Secondary's C.T. tied to Totem Pole Caps???

[Tobacco Soup]

Hi Folks!

I was just curious as to why the center tap of the mains transformer secondaries are tied to the junction of the power supply's (totem pole config'd) first stage filter capacitors? Does this effectively create a voltage doubler arrangement? With the FWB rectification scheme, I would think that one could float the C.T. entirely. TIA!

Oh, here's some schematics that illustrate what I am talking about, they are all pdf's. The Orange schematics are the more simple ones (2nd & 3rd):


http://www.schematicheaven.com/marsh...100w_2203u.pdf

http://www.schematicheaven.com/newam...e_mkii1973.pdf

http://www.schematicheaven.com/newam...e_mkii1972.pdf

http://www.schematicheaven.com/newam...ek_mig100h.pdf

[Old Tele man]

...it's a voltage doubler circuit

[loudthud]

The circuits you linked are not voltage doublers. The center tap connection is just used to insure equal voltage across the two filter caps that are in series. It's the same configuration that you see in solid state power amps with bipolar supplies except that the minus supply is grounded.

[Old Tele man]

The circuits you linked are not voltage doublers. The center tap connection is just used to insure equal voltage across the two filter caps that are in series.

...I stand corrected, so it's just a "hard-wired" voltage balance point. Obviously, I didn't look hard enough at the schematic.

[Tobacco Soup]

The circuits you linked are not voltage doublers. The center tap connection is just used to insure equal voltage across the two filter caps that are in series. It's the same configuration that you see in solid state power amps with bipolar supplies except that the minus supply is grounded.

Thank you VERY much guys! If I may pry just a tad more about this connection:

Is it the 'balance' of the secondary windings that does this? I'm trying to visualize how this functions... TIA!

HAPPY NEW YEAR!

[Old Tele man]

...I did a little "homework" and textbook "researching" and it's actually a 'voltage-stacking' re-configuration of the normal "Dual Complementry" rectifier circuit (Linear Magnetics App Note):



...the re-configuration from "dual ħ voltages" to 'voltage-stacking' is accomplished by simply moving the "ground" from between the two capacitors (and xfmr center-tap) over to the 'negative-side' of the two stacked capacitors; however, the final 'stacked' voltage is same as from normal BRIDGE ckt, so it's not a voltage-doubler.

...and, the xfmr-winding acts as the voltage-balancer for the two caps (taking the place of the 220K voltage-balancing resisitors typically used on stacked capacitors).

[CarlZ]

Umm...that's still not the Marshall connection. What you've got is a pretty standard split load supply. The Marshall version still grounds the anode side of the rectifier allowing only a single positive supply. You get two advantages here. First, a "standard" center tap transformer can be used with a bridge rectifier without fouling things up and the second advantage is that, as loud thud already stated, you've got an equal voltage across both capacitors.

Cornell Dublier used to have a rather large white paper on their site explaining all the pros and cons of several different capacitor connection arrangements. Don't know if it's still up or not as the site as undergone a massive overhaul since I was there last.

-Carl

[Old Tele man]

...the pix is of a "dual complementary" circuit, not the "voltage-stack" arrangement, it's just to illustrate where & how the "stack" arrangement is derived from.

[CarlZ]

Ok, found the app note. Very informatie read!

http://www.cde.com/catalogs/AEappGUIDE.pdf

-Carl

[Earl]

I PSpiced the 1st link that Tobacco posted, and it's a doubler.....

[Old Tele man]

I PSpiced the 1st link that Tobacco posted, and it's a doubler.....

...but did that assume PT-voltage was 'end-to-end' or PT-voltage was 'end-to-centertap'?

[Earl]

OTM - I just used 2. 1V peak SIN sources in series, and CT'd the junction of the two.

I guess, in 'normal' terms, that would be a 0.7 - 0 - 0.7 VRMS output..?