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

Thanks again for the images, surprisingly this time dropbox let me view them - usually doesn't.

IN: AC with source current maybe 30-50mA, compliance to 1kV OUT: approx 5Vdc, with variable current, adjusted with time envelope from

0.8A down to 50uA.

with source current that low, can't just feed it straight thru.

assuming NO losses... with input compliance at 80V and using all 50mA, supply the 5V at 0.8A You see why I first said current to current conversion?

After major floundering around [and rather embarrassingly] in front of all of you; I am starting to perceive the final topology as a multi-step: AC to DC at power required, then DC to DC at current required. But even 90% at each step yields a terrible 80% over all, so I was trying for a single step: AC to DC at current required.

I can always flip the diode to make it a positive supply. That does look like a 'single' step.

Tim's right about paying attention to the RFI/EMI kicking back into that source. Any parasitics and !!! It's going to be fun trying to filter out that 50V ON/OFF appearing across the MOSFET terminals let out into the world through that inductor at 1MHz.

I'm not quite understanding your requirement. You can send me details in private if you like. ...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.

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.

Thank you for your kind offer. I am being vague for two reasons:

1. purposely obfuscating the actual application/techniques under cloak of NDA.
2. inadvertantly floundering around, albeit embarrassingly, but in my defence, this is NEW territory here.

BTDT ;-) MANY of the projects I take on are new territory... that's what makes them fun. ...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.

Yes... and yes.

Commonly available with a photovoltaic gate "drive" as the smaller AC/DC SSRs. They switch in miliseconds.

You'll need an isolated gate driver for each switch, plus whatever coupling (optos?) and control (PWM something or other?) to make it go.

Obviously, substitute 9V and switch with whatever driver is suitable :)

Tim

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

milliseconds?! arrrgggg, need submicroseconds!

Thanks for the .gif

Your monitor could just be a 5W zener diode across the input (or a small zener + BJT).

What the heck source are you working with, if you can talk about it?

Whoa! Hey, a big word of caution Robert. I've not built a spms in my life . I'm taking this web course "Fundamentals of power electronics" by Robert Erickson. (Colorado U.) I've done two weeks of lectures and HW. So your question sparked the theoretical part of my brain. Which is great for me. But for a practical circuit, I'd feel a lot better if one of the smps guru 's signed off on it. Putting in your numbers, you're hoping for a current gain of ~16 at greater than 80% efficiency. The few curves I've looked at for voltage smps show that losses start to really bite into the efficiency with higher gains. So you'll need to put in some real numbers. (We've only started serious loss calculations this week.. so I'll know more after the weekend :^)* Maybe a combo of transformer followed by current smps would work?

Anyway good luck... and not to worry about floundering around on SED. That 's what's great about it. Throw out some crazy idea and see what sticks.

George H.

*Dr. Erickson seems to know his stuff. In this weeks lecture he was modeli ng switching losses and at one point paused and reminisced, (para phrasing) "We wasted several years with this model, because it lead u s to try and switch current and voltage separately in time and that just di dn't lead to any improvement in efficiency. Things are more complicated, b ut this model is a good starting point." I just love that sort talk. It s hows that everyone goes down dead ends.

the current charges a cap, which then supplies large amount of

As the president of a client said: If, immediately after accepting an assignment, you get a serious knot in your stomach it promises to be a really fulfilling kind of work. Or as John Wayne sad it, "Courage is being scared to death - and saddling up anyway".

--
Regards, Joerg 

http://www.analogconsultants.com/

1kV doesn't have to be destructive, they make FETs for well above that. AC presents a challenge but not an impossible one. Got to bridge-rectify that and your circuit must withstand a "brown-out" every 8.3msec.

--
Regards, Joerg 

http://www.analogconsultants.com/

That's what they invented flybacks for. Huge range, single step. But you need to employ a recuperating winding to get above your 90%. The magnetics design also promises to be "interesting".

If you need to go to 1kV compliance I would not operate at 1MHz.

--
Regards, Joerg 

http://www.analogconsultants.com/

But now, if it don't work right, Robert could claim "But George Harrold said it would!" :-)

I'm taking this web course "Fundamentals of power

Or get into a hot discussion about Obamacare :-)

--
Regards, Joerg 

http://www.analogconsultants.com/

Did he say 60Hz? I could imagine RF here.

The diodes only have to withstand the SMPS input voltage + one diode drop if the bridge rectifier output is clamped.

Well, that's the difficulty here, Robert can't divulge too much so all we can do is take potshots.

[...]

--
Regards, Joerg 

http://www.analogconsultants.com/

No, a simple shunt will NOT work. Remember, 50 mA will NOT provide the 800 mA. Only get that if the voltage coming in is allowed tor rise a bit.

Sorry, can't talk too much.

Doesn't matter about the 'source' of concepts, what matters is that you 'triggered' inside my brain an approach that almost in a single step does what I want. ....with a few changes.

grrrrr.

Actually, go ahead and try at 60Hz.