Triggering Buck-Boost's EN Pin Instead of a Relay?

[zacsophonist]

My current idea sends an ESP32 GPIO signal to trigger a relay to power a connected peripheral.
This relay is switching power from a buck-boost, nominal 12V DC to 12V DC.

Could I do away with the relay all together, and just send the GPIO signal to the EN pin of the buck-boost?

Thank you,
Z

 

[stenzer]

Hi,

if you are using a relay this has to be chosen with respect to the expected maximum current across the relay, which is intended to be interrupted.

Of course you can use the GPIO directly to enable/disable the BUCK-BOOST converter. You might need to include some protection devices (i.e. TVS), depending how your setup looks like? Is everyting located on a PCB (narrow) or are long cables (lagre inductences) involved?

BR

 

[KlausST]

Hi,

It depends on the EN pin function. If it completely switches OFF the output voltage then ... I see no reason why not.
Usually I expect the output to become zero, but we don't know your circuit. The datasheet should tell you.

What I mean:
in a usual step up converter (boost), if you disable the converter you still have voltage at the output due to the diode.

Klaus

 

[zacsophonist]

Hi,

if you are using a relay this has to be chosen with respect to the expected maximum current across the relay, which is intended to be interrupted.

Of course you can use the GPIO directly to enable/disable the BUCK-BOOST converter. You might need to include some protection devices (i.e. TVS), depending how your setup looks like? Is everyting located on a PCB (narrow) or are long cables (lagre inductences) involved?

BR

Everything will be located on a PCB. My proof of concept used relays for simplicity, and now I'm converting the whole project to a PCB.
My loads will be max 12V 3A

 

[dick_freebird]

Enable function could be shunt to ground or could be high
impedance.

There may be a soft start behavior which you like, or you don't.
Degree to which you can tailor that, varies. You can probably
find ones that are programmable from the host, although that
doesn't mean that you want such complexity.

What about a "load switch" IC? Probably cheaper and needing
less "stuff" than a DC-DC, if this is its only function or you could
use someone else's source.

 

[zacsophonist]

What about a "load switch" IC? Probably cheaper and needing
less "stuff" than a DC-DC, if this is its only function or you could
use someone else's source.

I do need the DC-DC function, as well. Originally I wanted to filter and regulate the board's input with one circuit, but since I'm looking at ~20A of potential load across 8 outputs, it would require large components and a lot of PCB space/copper.
My new approach is to use 8 separate filter & regulating circuits directly off the input; one for each output.

I like your idea of using a load switch instead of a relay. If I can't find an adequate BUCK-BOOST that allows an EN signal to turn off output voltage, I will go with this KTS1677AEVH-TR switch.

Z

 

[KlausST]

Hi,

We don't know what your load is. Is it a valve or motor (inductive) or heater (resistive) or some electronics with power supply capacitors (capacitive).

But I think building 8 DCDC converters is the most expensive and largest solution.
The cheapest I can think of is a single DCDC converter and 8 low side logic level mosfets.

It depends on your requirements.

Klaus

 

[zacsophonist]

My loads are all consumer electronics like a wireless router, security cam, RPi.
There is an exception which are a couple 120mm computer fans powered over USB cable.

Cheaper is great, as long as it's safe for all peripherals.
Someone in another thread mentioned: "Using individual 5 V buck-converters may be favourable due to several issues i.e. short current scenario. If you are using four buck converters each one with an adjustable current limit prevents an interference of the supply voltage of the other 3 USB outputs, if one fails short. You may also disable an individual buck-converter, if no load is connected."

Zac
edit: outputs are 12V 3A, and 5V 4A (a little more current than necessary)

 

[KlausST]

Hi,

For sure individual DCDC may give some benefits.

You talk about short circuit scenario.
Consider:
* how likely is a short circuit?
* how to treat it? (Switch off like a blown fuse, limit the current, automatic retry, manual retry...)
* what does it mean for overal function?
If the RPi power supply has a breakdown (short circuit) do you still need the fans? Or the router?
If one fan fails (usally rather open curcuit than short circuit) is there some redundance? Can other fans substitute?
Is there some other monitoring? Voltage, current, fan RPM, temperature ...?
Also: is there some intelligence (microcontroller) which can decide what to do in which case?
Warning, alarm, switch over to some backup function, force the RPi to a clean software shutdown...


*****
Outputs are:
12V: 8 ch x 3A ?
5V: ?? ch x 4A ?

Klaus

 

[zacsophonist]

Hi Klaus,

Short circuit isn't likely, but it is possible.
I'd like to handle that scenario with the Hiccup function on the converter first, before shutting down that converter.
-(if it's not possible to automate a shutdown after a set # hiccup cycles, then an endless Hiccup isn't the end of the world until someone can physically check on it.)

Each installation of this project will likely be setup differently; there will be variations on the types of devices connected to it, so I thankfully don't have to plan what to do in case of specific device breakdowns, so long as the rest of the devices won't be damaged from the short circuit.

Monitoring will likely include:
-Input voltage/current from battery
-Output voltage/current from each converter
-Ambient temp

Onboard will be an ESP32 module, likely WROOM-1U.

Outputs are:
12V: 4 ch x 3A
5V: 4 ch x 4A

Zac

 

[stenzer]

Hi,

have you already pre-selected buck-boost converters and buck converters? If so, it might be easier for us to give feedback for specific questions.

BR

 

[zacsophonist]

Hi stenzer,

As long as it's safe to use only two converters (12V & 5V), and to use another method of switching, these are my converter choices:
12V 10A: LM5176PWPR
5V 20A: LM25145RGYR

There will be up to 4 loads on each line, drawing up to 12V 2A and 5V 4A.
I'm looking for the cheapest & safest method of switching power to each load individually, via ESP32 GPIOs.

Zac