A PIC based boost converter

On a sunny day (Wed, 23 Nov 2011 08:39:31 -0800) it happened John Larkin wrote in :

This is sort of what I have been doing today, see my other posting, this PIC has several 10 bit ADC channels, and 2 hardware comparators. So I have now input and output voltages, I can also control the output voltage as I use the PIC DAC output as reference. It has a stable programmable internal reference too (1.024 V, x2, x4).

I like the RS232 interface, you do not normally see that on switcher chips :-)

Thank you. Yes, this will, once the final circuit is determined, go on those little eurocards with holes.

I have build a lot of stuff like this, spider web, we call it 'haystack', but I try to stay in 2 dimensions, even did a short wave receiver that took a whole table top, with CA3020 diff amps and CA3028 audio amp, or was it the other way around, XF9B crystal 9 MHz filters. Was a VERON (radio amateur club) design, I improved it a bit with better input stage. That thing was incredibly sensitive, took it apart again when it worked, just a fun experiment.

It looks really nice, dremel work? That is nice for RF.

Reply to
Jan Panteltje
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On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened " snipped-for-privacy@fonz.dk" wrote in :

mm but caps do not conduct DC?

Reply to
Jan Panteltje

True. That would make it short-circuit proof. Right?

Reply to
John S

On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S wrote in :

OK :-) But what about output?

Reply to
Jan Panteltje

What output?

Reply to
John S

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.

In that case, if these are really needed, your design is well justified.

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.

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 have not used SPI (yet), and I have not used that PIC, but that is = good to=20 know. Thanks!

either.

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

Reply to
P E Schoen

On a sunny day (Wed, 23 Nov 2011 15:07:48 -0600) it happened John S wrote in :

OK :-) But what about output?

Maybe like this? in | L | C a k ---||---------|>|--------- out | | | |MOSFET --- | /switch / \ === | --- --- | | | /// /// ///

2 diode losses..
Reply to
Jan Panteltje

On a sunny day (Wed, 23 Nov 2011 15:12:09 -0600) it happened John S wrote in :

DC ouput?

But I think I have that solved, see my other reply.

Reply to
Jan Panteltje

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

Reply to
John S

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

Reply to
langwadt

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.

Reply to
John S

On a sunny day (Wed, 23 Nov 2011 15:40:20 -0600) it happened John S wrote in :

Yes, sure, in some situations this could be a really good solution.

Reply to
Jan Panteltje

However, I don't like the current spikes it will produce. I would probably look for a cleaner solution.

Reply to
John S

"John S" wrote in message news:jajot1$qg2$ snipped-for-privacy@dont-email.me...

numbers.=20

I have changed the circuit a bit now, but I run the simulation long = enough=20 for the output to stabilize (5-10 mSec), and then I select the last 5 = mSec=20 or so for the calculation. I use I(V1)*V(IN) for input power, and=20 I(R3)*V(Vout) for output power.

I just ran the new circuit at 2 VDC with 5.25 Vout (292 mW), and = efficiency=20 is 81.8% between 10 mSec and 15 mSec.

At 3 VDC I got 88.3% efficiency with 5.49 Vout (341 mW). At this voltage = the=20 circuit operates in burst mode.

At 1.5 VDC I got 73% efficiency with 4.75 Vout (226 mW)

It even works down to 0.7 VDC with 1.78 Vout (31.4 mW), at 62% = efficiency.

I'm sure it can be optimized to do a bit better, and an actual circuit = may=20 not do as well, but I have built a similar circuit and it worked OK. I = even=20 built a more powerful version using a MOSFET and a gate driver, and I = think=20 it worked OK down to about 6 volts and as high as 16 volts, which were=20 beyond what I needed for the 12 VDC battery application. Adding a good=20 voltage reference and an op-amp with some hysteresis in the feedback,=20 controlling the MOSFET driver, should give tight regulation and high=20 efficiency, at the cost of some output ripple.

But mostly I think this circuit is handy to boost nominal 1.5 VDC to = about 5=20 VDC for logic and maybe 8 VDC for MOSFET gate drive.

Paul

Here's the newer circuit:

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Version 4 SHEET 1 1476 680 WIRE 768 -32 144 -32 WIRE -272 0 -320 0 WIRE -208 0 -272 0 WIRE -96 0 -208 0 WIRE 208 0 -96 0 WIRE 208 16 208 0 WIRE -96 32 -96 0 WIRE 672 64 592 64 WIRE 672 96 672 64 WIRE 208 112 208 96 WIRE 240 112 208 112 WIRE 464 112 304 112 WIRE 496 112 464 112 WIRE 592 112 592 64 WIRE 592 112 496 112 WIRE -208 128 -208 0 WIRE -320 160 -320 0 WIRE -96 160 -96 112 WIRE -16 160 -96 160 WIRE 208 160 208 112 WIRE 288 160 208 160 WIRE 496 160 496 112 WIRE 768 160 768 -32 WIRE -96 176 -96 160 WIRE -16 176 -16 160 WIRE 288 192 288 160 WIRE 592 192 592 112 WIRE 672 208 672 176 WIRE 704 208 672 208 WIRE 208 224 208 160 WIRE 672 240 672 208 WIRE -96 272 -96 256 WIRE -16 272 -16 240 WIRE -16 272 -96 272 WIRE 48 272 -16 272 WIRE 144 272 144 -32 WIRE 144 272 128 272 WIRE -96 304 -96 272 WIRE 288 336 288 256 WIRE 496 336 496 224 WIRE 496 336 288 336 WIRE 672 336 672 320 WIRE 672 336 496 336 WIRE -320 384 -320 224 WIRE -208 384 -208 208 WIRE -208 384 -320 384 WIRE -96 384 -96 368 WIRE -96 384 -208 384 WIRE 176 384 -96 384 WIRE 208 384 208 320 WIRE 208 384 176 384 WIRE 288 384 288 336 WIRE 288 384 208 384 WIRE 384 384 288 384 WIRE 592 384 592 272 WIRE 592 384 464 384 WIRE 768 384 768 256 WIRE 768 384 592 384 WIRE 176 432 176 384 FLAG 176 432 0 FLAG 464 112 Vout FLAG -272 0 IN SYMBOL npn 144 224 R0 WINDOW 0 43 29 Left 0 WINDOW 3 26 59 Left 0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL ind2 -80 128 R180 WINDOW 0 36 80 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName L1 SYMATTR Value 100=B5 SYMATTR Type ind SYMBOL ind2 192 0 R0 WINDOW 3 37 69 Left 0 SYMATTR Value 100=B5 SYMATTR InstName L2 SYMATTR Type ind SYMBOL res -112 160 R0 SYMATTR InstName R1 SYMATTR Value 220 SYMBOL voltage -208 112 R0 WINDOW 123 0 0 Left 0 WINDOW 39 7 138 Left 0 WINDOW 3 13 109 Left 0 SYMATTR SpiceLine Rser=3D.1 SYMATTR InstName V1 SYMATTR Value 1.5 SYMBOL schottky -80 368 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D3 SYMATTR Value 1N5818 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 240 128 R270 WINDOW 0 20 73 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D5 SYMATTR Value 1N5818 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 480 160 R0 SYMATTR InstName C1 SYMATTR Value 100=B5 SYMBOL schottky 304 256 R180 WINDOW 0 24 72 Left 0 WINDOW 3 -20 -2 Left 0 SYMATTR InstName D7 SYMATTR Value 1N5818 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap -336 160 R0 SYMATTR InstName C2 SYMATTR Value 100=B5 SYMBOL cap -32 176 R0 SYMATTR InstName C3 SYMATTR Value .002=B5 SYMBOL res 576 176 R0 SYMATTR InstName R2 SYMATTR Value 100 SYMBOL res 480 368 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 1 SYMBOL npn 704 160 R0 WINDOW 0 43 29 Left 0 WINDOW 3 26 59 Left 0 SYMATTR InstName Q2 SYMATTR Value 2N2222 SYMBOL res 656 80 R0 SYMATTR InstName R4 SYMATTR Value 4.3k SYMBOL res 656 224 R0 SYMATTR InstName R5 SYMATTR Value 750 SYMBOL res 144 256 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 47 TEXT 24 24 Left 0 !K1 L1 L2 1 TEXT -24 416 Left 0 !.tran 15m startup TEXT 792 48 Left 0 ;81.9% eff at 2 VDC, 32 kHz, 5.49V, 292mW output TEXT 792 72 Left 0 ;88.3% eff at 3 VDC, 27 kHz (burst), 5.3V, 340mW = output TEXT 792 0 Left 0 ;62% eff at 0.7 VDC, 28 kHz, 1.78V, 31 mW output TEXT 792 24 Left 0 ;73% eff at 1.5 VDC, 23 kHz, 4.75V, 226mW output

Reply to
P E Schoen

Even though its pulsed, it still is DC. Hint: current flows in one direction.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
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Reply to
Nico Coesel

Here is a variation of the circuit, which puts out a (roughly) constant=20 current of about 2 amps at up to 35 watts. It uses only 15 parts, = including=20 the load, which I represent as a 15 volt zener instead of a string of = high=20 power LEDs. I read efficiencies of about 87% from 10 to 15 volts, but = the=20 output actually drops at higher voltage. This circuit needs optimizing, = but=20 shows the possibilities for a very simple design.

Paul

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Version 4 SHEET 1 1048 680 WIRE -32 0 -208 0 WIRE 208 0 -32 0 WIRE -32 16 -32 0 WIRE 208 16 208 0 WIRE -32 112 -32 96 WIRE 208 112 208 96 WIRE 240 112 208 112 WIRE 320 112 240 112 WIRE 432 112 384 112 WIRE 560 112 432 112 WIRE -208 144 -208 0 WIRE 240 144 240 112 WIRE 432 192 432 112 WIRE -32 208 -32 192 WIRE -32 208 -112 208 WIRE -32 224 -32 208 WIRE 192 224 -32 224 WIRE -32 256 -32 224 WIRE -112 272 -112 208 WIRE 304 272 176 272 WIRE 336 272 304 272 WIRE 432 272 432 256 WIRE 432 272 400 272 WIRE 560 272 560 112 WIRE 240 288 240 240 WIRE 432 288 432 272 WIRE 48 304 32 304 WIRE 96 304 48 304 WIRE 176 304 176 272 WIRE 304 320 304 272 WIRE 48 352 48 304 WIRE 160 352 128 352 WIRE -208 384 -208 224 WIRE -112 384 -112 352 WIRE -112 384 -208 384 WIRE -32 384 -32 352 WIRE -32 384 -112 384 WIRE 160 384 160 352 WIRE 160 384 -32 384 WIRE 240 384 240 368 WIRE 240 384 160 384 WIRE 304 384 240 384 WIRE 432 384 432 368 WIRE 432 384 304 384 WIRE 560 384 560 336 WIRE 560 384 432 384 WIRE 560 416 560 384 FLAG 560 416 0 SYMBOL ind2 -16 112 R180 WINDOW 0 36 80 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName L1 SYMATTR Value 10=B5 SYMATTR Type ind SYMBOL ind2 192 0 R0 SYMATTR InstName L2 SYMATTR Value 10=B5 SYMATTR Type ind SYMBOL res -48 96 R0 SYMATTR InstName R1 SYMATTR Value 300 SYMBOL voltage -208 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL res 416 272 R0 SYMATTR InstName R2 SYMATTR Value 0.5 SYMBOL npn 32 256 M0 WINDOW 0 33 47 Left 0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 192 288 R90 WINDOW 0 2 38 VBottom 0 WINDOW 3 30 37 VTop 0 SYMATTR InstName R3 SYMATTR Value 499 SYMBOL schottky 320 128 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D3 SYMATTR Value MBR735 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 544 272 R0 SYMATTR InstName C1 SYMATTR Value 330=B5 SYMBOL schottky 400 288 M270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D4 SYMATTR Value 1N5818 SYMATTR Description Diode SYMATTR Type diode SYMBOL zener 448 256 R180 WINDOW 0 24 72 Left 0 WINDOW 3 -109 3 Left 0 SYMATTR InstName D1 SYMATTR Value BZX84C15L SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 288 320 R0 WINDOW 3 31 47 Left 0 SYMATTR Value 5=B5 SYMATTR InstName C3 SYMBOL res 144 336 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 23 51 VTop 0 SYMATTR InstName R4 SYMATTR Value 2k SYMBOL nmos 192 144 R0 SYMATTR InstName M1 SYMATTR Value STD30NF06L SYMBOL res -96 368 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R5 SYMATTR Value 100 SYMBOL res 224 272 R0 SYMATTR InstName R6 SYMATTR Value 0.2 TEXT 272 40 Left 0 !K1 L1 L2 1 TEXT -96 408 Left 0 !.tran 20m startup TEXT 480 32 Left 0 ;88% eff, 12 VDC in, 1.88 A, 33.75 W TEXT 480 0 Left 0 ;86.7% eff, 10 VDC in, 1.95 A, 35.3 W TEXT 480 64 Left 0 ;87.5% eff, 15 VDC in, 1.58 A, 26.62 W, 23 kHz=20

Reply to
P E Schoen

Ha, you're so funny.

Have fun with your endeavors..

Jamie

Reply to
Jamie

He has been.

He has supplied something of substance especially compared to your posts of almost indecipherable verbiage. What have you posted of any value other than your ill-informed criticism? Please point to something.

Reply to
John S

ge

GLE

So, you aren't doing peak current mode switching, as every switching circuit with a current sense and comparator does?

So, you don't mind that you have no DC current reference?

So in short, you've created a voltage-mode boost converter with current feedback that...just kind of sits there?

Yuuuuck.

Yes there is. The drain current stops for about half a cycle on average. Current transformers don't happen to work at DC.

Tim

Reply to
Tim Williams

I thought there were some problems with the design, but I was not = motivated=20 enough to analyze it. I think it's cool to have some of the features = that=20 the PIC offers, but the basic circuit seemed overly complex for whatever = the=20 specs may be. I looked at a previous thread on "Favorite boost = converter"=20 but there were no details. But if you really just need a power supply = with=20 normal specs, there are many available for cheap. I just bought an = LM2596=20 step-down converter on eBay for $3.25 including shipping:

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ame=3DADME:L:OC:US:1123

The same company has many other small boards available cheap, such as = this=20 LM3577 boost converter for $0.99 + $4.90 shipping:

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h=3Ditem3a6d0b77c2

This one is rated for an input of 0.9 to 6V, and an output of 3.3-9V, = for=20 $3.25 and free shipping.

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rs&hash=3Ditem3cbed8d3fc

I love to design my own circuits and add special features, but when you = just=20 need a particular solution for a need, there's usually something = available=20 better and cheaper than you can do it yourself. Faster? Not so much.=20 Shipping from China is about 3 weeks.

Paul=20

Reply to
P E Schoen

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