switching regulator with mcu
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From: Joerg on 20 Oct 2009 21:15 Martin Riddle wrote: > "michael nikolaou" <michaelnikolaou_rem_ove_(a)yahoo.com> wrote in message > news:hbl267$2l80$1(a)ulysses.noc.ntua.gr... >> 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. >> 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 >> ? >> Any other simple ideas ??? >> >> >> "Joerg" <invalid(a)invalid.invalid> wrote in message >> news:7k6faoF389blhU1(a)mid.individual.net... >>> Nico Coesel wrote: >>>> "michael nikolaou" <michaelnikolaou_remove_me_(a)yahoo.com> wrote: >>>> >>>>> Hi to newsgroup >>>>> >>>>> I'm making a mcu based device which i want to be very small and low >>>>> cost >>>>> The design consumes 100..120 ma @ 3.3V >>>>> The problem is the installation that requires 12 or 24 volts to >>>>> operate. >>>>> I don't want to use a switching regulator to make the voltage drop >>>>> since its to much >>>>> circuit involved and also not a zener since its to much heat >>>>> involved . >>>> Too much circuitry? Look at devices from TI like the TPS5410. Very >>>> small and it will run at a wide variety of input voltages. >>>> >>> But mucho Dolares. I'd try using the MCU if possible if this is a >>> high volume product. But it'll require lots of nifty engineering. For >>> low volume, yeah, don't bother and use a chip. Then I'd use the >>> MC34063 which costs under 20 cents. None of those high-faluting >>> newfangled ritzy ones ;-) >>> >>> -- >>> Regards, Joerg >>> >>> http://www.analogconsultants.com/ >>> >>> "gmail" domain blocked because of excessive spam. >>> Use another domain or send PM. >> > > What about a LDO? National, LP2952. 30V input. Dissapation isnt that > much at 120ma. > You could always stick some resistance in the input pin to lower Vin, > and device dissipation. > Be careful. I don't know the LP2952 but I had one of the 29-series go berserk when the source impedance became too large. It wasn't mentioned in the datasheet ... Bottomline is I stay away from LDOs. Besides the above there are also ESR-related stability issues. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Devereux on 21 Oct 2009 02:38 Joerg <invalid(a)invalid.invalid> writes: > 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. Hi Jeorg, Are you talking about a SEPIC/flyback arrangement here? I.e., 2N7001 drives a transformer? How do you stop the opamp railing during startup or a load step? The schmitt osc would stop and .. how does it go .... Phut! :) Also of course by the time he's actually bought a SEPIC transformer it could all approach his 1.8 Euros. Or are there some super-cheap ones now? -- John Devereux
From: michael nikolaou on 21 Oct 2009 03:40 I need to make clear so we avoid confusions The device uses a 2.2" tft lcd . This thing has a backlight and no matter what draws 60 ma @ 3.3V .That i can't avoid . So with 60 ma Arm7 consumption i end up to 120 ma. Now as i see whether i have a small switcher with huge inductor and capacitor so my board space is too large . The other solution is super fast switcher that has everything small but needs 2 euros at least . I imagine every engineer designing devices has faced this question . I'm sure though that a simple cpu controlled switcher could cope with the large dropout from 24V to 4-5 volts and then a simple linear regulator could take you to 3.3V so you play it safe.If things go wrong (cpu malfunction ) thermal shutdown from the linear regulator would reset the cpu and that would restart the system As i see it a simple fet switch with cpu pwm control should satisfy that . Any opinions or experience on that subject??? The 120 "Joerg" <invalid(a)invalid.invalid> wrote in message news:7k75l0F37imt0U1(a)mid.individual.net... > Martin Riddle wrote: >> "michael nikolaou" <michaelnikolaou_rem_ove_(a)yahoo.com> wrote in message >> news:hbl267$2l80$1(a)ulysses.noc.ntua.gr... >>> 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. >>> 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 ? >>> Any other simple ideas ??? >>> >>> >>> "Joerg" <invalid(a)invalid.invalid> wrote in message >>> news:7k6faoF389blhU1(a)mid.individual.net... >>>> Nico Coesel wrote: >>>>> "michael nikolaou" <michaelnikolaou_remove_me_(a)yahoo.com> wrote: >>>>> >>>>>> Hi to newsgroup >>>>>> >>>>>> I'm making a mcu based device which i want to be very small and low >>>>>> cost >>>>>> The design consumes 100..120 ma @ 3.3V >>>>>> The problem is the installation that requires 12 or 24 volts to >>>>>> operate. >>>>>> I don't want to use a switching regulator to make the voltage drop >>>>>> since its to much >>>>>> circuit involved and also not a zener since its to much heat involved >>>>>> . >>>>> Too much circuitry? Look at devices from TI like the TPS5410. Very >>>>> small and it will run at a wide variety of input voltages. >>>>> >>>> But mucho Dolares. I'd try using the MCU if possible if this is a high >>>> volume product. But it'll require lots of nifty engineering. For low >>>> volume, yeah, don't bother and use a chip. Then I'd use the MC34063 >>>> which costs under 20 cents. None of those high-faluting newfangled >>>> ritzy ones ;-) >>>> >>>> -- >>>> Regards, Joerg >>>> >>>> http://www.analogconsultants.com/ >>>> >>>> "gmail" domain blocked because of excessive spam. >>>> Use another domain or send PM. >>> >> >> What about a LDO? National, LP2952. 30V input. Dissapation isnt that much >> at 120ma. >> You could always stick some resistance in the input pin to lower Vin, and >> device dissipation. >> > > Be careful. I don't know the LP2952 but I had one of the 29-series go > berserk when the source impedance became too large. It wasn't mentioned in > the datasheet ... > > Bottomline is I stay away from LDOs. Besides the above there are also > ESR-related stability issues. > > -- > Regards, Joerg > > http://www.analogconsultants.com/ > > "gmail" domain blocked because of excessive spam. > Use another domain or send PM.
From: John Devereux on 21 Oct 2009 05:18 "michael nikolaou" <michaelnikolaou_remove_me_(a)yahoo.com> writes: > > > > > The 120 > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:7k75l0F37imt0U1(a)mid.individual.net... >> Martin Riddle wrote: >>> "michael nikolaou" <michaelnikolaou_rem_ove_(a)yahoo.com> wrote in message >>> news:hbl267$2l80$1(a)ulysses.noc.ntua.gr... >>>> 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. >>>> 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 ? >>>> Any other simple ideas ??? >>>> >>>> >>>> "Joerg" <invalid(a)invalid.invalid> wrote in message >>>> news:7k6faoF389blhU1(a)mid.individual.net... [...] >>>>> But mucho Dolares. I'd try using the MCU if possible if this is a high >>>>> volume product. But it'll require lots of nifty engineering. For low >>>>> volume, yeah, don't bother and use a chip. Then I'd use the MC34063 >>>>> which costs under 20 cents. None of those high-faluting newfangled >>>>> ritzy ones ;-) [...] >>> What about a LDO? National, LP2952. 30V input. Dissapation isnt that much >>> at 120ma. >>> You could always stick some resistance in the input pin to lower Vin, and >>> device dissipation. >>> >> >> Be careful. I don't know the LP2952 but I had one of the 29-series go >> berserk when the source impedance became too large. It wasn't mentioned in >> the datasheet ... >> >> Bottomline is I stay away from LDOs. Besides the above there are also >> ESR-related stability issues. (top post corrected) > I need to make clear so we avoid confusions > > The device uses a 2.2" tft lcd . This thing has a backlight and no matter > what > draws 60 ma @ 3.3V .That i can't avoid . So with 60 ma Arm7 consumption > i end up to 120 ma. > Now as i see whether i have a small switcher with huge inductor and > capacitor > so my board space is too large . > The other solution is super fast switcher that has everything small but > needs 2 euros > at least . > I imagine every engineer designing devices has faced this question . > I'm sure though that a simple cpu controlled switcher could cope with the > large dropout > from 24V to 4-5 volts and then a simple linear regulator could take you to > 3.3V so you play > it safe.If things go wrong (cpu malfunction ) thermal shutdown from the > linear regulator would > reset the cpu and that would restart the system > As i see it a simple fet switch with cpu pwm control should satisfy that . > Any opinions or experience on that subject??? I have never had the nerve to try a CPU-controlled switcher - but I never thought of a linear regulator as a "safety cutout" either. I'd say go for it! You have a couple of issues: * startup - maybe just a trickle of current if the circuit has a very low initial requirement * Configuration - either you need a high-side driver with a buck configuration or an easier low-side one that needs a transformer (SEPIC or flyback). Or I guess the simplest is inverting but that's nasty if you have to connect to anything else since incoming "ground" ends up being your positive rail. Also your "12-24V" sounds a bit automotive. If so be aware that there can be some very nasty spikes and voltage surges, meaning that a strict interpretation of the standards can require withstanding >>70V, not just 24. -- John Devereux
From: Jasen Betts on 21 Oct 2009 06:15
On 2009-10-20, michael nikolaou <michaelnikolaou_remove_me_(a)yahoo.com> wrote: > Hi to newsgroup > > I'm making a mcu based device which i want to be very small and low cost > The design consumes 100..120 ma @ 3.3V > The problem is the installation that requires 12 or 24 volts to operate. > I don't want to use a switching regulator to make the voltage drop since its > to much > circuit involved and also not a zener since its to much heat involved . > The mcu has A/D and PWM controller .Is it possible to use a simple mosfet > switch with > a capacitor to make a dropdown to half voltage if the mcu detects 24 volts > input ?. with just a cap and a mosfet? doiesn't seem possible, > Is there an easier way ?. linear regulator or buck regulator. > Any help would be appreciated . |