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Topic: Some ideas for a domestic antitheft system... and probably more. (Read 17 times) previous topic - next topic

Marco Signorini

Hi Dario.

It's a very good idea.
I'll do the best to have as least the holes for the connector.
Probably to be soldered on the back side would be an option.

Thank you for the feedback!

Regards,
Marco.

Marco Signorini

Hi.

A little update about the project status...
I've built a prototype of a new switching power supply as suggested by Dario. Below is a picture. I was able to test it at 400mAmps and a Vin Max of 31Volt DC.
The output voltage is 5V. I've measured about 200mV of ripple in these conditions.
I think it's good and I'll integrate as soon as possible in the target board.

Thanks!

Marco.

veseo

Hi Marco,

nice news. Does you have the oscilloscope graphs for the input and output voltage/current with the 400mA load?

It would be nice find out the switching efficiency.

Thanks for sharing.

Regards,
Dario.
Souliss - Open-source Distributed Home Automation with Arduino and Android

http://www.souliss.net
Follow at @soulissteam

@veseotech

Marco Signorini

Hello Dario.
Sorry for the delay... but my spare time is very limited...

Unfortunately I've not a current probe for the scope so I've modified a little bit the schematics inserting a 1ohm resistor series to the inductor. I've then used two scope channels to measure the voltage across the resistor terminals. I've also placed a multimeter measuring current flowing either on the input side, either on the output side.
In the attached picture you can see the results.

Channel1, the yellow line, is the output side voltage (more or less 5V). Channel 2, the cyan line, is the input voltage (an average of 31.4V).
Channel3 is the "hot" resistor terminal (the one attached to the inductor), Channel4, the green line, is the resistor on the capacitor side (i.e. it's attached to the same position of CH1 but the sensitivity on this channel is 1V). The red line is the difference between Ch3 and Ch4.
With a 1ohm resistor I can imagine to read Amps instead of Volts. Effectively we can see a sawtooth with an averaged value supposed to be a bit less than a half of Ampere.

The Frequency measurement on Ch3 reports that the switching is running at 24.3kHz. It's probably something I can modify changing the capacitor value connected to the switching IC... Probably increasing the frequency will rise up the efficiency... but I've to investigate about.

On the multimeter snapshots, below the scope picture, are the DC and AC current measurements at the input side (on the left) and at the output side (on the right).

With this collected data I can calculate:

Pin = Vin x Iin = 31.4*0.10 = 3.14W
Pout = Vout x Iout = 5.4*0.43 = 2.32W

having an efficiency of E = Pout/Pin *100 = 73.8%

I think is an interesting value, do you? We have to consider that there are some power losses introduced by the 1ohm resistor...

Thanks!

Marco Signorini.


veseo

Hi Marco,

the result is pretty nice and close to the maximum efficiency that you can have. Using a linear regulator with 31V input (if it doesn't burn before) has (5V/31V) 16% of efficiency because the input and output current are the same.

The frequency value is related to the power loss, bigger is the frequency lower is the efficiency. This because this type of devices has losses during the switching phase, rather during the ON or OFF phase the power that is lost is pretty low. On the other side, bigger frequencies gives you a lower ripple.

You may try to increase the efficiency with a lower frequency and a bigger output capacity, but I think that your result are good and also the output voltage is stable.

Thanks for sharing.

Regards,
Dario.

Souliss - Open-source Distributed Home Automation with Arduino and Android

http://www.souliss.net
Follow at @soulissteam

@veseotech

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