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Flyback vs half-bridge

Spice voltage sources are infinitely powerful; wall warts aren't. Lots of switchers have soft-start, too.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin
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I've got a copy of the second edition ISBN 0-07-052236-7

The chapter on magnetics is comprehensive, and even covers the skin effect, and the "proximity effect" which I've never heard of before. Pedagogically , it's rubbish - almost as bad as Snelling. The author assumes that the rea der understands the basics, and concentrates on the complicated detail.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

I think the torture-test is powering up the wall wart and then plugging it into the box. There'll be the usual polyfuse, whose cold resistance helps a bit, and I suppose I could do something fancier like a resistor parallelled by a MOSFET controlled by the POR chip, but that's way too fancy for just a few watts.

It's really the 1N4148s or BAV99s or whatever little diode I use that will be the issue--the turn-on surge will divide between the main -15V reservoir cap and the charge pump caps more or less proportionally with the size of the caps (neglecting ESR and diode drops). So I may use a much bigger reservoir cap and smaller charge pump caps, followed by RC filters ahead of the cap multipliers. Alternatively, just putting 50 or

100 ohms in series with the charge pumps will protect them OK, and will only cost a volt or two.

It's better from a certification standpoint if the voltages inside the box never exceed 60V even in fault conditions, so I'll need to put zeners on the +-45V outputs, so that even with an out-of-spec input voltage and the transzorb at its upper spec limit, I don't get over 60V.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

That's what most books about advanced technologies do. If they didn't then most of the forests on this planet would be depleted by now :-)

But seriously, a person with lacking EE basics should not be designing switchers without first becoming proficient enough, that's something the pros should do.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

That's a buck. If you already have a -15V switcher in there, why not hook into that as you had outlined earlier?

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I'm using it as an inverter, i.e. grounding the far end of the inductor and letting it pump its ground pin down to -15V. Works fine.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

That's what I was noticing... it's a switch current limit, not an output current limit. But probably safe. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Yup. It's the inrush that tests your specifications ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Yes, that's the old MC34063 method. But watch out for noise and loop stability.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

You might want to reconsider and add soft-start to your "cartoon"....

Subject: Hobb's Cartoon (SED) - HobbsCartoon-with_CL.png Date: Thu, 18 Jul 2013 11:19:26 -0700 Message-ID:

Using the LM2594, you're sort of caught between a rock and a hard-place... large load (on LM2594) capacitor, huge peak currents on your add-on inverter, smaller capacitor... sag your 16V. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson 

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net 

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--------------040407090803080109080400--
Reply to
Phil Hobbs
[...]

Not sure what you did for this post but it came through as a file attachment. No copy - paste, just click it and open into LTSpice. Cool.

Alternatively you might be able to provide an over-voltage lockout. TL431 -> input goes above 18V -> pulls current -> robs current from enabling circuit that serves pin 5 -> switcher goes silent. Pages 29/30 in the datasheet:

formatting link

[...] 
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

P.S.: Didn't you mention you wanted to place cap multipliers at the 45V outputs? Then you could hang zeners off of the bases, which would limit things.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

In my boost-doubler, I just replaced a BAV23S with a couple BAT46W's, and picked up a bunch of efficiency.

In a 9-to-48 volt boost converter, I was seeing over 100 volt spikes at the fet drain, blamed on forward conduction delay in the PN diodes. The BAT schottkies clamp hard at 48.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

I used to do that on Supernews, but they now reject posts with attachments, even text. I got an eternal-september.org account as well, and they apparently allow attachments. Good news.

That's pretty sensible. I'm planning to have the processor control the

+-15V and HV supplies, but a bit of (inexpensive) belt and suspenders never hurts.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

Nice part--like a 100V BAT54. That's a keeper.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

oK, Here is a duh question, When in LTSPICE, how do you save that top level *.asc file you show above?

Thanks, Harry

Reply to
Harry D

I don't think a wall-wart is going to look like 2 Ohms... it's going to be current limited... even if it is made in China ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

There are a couple of methods.

(BTW you should get a real newsreader and a (free) Eternal September account--lots of people round here killfile anyone from Google Groups because of the spam and the zillions of blank lines.

formatting link
).

If you have an eternal-september.org account, you can just use your mailer and attach the .asc file as you would any other file.

Otherwise, open the .asc file in a text editor, and cut-n-paste it into your post.

Mike Engelhardt understands the goodness of human-readable files!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

The 2 ohms is the initial resistance of the polyswitch in the input protection network. Quite a lot of computer wall warts have a big cap at the output, leading to crackling sounds when you plug them into the back of the machine. Anyway, their current limits will be up in the 5A range, which is way above what my little switcher will allow through on a steady state basis.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

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