Go Down

Topic: buck converter basics (Read 685 times) previous topic - next topic

wothke

Jun 29, 2018, 12:07 pm Last Edit: Jun 29, 2018, 02:38 pm by wothke
I am using one of these kind of buck converter for 12V to 5V conversion: https://www.picclickimg.com/00/s/ODAwWDgwMA==/z/LlQAAOSw~y9ZKUQt/$/MP1584-3A-DC-DC-Adjustable-Buck-Converter-Step-_1.jpg
 (As far as I know that PCB is based on an MP1584: https://www.monolithicpower.com/pub/media/document/MP1584_r1.0.pdf)

Does anyone have the schematics of the respective PCB?


I had thought that the two side-by-side pads used for the output voltage were actually
identical/redundant and just provided for convenience. I am using the outer ones and when verifying
with the multi-meter I often put the probes on the inner ones. But I now had the situation that my multimeter picked up the correct 5V (from the inner pins) while my device received 0V (from the
outer pins).. this seemed to be a transient phenomenon and most of the time the pins seem to be
in sync. Any ideas?


That buck converter will be the only source of current during "normal" operation of my device. But the
device may also be connected to USB (e.g. for programming, etc) in which case USB will also supply 5V. (Obviously the ~5V from the two sources might be slightly off, e.g. 5.1V vs 5V.)

1. Can the two sources be active safely at the same time, or would the buck-converter need to be powered-off while using USB?

2. Supposing the device is connected to USB's 5V and the buck-converter's 12V input is powered off (either the 12V lines might be directly disconnected or the 220V AC to 12V DC transformer might be unplugged from the wall - but still connected to the device, in which case
current crawling back from the device might have some effects in the coils of the transformer?).

Supposing the buck-converter's output pins are still connected to the circuit - i.e. they are receiving the 5V produced elsewhere rather than outputting: Is that safe or would the unused buck converter draw current from USB (or otherwise mess up the circuit), i.e. does the buck-converter need to be disconnected completely?


Finally I had observed an effect with regard to the microcontroller (ESP8266) PCB's built-in
3V3 regulator that I don't understand: As far as I know my ESP8266 comes with a RT9013
regulator which should be good for 500mA. Connected via the built-in USB connector the ESP8266 starts up reliably but when connected to the 5V of my buck converter (1A) instead, start-up often fails and I need to press the reset to get it going. I found a workaround that seems to fix this problem eventhough it surprises me that it does: I added a MCP1700 (at 250mA a much weaker regulator than what already comes with the ESP8266) and connected it directly to the ESP8266's 3V3 pin (which is thus actually using two 3V3 regulators... The two regulators actually seem to be slightly off too, whereas the MCP1700 seems to produce 3V3 the RT9013 seems to be closer to 3V6.) Again the main question (apart from the question why it makes any difference in the first place) is if this kind of duplicate regulator setup is safe to use or if it might provoke any problems?


 





caneradiyaman6

For question 1 and 2 i suggest you to use schottky diode to isolate two different power sources from each other. You will not concern about for the cases 1 and 2.

So far i worked with ESP8266-01 and ESP-12F none of them has a regulator on it. I always provide 3.3V. Can you be more specific about ESP8266 ? are you using NODEMCU or something else ?

wothke

So far i worked with ESP8266-01 and ESP-12F none of them has a regulator on it. I always provide 3.3V. Can you be more specific about ESP8266 ? are you using NODEMCU or something else ?
I am using a "Wemos D1 mini pro" which is based on ESP8266.

wvmarle

I had thought that the two side-by-side pads used for the output voltage were actually
identical/redundant and just provided for convenience.
That's indeed the case in my buck converters - and of course easy to measure. The two adjacent pads should be shorted. You should also see the PCB copper connect them (can't see that clear enough from the image, it appears to be the case).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

wothke

For question 1 and 2 i suggest you to use schottky diode to isolate two different power sources from each other. You will not concern about for the cases 1 and 2.
Excuse my ignorance of electronics .. would that be like using some regular rectifier diode? And would there not be a voltage drop created by the diode? Where would I place it / them?


ChrisTenone

Excuse my ignorance of electronics .. would that be like using some regular rectifier diode? And would there not be a voltage drop created by the diode? Where would I place it / them?


A Schottky diode is indeed like a rectifier diode, but the voltasge drop is less. Some can be as low as 0.2 volts (although 0.4 - 0.6 is more common.)
What, I need to say something else too?

Go Up