switching regulator with mcu
in [Basics]
|
Prev: ua741
Next: What is a unbalanced AC transformer?
From: Jon Kirwan on 20 Oct 2009 16:31 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? Jon
From: don on 20 Oct 2009 18:47 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. > 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 ??? > > It would appear that you are new to this engineering thing. Microcontrollers are so cheap because the manufactures figured you would spend the money to make it work. Power devices cost more then CPU silicon, always have. Welcome to the real world. Morpheus ;-)
From: langwadt on 20 Oct 2009 18:48 On 20 Okt., 16:27, Charlie E. <edmond...(a)ieee.org> wrote: > On Tue, 20 Oct 2009 13:30:39 +0300, "michael nikolaou" > > > > <michaelnikolaou_remove_...(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 ?. > >Is there an easier way ?. > >Any help would be appreciated . > > >MK > > Michael, > Probably not a good idea. You MCU will take a little while to come up > to speed before it can monitor those voltages, and take action. At > 24VDC, you chip is already fried by that time. That is a lot of > voltage to drop with just a linear regulator, esp. if that 24VDC is > not well regulated. It is possible, but it isn't simple... > > Charlie I think it is doable, switch, L and C before a linear regulator. out of reset have the switch on let the linear regulator regulate from the full 24V (or see if you can drop some over the switch) when the MCU is up and running, use PWM, the switch, L and C as a buck dropping the voltage before the linear regulator to 3.3 + dropout -Lasse
From: Joerg on 20 Oct 2009 18:49 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. 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 :-) 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: dagmargoodboat on 20 Oct 2009 19:12
On Oct 20, 2:14 pm, "michael nikolaou" <michaelnikolaou_rem_o...(a)yahoo.com> 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. > 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" <inva...(a)invalid.invalid> wrote in message > > news:7k6faoF389blhU1(a)mid.individual.net... > > > Nico Coesel wrote: > >> "michael nikolaou" <michaelnikolaou_remove_...(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. This isn't going to help you because your request is unreasonable, but it's about as few parts as you can get: (view in fixed font) +12-24V -+- | o D1 +------+----------------. .--|>|--+-----> +3.3v | | ) ( | R1 | L1 ) ( L2 | | |/ Q1 ) ( | +----| | '--. | | |>. | o | | | | ||--' === | .---' +----. ||<-. GND | Z1 ^ | | ||--+ Q2 | 4V | C1 --- | .---' | | | --- | | | | === | | | === | GND | | | GND | === '---)-------------------' GND | | PWM from ARM7 >-------' Q1 is a linear supply that runs the thing until the ARM gets going. When the ARM switches Q2, the voltage rises on Q1's emitter and it quits conducting. I used a transformer. An inductor would be cheaper of course, but then I'd have to draw yet another high-side MOSFET gate driver, and that's boring. You're really probably better off buying a switcher. If you _really_ need a tiny inductor, especially at 100mA, you're going to need something fast. That won't be free. -- Cheers, James Arthur |