Forums

Low power PWM controller, possibly the 555 (flame war coming)

Started by Klaus Kragelund August 30, 2012
Hi

I am working on a small 100mW forward converter and I need a very low power PWM control.

So the 555 comes up, along with some ultra low power opamps. But, isn't there a PWM chips out there with low operating current. Sofar I found the TPS5110 with sub mA current consumption:

http://www.ti.com/lit/ds/symlink/tps5110.pdf

Anyone used one with lower current?

Thanks

Klaus 
On a sunny day (Thu, 30 Aug 2012 04:05:39 -0700 (PDT)) it happened Klaus
Kragelund <klauskvik@hotmail.com> wrote in
<b82a88e9-a2b7-4bc4-ae9a-bb845ab075e5@googlegroups.com>:

>Hi > >I am working on a small 100mW forward converter and I need a very low power PWM control. > >So the 555 comes up, along with some ultra low power opamps. But, isn't there a PWM chips out there with low operating current. >Sofar I found the TPS5110 with sub mA current consumption: > >http://www.ti.com/lit/ds/symlink/tps5110.pdf > >Anyone used one with lower current? > >Thanks > >Klaus
I know it is an old song, but I am using PICs (PWM output, build in 2 comparators, calibration in EEPOM) for all that. Why go looking for chips when I have one in the box that can do almost anything, given some software capabilities.
On Aug 30, 1:33=A0pm, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
> On a sunny day (Thu, 30 Aug 2012 04:05:39 -0700 (PDT)) it happened Klaus > Kragelund <klausk...@hotmail.com> wrote in > <b82a88e9-a2b7-4bc4-ae9a-bb845ab075e5@googlegroups.com>: > > >Hi > > >I am working on a small 100mW forward converter and I need a very low po=
wer PWM control.
> > >So the 555 comes up, along with some ultra low power opamps. But, isn't =
there a PWM chips out there with low operating current.
> >Sofar I found the TPS5110 with sub mA current consumption: > > >http://www.ti.com/lit/ds/symlink/tps5110.pdf > > >Anyone used one with lower current? > > >Thanks > > >Klaus > > I know it is an old song, but I am using PICs (PWM output, build in 2 com=
parators,
> calibration in EEPOM) for all that. > Why go looking for chips when I have one in the box that can do almost an=
ything, given some software capabilities. Well, I have a Cortex M3 running at 4MHz, but the sw guys don't like me using that in a SW loop. I could generate a PWM to set the frequency, add F/F to set the output, and a comparator to reset the output (current mode control). Then add an voltage error amp to control the peak current level. Going further, I could use the internal comparator for the reset of the PWM for peak current control without CPU resources used, but the comparator has 2-4us propagation delay, seriously lowering the sensible frequency the converter can run at. I guess the delay is just a level shift of the peak current level and that is regulated back by the error amp anyway, so maybe it could work. Would however have a minimum duty cycle of 20% (for 100kHz and 2us propagation delay) For that solution I need to add a circuit to monitor the current and reset the CPU if it hangs. That takes some more parts in the wrong direction. But, I would like to see if there is a PWM controller that has low enough current anyway. Regards Klaus
On Thu, 30 Aug 2012 04:05:39 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>Hi > >I am working on a small 100mW forward converter and I need a very low power PWM control. > >So the 555 comes up, along with some ultra low power opamps. But, isn't there a PWM chips out there with low operating current. Sofar I found the TPS5110 with sub mA current consumption: > >http://www.ti.com/lit/ds/symlink/tps5110.pdf > >Anyone used one with lower current? > >Thanks > >Klaus
That's a buck controller, technically not what you'd use in a forward converter. Are you actually doing a non-isolated buck? What are your input and output voltages? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Thursday, August 30, 2012 4:24:03 PM UTC+2, John Larkin wrote:
> On Thu, 30 Aug 2012 04:05:39 -0700 (PDT), Klaus Kragelund > > <klauskvik@hotmail.com> wrote: > > > > >Hi > > > > > >I am working on a small 100mW forward converter and I need a very low power PWM control. > > > > > >So the 555 comes up, along with some ultra low power opamps. But, isn't there a PWM chips out there with low operating current. Sofar I found the TPS5110 with sub mA current consumption: > > > > > >http://www.ti.com/lit/ds/symlink/tps5110.pdf > > > > > >Anyone used one with lower current? > > > > > >Thanks > > > > > >Klaus > > > > That's a buck controller, technically not what you'd use in a forward > > converter. Are you actually doing a non-isolated buck? > > > > What are your input and output voltages? > > >
Yes, its a buck, and it has to large max duty cycle. Just an example of a low current PWM. My input voltage is from about 8V to 20V, output 3.3V. Transformer will probably be 1:1 so I can use off the shelf types approved for EN69650. Regards Klaus
On Thu, 30 Aug 2012 13:35:13 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>On Thursday, August 30, 2012 4:24:03 PM UTC+2, John Larkin wrote: >> On Thu, 30 Aug 2012 04:05:39 -0700 (PDT), Klaus Kragelund >> >> <klauskvik@hotmail.com> wrote: >> >> >> >> >Hi >> >> > >> >> >I am working on a small 100mW forward converter and I need a very low power PWM control. >> >> > >> >> >So the 555 comes up, along with some ultra low power opamps. But, isn't there a PWM chips out there with low operating current. Sofar I found the TPS5110 with sub mA current consumption: >> >> > >> >> >http://www.ti.com/lit/ds/symlink/tps5110.pdf >> >> > >> >> >Anyone used one with lower current? >> >> > >> >> >Thanks >> >> > >> >> >Klaus >> >> >> >> That's a buck controller, technically not what you'd use in a forward >> >> converter. Are you actually doing a non-isolated buck? >> >> >> >> What are your input and output voltages? >> >> >> > >Yes, its a buck, and it has to large max duty cycle. Just an example of a low current PWM. > >My input voltage is from about 8V to 20V, output 3.3V. Transformer will probably be 1:1 so I can use off the shelf types approved for EN69650. > >Regards > >Klaus
Transformer? A buck uses an inductor! What is the topology? -- 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
Well, a forward, isolated Buck. Sorry if that was not clear.
On Thu, 30 Aug 2012 04:51:28 -0700, Klaus Kragelund wrote:

> On Aug 30, 1:33&nbsp;pm, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote: >> On a sunny day (Thu, 30 Aug 2012 04:05:39 -0700 (PDT)) it happened >> Klaus Kragelund <klausk...@hotmail.com> wrote in >> <b82a88e9-a2b7-4bc4-ae9a-bb845ab075e5@googlegroups.com>: >> >> >Hi >> >> >I am working on a small 100mW forward converter and I need a very low >> >power PWM control. >> >> >So the 555 comes up, along with some ultra low power opamps. But, >> >isn't there a PWM chips out there with low operating current. Sofar I >> >found the TPS5110 with sub mA current consumption: >> >> >http://www.ti.com/lit/ds/symlink/tps5110.pdf >> >> >Anyone used one with lower current? >> >> >Thanks >> >> >Klaus >> >> I know it is an old song, but I am using PICs (PWM output, build in 2 >> comparators, calibration in EEPOM) for all that. >> Why go looking for chips when I have one in the box that can do almost >> anything, given some software capabilities. > > Well, I have a Cortex M3 running at 4MHz, but the sw guys don't like me > using that in a SW loop. > > I could generate a PWM to set the frequency, add F/F to set the output, > and a comparator to reset the output (current mode control). Then add an > voltage error amp to control the peak current level. > > Going further, I could use the internal comparator for the reset of the > PWM for peak current control without CPU resources used, but the > comparator has 2-4us propagation delay, seriously lowering the sensible > frequency the converter can run at. I guess the delay is just a level > shift of the peak current level and that is regulated back by the error > amp anyway, so maybe it could work. Would however have a minimum duty > cycle of 20% (for 100kHz and 2us propagation delay) > > For that solution I need to add a circuit to monitor the current and > reset the CPU if it hangs. That takes some more parts in the wrong > direction. > > But, I would like to see if there is a PWM controller that has low > enough current anyway. > > Regards > > Klaus
Use a 6-pin PIC, program it yourself, and pass it off as an analog component. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
Do something like this, but configured for forward operation instead:
http://t3sl4.dnsdynamic.net/Images/Deadbug_Sch.png
obviously, replace the amp-gobbling TL431 with something more frugal.

You can save the bias current wasted in the switching transistor by using 
a positive feedback winding, making the circuit a basic blocking 
oscillator instead.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Klaus Kragelund" <klauskvik@hotmail.com> wrote in message 
news:b82a88e9-a2b7-4bc4-ae9a-bb845ab075e5@googlegroups.com...
> Hi > > I am working on a small 100mW forward converter and I need a very low > power PWM control. > > So the 555 comes up, along with some ultra low power opamps. But, isn't > there a PWM chips out there with low operating current. Sofar I found > the TPS5110 with sub mA current consumption: > > http://www.ti.com/lit/ds/symlink/tps5110.pdf > > Anyone used one with lower current? > > Thanks > > Klaus
On Thu, 30 Aug 2012 13:58:31 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Thu, 30 Aug 2012 13:35:13 -0700 (PDT), Klaus Kragelund ><klauskvik@hotmail.com> wrote: > >>On Thursday, August 30, 2012 4:24:03 PM UTC+2, John Larkin wrote: >>> On Thu, 30 Aug 2012 04:05:39 -0700 (PDT), Klaus Kragelund >>>=20 >>> <klauskvik@hotmail.com> wrote: >>>=20 >>>=20 >>>=20 >>> >Hi >>>=20 >>> > >>>=20 >>> >I am working on a small 100mW forward converter and I need a very =
low power PWM control.
>>>=20 >>> > >>>=20 >>> >So the 555 comes up, along with some ultra low power opamps. But, =
isn't there a PWM chips out there with low operating current. Sofar I = found the TPS5110 with sub mA current consumption:
>>>=20 >>> > >>>=20 >>> >http://www.ti.com/lit/ds/symlink/tps5110.pdf >>>=20 >>> > >>>=20 >>> >Anyone used one with lower current? >>>=20 >>> > >>>=20 >>> >Thanks >>>=20 >>> > >>>=20 >>> >Klaus=20 >>>=20 >>>=20 >>>=20 >>> That's a buck controller, technically not what you'd use in a forward >>>=20 >>> converter. Are you actually doing a non-isolated buck? >>>=20 >>>=20 >>>=20 >>> What are your input and output voltages? >>>=20 >>>=20 >>>=20 >> >>Yes, its a buck, and it has to large max duty cycle. Just an example of=
a low current PWM.
>> >>My input voltage is from about 8V to 20V, output 3.3V. Transformer will=
probably be 1:1 so I can use off the shelf types approved for EN69650.
>> >>Regards >> >>Klaus=20 > >Transformer? A buck uses an inductor! > >What is the topology?
You clearly missed the isolation requirement implied by EN69650. ?-)