ~ terminals, and connect the + terminal to the positive of your first filter cap. Don't use the - terminal of the bridge package, and connect the secondary CT to ground (meaning the first filter cap's - terminal). You are now using your bridge package in a full-wave non-bridge rectifier configuration.

Yeah, I just made up the term "full-wave non-bridge" but you get the idea.

[SILVERGUN]

Thanks HBP,
Yeah, I had figured it out after I posted and thought (and read) about it a little more....I just figured I'd leave the post up and learn from it...I'm not too proud to be wrong.....just a little embarassed
I wound up going with the dual independant diode pictured (above), because of it's faster TRR, and the mounting worked perfectly where I wanted it.
I'm trying to start my build with a bullet proof power supply, and that thing qualifies.

Thanks again for taking the time to straighten me out...I've been so wrapped up with gathering parts and finalizing my layout, I kinda opened my mouth before I thought it through

And just to be sure, here's my understanding:

[HotBluePlates]

What you have there is correct.

[HotBluePlates]

HBP,

If I am reading your post correctly, by not grounding, the "Ground" Lug, on the bridge full wave rectifier, aren't you in effect only using two diodes ... ? 

Yes, because Silvergun's example circuit has a center-tapped secondary; if we used the bridge configuration and didn't ground the CT, the output voltage from the rectifier would be double what it was with the original full-wave arrangement. Therefore, since he likes the idea of the integrated package, I'm suggesting a way to use a bridge package in a full-wave non-bridge setting.

...  If I use 4 1N007 diodes rated at 1000 volts and 3.5 amps, in a full wave rectifier (on a non CT secondary), isn't my rectifier only rated at 1000 volts and 3.5 amps? ...

If you mean full-wave bridge, then yes. I suppose you could make the argument that it could be rated 2kV, 3.5A because on each end of the continuous secondary winding there's a diode conducting at any instant. NOTE: Of the 4 diodes in a bridge, 2 are conducting at any moment. Confirm for yourself by marking one end of the secondary + and the other -, then figuring out what diodes are forward-biased at that moment (hint: there will be 2 of them). Switch polarity markings and repeat (hint: the other two will now be forward-biased).

...  If I use the same diodes on a CT secondary, with two series on each hot leg, isn't my rectifier now rated about 2000 volts and 3.5 amps? 

Yes, because there are 2 diodes in series on each leg, so voltage rated is the sum of the individual ratings and current rating remains the same.

But this is moving afield from Silvergun's question, because he can't move the 2 unused diodes to be in series with the 2 he will be using if he uses a bridge package in a full-wave rectifier with a center-tapped secondary.

[bigugly]

HBP, our thinking is not very different, as you and I agree there are two unused diodes in the bridge when using a center tap xfrmer.  I am not sure of the reasoning behind rating a bridge full wave at double the diode voltage rating.   

Even with a package bridge, I would consider using caps in series with the diodes, similar to the approach taken with a soundcity 120.  Those industrial diodes may be "noisy" when switching. 

put a UF4007 in series after the bridge and all those "noises" go away. The switching noise is now set by the characteristics UF4007.

[SILVERGUN]

Thanks Big, I'm taking notes all the way here...

[SILVERGUN]

Just for the record, I talked to one of my techs here and he gave me one of these to use ....they're not cheap, but man does it fill my need for overkill
(dual independant fast recovery rectifier--- 1000 volt, 60 amp, 35ns trr):

UPDATE 10/20
Hooked up dual independant diode and it worked for about a minute until one of the diodes shorted and popped the fuse in my amp...
I was just testing the power supply and that thing did not like having the "output" side jumpered together....Ht going in was 340 vac and for that one minute I had 320 vdc coming out,,,BUT, upon further review (I took a sledge hammer to it to see how it was made), it would appear as though the "independant " paths inside of this thing are just too close and not well insulated,,,,still not sure why it shorted, but I don't care....that's what I get for attempting to "invent " a use for something.......
I'll be stringing up some 1N4007s today, and do it the "old fashioned way"

[HotBluePlates]

Hooked up dual independant diode and it worked for about a minute until one of the diodes shorted and popped the fuse in my amp...
I was just testing the power supply and that thing did not like having the "output" side jumpered together. ... upon further review (I took a sledge hammer to it to see how it was made), it would appear as though the "independant " paths inside of this thing are just too close and not well insulated,,,,

I don't understand what you're saying.

You say, "dual independant diode" which makes me think you're using 1N4007's and placing them in series, but then you say, "... (I took a sledge hammer to it to see how it was made), it would appear as though the "independant " paths inside of this thing are just too close..." That sound like the integrated bridge package.

If it is a bridge package, you shouldn't be "jumpering" anything. If you're trying to hook up 2 of them, you're leaving out detail.

If you used the 1000v bridge package you mentioned before, there should be no way to kill it with 340vac input.

So, I'm thinking you're not telling us everything... 

[Willabe]

So, I'm thinking you're not telling us everything... 

Or he wired it up wrong?

Maybe grounded the CT and the rect. bridge?


               Brad     

[SILVERGUN]

Hey guys....
I used the integrated dual independant diode listed above...and see here:
http://www.newark.com/jsp/search/productdetail.jsp?SKU=96K8783
This is not a bridge assy. ,,,just two diodes side by side in a housing...
spec sheet here: http://www.farnell.com/datasheets/34674.pdf

I had the two 340 VAC secondary leads from the PT wired to the anode sides, and the cathode sides jumpered together with no further connections made, and it was popping the fuse....CT of PT is grounded and diode assy. has no ground point
At first there was 320 VDC there but it wasn't long until it popped the fuse....I checked each diode and one of them was shorted
I didn't wire anything wrong and it was the second one to do it to me (I though the first one was a fluke, so I bought another )

There is NO WAY that I did anything wrong

I then proceeded to cut a small section of board material and string up some 1N4007s and everything is now fine.....argh

[Willabe]

Man, that's a hard one. $24 a piece x2?     


            Brad       

[SILVERGUN]

Oh yeah...and get this!!!
Since this pissed me off pretty good today I wired up one of those FWB assy on my bench just to see it work and this was the result,,,, with the PT CT grounded and both legs of 340 vac tied to the AC tabs, no connection to the DC negative tab, I was reading 655 VDC from the positive terminal on the FWB to the PT CT  

[Willabe]

Somethings not right.    

340vac x 1.4=476vdc no load not including the 2 diode voltage drops. And your getting 665vdc?

You do have to have at least 1 filter cap (B+ to ground, 20uF or so would be fine) to get a stable measurement. It has to have something to work against.

            Brad      

[SILVERGUN]

No cap connection...just straight voltage reading...stable as could be....try it....I couldn't believe my eyes

Just when I thought I was getting smarter  

[Willabe]

So you added a filter cap to the B+ output?

What do you get for a B+ dcv reading now?

IIRC, if you don't have a filter cap hooked up the B+ can float up to the full secondary acv x 2. So 340acv + 340acv = 680acv. That does not include the PT's regulation losses. At least >10% is to be expected and can be more, but that's with a load.

What size filter cap did you put in? A larger cap up to a point will hold up a larger dcv.

So 10% of 680 is 68. So 680 - 68 = 612, but your PT is not loaded so 655 doesn't sound wrong to me.

Wait and see if someone else confirms my thinking on this.
 

                Brad        
                

[SILVERGUN]

So you added a filter cap to the B+ output?

Nope, I wasn't going to use it in the amp, just experimenting....once I saw 655 vdc there, i shut it down...
I imagine that if I added a cap to the mix we would get your X 1.4 equation and wind up with 917 vdc B+

[Willabe]

No, no, no. Stop imagining, do the test.

1.4 x only 1 side of the PT. So 340 x 1.4.

Put a cap on the B+ and see what happens. Clip your meater on it to read the B+dcv and if it starts to climb past the filter caps voltage raiting, shut the amp down so you don't blow up the cap.


                Brad    

[SILVERGUN]

1.4 x only 1 side of the PT.

 

[Willabe]

When you have a PT with CT, whether your using a rect. tube or SS diodes, you only use 1 side of the PT's secondary to do the math.

Why, because with a full wave half bridge, which is what we're talking about, your only using 1 side of the PTs primary secondary at a time. We don't get the benefit of adding up both sides of the PT's secondary together, only 1 side of the secondary is supporting the rect. at a time.

A full wave full bridge uses both sides of the PT at the same time.

PRR, HBP, or a number of our friends can clarify this where I'm wrong.

 
                Brad      

[Willabe]

SG, sorry for the confusion last night. Sometimes I have no idea what I'm thinking   

Have you seen this from Merlins site? These might help clear things up.

http://www.valvewizard.co.uk/fullwave.html

http://www.valvewizard.co.uk/bridge.html

(I think I need to go golfing too.      )
              

                           Brad        

[HotBluePlates]

Oh yeah...and get this!!!
Since this pissed me off pretty good today I wired up one of those FWB assy on my bench just to see it work and this was the result,,,, with the PT CT grounded and both legs of 340 vac tied to the AC tabs, no connection to the DC negative tab, I was reading 655 VDC from the positive terminal on the FWB to the PT CT  

Something's not right. We'd need a picture of your test setup to figure out what's going on.

I say that because "you can't get there from here" if you truly have what you're telling us. Therefore, I believe you have an error somewhere, but just aren't seeing it.

If you truly have the rectifier hooked up as your diagram shows, with a true 340-0-340v transformer, you could only have a peak output voltage of 340v*1.414 = 480v.

If you have no filter cap, you do not have a steady d.c., no matter what your meter says. Instead, you have an output pulsating from 0v to the full peak voltage of 480v, and your meter is averaging it to make sense of it.

If you're getting 600v+, that's impossible with a full-wave rectifier and 340-0-340v of input, which is what your diagram shows. So either your PT voltage has to be much greater, or you have to be operating the rectifier as a bridge.

But a bridge with 340-0-340v input really sees a total 680v input, and would output a peak of 680v*1.414 = 961v! Your meter might get confused by this pulsing from 0v to 961v, and might average it. Average voltage of an a.c. sine wave is ~0.637 * peak, or 612v in your case. RMS would be 0.7071 * peak, or 680v. Somewhere in-between gives the ~650v reading you're getting.

If you hooked a filter cap to the output of the rectifier, and *if* you have a 340-0-340v wired with a bridge, the diodes biased off would see 961v at the filter cap and another 961v peak from the transformer, totaling 1922v. The bridge will pop instantly and violently, since it's only rated for 1kV reverse-voltage.

Geezer, I think, has used these bridge packages in amps, set up for normal full-wave operation and with center-tapped PT secondaries (same as what you've been asking about). It worked out well for him, so there's no magic to it. I respectfully suggest that has to be an error that you're just not seeing yet.

[SILVERGUN]

Thanks HBP....I'm definitely gonna run a test on a smaller scale on Mon. at work....I have a little 12 VCT Radio Shack xfmr and I can hook it up the exact same way......I swear I'm not stupid .....I think
The hookup was exactly as pictured....I mounted the FWB assy. to a piece of wood and connected the PT secondary (340-0-340)
I put the 2- 340 vac legs on the AC tabs of the bridge....the CT was still grounded to the chassis of my amp, and I read 655 VDC from the + tab on the bridge to the CT (with no connection on the (-) tab of the bridge assy.).................
I wasn't high but I might have been tired...

Thanks for making me question myself....I'm trying to find answers and you guys are a huge help

I'll snap a pic of the meter setup during testing,,,,,unless I'm wrong, and then i'll try to act like this never happened

No offense ever taken,,,,I really appreciate you guys taking the time to teach us here

[SILVERGUN]

SG, sorry for the confusion last night.

No apology necessary.... I apreciate any help that any of you guys give.....I just wasn't quite understanding you , and I thought you didn't understand how I had it hooked up.....I WILL try it again tomorrow and report back

No caps, just ac in to ac tabs, no ground connection on FWB assy (-) terminal, and measure DC (+) tab with one meter lead while the other one is connected to the PT CT......maybe this time I'll get some sleep first

[SILVERGUN]

Alright HBP...the results are in....and now I'm really scratching my head

Transformer is 6.3-0-6.3 (radio shack 12.6 v CT)
Wall voltage is ~124 vac
AC out of xfmr measured leg to leg (yellow to yellow from xfmr)  is ~14.5 vac and is connected to AC tabs on FWB assy. (meter pictured on left)

 +DC output is ~6.8 vdc measured from the (+) tab to the xfmr CT (meter picture on right)
Nothing is connected to the (-) tab on the FWB

It just doesn't matchup with what I saw yesterday when I had "my" PT connected......maybe I really was just that tired

[sluckey]

A little more food for thought....

Don't change anything about your transformer/bridge wiring. Measure the voltage between transformer CT and bridge negative terminal and you will get -6.8vdc. Measure voltage between bridge positive and negative terminals and you will get 13.6vdc. All these dc voltages will increase with a filter cap placed between the positive terminal to CT and another placed between the negative terminal and CT. Increased unloaded voltages will be about +10, -10, and 20.

[phsyconoodler]

That result is right on with no filer cap connected.When you connect a filter cap to the B+ your voltage will come up abit.
  There is something wonky the way you did it with your PT for sure!

[SILVERGUN]

Thanks a lot guys....luckily I have got a good tech here who had some time today and we talked about peak vs. rms....I've never had to give this much thought before, and it can definitely be confusing, especially if you're not giving yourself enough time to digest the results....

One thing that I did figure out today, slightly off topic, is that because I bought a PT that has a much higher secondary mA rating than what I needed, the load of the circuit has little or no effect on my voltages.......I was told to expect a 10-15% drop in B+ under load , but it's just not happening that way because the transformer is not really even "feeling" the load

xfmr RATING is 120 vac primary } 640 vac CT sec. (518mA) = 320-0-320
BUT, actual input volt. is ~124 vac } sec. reading = ~340-0-340 (unloaded)
 320vdc after rectification (with stby. switch interupting DC to cap)
 ~480vdc B+ after filtering

I was EXPECTING 320vac x 1.4 = 448 vdc after rect. and filter......and then 10% dropped under load to get me to desired B+ of around 410vdc

,,, and now I'm shopping for a PT with lower secondary

[SILVERGUN]

Thanks drgonzonm.....yeah, that would be perfect because my heater tap is high also...
I hooked up a variac to the input yesterday and took the input volt. down to 105vac and it calmed the amp down plus put my heaters right where they should be...
The result was that by dropping down the input by 20vac it lowered my B+ by almost 80vdc and brought my heaters down from 6.8vac to 6.1
I really don't want to use the zener method, and I'll have to look at sluckey's post......I don't know why i didn't think of that step transformer , BUT THANK YOU

[SILVERGUN]

Thanks again brother drgonzonm......I'm in!!
I will be trying this in the near future and will report back......so simple, I love it