using 3-15v buckboost but requires 5volt to enable?

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#1
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Not really AVR related but using this with an AVR project.

 

I bought a DC-DC 3V-15V to 5V Fixed Output Automatic Buck Boost Step Up Step Down Power modal.

 

Is it just me or the author nutty? In order to use it I must pull up on the EN pin. Strangely the enable pin requires more then 3.4 volts? In my application I only have 3.4 volts available.How can I satisfy the TTL ? use a voltage multiplier maybe 2 caps, 2 diodes?

 

 

Last Edited: Sat. Sep 7, 2019 - 05:41 PM
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using two caps and two 1n4148 diodes (in a v doubler paradigm) I can make it work but I must touch the vout. So clearly my capacitance is wrong. I tried two 1uf's and played with this calculator.
https://www.extremeelectronics.c...
but I'm not sure what the frequency would be in the design I used.

Last Edited: Sat. Sep 7, 2019 - 08:08 PM
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Voltage doublers (using diodes and capacitors) only work with an A.C. input voltage.  A D.C. input voltage is put into the DC-DC module.  When you touch Vout you are causing 'something' to oscillate.  And those oscillations are creating the output voltage from the doubler.

 

  Personally, I would never touch with my actual fingertip anything that is connected to a circuit designed to increase voltage.  But I am one of those electronic technicians that love data but hate electricity.  Anything over +9V and I want hazardous-duty extra pay.  I'm glad that I don't have to deal the +300 volt levels that used to be needed for vacuum tubes that worked with milliVolt input signal levels.

 

How do you know what the connections are on the DC-DC module that you have bought?   I can find no schematic on the web for the red board shown in the image.  I found several photos of the the board shown in the message, but no documentation.   Do you have a schematic?   What is the six-pin IC that is doing the switching?  Do you have a data sheet for it?

Last Edited: Sat. Sep 7, 2019 - 08:24 PM
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So I'd need to create an oscillation, not sure I want that.

 

The module is marked on back.

 

vin-

vin+

vout-

vout+

en

 

example 1 that I tried.

vin-  -> gnd

vin+ -> 7v

vout- -> gnd

vout+ -> 5v

en -> 7v

 

example 2 that I tried.

vin-  -> gnd

vin+ -> 3.4v

vout- -> gnd

vout+ -> 2.1v

en -> 3.4v

 

example 3 that I tried.

vin-  -> gnd

vin+ -> 5v

vout- -> gnd

vout+ -> 5v

en -> 5v

 

and also this one works

vin-  -> gnd

vin+ -> 3.4v

vout- -> gnd

vout+ -> 5v

en -> 5v

 

but I do not have any 5v input.

 

 

" What is the six-pin IC that is doing the switching? "  I was guessing a buckboost but no I do not know. it reads

b6289u

My guess is this one

https://translate.google.com/tra...

 

 

 

 

Last Edited: Sat. Sep 7, 2019 - 09:15 PM
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Try tying your EN to Vin......assuming EN can tolerate 15V.   At low voltages, the trip voltage may move down (cmos is often spec's as % of the supply, perhaps with some other constraints) .

 

Quit trying to calibrate the unit by trimming off part of the inductor angel

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Looks the same as this 'S09 buck boost' module on aliexpress: https://www.aliexpress.com/item/...

 

The questions & answers on that link say that the EN input turns the module off if connected to gnd and turns the module on if left open or connected to the +vin

 

There is a specification pdf for the 12v output version of the module here (under Related Information): https://handsontec.com/index.php...

Last Edited: Sun. Sep 8, 2019 - 09:02 AM