General > General Technical Chat
Why not CMOS?
David Hess:
--- Quote from: Ian.M on January 29, 2022, 10:51:17 am ---CMOS SRAM typically uses six* MOSFETs per memory cell. FLASH uses one MOSFET, with a regular gate stacked on top of the floating gate that stores the charge that holds the state. Additionally more than one bit can be stored per FLASH cell (MLC FLASH) by treating the stored charge as an analog quantity and decoding it via a fast two or three bit ADC in the on-chip sense amplifiers.
Therefore FLASH wins over SRAM of the same generation technology, as it typically offers an order of magnitude more memory density.
--- End quote ---
That is an apples to oranges comparison because the Flash memory you are describing does not qualify as RAM in the same sense of random access memory that SRAM does. EEPROM qualifies though and is much more comparable to SRAM.
SRAM could be preferred to EEPROM, and by extension all Flash memory types, for performance and endurance reasons.
Kim Christensen:
--- Quote from: Rick Law on January 29, 2022, 10:37:13 pm ---I use a cheapo $15 USD B3603 digitally controlled CC/CV as my bench supply. The thing still "works" except it will no no longer store calibration data. It still "works" only in the sense that if I ignore the build-in display and use external DMM for V/I display. After testing it every way I can think of, my conclusion is that the EEPROM or flash base calibration data storage failed.
That is what made me think why not CMOS to begin with. If only the calibration storage hasn't fail...
--- End quote ---
Sounds like a bad design or something. I mean, how often would it need to update the calibration data anyway? Usually the only time it would write to the flash would be when you put it in calibration mode and ran through the calibration procedure. Otherwise, it's just reads the Cal data from the flash which doesn't cause wear...
Rick Law:
--- Quote from: Kim Christensen on January 30, 2022, 05:11:52 am ---
--- Quote from: Rick Law on January 29, 2022, 10:37:13 pm ---I use a cheapo $15 USD B3603 digitally controlled CC/CV as my bench supply. The thing still "works" except it will no no longer store calibration data. It still "works" only in the sense that if I ignore the build-in display and use external DMM for V/I display. After testing it every way I can think of, my conclusion is that the EEPROM or flash base calibration data storage failed.
That is what made me think why not CMOS to begin with. If only the calibration storage hasn't fail...
--- End quote ---
Sounds like a bad design or something. I mean, how often would it need to update the calibration data anyway? Usually the only time it would write to the flash would be when you put it in calibration mode and ran through the calibration procedure. Otherwise, it's just reads the Cal data from the flash which doesn't cause wear...
--- End quote ---
Bad design - I imagine so as well. It has other quirks to make me think the design isn't great. It however did the CC/CV very nice.
It also stores output settings so it can reboot and auto restart the output to prior setting, so there is more EEProm/Flash writes than just calibration. Even with that, I am very doubtful I changed the output voltage or current limit thousands of times to wear out the non-volatile memory (EEProm or flash) in about 4 to 5 years.
I will see how long my replacement lasts. For a cheapo, I considered it very durable at 4 to 5 years of regular use.
T3sl4co1l:
I guess no one's extracted/RE'd the original to tell, but there appears to be a replacement:
https://github.com/baruch/b3603
Question, is the setting persistent, i.e. you set it to 5V 1A, turn it off, come back the next day it's still on 5V 1A? If so, then that's probably wearing NV memory.
Tim
Siwastaja:
--- Quote from: Rick Law on January 30, 2022, 06:02:14 am ---Bad design - I imagine so as well. It has other quirks to make me think the design isn't great. It however did the CC/CV very nice.
--- End quote ---
Flash works perfectly for storing calibration data. It has to store the firmware, anyway. The very same flash technology then stores calibration data. If the flash fails, you are doomed anyway. But longevity of MCU internal flash is very well tested and though out, it's many many decades at very least if not over a century. There are very little failures in early flash-based MCUs from the 1990's, OTOH nearly 100% of battery based SRAM from the same era have died already. If the SRAM holds factory calibration or other vital data, the units are bricked.
Battery-based SRAM storage is at least an order of magnitude more finicky, easier to get wrong, and even with everything done right, will die in 10-20 years.
Your unit just failed, because crappy design can always fail for whatever reason. Changing to fundamentally more unreliable technology will only make it even less reliable.
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