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DC/DC Boost Converter Startup Problem with Very Slowly Rising Input Voltage
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bendras:
I am trying to use a DC/DC boost converter to increase voltage coming from a super capacitor from 2.5V to 3.3V (see the schematic below). The problem is that since the power source can provide only a few mA of current the supper capacitors takes multiple seconds to charge up  and in turn the slow voltage rise makes the boost converter oscillate and then output around 1.2V instead of the expected  3.3V (see the graph below). Anybody has any ideas on how could this be solved?

Note: The DC/DC converter enable threshold voltage is  0.8V

Schematic:


Graph:



mikerj:
You will likely need to add some kind of supply supervisor to hold the switcher in it's disabled state until the caps have charged to sufficient voltage.  You can get reset controllers in three pin packages (TO92, SOT23 etc) with various voltage thresholds which may be suitable.
ogden:
R1 and R2 supposedly shall be KOhms, not Ohms. Also try using capacitor values which charges within 1sec or so. Now your simulation is kinda useless, at least for others - because it covers just input 0.8V to 0.9V range and that's it. I want to see whole 0V to 2.5V

[edit] Also C6 shall be some real electrolytic capacitor, with some internal ESR.


--- Quote from: mikerj on June 03, 2019, 09:14:40 pm ---You will likely need to add some kind of supply supervisor to hold the switcher in it's disabled state until the caps have charged to sufficient voltage.

--- End quote ---

There is built-in supervisor in form of EN pin. It triggers at 0.9V 0.8V. So what you do is - add voltage divider. If you add 200K/200K resistors - it supposedly will start at 1.6V
mikerj:

--- Quote from: ogden on June 03, 2019, 09:20:32 pm ---There is built-in supervisor in form of EN pin. It triggers at 0.9V 0.8V. So what you do is - add voltage divider. If you add 200K/200K resistors - it supposedly will start at 1.6V

--- End quote ---

No hysteresis though, so still likely to get instability at switch on threshold.
ogden:

--- Quote from: mikerj on June 04, 2019, 09:44:55 am ---
--- Quote from: ogden on June 03, 2019, 09:20:32 pm ---There is built-in supervisor in form of EN pin. It triggers at 0.9V 0.8V. So what you do is - add voltage divider. If you add 200K/200K resistors - it supposedly will start at 1.6V

--- End quote ---

No hysteresis though, so still likely to get instability at switch on threshold.

--- End quote ---

Which exactly datasheet did you read, if any? I see 0.25/0.8 V hysteresis:


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