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| Low quiescent/ standby boost regulator 3.3-500V |
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| Amper:
Mhhh well... Sadly my detector will not be sensitive enough for this particular incident but i can see exactly where your idea is coming from and its definitely a thought in the back of my head i cant get out. My family owns a small hydroelectric power station near lyon (see my older posts about the lithium welder if you are interested) and all the way from the eighties when my dad bought it he wanted to install a permanent radiation logger there for the reason of not trusting governments about this particular topic. Its not like we trust our own one any further but you see where everything is coming from... Maybe some time i will get around to building a better detector, material is almost all in my stock already but the time issue.... Oh and there is much more radiologic stuff going on then you may expect, i have a friend who worked in decontamination as a students job and he made me aware of an incident in Munich, some guy in a company took an angle grinder to a 1TBq source and roughly 1% of its contents left the building via the hot cells exhaust, the entire neighborhood was covered in radioactive dust in an amount that is actually a health risk. But except for a tiny article in a local newspaper there was no mention to the public, you could have walked there and absorbed the stuff... |
| Amper:
Aaaaand im back. Had some spare time and continued the prototype a little bit. It now is made almost entirely from surface mount components that are affordable and the footprint will be tiny once on a pcb. Im now controlling it by only an attiny13 and the control scheme mentioned before. Atm im down to 50uA but my method of measuring it is not the best and likely the actual draw will be even smaller. On a single 2Ah lithium battery 40000h or 4.5 years of continuous supply to the geiger tube is now possible. I still aim to get at least a decade just to beat the gammascout and m pretty confident it will work with jus a few tweaks here and there now. And here is the mess that this ended up being for now but it seems to work beautifully :D |
| jbb:
Hi Amper Glad to see things are going well. This is obviously a difficult design. I have a couple of thoughts that might help with things. * The internal resistance of your battery will go up a lot as the battery discharges, especially if it’s cold. This can significantly reduce the useful mAh capacity of the cell. The remedy is to try to limit the peak current applied to the cell. You may be able to pursue strategies like trying not to turn on beepers or LEDs or radios at the same time as the boost converter. * Large capacitors across the battery can help support peak currents, but their leakage current will drain the battery. There will be a trade off... * Have you considered a tapped inductor boost converter? This is a method to get higher voltage gains out of a boost converter without really large duty cycles. Downside is you’ll need a higher voltage diode (due to transformer action in the tapped inductor when the main switch is on). * Diodes with good switching characteristics (eg very low capacitance and Qrr) may not have the best leakage current. You could combine a very good switching diode with a very low leakage diode to get the best of both. * If you want to sense the main capacitor voltage, you could switch the divider in and out of circuit (eg use a 600V logic level FET). This way you can have reasonable divider resistors without burning too much current * Circuit behaviour could be quite different at higher and lower temperatures (diode Qrr and leakage are particularly sensitive to temperature) And finally, please be careful of the high voltages, especially if you have any large-ish caps about.0 |
| schmitt trigger:
--- Quote from: Amper on July 13, 2019, 04:46:22 pm --- on a breadboard with film caps and 1N4007, it works beautifully. --- End quote --- Are you absolutely positive that you are using plain vanilla 1N4007 diodes? The recovery time for those is orders of magnitude longer than your switching period of 500 Khz. |
| Amper:
@jbb: Now lets break this down step by step :D -Yes, this is a problem, though there is sufficiently low leak super caps and larger lithium batteries will be able to supply quite a bit of current without this problem. The average charge pulse is slightly more than 15mJ (charging 50nF from 0 to 500V and trickling the storage cap). One other reason is that i can actually control the shape of the pulse since i use a micro controller. At the moment i do a few hundred pulses to the boost converter, then wait for 500us, take a voltage reading and then continue charging. This way i can stretch the input current pulse to a certain extent and the 500uS can be swallowed by any ceramic input cap. -Yes, i considered and even tried this a while ago but i wasnt happy with it. It could work much better than igot it to run but in the end there is a very small selection of smd coupled inductors, its a pain to select one and they are almost never rated 500+V and i dont like to use parts out of spec any more. Due to the winding they usually ave the inductances and maximum currents also dont match this application very nicely. One other downside is, there is geiger tubes and other interesting kit that need up to 1500V, so trying a multiplier topology right fro the beginning gives me an opportunity to just extend and have more voltage. Maybe in the future ill try again. -The diodes im using right now for all the steps are GSD2004S. They arerated 50ns but at full current which they will never see in my case and a nominal leak of 100nA@ 300V. Since i only do 50kHz and for the "checkvalve" on the storage cap i use two pair of them (150V per diode = turns out to be less than 10nA) there is no real problem. -The topology i using actually does almost this as i drain the multiplier after each charge. This way im using 66MOhm right now but most likely later it will be only a single 10M precision resistor, mostly for reasons of having less possibility for moisture to change the divider. Your Idea using a FET is interesting, it may come in handy later... Though in this case it will be a Problem since even using logic level with 2Vth when adding the 1.5-2V divider voltage i wont be able to turn it on using a 3-3.3V battery. Also while im still using the multiplier approach, i will have to discharge the multiplier anyways since the ceramics have bad leakage characteristics and a dozen film caps are not very surface mount :D For example the 1.2uF 630V ceramic i first intended turned out to have 80nA leak which corresponds to 6GOhm, the Vishay film cap i turned to now has less than 5nA leak @ 1uF confirmed by the datasheet stating >=100GOhm). Though this also means, any 100GOhm parallel resistance added by parasitics will half my run time between recharges and doing proper continuous measurements of the voltage decay can only be done by such a 100G resistor and an electrometer like my keithley 616. -Yes, the temperature still worries me. But it will mostly be a Problem of the double pair which can be extended without to much additional dropout. The gammascout uses only two BYV26E which are actually really bad, so i hope i will be fine too. Regarding high voltage, dont worry, i have my fair share of experience with very deadly levels of high voltage up to 20kV 1.5A 3phase, pulsed stuff, tesla, and a whole lot of mains installation. One small Project i did lately you can see here: https://www.eevblog.com/forum/projects/zvs-driver-lockup/25/ 20uF@500V with a boost converter delivering 100W+, much better chances of killing myself :D @schmitt trigger I used 1n4007 only int the first tests because thats what i had stock of. I dont remember the Frequencies i tried but 50-100kHz are no Problem at all. The leakage current is a bigger problem though, these things show their age, 10uA leak compared to just 50-100nA with modern devices. Also the size is not suitable for my application, even the sot23 double diodes take away quite a lot of board space... |
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