Forums

A PIC based boost converter

Started by Jan Panteltje November 22, 2011
On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened
"langwadt@fonz.dk" <langwadt@fonz.dk> wrote in
<761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>:

>On 23 Nov., 12:08, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote: >> >snip >> It would be short circuit proof IF it was not for the >> boost configuration where the diode would conduct from input to output. >> So for that in this sort of regulator you need a normal fuse. >> For the rest of loads it nicely current limits. > >I remember seeing some put a cap in series with the diode to make it >short >circuit proof
mm but caps do not conduct DC?
> >-Lasse > >
On 11/23/2011 3:05 PM, Jan Panteltje wrote:
> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened > "langwadt@fonz.dk"<langwadt@fonz.dk> wrote in > <761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>: > >> On 23 Nov., 12:08, Jan Panteltje<pNaonStpealm...@yahoo.com> wrote: >>> >> snip >>> It would be short circuit proof IF it was not for the >>> boost configuration where the diode would conduct from input to output. >>> So for that in this sort of regulator you need a normal fuse. >>> For the rest of loads it nicely current limits. >> >> I remember seeing some put a cap in series with the diode to make it >> short >> circuit proof > > mm but caps do not conduct DC? > >> >> -Lasse >> >>
True. That would make it short-circuit proof. Right?
On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S
<sophi.2@invalid.org> wrote in <jajnb8$qg2$1@dont-email.me>:

>On 11/23/2011 3:05 PM, Jan Panteltje wrote: >> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened >> "langwadt@fonz.dk"<langwadt@fonz.dk> wrote in >> <761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>: >> >>> On 23 Nov., 12:08, Jan Panteltje<pNaonStpealm...@yahoo.com> wrote: >>>> >>> snip >>>> It would be short circuit proof IF it was not for the >>>> boost configuration where the diode would conduct from input to output. >>>> So for that in this sort of regulator you need a normal fuse. >>>> For the rest of loads it nicely current limits. >>> >>> I remember seeing some put a cap in series with the diode to make it >>> short >>> circuit proof >> >> mm but caps do not conduct DC? >> >>> >>> -Lasse >>> >>> > >True. That would make it short-circuit proof. Right?
OK :-) But what about output?
On 11/23/2011 3:10 PM, Jan Panteltje wrote:
> On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S > <sophi.2@invalid.org> wrote in<jajnb8$qg2$1@dont-email.me>: > >> On 11/23/2011 3:05 PM, Jan Panteltje wrote: >>> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened >>> "langwadt@fonz.dk"<langwadt@fonz.dk> wrote in >>> <761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>: >>> >>>> On 23 Nov., 12:08, Jan Panteltje<pNaonStpealm...@yahoo.com> wrote: >>>>> >>>> snip >>>>> It would be short circuit proof IF it was not for the >>>>> boost configuration where the diode would conduct from input to output. >>>>> So for that in this sort of regulator you need a normal fuse. >>>>> For the rest of loads it nicely current limits. >>>> >>>> I remember seeing some put a cap in series with the diode to make it >>>> short >>>> circuit proof >>> >>> mm but caps do not conduct DC? >>> >>>> >>>> -Lasse >>>> >>>> >> >> True. That would make it short-circuit proof. Right? > > OK :-) > But what about output? >
What output?
"Jan Panteltje"  wrote in message news:jaik8d$nv5$1@news.datemas.de...

> Yes, that will work, but: > The output regulation will be inferior, depend on the Vbe temperature > drift multiplied by Uout / .7, there is no clear current limit, > there is also some power loss in the 1 Ohm resistor.
My design is not optimized, and the 1 ohm resistor was added only for=20 convenience in simulation. I don't have the specs for what you are=20 designing, so I just wanted to see how a cheap, simple design compared. = I=20 think it may be useful for some purposes, especially when trying to use = a=20 single cell battery or very low voltage to provide enough voltage to = drive a=20 MOSFET and power 3.3V or 5V logic and PICs.
> Mine has a RS232 interface, exact reference, no temp drift, > will have a 100% battery switch off MOSFET added.
In that case, if these are really needed, your design is well justified.
> I must say, that going for a simpler design is not always the best=20 > solution.
I agree, and I chose my PIC design for similar reasons. But maybe even = more=20 important was my fascination with PICs and the fact that they can be=20 reprogrammed to achieve various different behavior without major = hardware=20 changes.
> The reason I threw out that other thing is that it would not start=20 > reliably > with huge capacitive loads (and then overheat the transistor). > Think 2700 uF (in the scintillation probe). > Maybe yours will start because of that resistor current limit. > But also with an expensive LCD, 2 more PICs powered from it, plus a > HV generator, plus pre-amp, I need quiet (smooth ripple), accurate > (voltage regulation), no thermal drift > (data acquisitions can take up to 24 hours). > And full battery protection against over-discharge. > My design can do that. > Further more the RS232 status is used in all the PICs (they talk with > each other), and allows for remote control and debugging, also=20 > data-logging.
I need to check your other thread to see what the original design was, = along=20 with the requirements. I "jumped the gun" a bit.
> I dunno about 'instabilities' with PICs, one point where I would > really have seen instabilities is my 3 PIC LED light controller with > ethernet interface. > So far none. Also there the PICs talks to each other via RS232. > As you know the SPI hardware unit in the 18F14K22 does not work > as advertised, so I did that in software.
I have not used SPI (yet), and I have not used that PIC, but that is = good to=20 know. Thanks!
> I have not seen any instabilities in any of the other PIC designs =
either.
> And I am not payed by Microchip to say this.
The design I was working on usually seemed OK, but sometimes "burped". = It=20 was a high power flashlight which used 12 VDC from an SLA battery, = driving a=20 bank of either seven or thirteen high power white LEDs at about 3W each. = So=20 battery current could be as high as 5 amps, and output voltage could be = as=20 much as 60 volts, and this was on a tiny 1" x 2.5" PCB. I monitored = battery=20 voltage, output voltage, and (primarily) output current. I also had a = low=20 and high brightness setting which was selected just by switching input = power=20 on and off. There were to be no other controls, as this was a sealed = unit=20 for diving purposes. I worked on this design on and off for a couple of years, and my = customer=20 always seemed to find new LEDs that were brighter and/or more efficient, = so=20 his specs kept changing. I started with a PIC16F684 design, then, on = advice=20 from a friend with more experience with switchers, I made a design using = an=20 LT1247. Finally I made a third design using a PIC16F616, but still had=20 problems. Then when the economy tanked the demand for such diving = equipment=20 dried up and the project was put on hold. Now my customer is using a design, made by a Chinese company, that is = much=20 more complex and (I think) not as good, but they did it for cheap and he = seemed happy enough when they finally got it working. But he came to me = many=20 times complaining that they didn't understand what he wanted. I think = part=20 of the problem is that it is difficult to make a 40 watt boost converter = in=20 a volume of 2 cubic inches, especially with efficiency greater than 85%. It becomes much more difficult when it must be boosted from a low = battery=20 voltage of about 11 VDC to an output of 55 VDC, using a single inductor = (and=20 not a step-up transformer). The peak currents through the inductor,=20 capacitors, and MOSFET became very high, and I think there may have been = some RF interference into the PIC that caused erroneous readings from = the=20 ADCs that caused instability. It was also a learning experience for me, = and=20 not exactly my area of expertise. I can post a schematic and PIC code if anyone is interested. And I have = a=20 bunch of PC boards and parts if anyone can use them. Paul=20
On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S
<sophi.2@invalid.org> wrote in <jajnb8$qg2$1@dont-email.me>:

>On 11/23/2011 3:05 PM, Jan Panteltje wrote: >> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened >> "langwadt@fonz.dk"<langwadt@fonz.dk> wrote in >> <761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>: >> >>> On 23 Nov., 12:08, Jan Panteltje<pNaonStpealm...@yahoo.com> wrote: >>>> >>> snip >>>> It would be short circuit proof IF it was not for the >>>> boost configuration where the diode would conduct from input to output. >>>> So for that in this sort of regulator you need a normal fuse. >>>> For the rest of loads it nicely current limits. >>> >>> I remember seeing some put a cap in series with the diode to make it >>> short >>> circuit proof >> >> mm but caps do not conduct DC? >> >>> >>> -Lasse >>> >>> > >True. That would make it short-circuit proof. Right?
OK :-) But what about output? Maybe like this? in | L | C a k ---||---------|>|--------- out | | | |MOSFET --- | /switch / \ === | --- --- | | | /// /// /// 2 diode losses..
On a sunny day (Wed, 23 Nov 2011 15:12:09 -0600) it happened John S
<sophi.2@invalid.org> wrote in <jajnjd$qg2$2@dont-email.me>:

>On 11/23/2011 3:10 PM, Jan Panteltje wrote: >> On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S >> <sophi.2@invalid.org> wrote in<jajnb8$qg2$1@dont-email.me>: >> >>> On 11/23/2011 3:05 PM, Jan Panteltje wrote: >>>> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened >>>> "langwadt@fonz.dk"<langwadt@fonz.dk> wrote in >>>> <761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>: >>>> >>>>> On 23 Nov., 12:08, Jan Panteltje<pNaonStpealm...@yahoo.com> wrote: >>>>>> >>>>> snip >>>>>> It would be short circuit proof IF it was not for the >>>>>> boost configuration where the diode would conduct from input to output. >>>>>> So for that in this sort of regulator you need a normal fuse. >>>>>> For the rest of loads it nicely current limits. >>>>> >>>>> I remember seeing some put a cap in series with the diode to make it >>>>> short >>>>> circuit proof >>>> >>>> mm but caps do not conduct DC? >>>> >>>>> >>>>> -Lasse >>>>> >>>>> >>> >>> True. That would make it short-circuit proof. Right? >> >> OK :-) >> But what about output? >> > >What output?
DC ouput? But I think I have that solved, see my other reply.
On 11/22/2011 7:57 PM, P E Schoen wrote:
> "Jan Panteltje" wrote in message news:jagk8l$o1f$1@news.datemas.de... > >> A PIC based boost converter > > I like to use PICs almost everywhere, and I designed a circuit using a > PIC16F616 that took 12 VDC nominal from a battery and produced as much > as 40 watts, on a little PCB about 1" x 2.5". It drove a string of up to > 13 high power LEDs in series so the output voltage was close to 50 VDC. > But it had problems with stability and I could only get about 70-80% > efficiency at best. > > A while ago we were discussing the "Joule Thief" circuit, and I played > around with LTSpice and I actually built a deadbug circuit about as ugly > as yours, that worked pretty well to light two white LEDs in series from > 1.5 volts to 3 volts or so. > > I don't know how much power you are looking for, or how tightly you need > to regulate the output, but I just put together an LTSpice simulation > for a similar circuit, using only two 2N2222s and a dual winding 100uH > inductor that works down to 1 volt and has efficiency up to 89% at 3 > volts, with an output of 5 VDC nominal into 100 ohms (about 250-360mW). > > At the very least, this circuit could be used to provide a good voltage > for the PIC and a solid turn-on for a honking big MOSFET. And the whole > thing can be built for less than a dollar, without any programming. I'm > going to use my PICs for more demanding applications. The ASCII file > follows, with the actual figures for output in the text at the bottom . > > Paul
Hi, Paul - I would be interested to know how you arrived at your efficiency numbers. I have run your circuit and I cannot get the same results. I used the LTSpice ability to get the power in R2, averaged it, then got the (negative) power in V1, averaged it, then divided output by the input. I got about 69.8% with V1 at 3V. Cheers, John S
On 23 Nov., 22:05, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened > "langw...@fonz.dk" <langw...@fonz.dk> wrote in > <761a9bb1-4083-4555-afa8-eef6d073f...@h3g2000yqa.googlegroups.com>: > > >On 23 Nov., 12:08, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote: > > >snip > >> It would be short circuit proof IF it was not for the > >> boost configuration where the diode would conduct from input to output. > >> So for that in this sort of regulator you need a normal fuse. > >> For the rest of loads it nicely current limits. > > >I remember seeing some put a cap in series with the diode to make it > >short > >circuit proof > > mm but caps do not conduct DC? >
in normal operation the switch node is not DC but when there's no dc path from input to output, current flow stops when you stop switching -Lasse
On 11/23/2011 3:28 PM, Jan Panteltje wrote:
> On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S > <sophi.2@invalid.org> wrote in<jajnb8$qg2$1@dont-email.me>: > >> On 11/23/2011 3:05 PM, Jan Panteltje wrote: >>> On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened >>> "langwadt@fonz.dk"<langwadt@fonz.dk> wrote in >>> <761a9bb1-4083-4555-afa8-eef6d073f27f@h3g2000yqa.googlegroups.com>: >>> >>>> On 23 Nov., 12:08, Jan Panteltje<pNaonStpealm...@yahoo.com> wrote: >>>>> >>>> snip >>>>> It would be short circuit proof IF it was not for the >>>>> boost configuration where the diode would conduct from input to output. >>>>> So for that in this sort of regulator you need a normal fuse. >>>>> For the rest of loads it nicely current limits. >>>> >>>> I remember seeing some put a cap in series with the diode to make it >>>> short >>>> circuit proof >>> >>> mm but caps do not conduct DC? >>> >>>> >>>> -Lasse >>>> >>>> >> >> True. That would make it short-circuit proof. Right? > > OK :-) > But what about output? > > Maybe like this? > in > | > L > | C a k > ---||---------|>|--------- out > | | | > |MOSFET --- | > /switch / \ === > | --- --- > | | | > /// /// /// > > 2 diode losses.. >
Yes. If no added diode, no output. That's why I said "What Output?" However, you must admit that it will work to limit current.