voltage tripler/relay/voltage regulator help...

[HTH]

The attached voltage doubler circuit was something Steven O'Connor posted a while back and I've saved it for reference.

I'm using the 5vac CT rectifier winding on a Hammond 370HX PT and want a voltage tripler circuit but none of the circuits I can find use a centre-tapped PT.

I'm wanting to use the voltage tripler to get 15vac, then rectify it to DC to feed a 12vdc voltage regulator for the relays.

Anyone got a link/schematic for an appropriate tripler circuit using a CT PT like in the circuit attached? Or, can anyone rejig the doubler circuit attached to provide 3x the input voltage?

Cheers

[loudthud]

Did you see this?

http://music-electronics-forum.com/s...age+multiplier

It's a basic circuit. You don't need as many stages. You don't get very good voltage regulation so you might need to run four stages to get around 25V and regulate down to 12V depending on how much current you need to supply. Build an air-wire prototype first to find a cap value that works. You might need 1000uF.

[HTH]

Did you see this?

http://music-electronics-forum.com/s...age+multiplier

It's a basic circuit. You don't need as many stages. You don't get very good voltage regulation so you might need to run four stages to get around 25V and regulate down to 12V depending on how much current you need to supply. Build an air-wire prototype first to find a cap value that works. You might need 1000uF.

yep, but I'm not sure how that would work in my application - I'm using a CT winding.

If I leave the CT unused (taped up/isolated) and run the -'ve and +'ve sections of that octupler circuit into a bridge rectifier (grounding the bottom of the bridge) I think that'd work ok ????

[HTH]

how about this?

[loudthud]

That circuit may actually work but you don't need the bridge. (you do need a single diode to the last cap) It only adds and extra diode drop and only two of the diodes ever conduct. Just ground the bottom side of the transformer. The ground side of the cap at the input to the regulator should go to the + side of the cap that's grounded but it will work as drawn.

[HTH]

That circuit may actually work but you don't need the bridge. (you do need a single diode to the last cap) It only adds and extra diode drop and only two of the diodes ever conduct. Just ground the bottom side of the transformer. The ground side of the cap at the input to the regulator should go to the + side of the cap that's grounded but it will work as drawn.

I must be missing something here - if I don't have the bridge, the voltage tripler will just triple the 5vac to 15vac. the bridge is to get it rectified to dc (unless the tripler does this too ???)

[defaced]

The voltage multiplier rectifies the AC into DC. From the stuff I've read it's like a half wave rectifier. For each multiplier, you lose that much ability to supply current. Multiply voltage buy three, the current sourcing ability drops to 1/3 of the original.

Because relays have very large operation tolerances, I'd just use a full wave bridge for your relay supply and cap off the CT of your transformer. That'll give you 10v AC which with the bridge will give you ~14v DC which is 12v + 16% tolerance. With sag from the power supply, you should be good. If you have to, add a series resistor to knock the voltage down just a hair. The regulator is overkill because of the huge tolerance of the relay.

[HTH]

The voltage multiplier rectifies the AC into DC. From the stuff I've read it's like a half wave rectifier. For each multiplier, you lose that much ability to supply current. Multiply voltage buy three, the current sourcing ability drops to 1/3 of the original.

Because relays have very large operation tolerances, I'd just use a full wave bridge for your relay supply and cap off the CT of your transformer. That'll give you 10v AC which with the bridge will give you ~14v DC which is 12v + 16% tolerance. With sag from the power supply, you should be good. If you have to, add a series resistor to knock the voltage down just a hair. The regulator is overkill because of the huge tolerance of the relay.

this whole amp is overkill, over-engineered to the max. it's a SE EL34 amp and the PT can handle 200mA while the OT can handle 100mA. the bass is solid as any PP amp I've ever had with all the articulation you could ever want.

I'm all for simplicity, I'll just try a bridge rectifer right off the 5v winding and see how that works out. Not sure of the current requirements of the relay, but the 5v winding is rated for 3A which is much more than I'd expect a relay to need.

The voltage regulator is just for kicks as I have one here and have never used one - I always like to try something new to push the personal envelope on each amp build otherwise you're not learning anything new.

[defaced]

Unless you've got a big honkin relay in there, I wouldn't expect for it to need more than a 100ma.

[HTH]

ok, this is wierd. taped up the yellow/black CT for the 5v winding and used the two yellow wires from the 5v winding to feed a bridge rectifier.

I'm getting 5.98vac across the 5v winding which is to be expected when it's an unloaded 3A winding. BUT, the rectified DC voltage out of the bridge is 64.75vdc - is this purely because it's unloaded?

[HTH]

ok, so I'm now getting expected results with a 22uF cap to ground (and a 220k bleeder resistor across it) at the output of the bridge ...

* 5.85vac into the bridge
* 7.1dvc at 'output' of bridge

once the losses across the diodes are taken into consideration, thats about right. 7.1vdc isn't gonna be enough to energise a 12v relay, is it?

[defaced]

Not likely, you're in 5v relay territory now. Is this a 5-0-5 winding or a 2.5-0-2.5 winding? If it's the former, then something is not wired right. If is the latter, then you're either going to be using a voltage multiplier and 12v relays or a bridge and 5v relays.

[HTH]

Not likely, you're in 5v relay territory now. Is this a 5-0-5 winding or a 2.5-0-2.5 winding? If it's the former, then something is not wired right. If is the latter, then you're either going to be using a voltage multiplier and 12v relays or a bridge and 5v relays.

it's a CT'd 5vac winding afaik, the PT is a Hammond 270HX - I'd expect it's 2.5-0-2.5

I get 5.85vac across the outside windings with the CT taped up, so it seems to be 2.5-0-2.5

5.85 x 1.4 = 8.19vdc, once the diode losses have been taken into account, 7.1vdc seems about right to me (and what I expected initially, hence the voltage doubler/tripler idea).

Since I'm getting 7.1vdc out of the straight diode bridge, a doubler should give me around 12v once the diode losses are taken into consideration. Gonna wire up a straight doubler and see what I get from that.

btw, do voltage regulators only regulate DOWN, i.e. if I feed it with 20v I'll get 12v out. but if I feed it 10v will I get 12v out?

[defaced]

Yes, regulators only regulate down. There is a window for the input voltage. Typically the window starts at 3v DC above the rating of the regulator and stops well above the regulated voltage. For example, the first 7812 on mouser has an input voltage window from 14.5v to 27v.

When you wire up your regulator, check out the spec sheet for a recommended wiring. Usually there will be a big filer cap at the voltage input, and a smaller cap (0.1uF is what I've often seen) at the output. That small cap helps the regulator do it's job.

Sorry about the goose chase. When I read 5v CT winding, I was thinking 5-0-5, not 2.5-0-2.5, and Hammond omits these sorts of details on their website.

[HTH]

Yes, regulators only regulate down. There is a window for the input voltage. Typically the window starts at 3v DC above the rating of the regulator and stops well above the regulated voltage. For example, the first 7812 on mouser has an input voltage window from 14.5v to 27v.

When you wire up your regulator, check out the spec sheet for a recommended wiring. Usually there will be a big filer cap at the voltage input, and a smaller cap (0.1uF is what I've often seen) at the output. That small cap helps the regulator do it's job.

Sorry about the goose chase. When I read 5v CT winding, I was thinking 5-0-5, not 2.5-0-2.5, and Hammond omits these sorts of details on their website.

it's an L78S00 series regulator, data-sheet shows a 0.33uF cap on the input and a 0.1uF cap on the output. Max input voltage is 35vdc.

a 5v relay would've been MUCH easier, but I've got two 12v relays here doing nothing so might as well use them up rather than buy new parts.