1. Home
  2. Electronics Design
  3. inverting dc-dc converter circuit
  4. Page 3

inverting dc-dc converter circuit

MooseFET wrote:

in a pinch, I would use something like this for a low level -33 volts . I changed the values to fit the thread that was going on here. PS. It uses a 555 :), just to stir the pot!

Version 4 SHEET 1 880 680 WIRE 240 -80 64 -80 WIRE 240 -64 240 -80 WIRE -192 -48 -320 -48 WIRE 64 -48 64 -80 WIRE 64 -48 -192 -48 WIRE 96 -16 80 -16 WIRE -192 48 -192 -48 WIRE -192 64 -192 48 WIRE -160 128 -192 128 WIRE 80 128 80 -16 WIRE 80 128 64 128 WIRE 240 128 240 32 WIRE 272 128 240 128 WIRE 400 128 336 128 WIRE 496 128 400 128 WIRE 240 144 240 128 WIRE 496 160 496 128 WIRE 400 176 400 128 WIRE -192 192 -192 128 WIRE -160 192 -192 192 WIRE 144 192 64 192 WIRE -320 256 -320 -48 WIRE -288 256 -320 256 WIRE -160 256 -288 256 WIRE 96 256 64 256 WIRE 240 256 240 224 WIRE 240 256 96 256 WIRE 400 256 400 240 WIRE 400 256 240 256 WIRE 496 256 496 224 WIRE 496 256 400 256 WIRE 96 288 96 256 WIRE -288 304 -288 256 WIRE -192 320 -192 272 WIRE 144 320 144 192 WIRE 144 320 -192 320 WIRE -192 336 -192 320 WIRE -288 400 -288 384 FLAG 96 288 0 FLAG -288 400 0 FLAG -192 400 0 SYMBOL Misc\\NE555 -48 160 R180 SYMATTR InstName U1 SYMBOL voltage -288 288 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMATTR SpiceLine Rser=0 SYMBOL res -208 32 R0 WINDOW 3 -64 71 Left 0 SYMATTR InstName R2 SYMATTR Value 2000 SYMBOL cap -208 336 R0 SYMATTR InstName C2 SYMATTR Value 0.01µf SYMBOL res -208 176 R0 WINDOW 3 -60 41 Left 0 SYMATTR InstName R1 SYMATTR Value 1500 SYMBOL ind 224 128 R0 SYMATTR InstName L1 SYMATTR Value 1mh SYMBOL schottky 336 112 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D2 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 384 176 R0 SYMATTR InstName C1 SYMATTR Value .5µf SYMBOL res 192 -32 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL pnp 176 32 M180 SYMATTR InstName Q1 SYMATTR Value BCW68F SYMBOL zener 480 160 R0 SYMATTR InstName D1 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode TEXT 416 408 Left 0 !.tran 0 0.010 0 1 startup

Reply to
Jamie
Loading thread data ...

:

If you want more efficient operation, you could do this:

Version 4 SHEET 1 880 680 WIRE 240 -80 64 -80 WIRE 240 -64 240 -80 WIRE -320 -48 -448 -48 WIRE 64 -48 64 -80 WIRE 64 -48 -320 -48 WIRE 96 -16 80 -16 WIRE -320 48 -320 -48 WIRE -320 64 -320 48 WIRE -160 128 -320 128 WIRE 80 128 80 -16 WIRE 80 128 64 128 WIRE 240 128 240 32 WIRE 272 128 240 128 WIRE 400 128 336 128 WIRE 720 128 400 128 WIRE 240 144 240 128 WIRE 720 160 720 128 WIRE 400 176 400 128 WIRE -320 192 -320 128 WIRE -160 192 -320 192 WIRE 144 192 64 192 WIRE -448 256 -448 -48 WIRE -416 256 -448 256 WIRE -160 256 -416 256 WIRE 96 256 64 256 WIRE 240 256 240 224 WIRE 240 256 96 256 WIRE 400 256 400 240 WIRE 400 256 240 256 WIRE 512 256 400 256 WIRE 720 256 720 224 WIRE 720 256 592 256 WIRE 96 288 96 256 WIRE -416 304 -416 256 WIRE 848 304 784 304 WIRE -320 320 -320 272 WIRE -192 320 -320 320 WIRE 144 320 144 192 WIRE 144 320 -192 320 WIRE -320 336 -320 320 WIRE -192 336 -192 320 WIRE 720 352 400 352 WIRE 144 368 144 320 WIRE 400 368 400 352 WIRE 400 368 144 368 WIRE -416 400 -416 384 WIRE -192 400 -320 400 FLAG 96 288 0 FLAG -416 400 0 FLAG -320 400 0 FLAG 848 304 0 SYMBOL Misc\\NE555 -48 160 R180 SYMATTR InstName U1 SYMBOL voltage -416 288 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR SpiceLine Rser=3D0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL res -336 32 R0 WINDOW 3 -64 71 Left 0 SYMATTR Value 2000 SYMATTR InstName R2 SYMBOL cap -208 336 R0 SYMATTR InstName C2 SYMATTR Value 0.01=EF=BF=BDf SYMBOL res -336 176 R0 WINDOW 3 -60 41 Left 0 SYMATTR Value 1500 SYMATTR InstName R1 SYMBOL ind 224 128 R0 SYMATTR InstName L1 SYMATTR Value 1mh SYMBOL schottky 336 112 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D2 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 384 176 R0 SYMATTR InstName C1 SYMATTR Value .5=EF=BF=BDf SYMBOL res 192 -32 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL pnp 176 32 M180 SYMATTR InstName Q1 SYMATTR Value BCW68F SYMBOL zener 704 160 R0 SYMATTR InstName D1 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode SYMBOL npn 784 352 R180 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 608 240 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 10k TEXT 416 408 Left 0 !.tran 0 0.010 0 1 startup

Reply to
MooseFET

Yes, good old common base biasing. fits the bill ;)

Reply to
Jamie

formatting link
Oh that circuit has a name? ;-) Thanks.

Reply to
miso

Here's my inverter, sort of similar.

ftp://jjlarkin.lmi.net/Inverter.jpg

The thevenin impedance seen by the emitter determines loop gain. I needed the ESR of the tantalum in the output to get good loop stability; startup dV/dT is low enough that a tantalum appears safe here.

Load regulation is surprisingly good, about a tenth of a volt from 80 to 500 mA.

John

Reply to
John Larkin

ote:

I see a start up problem here. Look at the UVL of the LM5112. Won't this circuit whack the inductor while starting up?

Reply to
miso

It's designed to start up at about 70% duty cycle. When the output gets close to -12, the transistor turns on and backs off the duty cycle to whatever it needs, which should be a bit over 50%.

John

Reply to
John Larkin

I'm talking about the first pulse. The P-fet will be on because of the UVL being designed with a N-fet in mind. You should be able to see this on a storage scope.

I see a lot of people rolling their own converters and have read the justifications, but seriously, controller chips have (or should have if done well) every contingency in mind. The first pulse, the initial ramp up (soft start), etc. Linear Tech, Maxim, etc parts have been tied to the whipping post and flogged without mercy. If you sell millions of a component, even problems with 1% of them is a total disaster.

Reply to
miso

No, often they haven't. By far the biggest conceptual mistake is running the internal VCC regulator at around 7.5V. Pretty much none of the FETs above 200V Vds are guaranteed at less than 10V gate drive. Don't they _read_ datasheets? What are they thinking? So you end up with some external sauerkraut to correct that mistake with discrete parts. BTDT. Great.

Then there's more, for example a lack of a 2nd FB input to current-limit. So, more sauerkraut externally. At some point you might as well roll the whole thing your self, and I often do.

I could go on. But the final clincher is the old $$$. A chip that costs $2 or more in qties just doesn't fly in many designs. What the world needs is a MC34063 in FET technology and running at up to a MHz. And a similar TL494. Whoever brings that to market at reasonable pricing will rake in tons of sales.

[...] 
--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Reply to
Joerg

I was looking at a UCC something PFC controller the other day. It was designed for 48-96V input service, for telecom supplies. Okay, fine. Maybe it's still useful at 88-265V, just a few resistors away. It had a 3.3V internal reference: whatever, the UC3842 gets away with 1.25V. But, they powered the output stage from Vref! That's just barely within the range of an average MOS driver (usually a guaranteed TTL level input), and not enough for any transistor directly, even if it had a beefy output stage (which it didn't, only ~10mA).

Why two current limits? Is that for, say, accurate output current limiting (for a square output characteristic), plus inverter current limiting (via CT or whatever)?

Yeah, I was recently looking for forward controllers... now, there's millions of flyback sorts of devices, and (usually with slope compensation) these can be built into half wave forward converters too. But TL494 and TL598 (totem pole output, cf. SG3524 and 3525) are the only push-pull forward controllers I've seen. I was shocked to see there is well and truely nothing new in this market, where the old, slow bipolar devices still rule.

I would love to have one with beefy CMOS output (0.2 to 2A gate drive). CMOS is more than capable of implementing the internal circuitry. A speed upgrade besides and you've got a lovely IC.

What is LT doing? I know they've made lots of single-chip and HF sorts of devices, but I never find anything from LT in searches like this.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

In medieval Europe they had a remedy for that: Dunking the people who screwed up into a moat a couple of times, in front of an audience from town. Had a very sobering effect :-)

Besides the current-mode control or a natural power limit you often need to protect a load from over-current. The only way to do this with most switchers is to have some external semiconductors and tug on the FB node via a diode. Not pretty, had to do it many times.

The more common scenario in my case is that the client wants a steerable current source but have it capped at xx volts so nothing gets fried if the load opens up. Same problem, needs two FB inputs but there ain't more than one.

Luckily there's the MIC4421/22 series but that always means two more chips. Not much news in that domain :-(

My current favorite is the LT3757, sweet little chip, very tiny. Nice thing is it can sense negative voltages. Plus they have LTSpice models and that is the best thing since pivot irrigation. Less splatters, transistor pieces and molten solder on the lab bench ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Reply to
Joerg

The original waterboarding?

Jim

Reply to
RST Engineering

Have you seen the UCC25600 LLC Resonant mode controller.Can only sink source 0.4A-0.8A . The absolute minimum guaranteed gate drive output is 9V

formatting link

formatting link

Coilcraft has the gate drive transformer. I have a couple they are tiny.

formatting link

Reply to
Hammy

I'm not seeing Joerg's posts lately. I wonder why.

John

Reply to
John Larkin

Hmm, I've use the spambot evade address the provider suggested but put a fully legit (a.k.a. working) reply-to in the header. Shouldn't be filtered away by any ISP. Or is it?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Reply to
Joerg

Good point, except that it seems to work fine, even from a current-limited bench supply. The UVLO is typically 3 volts, and that klunky old NDT2955 has a 2.6 volt threshold, so it's barely on before the oscillator starts.

But "storage scope"? Is there any other kind?

There aren't many inverting switchers around. The trick of having a regular buck wind its own "ground" rail negative is OK, but usually gets into trouble at higher output voltages. This circuit soft-starts because the +5 reference comes up fairly slowly, by design. That protects the tantalum on the output.

And designing circuits is fun.

But we've had a lot of problems with LDOs and switchers, way more than

1% of the various parts we've used.

National did this to us, LM3102:

ftp://jjlarkin.lmi.net/SwitcherRise.JPG

which cost a whole board spin.

John

Reply to
John Larkin

Ooh, I should revise my induction heater design with one of those. That's basically what I'm doing, except the transformer secondary is a hunk of metal. ;-)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

And next time you demo it with a piece of tube held upwards into the coil at least wear welders gloves :-)

Man, just looking at the video scared me. A guy in the army told me about a similar experiment except that in his case a chunk of white-hot metal decided to follow gravity. Missed his hands but landed right onto one of his shoes ... phssssss ... through the shoe ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Reply to
Joerg

Y...no, I guess not:

formatting link

Although to be fair, the camera's 10 second exposure really gets all the credit.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

Pssh... I ruined my last pair of welding gloves handling the still-hot electrochemical cell when I was cooking up chlorate one summer:

formatting link
That square stainless tank is a little too hot to handle bare, but inevitable spills result in sodium chlorate soaking into the gloves. Needless to say I kept the gloves well away from welding after that. ;-)

Nice one! A classic welding incident, too.

I'll keep that in mind when I get the 10kW beast running. For now, I know exactly how much power I'm delivering, and fortunately, it's not enough to melt steel. So I've been staying out of the hot convection instead.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.