Forums

150W current source, with a current-mode switcher

Started by Winfield Hill May 5, 2016
Here's something for y'all to knaw on, a 150W current-source SMPS, made with a
current-mode controller.  It has external monitoring and programming with
0-to-5V signals.

Most power supplies have low-Z voltage-source outputs, and when operated in
current-limit mode they simply servo the voltage to the achieve the desired
output current.  A true current source has a low effective output capacitance
and its output voltage can change rapidly to maintain a constant current into a
changing load.

Current-mode controllers have by their nature constant-current outputs, from the
buck inductor anyway, but this is morphed into a voltage source with a big
output capacitor and the controller's feedback.  So I figured, why not implement
one with a small capacitor and constant-current feedback?  This turned out to be
awkward with most controllers I considered, but NSC's (TI's) LM25117 was an
exception.  Among its many features is a fast current-monitor output using a
cycle-by-cycle S/H circuit, which was helpful and inspiring.

https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0

My project name is PWR-758.  My PCB layout uses mostly SMT parts, but I avoided
the temptation to place any parts on the bottom.  I got a bit carried away with
bells and whistles, like programmable compliance ranges, external meter,
external disable, etc., plus configuration modifications with a 10-mode
jumper-header, labeled A,B,C to I, extra connectors, etc.  I was forced to stop
adding features when I ran out of space on my size-A schematic drawing and my
4x4-inch PCB layout.  :-)

When operating in constant-current mode, one option uses the controller's S/H
circuit, and another option uses an LTC6102 output current-sense IC, which is
fast and has very low offset voltages.  The PWR-758 also has ordinary
voltage-source mode options.  Please take the compensation part values with a
grain of salt, because I have not yet properly evaluated them, nor made a
working copy of the circuit.  In fact, take the entire circuit with big grains
of salt!


-- 
 Thanks,
    - Win
Winfield Hill wrote...
> > Here's something for y'all to gnaw on, a 150W > current-source SMPS, made with a current-mode > controller. [snip] > >https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0 > > [snip ] Please take the compensation part values > with a grain of salt ... In fact, take the entire > circuit with big grains of salt!
But kindly give me some feedback. Also, your time will be well spent studying the LM25117 datasheet. http://www.ti.com/product/lm25117?keyMatch=LM25117 -- Thanks, - Win
On 5 May 2016 14:41:26 -0700, Winfield Hill <hill@rowland.harvard.edu>
wrote:

>Winfield Hill wrote... >> >> Here's something for y'all to gnaw on, a 150W >> current-source SMPS, made with a current-mode >> controller. [snip] >> >>https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0 >> >> [snip ] Please take the compensation part values >> with a grain of salt ... In fact, take the entire >> circuit with big grains of salt! > > But kindly give me some feedback. Also, your time > will be well spent studying the LM25117 datasheet. > http://www.ti.com/product/lm25117?keyMatch=LM25117
Lawdy, lawdy, there's even a PSpice model that's NOT encrypted >:-} ...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 | The touchstone of liberalism is intolerance
On 2016-05-05 11:12, Winfield Hill wrote:
> Here's something for y'all to knaw on, a 150W current-source SMPS, made with a > current-mode controller. It has external monitoring and programming with > 0-to-5V signals. > > Most power supplies have low-Z voltage-source outputs, and when operated in > current-limit mode they simply servo the voltage to the achieve the desired > output current. A true current source has a low effective output capacitance > and its output voltage can change rapidly to maintain a constant current into a > changing load. > > Current-mode controllers have by their nature constant-current outputs, from the > buck inductor anyway, but this is morphed into a voltage source with a big > output capacitor and the controller's feedback. So I figured, why not implement > one with a small capacitor and constant-current feedback? This turned out to be > awkward with most controllers I considered, but NSC's (TI's) LM25117 was an > exception. Among its many features is a fast current-monitor output using a > cycle-by-cycle S/H circuit, which was helpful and inspiring. > > https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0 > > My project name is PWR-758. My PCB layout uses mostly SMT parts, but I avoided > the temptation to place any parts on the bottom. I got a bit carried away with > bells and whistles, like programmable compliance ranges, external meter, > external disable, etc., plus configuration modifications with a 10-mode > jumper-header, labeled A,B,C to I, extra connectors, etc. I was forced to stop > adding features when I ran out of space on my size-A schematic drawing and my > 4x4-inch PCB layout. :-) > > When operating in constant-current mode, one option uses the controller's S/H > circuit, and another option uses an LTC6102 output current-sense IC, which is > fast and has very low offset voltages. The PWR-758 also has ordinary > voltage-source mode options. Please take the compensation part values with a > grain of salt, because I have not yet properly evaluated them, nor made a > working copy of the circuit. In fact, take the entire circuit with big grains > of salt! >
That's almost like an old-style Japanese schematic, every square inch is occupied. Just a quick comment: I'd add 0.1uF caps at input and output. Otherwise you might run into issues at the EMC test lab. Some high-current ferrite beads from Laird or another manufacturer can't hurt either. I just had a client design review where that was a problem (at the EMC lab). Why a 100ohms gate resistor for Q2? That sounds high. -- Regards, Joerg http://www.analogconsultants.com/
Joerg wrote...
> >On 2016-05-05 11:12, Winfield Hill wrote: >> >> https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0 > > That's almost like an old-style Japanese > schematic, every square inch is occupied. > > Just a quick comment: I'd add 0.1uF caps > at input and output.
I like that as well as adding inductance.
> Why a 100 ohms gate resistor for Q2?
Yes. The gate resistor is R15, 3.3 ohms. It's certainly an overly-crowded drawing. You comments on EMC testing are good. -- Thanks, - Win
Jim Thompson wrote...
> >On 5 May 2016 14:41:26 -0700, Winfield Hill <hill@rowland.harvard.edu> >wrote: > >>Winfield Hill wrote... >>> >>> Here's something for y'all to gnaw on, a 150W >>> current-source SMPS, made with a current-mode >>> controller. [snip] >>> >>>https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0 >>> >>> [snip ] Please take the compensation part values >>> with a grain of salt ... In fact, take the entire >>> circuit with big grains of salt! >> >> But kindly give me some feedback. Also, your time >> will be well spent studying the LM25117 datasheet. >> http://www.ti.com/product/lm25117?keyMatch=LM25117 > > Lawdy, lawdy, there's even a PSpice model that's NOT encrypted >:-}
SPICE models are often encrypted nowadays? The same *stupid* mindset that leads to encrypted datasheets? -- Thanks, - Win
Is it one-upsmanship if I say mine's 2kW?

https://www.youtube.com/watch?v=DZsdkVIjMvE

Granted I didn't test it at full power, but it sounds very similar.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com


"Winfield Hill"  wrote in message news:ngg2du02sie@drn.newsguy.com...

Here's something for y'all to knaw on, a 150W current-source SMPS, made 
with a
current-mode controller.  It has external monitoring and programming with
0-to-5V signals.

Most power supplies have low-Z voltage-source outputs, and when operated 
in
current-limit mode they simply servo the voltage to the achieve the 
desired
output current.  A true current source has a low effective output 
capacitance
and its output voltage can change rapidly to maintain a constant current 
into a
changing load.

Current-mode controllers have by their nature constant-current outputs, 
from the
buck inductor anyway, but this is morphed into a voltage source with a big
output capacitor and the controller's feedback.  So I figured, why not 
implement
one with a small capacitor and constant-current feedback?  This turned out 
to be
awkward with most controllers I considered, but NSC's (TI's) LM25117 was 
an
exception.  Among its many features is a fast current-monitor output using 
a
cycle-by-cycle S/H circuit, which was helpful and inspiring.

https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0

My project name is PWR-758.  My PCB layout uses mostly SMT parts, but I 
avoided
the temptation to place any parts on the bottom.  I got a bit carried away 
with
bells and whistles, like programmable compliance ranges, external meter,
external disable, etc., plus configuration modifications with a 10-mode
jumper-header, labeled A,B,C to I, extra connectors, etc.  I was forced to 
stop
adding features when I ran out of space on my size-A schematic drawing and 
my
4x4-inch PCB layout.  :-)

When operating in constant-current mode, one option uses the controller's 
S/H
circuit, and another option uses an LTC6102 output current-sense IC, which 
is
fast and has very low offset voltages.  The PWR-758 also has ordinary
voltage-source mode options.  Please take the compensation part values 
with a
grain of salt, because I have not yet properly evaluated them, nor made a
working copy of the circuit.  In fact, take the entire circuit with big 
grains
of salt!


-- 
Thanks,
    - Win 


Tim Williams wrote...
> > Is it one-upsmanship if I say mine's 2kW? > https://www.youtube.com/watch?v=DZsdkVIjMvE > Granted I didn't test it at full power, > but it sounds very similar.
Sounds interesting, is the schematic available? -- Thanks, - Win
"Winfield Hill" <hill@rowland.harvard.edu> wrote in message 
news:ngi0ic0apk@drn.newsguy.com...
> Sounds interesting, is the schematic available?
No, I don't have it handy... The basic design is pretty standard. Oscillator and PWM comparator; two error amps, one for voltage, one for current. Average current mode feedback (via ground referenced shunt in series with power input). Made the mistake of using all LM358s and not filtering often, which got noisy when I added the next part (a modest frequency inverter for induction heating). :^) Probably, the most novel part of the circuit is the limiter. It has independent max(V) and max(I) inputs; it regulates to whichever is largest. That means the V error amp runs all the time, but its output (the current setpoint) may be clamped, by the current max signal. (The current error amp always has total control. Its output is scaled so PWM goes 0-90% or something like that, as necessary for gate drive operation.) That little block is: http://seventransistorlabs.com/Images/Limiter2.png This doesn't have a "V limit/I limit" detect output, but that should be easy and/or obvious enough to add. The design goal was preventing integrator windup: this wraps around the volt error amp itself, keeping its output below Max. You're all welcome to critique and improve it; lower parts count and higher accuracy are always welcome. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
On 5 May 2016 11:12:14 -0700, Winfield Hill <hill@rowland.harvard.edu>
wrote:

>Here's something for y'all to knaw on, a 150W current-source SMPS, made with a >current-mode controller. It has external monitoring and programming with >0-to-5V signals. > >Most power supplies have low-Z voltage-source outputs, and when operated in >current-limit mode they simply servo the voltage to the achieve the desired >output current. A true current source has a low effective output capacitance >and its output voltage can change rapidly to maintain a constant current into a >changing load. > >Current-mode controllers have by their nature constant-current outputs, from the >buck inductor anyway, but this is morphed into a voltage source with a big >output capacitor and the controller's feedback. So I figured, why not implement >one with a small capacitor and constant-current feedback? This turned out to be >awkward with most controllers I considered, but NSC's (TI's) LM25117 was an >exception. Among its many features is a fast current-monitor output using a >cycle-by-cycle S/H circuit, which was helpful and inspiring. > >https://www.dropbox.com/sh/7gxz196y8gz1cur/AABrMianvgU-S7eWZ-29_lZHa?dl=0 > >My project name is PWR-758. My PCB layout uses mostly SMT parts, but I avoided >the temptation to place any parts on the bottom. I got a bit carried away with >bells and whistles, like programmable compliance ranges, external meter, >external disable, etc., plus configuration modifications with a 10-mode >jumper-header, labeled A,B,C to I, extra connectors, etc. I was forced to stop >adding features when I ran out of space on my size-A schematic drawing and my >4x4-inch PCB layout. :-) > >When operating in constant-current mode, one option uses the controller's S/H >circuit, and another option uses an LTC6102 output current-sense IC, which is >fast and has very low offset voltages. The PWR-758 also has ordinary >voltage-source mode options. Please take the compensation part values with a >grain of salt, because I have not yet properly evaluated them, nor made a >working copy of the circuit. In fact, take the entire circuit with big grains >of salt!
--- A truly beautiful schematic, which can only be appreciated juxtaposed to that of 2-TEL's TRAC III 'phone patch, which I'll post later. BTW, I love the Kelvin connections but, just as an aside, is R26 an Ohmite LVK20R040, just like R25? John Fields