switching regulator with mcu
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From: michael nikolaou on 20 Oct 2009 06:30 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
From: Charlie E. on 20 Oct 2009 10:27 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... Charlie
From: michael nikolaou on 20 Oct 2009 12:48 Hi charlie Thanks fot the reply If i halve the duty cycle is should get from 6 to 12 volts input . This can be regulated to 3.3V with no problem . Is there no simple circuit, switched capacitor possibly , to make this voltage halving ???? "Charlie E." <edmondson(a)ieee.org> wrote in message news:b0ird55sv4h65492pasfj3o4inu6dlsv4r(a)4ax.com... > 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... > > Charlie
From: Tim Wescott on 20 Oct 2009 12:54 On Tue, 20 Oct 2009 13:30:39 +0300, michael nikolaou 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 . Switched-capacitor voltage doublers work pretty well, but I doubt that a switched-capacitor voltage halver would be less complex than a switching regulator. If your production volumes aren't too terribly high there are some nice switching regulator modules out there. TI makes a wide variety with a good size/power ratio, that'll take 12-24V easily. I'm sure that TI isn't the only one. -- www.wescottdesign.com
From: Hammy on 20 Oct 2009 14:03
On Tue, 20 Oct 2009 11:54:39 -0500, Tim Wescott <tim(a)seemywebsite.com> wrote: >If your production volumes aren't too terribly high there are some nice >switching regulator modules out there. TI makes a wide variety with a >good size/power ratio, that'll take 12-24V easily. I'm sure that TI >isn't the only one. For that matter a switcher with an integrated switch and a fixed output of 3.3V could be had. This would require less real-estate then either a TO-220 with a heatsink or your switched capacitor circuit. Search Digikey and you'll find some 3.3V switchers in a dpak only requiring a few external components and pretty well idiot proof. A small SOD Schottkey and a tiny smd cap and inductor would be the only external components you need. You could build it on a separate PCB and mount it vertically to your main PCB. I've done that a few times. For 120 mA output you should be able to get it down around 1/2" x �". Mount the DPAK on the ground side put your 3 or 4 other components on the other side. |