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

Started by RobertMacy October 16, 2013
On 2013-10-20, John S <Sophi.2@invalid.org> wrote:

>>>> >>>> +--+-FET--+--|<------- >>>> | | >>>> === 3|| >>>> | 3|| >>>> | | >>>> +--+------+-----------
>> if you want to simulate this arrange the simulation to start with the >> switch closed. > > Do you have a simulation you can share with us?
lt-spice crashed before I coiuld save it. when I had it start with the switch open it'd put 15GV on the capacitor -- &#9858;&#9859; 100% natural --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On 10/20/2013 7:53 PM, George Herold wrote:
> On Sunday, October 20, 2013 9:05:15 AM UTC-4, John S wrote: >> On 10/19/2013 4:50 PM, Jasen Betts wrote: >> >>> On 2013-10-19, John S <Sophi.2@invalid.org> wrote: >> >>>> On 10/19/2013 2:26 AM, Jasen Betts wrote: >> >>>>> On 2013-10-17, RobertMacy <robert.a.macy@gmail.com> wrote: >> >>>>>> On Thu, 17 Oct 2013 06:01:01 -0700, George Herold <gherold@teachspin.com> >> >>>>> current buck-boost converter. >> >>>>> >> >>>>> +--+-FET--+--|<------- >>>>> | | >>>>> === 3|| >>>>> | 3|| >>>>> | | >>>>> +--+------+----------- >> >>>>> >> >>>>> the more time the switch (FET in the diagram) >> >>>>> spends off the larger the current output >> >>>>> >> >>>> >> >>>> I don't understand how you can get more current out of the inductor than >> >>>> it had when the switch opened. >> >>> >> >>> You can't, that's why decreasing the on-time increses the current. >> >>> >>> That capacitor on the left that looks like it's doing nothing >>>> is actually essential, you turn on the switch briefly and >> > the capacitor supplies the bulk of the current to wind the inductor up. >>> if you want to simulate this arrange the simulation to start with the >> >>> switch closed. >> > >> Do you have a simulation you can share with us? > I was going to say it looked a bit like what I drew for a current boost. But I had the diode and inductor switched around. > > +----+--FET--+-LLL--+ > | | | | > ^ C _ R > I C ^ R > | | | | > +----+-------+------+ > > Something like that, > > George H.
Thanks, George. It believe this is a standard buck switcher without the output filter capacitor.
On 10/21/2013 1:08 AM, Jasen Betts wrote:
> On 2013-10-20, John S <Sophi.2@invalid.org> wrote: > >>>>> >>>>> +--+-FET--+--|<------- >>>>> | | >>>>> === 3|| >>>>> | 3|| >>>>> | | >>>>> +--+------+----------- > >>> if you want to simulate this arrange the simulation to start with the >>> switch closed. >> >> Do you have a simulation you can share with us? > > lt-spice crashed before I coiuld save it. > > when I had it start with the switch open it'd put 15GV on the > capacitor >
No matter what you do, you will never get more current out of the circuit than the amount of peak current in the inductor at the moment your FET switch opens.
On 10/21/2013 1:08 AM, Jasen Betts wrote:
> On 2013-10-20, John S <Sophi.2@invalid.org> wrote: > >>>>> >>>>> +--+-FET--+--|<------- >>>>> | | >>>>> === 3|| >>>>> | 3|| >>>>> | | >>>>> +--+------+----------- > >>> if you want to simulate this arrange the simulation to start with the >>> switch closed. >> >> Do you have a simulation you can share with us? > > lt-spice crashed before I coiuld save it. > > when I had it start with the switch open it'd put 15GV on the > capacitor >
That's probably because your input is a current source and you waited too long to close the switch.
On 21 Oct 2013 06:08:47 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

>On 2013-10-20, John S <Sophi.2@invalid.org> wrote: > >>>>> >>>>> +--+-FET--+--|<------- >>>>> | | >>>>> === 3|| >>>>> | 3|| >>>>> | | >>>>> +--+------+----------- > >>> if you want to simulate this arrange the simulation to start with the >>> switch closed. >> >> Do you have a simulation you can share with us? > > lt-spice crashed before I coiuld save it. > > when I had it start with the switch open it'd put 15GV on the > capacitor
Bwahahahahahaha >:-} ...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.
krw@attt.bizz wrote:
> On Sun, 20 Oct 2013 12:51:26 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> krw@attt.bizz wrote: >>> On Sun, 20 Oct 2013 09:33:54 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> krw@attt.bizz wrote: >>>>> On Sun, 20 Oct 2013 07:21:15 -0700, Joerg <invalid@invalid.invalid> >>>>> wrote: >>>>> >>>>>> krw@attt.bizz wrote: >>>>>>> On Sat, 19 Oct 2013 16:36:45 -0700, Joerg <invalid@invalid.invalid> >>>>>>> wrote: >>>>>>>
[...]
>> Oops, I probably mixed you up with someone else. I thought it was stage >> electronics for rock bands and stuff. > > That was the last job. ;-) I've done a few career changes in the > last 10 years. Before that, one employer, oneish (perhaps two) > markets, but very different jobs every five to eight years. >
5-8 years would be a bit much for me.
>>>> I work for numerous clients who are all in very different >>>> markets. This keeps our jobs interesting. But after talking to >>>> automotive designers I'd be bored stiff if I had to do their job for >>>> more than a year. >>> Perhaps but I think you have a pretty small view of that world. >> >> Nope. Medical devices for hospitals, low cost medical devices for >> consumers (over-the-counter), aircraft electronics, spacecraft stuff, >> chemical pump controllers, power generation, oil/gas exploration >> electronics, NDT, commercial automotive (trucks), and so on. > > You have a very small view of the automotive market. That is for > sure. >
I see it from two view points. One is the actual product and that often doesn't look very good, both from a quality point of view and sometimes also from an engineering point of view (flickering LED backlights anyone?). Then from a people perspective and here talking to folks who actually work in that field helps. Pretty much all of them reported extreme pressure to keep NRE and R&D schedules down, which explains a lot of the quality issues. To the point I wouldn't want to work there. As a consultant maybe but niot if they'd demansd unrealistic timelines like they often do from their employees. There are automotive electronics that work quite well, mostly in Japanese cars. In the end it boils down to the reliability ratings of the various entities in the know.
>>> However, I've been involved in many different markets at many >>> different levels, over the years. It's a *big* field. There is no >>> reason to do the same thing for forty years. Impossible, actually. >>> >> Not impossible. I met people who worked in one particular field such as >> engine control units for over 30 years. I'd have a hard time doing that, >> after being a consultant for this long. > > ECUs have changed more than a little in 30 years. They will change > drastically, again, over the next ten. ...
Sure, incremental change. Same in medical ultrasound which is my home turf. But ... after we built a flagship product in the late 80's and the satellite R&D location was closed afterwards I wasn't too unhappy that I could jump into consulting for the first time, and do something else.
> ... Hell, you'd have a hard time > showing up for work with your pants on, after being a consultant that > long. ;-)
As a consultant I get to wear shorts all summer long. When a web conference with bigshots is coming up I have a "dress shirt on duty" hanging in the lab closet :-) -- Regards, Joerg http://www.analogconsultants.com/
On Monday, October 21, 2013 8:57:43 AM UTC-4, John S wrote:
> On 10/20/2013 7:53 PM, George Herold wrote: > > > On Sunday, October 20, 2013 9:05:15 AM UTC-4, John S wrote: > > >> On 10/19/2013 4:50 PM, Jasen Betts wrote: >
<snip>
> > I was going to say it looked a bit like what I drew for a current boost. But I had the diode and inductor switched around. > > > > > > +----+--FET--+-LLL--+ > > | | | | > > ^ C _ R > > I C ^ R > > | | | | > > +----+-------+------+ > > > > > > Something like that, > > > > > > George H. > > > > Thanks, George. It believe this is a standard buck switcher without the > > output filter capacitor.
Hi John, Here's the current to current buck that I drew... from upstream https://www.dropbox.com/s/h2a8dyz0vzoovev/DSCF0031.JPG I guess I could try simulating these, if I ever get 'free' time. George H.
On 10/17/2013 9:58 AM, RobertMacy wrote:
> On Wed, 16 Oct 2013 09:43:03 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote: > >>> ...snip... >> >> So SMPS SHUNT regulator ?:-} >> >> ...Jim Thompson > > > Alas, the compliance current is around 50mA with a compliance voltage as > high as 1kV, which is destructive. A 'straight' shunt regulator either > shorts out the incoming 50 mA or let's it pass thru, but in this case I > sometimes need 800mA at a small 5Vdc. So, need some 'multiplication' of > the current - a capacitor. There is sufficient power if the system > operates with the compliance at around 80V at 50mA just have to somehow > convert that to 5Vdc at 800mA. But, in this case it will be super > necessary to monitor compliance voltage so it won't EVER go above 100V > in order to NOT kill parts. In this supply that protection circuit, or > 'voltage limit', is the corollary of the standard 'current limit' in a > voltage supply! > > So far it appears a variation of George Herold's approach may get me > there. the current charges a cap, which then supplies large amount of > power. Aain, corollary, using cap instead of inductor for the energy > storage/conversion.
Hi, Robert - The thread has grown more to than I can re-read to capture all your requirements. However, here are my thoughts... Max allowed input voltage: 100V Input current capability: 50mA Output voltage required: 5V Output current required: .8A Rather than thinking about this as a current-to-current topology, think about how much power you can put into the topology within your constraints. You can't get more power out than your input capability and limits. But, you know that. A normal buck switching topology will provide all this. One thing to note is that you cannot get more than 5W out if your max input voltage is limited to 100V and your (constant) current is .05A. So, you can forget the 10W requirement because of your 100V limit. It seems to me that, using the standard buck topology, you will need to adjust your control loop (and thinking) as follows: -Never let the input voltage get above 100V. As it approaches that limit, increase the duty cycle. This is equivalent to current limit. After all, if you are able to reduce the voltage while the current remains the same, input and output power is reduced. Note that this requires some kind of load just as in a current transformer. -If the load is reduced, the voltage will tend to rise. Increase the duty cycle even more to hold the voltage. By increasing the duty cycle to a much higher value, you will cause the input voltage to plummet which will reduce the available input power. What is your maximum load resistance? -If it can be open or very high, then you need to provide another device at the input, perhaps a depletion FET capabale of about 100mA at a few hundred volts to stop things when the duty cycle is commanded to be at 100% or a bit less. Just some thoughts. I apologize if I have stepped on any toes.
On 10/21/2013 9:53 AM, George Herold wrote:
> On Monday, October 21, 2013 8:57:43 AM UTC-4, John S wrote: >> On 10/20/2013 7:53 PM, George Herold wrote: >> >>> On Sunday, October 20, 2013 9:05:15 AM UTC-4, John S wrote: >> >>>> On 10/19/2013 4:50 PM, Jasen Betts wrote: >> > <snip> > >>> I was going to say it looked a bit like what I drew for a current boost. But I had the diode and inductor switched around. >> >>> >> >>> +----+--FET--+-LLL--+ >>> | | | | >>> ^ C _ R >>> I C ^ R >>> | | | | >>> +----+-------+------+ >> >>> >> >>> Something like that, >> >>> >> >>> George H. >> >> >> >> Thanks, George. It believe this is a standard buck switcher without the >> >> output filter capacitor. > > Hi John, Here's the current to current buck that I drew... from upstream > https://www.dropbox.com/s/h2a8dyz0vzoovev/DSCF0031.JPG > I guess I could try simulating these, if I ever get 'free' time. > > George H.
Yes, thank you, George. I saw it. But your image and your ASCII drawing above do not agree. Your ASCII drawing is a standard buck without an output filter capacitor. I agree with your ASCII (with, possibly, the requirement for an output filter capacitor) for a scheme which could work.
On Mon, 21 Oct 2013 08:00:04 -0700, John S <Sophi.2@invalid.org> wrote:

>> ...snip.... > > Hi, Robert - > > The thread has grown more to than I can re-read to capture all your > requirements. However, here are my thoughts... > > Max allowed input voltage: 100V > Input current capability: 50mA > Output voltage required: 5V > Output current required: .8A >....snip...loss of extra thoughts due to using AIOE that won't let me > quote more than ?? number of lines... >-If it can be open or very high, then you need to provide another device > at the input, perhaps a depletion FET capabale of about 100mA at a few > hundred volts to stop things when the duty cycle is commanded to be at > 100% or a bit less. > > Just some thoughts. I apologize if I have stepped on any toes.
You've got the gist of the problem. I made up some of the numbers and didn't notice they didn't quite correlate. But you see the premise for the problem. To maintain some semblance of efficiency, I can't simply 'shunt' unused power off.