Electronics > Projects, Designs, and Technical Stuff
Low quiescent/ standby boost regulator 3.3-500V
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Amper:
They basically have a box standard boost converter but the output capacitor is isolated by a string of high voltage diodes. In a usual boost converter this wont work without a load but if you do intelligent pulse skipping up so minutes at a time this way the actual boost converter can be at 0V for the majority of the time while the cap stays charged. Since the discharge rate is so slow its enough to do an active measurement every now ant then at predicted intervals depending on count rate and time.

SiliconWizard:
Well, it's just a discrete high voltage boost converter... ;D
Of course you need a transistor that can take the punishment (the BSP125 has a VDSmax of 600V), the inductor should be able to take it as well.

Putting the feedback network BEFORE the diodes (whereas we would normally rather put it after) allows to have it NOT draw current from the output capacitor, but then it requires something a bit more intelligent than just a simple comparator since the feedback voltage is not exactly a fraction of the output voltage... using an MCU to do this solves a lot of problems. :-+
Amper:
Thats exactly what i was saying ^^ Thats also why it wont work with any off the shelve part that i know of as ist not just pulse skipping. Since every ionization of the tube is a very well defined amount of charge its possible to count them and know the voltage of the cap very closely. Then just have a timer for low count rates and fault conditions, more or less a watchdog and make the converter do a short sounding pulse to the boost.

Though i suspect my tube will reduce battery life a bit more since the si8b is faar more sensitive than the original one used in the gamma scout. I will have a whopping 150 pulses a second with no radioactivity present and up to 5000 per second with sources close to the legal limit.
SiliconWizard:
I'm not very comfortable not being able to monitor the output voltage though... I suppose you can indeed estimate it, but I wouldn't be so sure about the "very closely"... but at least here, being able to monitor the transistor's drain voltage allows the circuit to 1/ estimate when the target output voltage has first been reached (approximately) and 2/ avoid burning up the transistor and inductor... unless of course, there is a software bug.



Amper:
nooooooo. You didnt get how it operates ^^ Its not guessing the voltage, its just predicting the voltage drop so it knows how long it can stay silent taking zero power. When timer or prediction tell that its time for a checkup the boostconverter is powered up, in this moment the diodes will conduct as the boostconverter obviously has a higher output voltage as the cap. This way you can exactly measure the capacitors voltage as long as the converter is running. After shutdown the decay of the voltage is estimated with a safety margin and when it drops a few volts in the calulation the boost converter is started up again for a few cycles and a new measurement can be taken. According to that measurement the boost converter is run until the nominal voltage is exactly reached again, then the next sleep cycle starts and everything is completely currentless besides the microcontroller waiting for interrupts.
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