switching regulator with mcu
in [Basics]
|
Prev: ua741
Next: What is a unbalanced AC transformer?
From: Joerg on 20 Oct 2009 14:27 Charlie E. wrote: > On Tue, 20 Oct 2009 13:30:39 +0300, "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 ?. >> 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... > You could do it, this way: Resistor and zener to CPU but much higher zener voltage than the CPU uses in normal operation, meaning the MCU should have lots of headroom. Start MCU with bare minimum in code, basically doing nothing other than the switcher. Now fire up a buck or whatever switcher from 12-24VDC, MCU controlled hysteretic for example. When that gets into the green zone let the MCU commence its normal job because now that the switcher has started it can use all the power it wants. If you can't spread zener voltage and normal operating voltage that far, add an extra transistor that turns off the zener after the switcher start process has run its course. This will cost another port pin. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Nico Coesel on 20 Oct 2009 14:35 "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. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... "If it doesn't fit, use a bigger hammer!" --------------------------------------------------------------
From: Joerg on 20 Oct 2009 14:54 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.
From: michael nikolaou on 20 Oct 2009 15:14 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.
From: Joerg on 20 Oct 2009 15:52
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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |