Show Posts
Pages: [1]
1  Using Arduino / General Electronics / SMPS efficiency calculation on: March 05, 2013, 04:27:04 pm
Hello !

I build a SMPS driven by arduino (see post http://arduino.cc/forum/index.php?topic=130165) and I would like to calculate the efficiency of my project. Is there a way to easily get this, or, I have to use amp-meter and voltage meter on the output and input of the SMPS ?
 
I found this related page ! But in that case i need 4 of these devices !
http://www.electronicproducts.com/Power_Products/Power_Management/Avoiding_common_errors_when_designing_an_SMPS.aspx


Can anyone help ?
2  Using Arduino / Programming Questions / strange problem with Serial.print on: March 03, 2013, 01:25:09 pm
Hi guys,

I experience a strange problem with serial communication with my project.
I realized a buckboost switched power supply with Arduino to power HB LEDs (see this post : arduino.cc/forum/index.php?topic=130165 to see schemes).
The project works very well and I use Serial functions to get debug  informations.

When LEDs are driven with current bellow 0.7A. Serial.print function seem to works as expected. After that, serial communication display something totally wrong (you can see screenshot attached) !
For information, I do not use a USB connector directly attached to the arduino uno board. But use a FTDI board with Rx & Tx connected to the arduino uno (i do this to avoid USB power & battery to be connected at the same time on the board).

Furthermore, when I change the current flawing to the LED (by changing duty cycle/OCR1A register), serial communications return to normal operations. So the arduino is not crashed !

Did anyone understand what's going on ?

Thanks for your help.
BR
3  Using Arduino / General Electronics / Re: Current sensing for buck boost converter on: February 26, 2013, 12:23:38 pm
hi !

I finally read a lot on OPAMP because many values seen on tech-doc were completely unknown for me.

My choice for the op-amp is now Maxim MAX4167, this one is a rail to rail input and output op-amp ! While the input can vary from 0.0165V to 0.33V the rail to rail input aspect is very important. The MAX4167 have a 0.25mV-0.85mV Input Offset Voltage so my input voltage will be correctly processed. The Gain-Bandwith is around 36Mhz (input is 170Khz)

My problem is the op-amp gain. I use a non inverting amplifier so Vout = (1+(R2/R1))Vin
With a digital multimeter (and with arduino ADC), I sense a  ~0.010V voltage. On the opamp output, voltage is "only" ~0.016V... Something is wrong somewhere because i expect somewhat x10 ? I double check R1 & R2 value everything seem to be okay.

What wrong with this ?
I can attach a photo of the breadboard if you need !

Thanks for your help.
BR
4  Using Arduino / General Electronics / Re: Current sensing for buck boost converter on: January 21, 2013, 06:40:38 pm
See attached peak detector schematic. R1 is the current sense resistor. (R2 + R3)/R2 defines the op amp gain, and C1 * (R2 + R3) defines the time constant, which should be large compared to 1/f where f is the PWM frequency.

Ok !
So if I want to get the voltage value of Rsense I have to integrate the diode drop voltage  ?

Basically :
Vc1 = Vr1 * gain - Vdrop
Otherwise my Ir1 evaluation will be lowered by a 0,7v factor !

Is that  right ?
5  Using Arduino / General Electronics / Re: Current sensing for buck boost converter on: January 17, 2013, 10:40:12 am

Alternatively, use a diode and capacitor to turn your current sense op amp circuit into a peak or average current detector, then you can modify the PWM amount according to the current, and use a supersonic switching frequency.
Hi dc42!
Thanks again for your reply.
I did not understand what do you mean by using a diode and a capacitor to switch on the op amp. Can your draw a quick scheme or just explain a little bit more ?

6  Using Arduino / General Electronics / Re: Current sensing for buck boost converter on: January 17, 2013, 03:14:21 am
hi guys,
i resurect this old thread because i was not able to acheive my goal : sense current in a led thread.
Your advices where very usesfull but I still have some problems sensing the current on the mosfet leg. In fact I have unstable values return buy the arduino when i sense the voltage from the output of the OPA. After searching, i think this can be linked to the switching frequency. Is that right ?

If yes do I have to set a low-pass or high-pass filter between the OPA and rsense ?

I would also give some thought to the Hall effect current sensors made by Allegro (ACH712) as they will produce a voltage that can be above Vcc/2 or below it at up to 185mV/amp, are inexpensive and don't require a sense resistor. All in all they are at first glance an ideal solution and work off of 5 volts too.  I took the liberty of attaching a data sheet.
Bob
Did anyone know a Hall effect current sensor product (like the one Docedison told) but in DIP package ? I was unable to find this kind of device produced by those manufacturers: linear, allegro or maxim

Thanks  for your time !

BR
7  Using Arduino / General Electronics / Re: Current sensing for buck boost converter on: November 05, 2012, 03:44:55 pm
I don't really have anything to add, except that I think a software-controlled boost-buck driver is a super-cool application for a microcontroller (no need for messing with PWM for dimming, simply vary the switch mode duty cycle, in software, to alter output current). So I'd love to see the final design!
For information, the final design is to drive one or more High Brightness Led in the most efficient way to use it in caving lighting (helmet mount) or dive lighting.

[...] the LM358 isn't a rail to rail device so you loose some range...
I would also give some thought to the Hall effect current sensors made by Allegro (ACH712) as they will produce a voltage that can be above Vcc/2 or below it at up to 185mV/amp, are inexpensive and don't require a sense resistor.
Thanks for the advice about Hall sensor I check the datasheet and seems it can sense up to 5A in normal operating mode it feet perfectly the usage. I'll check later on that.

The attached schematic shows a simpler way for you to monitor the current and smooth the reading. Choose the ratio R2/R1 to get the range you need, and the capacitor in parallel with R2 to get the smoothing time constant you want.
However, the average power supply current is not the same as the average LED current. Maybe you should be monitoring the peak current passed by the mosfet instead?
Thank you for the schematic, I don't know why I do not use it before ! It's just a non-inverter smiley.
About the average LED current/ power supply current. I thought the power consume by the CPU and other components was negligible vs LED power (~0,7A to 3A).
For the capacitor value do you have any tips to size the capacitance ?

Thanks all for your help and time.
8  Using Arduino / General Electronics / Current sensing for buck boost converter on: November 01, 2012, 05:30:50 am
Hi guys,

I'm actually working on a buck-boost led driver to power high brightness LED.
As theses LED must be driven by constant current I wish to monitor the current flowing through the LEDs, and limit it when it reach the operating current i wish for the LEDs

a) can someone comment my schematic, and point me out what's wrong ? I just have some basis in electronics so this schematics is not the best one

b) for the  current sensing application what kind of algorithm should I use to have the most stable current to the leds.
   ie :
  arduino sense voltage out the OpAmp
   while current > xAmp      // derived from OpAmp out
       lower dutyCycle of MOSFET
   end
   set dutyCycle to theoretical value

c) The frequency use for  driving the mofset is ~100khz which king of filter should I use on the OpAmp input ? A simple capacitor ?

Thanks for you time
BR

Note : Rsense =  0,02
          All OpAmp resistors do not have the good value so gain
         
         
Pages: [1]