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| DC-DC 3v to 400v step up |
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| acorn222:
Hi, I am looking for a way to get DC-DC step up from 3v to 400v, only needing to deliver 5mA max at 400v, I have looked for a while now and have found some bulky modules, however I cannot find a way to do this in a compact mannor for a reasonable price (under $15), It needs to be able to be turned on and off at a logic level (which I know how to do externally, it would be nice to find a chip which could do this with it built in). The only modules I have found that can do this are for over $40 which seems way too much for what it is. My question is, are there any modules or chips I should know about that would help me? Thanks |
| Buriedcode:
The only thing I can think of is a flyback converter. With such a high step up ratio, a boost converter would struggle having such a low duty, but may be possible to get 3 to 75V with a boost converter, followed by a couple of stages of a voltage multiplier. Off the shelf flyback transformers (technically coupled inductors) are available for xenon camera flash and strobe circuits, often with the turns ratio of 1:10 or 1:12. There are also chips specifically designed to drive said inductors (deisnged to run off 2 AA's or Lithium = ~3V input), but these are more for charging photoflash capacitors rather than for a continuous DC output. I would say any boost converter chip with a maximum peak output >40, and one of the mentioned transformers. If you use a converter with an external MOSFET it'll be easier as you could pick a MOSFET with a higher Vds breakdown. |
| Ian.M:
Oops! See Ejeffrey's comment below. |O Assuming 90% efficiency, 5mA @400V out needs 7.4A @3V in. Pushing 22W through a flyback transformer while keeping efficiency up around 90% with only a 3V supply is going to be challenging. IMHO it needs a push-pull forward converter. That's gong to need a switching transformer with the right pri:sec ratio, with a center-tapped primary, some big low Vgs threshold MOSFETS to drive the ends of the primary and a controller chip to provide antiphase gate drive, with current and voltage feedback, that will run at 3V. It *MAY* be easier to boost the 3V to 12V just for the controller chip and MOSFET gate drive to allow a wider choice of parts. The primary supply to the transformer would still be at 3V. I doubt you could get the parts for $40 - custom magnetics that can handle approx 15A* primary current without saturation don't come cheap. You *MIGHT* get there with a transformer from an PC PSU driven backwards, using its 3.3V winding as the primary, and its original primary as the secondary, operating into a voltage doubling rectifier. * When driving an inductor with a square voltage pulse, provided the flux resets to zero between pulses, the peak current is double the average current during the on time. |
| ejeffrey:
--- Quote from: Ian.M on July 08, 2019, 08:38:07 pm ---Assuming 90% efficiency, 5mA @400V out needs 7.4A @3V in. Pushing 22W through a flyback transformer while keeping efficiency up around 90% with only a 3V supply is going to be challenging. --- End quote --- It's 2 W not 20 W :) |
| MagicSmoker:
--- Quote from: acorn222 on July 08, 2019, 07:32:44 pm ---Hi, I am looking for a way to get DC-DC step up from 3v to 400v, only needing to deliver 5mA max at 400v, I have looked for a while now and have found some bulky modules, however I cannot find a way to do this in a compact mannor for a reasonable price (under $15) --- End quote --- This is just about the right voltage and power for the photoflash charger used in old (pre-LED) cameras. You should find lots of circuits and pre-assembled boards that can be used as-is or slightly modified. The specific topology is self-oscillating flyback, also called a blocking oscillator (obsolete term). EDIT - found a good example for you: http://www.talkingelectronics.com/projects/XenonFlasher/XenonFlasher.html |
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