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Need the topology for a current to current SMPS, not voltage to voltage SMPS

Started by RobertMacy October 16, 2013
Need a current to current SMPS, with greater than 95% efficiency. and NOT  
a transformer! because has to be variable.

The output will be a 'defined' current-time profile. Output Power is low,  
less than 5-10W delivered. Voltage compliance is low, less than 10 Vdc.  
I'm having difficulty wrapping my brain around potential topologies, need  
some help here.

Anybody ever do this, or have some URL's with topologies?

Problem hint: voltage to voltage means unused input power is OPEN, but  
current to current means unused power is SHORTED. See the difference?
On Wed, 16 Oct 2013 09:35:10 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>Need a current to current SMPS, with greater than 95% efficiency. and NOT >a transformer! because has to be variable. > >The output will be a 'defined' current-time profile. Output Power is low, >less than 5-10W delivered. Voltage compliance is low, less than 10 Vdc. >I'm having difficulty wrapping my brain around potential topologies, need >some help here. > >Anybody ever do this, or have some URL's with topologies? > >Problem hint: voltage to voltage means unused input power is OPEN, but >current to current means unused power is SHORTED. See the difference?
So SMPS SHUNT regulator ?:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Wed, 16 Oct 2013 09:35:10 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>Need a current to current SMPS, with greater than 95% efficiency. and NOT >a transformer! because has to be variable. > >The output will be a 'defined' current-time profile. Output Power is low, >less than 5-10W delivered. Voltage compliance is low, less than 10 Vdc. >I'm having difficulty wrapping my brain around potential topologies, need >some help here. > >Anybody ever do this, or have some URL's with topologies? > >Problem hint: voltage to voltage means unused input power is OPEN, but >current to current means unused power is SHORTED. See the difference?
--- So you want to pump, say, 0->1mA into an input with an impedance of zero ohms and output, say, 0->1A into a load from an infinite source impedance? What's your: 1. Supply voltage? 2. Input current range? 3. Output current range? 4. Load resistance range? 5. What do you mean by "Current-time profile? -- JF
On Wednesday, October 16, 2013 12:35:10 PM UTC-4, Robert Macy wrote:
> Need a current to current SMPS, with greater than 95% efficiency. and NOT=
=20
>=20 > a transformer! because has to be variable. >=20 >=20 >=20 > The output will be a 'defined' current-time profile. Output Power is low,=
=20
>=20 > less than 5-10W delivered. Voltage compliance is low, less than 10 Vdc. =
=20
>=20 > I'm having difficulty wrapping my brain around potential topologies, need=
=20
>=20 > some help here. >=20 >=20 >=20 > Anybody ever do this, or have some URL's with topologies? >=20 >=20 >=20 > Problem hint: voltage to voltage means unused input power is OPEN, but =
=20
>=20 > current to current means unused power is SHORTED. See the difference?
So you've got a current source driving it? =20 Do you need more current/ less current or both? =20 (I'm taking a smps on the web... which means I know enough to say something= stupid.) My first thought was to switch around the L and C and then chang= e shunt and series... so a shunt cap on the input side and a series L on th= e output. (I'd have to play with it some though...) George H.
RobertMacy wrote:
> Need a current to current SMPS, with greater than 95% efficiency. and > NOT a transformer! because has to be variable. > > The output will be a 'defined' current-time profile. Output Power is > low, less than 5-10W delivered. Voltage compliance is low, less than 10 > Vdc. I'm having difficulty wrapping my brain around potential > topologies, need some help here. > > Anybody ever do this, or have some URL's with topologies? > > Problem hint: voltage to voltage means unused input power is OPEN, but > current to current means unused power is SHORTED. See the difference?
You didn't give much data here. Assuming that measuring the load current is iffy (because it usually it) one could instead measure the waste current. This has to include the current used by the converter itself. You could have a sense resistor and run a sync buck into that, which except for this sense resistor would be a dead short situation. The ground of the converter would also connect to the top of that current sense resistor so it includes its own consumption. Now set the loop so it sinks away the portion of the input current you don't want to reach the output into ground. The load would hang on it's input and would see the balance of the current. Use a converter that will not go into foldback mode or goose it into regular mode, for example by fooling the voltage control (which is otherwise disabled). -- Regards, Joerg http://www.analogconsultants.com/
In the current domain, the conventional topologies (boost, buck, etc.) 
work just fine with capacitors.  Waveforms are an exercise for the student 
:)

I'm not so sure about isolation (flyback, forward), that might look like a 
signal coupled with two capacitors, one for power and one for ground 
return.

How ideal is the source it's attached to?  If it's got a honking big 
bypass cap, it's not very constant for SMPS purposes.  If it's got a 
massive inductor (or an open collector or something like that), chances 
are it's a pretty good current source.

Tim

-- 
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com

"RobertMacy" <robert.a.macy@gmail.com> wrote in message 
news:op.w4120wns2cx0wh@ajm...
> Need a current to current SMPS, with greater than 95% efficiency. and > NOT a transformer! because has to be variable. > > The output will be a 'defined' current-time profile. Output Power is > low, less than 5-10W delivered. Voltage compliance is low, less than 10 > Vdc. I'm having difficulty wrapping my brain around potential > topologies, need some help here. > > Anybody ever do this, or have some URL's with topologies? > > Problem hint: voltage to voltage means unused input power is OPEN, but > current to current means unused power is SHORTED. See the difference?
On Wed, 16 Oct 2013 09:35:10 -0700, RobertMacy wrote:

> Need a current to current SMPS, with greater than 95% efficiency. and > NOT a transformer! because has to be variable. > > The output will be a 'defined' current-time profile. Output Power is > low, > less than 5-10W delivered. Voltage compliance is low, less than 10 Vdc. > I'm having difficulty wrapping my brain around potential topologies, > need some help here. > > Anybody ever do this, or have some URL's with topologies? > > Problem hint: voltage to voltage means unused input power is OPEN, but > current to current means unused power is SHORTED. See the difference?
Bandwidth? Allowed current ripple? Must the load be ground-referenced, or can it float? Can it _include_ a transformer? Expected load reactance? If the bandwidth is well below the switching frequency, and the load is not strongly capacitive, then why not a 'plain old' voltage SMPS wrapped with a current loop? If you can float the load all the better -- sense the load current with a resistor to ground. If you can't float the load but you can have a transformer, then do something that's transformer isolated and sense the current with a resistor from ground to the output section's "ground". -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Wednesday, October 16, 2013 2:04:35 PM UTC-4, Tim Williams wrote:
> In the current domain, the conventional topologies (boost, buck, etc.) > > work just fine with capacitors. Waveforms are an exercise for the student > > :) >
I scribbled this at lunch... which I think works as a current buck. https://www.dropbox.com/s/h2a8dyz0vzoovev/DSCF0031.JPG (Fun question) George H.
> > > I'm not so sure about isolation (flyback, forward), that might look like a > > signal coupled with two capacitors, one for power and one for ground > > return. > > > > How ideal is the source it's attached to? If it's got a honking big > > bypass cap, it's not very constant for SMPS purposes. If it's got a > > massive inductor (or an open collector or something like that), chances > > are it's a pretty good current source. > > > > Tim > > > > -- > > Seven Transistor Labs > > Electrical Engineering Consultation > > Website: http://seventransistorlabs.com > > > > "RobertMacy" <robert.a.macy@gmail.com> wrote in message > > news:op.w4120wns2cx0wh@ajm... > > > Need a current to current SMPS, with greater than 95% efficiency. and > > > NOT a transformer! because has to be variable. > > > > > > The output will be a 'defined' current-time profile. Output Power is > > > low, less than 5-10W delivered. Voltage compliance is low, less than 10 > > > Vdc. I'm having difficulty wrapping my brain around potential > > > topologies, need some help here. > > > > > > Anybody ever do this, or have some URL's with topologies? > > > > > > Problem hint: voltage to voltage means unused input power is OPEN, but > > > current to current means unused power is SHORTED. See the difference?
On 10/16/2013 11:35 AM, RobertMacy wrote:

> Need a current to current SMPS, with greater than 95% efficiency. and > NOT a transformer! because has to be variable. > The output will be a 'defined' current-time profile. Output Power is > low, less than 5-10W delivered. Voltage compliance is low, less than 10 > Vdc. I'm having difficulty wrapping my brain around potential > topologies, need some help here.
Current output = some sort of flyback topology.
> Anybody ever do this, or have some URL's with topologies?
Done that. Stability of the control loop could be tricky.
> Problem hint: voltage to voltage means unused input power is OPEN, but > current to current means unused power is SHORTED. See the difference?
It could be actually simpler to take classic voltage controlled buck or boost as a base for design; and implement whatever current control loop around it using MCU. This would be easy to do using standard SMPS ICs. Vladimir Vassilevsky DSP and Mixed Signal Designs www.abvolt.com
On Wed, 16 Oct 2013 09:35:10 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>Need a current to current SMPS, with greater than 95% efficiency. and NOT >a transformer! because has to be variable. > >The output will be a 'defined' current-time profile. Output Power is low, >less than 5-10W delivered. Voltage compliance is low, less than 10 Vdc. >I'm having difficulty wrapping my brain around potential topologies, need >some help here. > >Anybody ever do this, or have some URL's with topologies? >
A synchronous buck running at fixed duty cycle is the electronic equivalent of a pair of gears, or an ideal autotransformer. Current out is current in times 1/n where n is duty cycle. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation