I had to make +100...+400V from +9V at power level up to 10W. The obvious solution was flyback convertor; using wal-wart power supply transformer in backwards mode. However the particularly septic thing about it was huge stray inductance both on primary and secondary side. So, after scorching some parts, I came up with following antiseptic solution:
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This antiseptic convertor topology works great. Delivers 10W with no heat and no dissipation in snubbers. The transformer is standard off the shelf part; there are dozens of suitable transformers available.
Cute idea--turning the leakage inductance from a bug into a feature. I suppose there are limits on the turns ratios and so forth--the catch winding will need to be similar to the primary, right?
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
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Yep, Clever, Recovering energy from the "snubber".
An idea worth playing with to find the trade-offs. ...Jim Thompson
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| James E.Thompson | mens |
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I love to cook with wine. Sometimes I even put it in the food.
The problem with this is how to turn power off. I could remove the whole sepic part by connecting diode directly to FET drain like in boost topology. But then it would require separate switch so to be able to turn off +9V from load.
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
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
I worked for a teeny while on a group whose product featured a DC-DC converter with "active snubbers" -- basically, they recovered the energy in the snubbers with little switching supplies that dumped the result into the main rail.
It's not something that'd be worth it for a 10W supply, unless the end use was way esoteric, but it was my first introduction to the idea, and interesting.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I did that on one off-line switcher for OmniComp/GenRad. Back in the days when the device of choice was MJE?????, an HV bipolar device.
I used diodes, capacitors, resistors and pot cores for the snubbers.
This was the infamous switcher where I removed the flag heat sinks, then forgot the voltage when I grabbed one flag to check the temperature.
Got knocked on my keezer, much to the delight of the technicians ;-) ...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.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
I'm probably going to do that, some day. Quasi-resonant snubbers aren't always appropriate, and you can incur a lot of VAs pushing volts around, especially at high frequencies.
I was playing with a PP design recently that, it seems, simply cannot have low switching losses. I can't convince myself that it is fundamentally different from anything else (half bridge, say), but for the range of component values I tried, it seems 20% of total output going into the snubber (hopefully, to be recycled!) is nearly optimal.
Magnitude of the snubber recovery can vary -- a PP snubber is of course dV/dt or Vpeak only (that is to say, you could do dI/dt or Ipk as well, but with most of the stray inductances hidden in the transformer, you'd have a hard time getting at it), and in either case sees a voltage of about 2*Vcc. So you only need a 50% buck to recover that. Vpk snubbing on most things (say, the stray inductance in any conventional bridge, including buck, boost, half- and full-) might only generate a little voltage, maybe 10% of supply, but it's floating on top of the supply, too. So you'd need, say, a 30-to-300V flyback to recover it. Sometimes, those are just cheaper to burn off in resistors.
Must be 13k or 18k series?
The small ones (13003 or so; TO-126 package) are used in massive quantity for CFLs.
Early in my induction heating developments, I tried paralleling a bunch of MJE18008s for a bigass power oscillator -- didn't get the current sharing right (or they oscillated between) and one politely erupted into flames. :)
Tim
--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com
Switching locus virtually following along right on the axes. Thus very little heating.
That was also my first use of an OptoCoupler in the feedback loop (controlled by a TL431 configured as an OpAmp ;-) ...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.
Insert-controller-chip-here. Probably, the source is also not exactly grounded, but has a shunt resistor for current sense. At 9V, a UC3843 would do just fine. Follow the datasheet's standard circuit, patching in this schematic for all the post-MOSFET business.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com
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