switching regulator with mcu
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From: Jon Kirwan on 30 Oct 2009 20:13 On Fri, 30 Oct 2009 17:06:28 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Tue, 20 Oct 2009 16:16:48 -0700, Jon Kirwan ><jonk(a)infinitefactors.org> wrote: > >>On Tue, 20 Oct 2009 15:49:59 -0700, Joerg <invalid(a)invalid.invalid> >>wrote: >> >>>Jon Kirwan wrote: >>>> On Tue, 20 Oct 2009 12:52:04 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> michael nikolaou wrote: >>>>>> Guys >>>>>> >>>>>> Thanks for all your replies >>>>>> >>>>>> My small research has found that switcher solutions are. >>>>>> 1. simple and small sized switcher solutions are expensive. >>>>>> 2. Mc33063 are ok in terms of price but the inductor plus the capacitors are >>>>>> too much board estate >>>>>> 3. Small size means high frequency and so you start with selective >>>>>> components etc. >>>>> Not really, the passive parts are easy. But the challenge will be to >>>>> find a mainstream (meaning inexpensive) small switcher chip. The cheap >>>>> ones are all old and slow, 300kHz or less. This will take some time >>>>> because you must always check pricing. You could start by looking at >>>>> chips for the Power over Ethernet (PoE) market. >>>>> >>>>>> I NEED ONLY 120 ma is there nothing low cost and simple ?. >>>>>> One switcher i located used 10 uH inductor , 47 uF output capacitor @ 6.3V >>>>>> and 2.2uF input capacitor >>>>>> but total cost was 1.8 euros. I's using one ARM7 mcu that costs 3 euro and >>>>>> i don't want to spend as much for the PSU. >>>>>> Some lower consumption devices @ 50 mA were using uA78M33 regulator with a >>>>>> zener if 24 volts was used. >>>>>> Joerg do you have schematic to study about the idea you are proposing ? >>>>> No, that would be a little R&D project. Requires tight reigns on the >>>>> firmware because the switcher must never skip a beat. But if you have a >>>>> free timer in your ARM MCU it can be done. >>>>> >>>>>> Any other simple ideas ??? >>>>> Another option would be to use a CD40106 or something similar as a >>>>> Schmitt oscillator, with its VCC capped/zenered around 6-8V. This can >>>>> drive a little FET, a simple logic level device like a 2N7002 as long as >>>>> doesn't cost much. Pipe Vref out of your MCU (hoping it has that ...) >>>>> and use a cheap opamp to pull the Schmitt oscillator input "to the side" >>>>> when the target voltage is reached. That reduces the duty cycle as much >>>>> as needed to maintain regulation, pretty much like the throttle on a >>>>> gasoline-powered generator. If the target voltage doesn't have to be >>>>> very precise you could also use a NPN plus zener for that, without a >>>>> reference source. Probably a TL431-type device would work as well and >>>>> those are quite cheap, in the penny range. >>>> >>>> This has been an interesting discussion. What is bothering me a lot, >>>> in reading it, is the "ONLY 120mA" thing! 120mA? Only? Cripes. If >>>> I were imagining being as space-constrained as the OP suggests, I'd IN >>>> THE FIRST PLACE start asking myself why I actually need 120mA! Is it >>>> the processor, itself? If so, look to get rid of it and find >>>> something else. Doing so may put constraints on the application >>>> itself (doing logarithms on a PIC16 is quite different in speed than >>>> doing them on an ARM9, for example), but it may greatly relax the >>>> power supply design issues. Everything is trade-off. But I'm >>>> bothered by the casual acceptance of a 120mA spec as gospel when there >>>> is a serious space and cost issue here. >>>> >>>> What is sucking that power? Can it be changed? If not, why not? >>> >>>I sure hope it's not the MCU alone because that would spell trouble. >> >>It sounds familiar. I've looked at these 'low power' ARM chips, >>noticed that many seem to average 20-50mA, with the lower figure only >>on a good day and many requiring more. It was NOT a shock to me to >>see 120mA with ARMs. In fact, I'm just fine with that. But when the >>OP writes, "I'm making a mcu based device which i want to be very >>small and low cost" and then out the other side of the mouth says >>"only 120mA" then I'm truly wondering. >> >>One of the BIG tradeoffs is power __AND__ heat. And by the time you >>get anywhere near 120mA, you've often got both problems in spades. >>It's a fundamentally different domain. >> >>I guess that's why I just went _white_ when I read those figures and >>the OP's language in the same context. The only way 120mA is a >>little, these days, is if you are used to x86 processors running at >>GHz and requiring multiple power supply rails to help contain heat >>problems better. >> >>If you live in that world, I can see it. But that sure isn't MY >>embedded world perspective. I consider moving into the 120mA domain >>as being akin to a "damn-the-torpedoes, devil-may-care" world. At >>that point, you are already spending dollars, not pennies, and have >>board room to spare. And if you are chugging 120mA, you NEED space, >>anyway. >> >>>Often there are other things like ADCs, analog stuff etc. 120mA is >>>really a piece of cake from a power converter point of view. After all, >>>that's only 600mW if his VCC is 5V. Low enough for an energy star :-) >> >>Hehe. Yeah. If we are talking washing machines, 120mA is no problem. >>But room isn't a problem, then, either. There's always a corner, plus >>one HUGE heat sink, too. ;) >> >>>Michael may have to go with a SEPIC if he wants the FET to switch to GND >>>but that's not a big deal either, just two parts more. Since the advent >>>of PoE he's got plenty of options. >> >>I'd recommend that Michael rethink 120mA. I mean, jeeez! If you >>nearing a watt already, with overhead, you need space and you expect >>to spend something on the power supply, too. Or some serious, crafted >>time. Or both. >> >>Almost two decades ago, I was worrying over a thermal cooling stack >>with two Peltier stages and the bottom stage was consuming half a >>watt. I was worried about that much heat. And the tiny micro device >>plus analog circuits at the top was burning some 30mW. Now that's the >>kind of thing you get with 120mA! 2-stage Peltier coolers AND a >>micro. 20 years ago. >> >>This is crazy-making to think about 120mA! Yeah, if you are making an >>iPhone or internet interface device with RF and all. I mean, you need >>to actually broadcast maybe 1/4 watt or so. So yeah. But "I'm making >>a mcu based device which i want to be very small and low cost?" >> >>The OP and I must come from different universes! >> >>Jon > >You may be on to something. OP seems to also be considering a linear >regulator from 24 V to 3.3. Talk about power waste. OMG! Are you kidding? (I must have missed reading and/or connecting the dots on posts you saw.) Jon
From: JosephKK on 3 Nov 2009 00:26
On Fri, 30 Oct 2009 17:13:07 -0700, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Fri, 30 Oct 2009 17:06:28 -0700, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Tue, 20 Oct 2009 16:16:48 -0700, Jon Kirwan >><jonk(a)infinitefactors.org> wrote: >> >>>On Tue, 20 Oct 2009 15:49:59 -0700, Joerg <invalid(a)invalid.invalid> >>>wrote: >>> >>>>Jon Kirwan wrote: >>>>> On Tue, 20 Oct 2009 12:52:04 -0700, Joerg <invalid(a)invalid.invalid> >>>>> wrote: >>>>> >>>>>> michael nikolaou wrote: >>>>>>> Guys >>>>>>> >>>>>>> Thanks for all your replies >>>>>>> >>>>>>> My small research has found that switcher solutions are. >>>>>>> 1. simple and small sized switcher solutions are expensive. >>>>>>> 2. Mc33063 are ok in terms of price but the inductor plus the capacitors are >>>>>>> too much board estate >>>>>>> 3. Small size means high frequency and so you start with selective >>>>>>> components etc. >>>>>> Not really, the passive parts are easy. But the challenge will be to >>>>>> find a mainstream (meaning inexpensive) small switcher chip. The cheap >>>>>> ones are all old and slow, 300kHz or less. This will take some time >>>>>> because you must always check pricing. You could start by looking at >>>>>> chips for the Power over Ethernet (PoE) market. >>>>>> >>>>>>> I NEED ONLY 120 ma is there nothing low cost and simple ?. >>>>>>> One switcher i located used 10 uH inductor , 47 uF output capacitor @ 6.3V >>>>>>> and 2.2uF input capacitor >>>>>>> but total cost was 1.8 euros. I's using one ARM7 mcu that costs 3 euro and >>>>>>> i don't want to spend as much for the PSU. >>>>>>> Some lower consumption devices @ 50 mA were using uA78M33 regulator with a >>>>>>> zener if 24 volts was used. >>>>>>> Joerg do you have schematic to study about the idea you are proposing ? >>>>>> No, that would be a little R&D project. Requires tight reigns on the >>>>>> firmware because the switcher must never skip a beat. But if you have a >>>>>> free timer in your ARM MCU it can be done. >>>>>> >>>>>>> Any other simple ideas ??? >>>>>> Another option would be to use a CD40106 or something similar as a >>>>>> Schmitt oscillator, with its VCC capped/zenered around 6-8V. This can >>>>>> drive a little FET, a simple logic level device like a 2N7002 as long as >>>>>> doesn't cost much. Pipe Vref out of your MCU (hoping it has that ....) >>>>>> and use a cheap opamp to pull the Schmitt oscillator input "to the side" >>>>>> when the target voltage is reached. That reduces the duty cycle as much >>>>>> as needed to maintain regulation, pretty much like the throttle on a >>>>>> gasoline-powered generator. If the target voltage doesn't have to be >>>>>> very precise you could also use a NPN plus zener for that, without a >>>>>> reference source. Probably a TL431-type device would work as well and >>>>>> those are quite cheap, in the penny range. >>>>> >>>>> This has been an interesting discussion. What is bothering me a lot, >>>>> in reading it, is the "ONLY 120mA" thing! 120mA? Only? Cripes. If >>>>> I were imagining being as space-constrained as the OP suggests, I'd IN >>>>> THE FIRST PLACE start asking myself why I actually need 120mA! Is it >>>>> the processor, itself? If so, look to get rid of it and find >>>>> something else. Doing so may put constraints on the application >>>>> itself (doing logarithms on a PIC16 is quite different in speed than >>>>> doing them on an ARM9, for example), but it may greatly relax the >>>>> power supply design issues. Everything is trade-off. But I'm >>>>> bothered by the casual acceptance of a 120mA spec as gospel when there >>>>> is a serious space and cost issue here. >>>>> >>>>> What is sucking that power? Can it be changed? If not, why not? >>>> >>>>I sure hope it's not the MCU alone because that would spell trouble. >>> >>>It sounds familiar. I've looked at these 'low power' ARM chips, >>>noticed that many seem to average 20-50mA, with the lower figure only >>>on a good day and many requiring more. It was NOT a shock to me to >>>see 120mA with ARMs. In fact, I'm just fine with that. But when the >>>OP writes, "I'm making a mcu based device which i want to be very >>>small and low cost" and then out the other side of the mouth says >>>"only 120mA" then I'm truly wondering. >>> >>>One of the BIG tradeoffs is power __AND__ heat. And by the time you >>>get anywhere near 120mA, you've often got both problems in spades. >>>It's a fundamentally different domain. >>> >>>I guess that's why I just went _white_ when I read those figures and >>>the OP's language in the same context. The only way 120mA is a >>>little, these days, is if you are used to x86 processors running at >>>GHz and requiring multiple power supply rails to help contain heat >>>problems better. >>> >>>If you live in that world, I can see it. But that sure isn't MY >>>embedded world perspective. I consider moving into the 120mA domain >>>as being akin to a "damn-the-torpedoes, devil-may-care" world. At >>>that point, you are already spending dollars, not pennies, and have >>>board room to spare. And if you are chugging 120mA, you NEED space, >>>anyway. >>> >>>>Often there are other things like ADCs, analog stuff etc. 120mA is >>>>really a piece of cake from a power converter point of view. After all, >>>>that's only 600mW if his VCC is 5V. Low enough for an energy star :-) >>> >>>Hehe. Yeah. If we are talking washing machines, 120mA is no problem. >>>But room isn't a problem, then, either. There's always a corner, plus >>>one HUGE heat sink, too. ;) >>> >>>>Michael may have to go with a SEPIC if he wants the FET to switch to GND >>>>but that's not a big deal either, just two parts more. Since the advent >>>>of PoE he's got plenty of options. >>> >>>I'd recommend that Michael rethink 120mA. I mean, jeeez! If you >>>nearing a watt already, with overhead, you need space and you expect >>>to spend something on the power supply, too. Or some serious, crafted >>>time. Or both. >>> >>>Almost two decades ago, I was worrying over a thermal cooling stack >>>with two Peltier stages and the bottom stage was consuming half a >>>watt. I was worried about that much heat. And the tiny micro device >>>plus analog circuits at the top was burning some 30mW. Now that's the >>>kind of thing you get with 120mA! 2-stage Peltier coolers AND a >>>micro. 20 years ago. >>> >>>This is crazy-making to think about 120mA! Yeah, if you are making an >>>iPhone or internet interface device with RF and all. I mean, you need >>>to actually broadcast maybe 1/4 watt or so. So yeah. But "I'm making >>>a mcu based device which i want to be very small and low cost?" >>> >>>The OP and I must come from different universes! >>> >>>Jon >> >>You may be on to something. OP seems to also be considering a linear >>regulator from 24 V to 3.3. Talk about power waste. > >OMG! Are you kidding? (I must have missed reading and/or connecting >the dots on posts you saw.) > >Jon And it is possible that i misread instead. YMMV. |