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#qmx Power supplies and the measured PWM #qmx

 

Hi all,

I am a little bit confused, maybe someone can give me a helpfull hint:

Wondering about my very low power output I started some measurements - beginning with the power supplys.
Regarding to the diagnostics screen in the terminal the 3V3 SMPS and the 5V SMPS are marked with 3,3 V and 5 V - everything seems to be ok:


During measurements I could confirm the values in the 3V3 section: Voltage ok, duty cycle ok.:



But the 5V section: Instead of 5 V my scope measures only 3,43V - but duty cycle nearly ok (+ 1%).:



What is it, what I do not understand or not see?

73 Frank
 

Hi Frank

All signals from the processor are 3.3V so the 3.3V rectangular wave PWM on the 5V side is also correct. It's a 3.3V logic level output that switches the Buck converter circuit. If I have not understood the question correctly, my apologies.

73 Hans G0UPL


On Wed, Aug 16, 2023, 8:46 PM Frank <dc8fg@...> wrote:
Hi all,

I am a little bit confused, maybe someone can give me a helpfull hint:

Wondering about my very low power output I started some measurements - beginning with the power supplys.
Regarding to the diagnostics screen in the terminal the 3V3 SMPS and the 5V SMPS are marked with 3,3 V and 5 V - everything seems to be ok:


During measurements I could confirm the values in the 3V3 section: Voltage ok, duty cycle ok.:



But the 5V section: Instead of 5 V my scope measures only 3,43V - but duty cycle nearly ok (+ 1%).:



What is it, what I do not understand or not see?

73 Frank

 

Hi Hans,?

no you understood it right - the mistake was on my side ;-)
Thanks a lot!

73 Frank
 

Hi,
a question to Hans:
What if the PCB #2 SMPS card is not present (or is faulty)? So the ADC 3V3 signal line would be open.
Does the FW algorithm let the 3V3 linear regulator work for VDD instead?
And does the LDO in this case withstand the constant dissipation?

In other words, if one decides to operate the 3V3 rail from a linear regulator or to just troubleshoot using this option (without the PCB #2), would it be enough to ground the ADC 3V3 line on the connector?

73 Bojan S53DZ
 

Hi Bojan

The firmware needs to see the voltage at the 3.3V ADC line exceed 1.65V and that at the 5V ADC line exceed 2.5V. So it SHOULD work if you provided externally produced 3.3V and 5V rails, as long as the ADC inputs were sufficient for it to get past the SMPS initialization. Connecting both ADC inputs to?+3.3V Vdd would work.?

As for power dissipation if the 3.3V regulator is permanently used... I don't think there would be any problem with the 78M33 being able to cope with it. But I have not tested this scenario at say 12V supply.?

73 Hans G0UPL



On Thu, Aug 17, 2023 at 7:26?PM Bojan Naglic <bojan.naglic@...> wrote:
Hi,
a question to Hans:
What if the PCB #2 SMPS card is not present (or is faulty)? So the ADC 3V3 signal line would be open.
Does the FW algorithm let the 3V3 linear regulator work for VDD instead?
And does the LDO in this case withstand the constant dissipation?

In other words, if one decides to operate the 3V3 rail from a linear regulator or to just troubleshoot using this option (without the PCB #2), would it be enough to ground the ADC 3V3 line on the connector?

73 Bojan S53DZ

 

OK, thank you for the answer to that.
But holding both ADC lines (3V3 and 5V) at 3V3 would mean the LIN_REG_EN signal to go low I assume.
So it would switch off the on-board 78M33 and thus prevent the?QMX to operate without the PCB #2 for testing.

73 Bojan S53DZ
 

Hello Bojan

I'm unclear what you're asking. I reviewed the previous posts again and I'm still unclear. It appeared to me that you wanted to know if PCB #2 was absent and you were using an external 3.3V source, if that would be OK. But in your latest post you are speaking about?LIN_REG_EN and the onboard 78M33. But "onboard 78M33" is on PCB #2, which you say you want to operate without. So I got really?confused.?

73 Hans G0UPL



On Sat, Aug 19, 2023 at 1:40?AM Bojan Naglic <bojan.naglic@...> wrote:
OK, thank you for the answer to that.
But holding both ADC lines (3V3 and 5V) at 3V3 would mean the LIN_REG_EN signal to go low I assume.
So it would switch off the on-board 78M33 and thus prevent the?QMX to operate without the PCB #2 for testing.

73 Bojan S53DZ

 

Hi Hans,
sorry, my bad. I thought the 78M33 was on the main board. I wanted to run the 3V3 from there if in trouble.? All clear now.??

Thanks,
73 Bojan S53DZ

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