Forums

SMPS Topologies

Started by Cursitor Doom July 3, 2017
Gentlemen,

What's the exact technical term for the switcher topology where you only 
have one large toroidal (typically) transformer right at the mains entry 
point which takes line AC and outputs it at a lower voltage level 
whereupon it's fed into the bridge rectifier and thence into a large 
storage cap whereupon it can be chopped up, regulated and finally 
filtered, there being no other transformers involved?

thanks.
Cursitor Doom wrote:

> Gentlemen, > > What's the exact technical term for the switcher topology where you only > have one large toroidal (typically) transformer right at the mains entry > point which takes line AC and outputs it at a lower voltage level > whereupon it's fed into the bridge rectifier and thence into a large > storage cap whereupon it can be chopped up, regulated and finally > filtered, there being no other transformers involved? > > thanks.
Hmm, not sure there is an exact name for this. Sounds like an offline 60Hz transformer/rectifier/capacitor-input filter, and then a buck regulator. The regulator would have an inductor in it. Jon
On Monday, July 3, 2017 at 1:26:34 PM UTC-4, Cursitor Doom wrote:
> Gentlemen, > > What's the exact technical term for the switcher topology where you only > have one large toroidal (typically) transformer right at the mains entry > point which takes line AC and outputs it at a lower voltage level > whereupon it's fed into the bridge rectifier and thence into a large > storage cap whereupon it can be chopped up, regulated and finally > filtered, there being no other transformers involved? > > thanks.
The new way to do this is with a small transformer running in the multi-hundreds of kHz and even into the Mhz region. The toroidal 60Hz transformers are Big, Heavy, and expensive.
On Mon, 03 Jul 2017 11:56:12 -0700, Yzordderrex wrote:

> The new way to do this is with a small transformer running in the > multi-hundreds of kHz and even into the Mhz region. The toroidal 60Hz > transformers are Big, Heavy, and expensive.
True, but they're also the quietest option when you can't afford the least itty bit of noise riding on the output - and this is in a high-end signal generator where purity is a major criterion.
On 07/03/2017 01:22 PM, Cursitor Doom wrote:
> Gentlemen, > > What's the exact technical term for the switcher topology where you only > have one large toroidal (typically) transformer right at the mains entry > point which takes line AC and outputs it at a lower voltage level > whereupon it's fed into the bridge rectifier and thence into a large > storage cap whereupon it can be chopped up, regulated and finally > filtered, there being no other transformers involved? > > thanks. >
an antique switcher topology
On 2017-07-03 10:22, Cursitor Doom wrote:
> Gentlemen, > > What's the exact technical term for the switcher topology where you only > have one large toroidal (typically) transformer right at the mains entry > point which takes line AC and outputs it at a lower voltage level > whereupon it's fed into the bridge rectifier and thence into a large > storage cap whereupon it can be chopped up, regulated and finally > filtered, there being no other transformers involved? >
In Europe they were often called "ironless transformer" because they used a small ferrite transformer. IIRC often used to drive LV halogen lamps or lamp chains but that is probably a market of the past now that everything goes LED. -- Regards, Joerg http://www.analogconsultants.com/
On Mon, 3 Jul 2017 19:56:42 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>On Mon, 03 Jul 2017 11:56:12 -0700, Yzordderrex wrote: > >> The new way to do this is with a small transformer running in the >> multi-hundreds of kHz and even into the Mhz region. The toroidal 60Hz >> transformers are Big, Heavy, and expensive. > >True, but they're also the quietest option when you can't afford the >least itty bit of noise riding on the output - and this is in a high-end >signal generator where purity is a major criterion.
I'm 'old school', most of my G-job SMPS's run at just over 20kHz ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website. Thinking outside the box... producing elegant solutions.
On 2017-07-03 13:37, Jim Thompson wrote:
> On Mon, 3 Jul 2017 19:56:42 -0000 (UTC), Cursitor Doom > <curd@notformail.com> wrote: > >> On Mon, 03 Jul 2017 11:56:12 -0700, Yzordderrex wrote: >> >>> The new way to do this is with a small transformer running in the >>> multi-hundreds of kHz and even into the Mhz region. The toroidal 60Hz >>> transformers are Big, Heavy, and expensive. >> >> True, but they're also the quietest option when you can't afford the >> least itty bit of noise riding on the output - and this is in a high-end >> signal generator where purity is a major criterion. > > I'm 'old school', most of my G-job SMPS's run at just over 20kHz ;-) >
That's nasty for animals. Mine mostly run north of 300kHz. Once when our Shepherd mix was still with us I had a SMPS prototype go into choking. I couldn't hear it but the scope showed it. She gave me "the look" and left the office with a sigh that I am sure she did on purpose. -- Regards, Joerg http://www.analogconsultants.com/
On Monday, July 3, 2017 at 1:00:37 PM UTC-7, Cursitor Doom wrote:
> On Mon, 03 Jul 2017 11:56:12 -0700, Yzordderrex wrote:
[about transformer/rectifier/filter/DC converter power supplies]
> > The new way to do this is with a small transformer running in the > > multi-hundreds of kHz and even into the Mhz region. The toroidal 60Hz > > transformers are Big, Heavy, and expensive.
> True, but they're also the quietest option when you can't afford the > least itty bit of noise riding on the output - and this is in a high-end > signal generator where purity is a major criterion.
There are some VERY quiet power supplies in the switchmode camp. 'least itty bit' isn't how the manufacturer describes 'em, though. Size and efficiency matter; a low-power supply can easily get LOTS of RF filtering from the big 60 Hz magnetics, and those are lossy at lower frequency, too. It's a 'free' broadband filter. A switchmode topology can be just as quiet, with similar bulk and expense, if filtering is designed into it. That filtering is the place to study, not the block-diagram.
Cursitor Doom wrote:

> On Mon, 03 Jul 2017 11:56:12 -0700, Yzordderrex wrote: > >> The new way to do this is with a small transformer running in the >> multi-hundreds of kHz and even into the Mhz region. The toroidal 60Hz >> transformers are Big, Heavy, and expensive. > > True, but they're also the quietest option when you can't afford the > least itty bit of noise riding on the output - and this is in a high-end > signal generator where purity is a major criterion.
In that case, if the power is low enough, skip all the switching crap, and use a linear regulator. If not, then serious shielding and filtering is required. This is some of the stuff that can keep you awake at night. Jon