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Forum Index : Microcontroller and PC projects : uM2(+): Constant Current/Voltage PSU

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Bill7300
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Joined: 05/08/2014
Location: Australia
Posts: 159
Posted: 06:45pm 03 Aug 2016
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12,000uF would be a mighty large capacitor, dwarfing the pcb and all on it. If they are bypass capacitors on the supply rails, 0.1uF would be the go.
Bill
 
Spacedementia87
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Joined: 03/08/2016
Location: United Kingdom
Posts: 26
Posted: 07:24pm 03 Aug 2016
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  Bill7300 said   12,000uF would be a mighty large capacitor, dwarfing the pcb and all on it. If they are bypass capacitors on the supply rails, 0.1uF would be the go.


Hi bill,

I know, I was intentionally exaggerating. 12,000 would be insane.

But thanks for the value. 0.1 is what I have used before for filtering.
 
robert.rozee
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Joined: 31/12/2012
Location: New Zealand
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Posted: 01:27am 04 Aug 2016
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  Spacedementia87 said  2. Would an ATmega chip work as a replacement for the micromite? I already have an act programmer etc... Setting up be be able to program a micromite is quite a bit more up front.


you can use an arduino to create a micromite using a small program called pic32prog. see various threads about this. an arduino nano costs only a few dollars on ebay (including delivery), or you can use any other (5v/16MHz) 328p based arduino board you happen to have around the place.

btw, pic32prog will also program mx170 and mx470 devices using a pickit2. a pickit2 clone can be had pretty cheaply from ebay for around us$10 delivered. there are also a couple of other simple/cheap programming options.


cheers,
rob :-)Edited by robert.rozee 2016-08-05
 
Spacedementia87
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Posted: 07:45am 04 Aug 2016
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Ahh OK, well I do have an arduino nano already so I just need to buy the pic32 then.

I'll give it a go!

Any ideas on the specs for the unlabelled diodes?
 
centrex

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Joined: 13/11/2011
Location: Australia
Posts: 320
Posted: 11:37am 04 Aug 2016
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If you mean D1 and D2 they are 1N5819 Schottky.
ZD1 is a 5.1 volt zener
D3 is a 1N4004Edited by centrex 2016-08-05
Cliff
 
Spacedementia87
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Posted: 07:50pm 04 Aug 2016
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D3 was the main one.

Does the Zener diode need a power rating? Would a 500mW be too small?

Thanks for all the help?
 
matherp
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Joined: 11/12/2012
Location: United Kingdom
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Posted: 09:43pm 04 Aug 2016
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  Quote  Does the Zener diode need a power rating? Would a 500mW be too small?


It is probably not needed at all. It is just to protect the uP if something goes wrong with the current limit detection. 500mW would be fine
 
Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667
Posted: 10:39am 05 Aug 2016
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Considering this for an upgrade of the Dinosaur I built when 16.

  matherp said   Here as promised are the basic steps for calibrating the power supply. To do this you need a decent quality multimeter and a 10ohm 25W power resistor

Connect the resistor across the output
Connect the supply voltage and set the output voltage to 5V and the output current to 1A
Measure the voltage drop across the protection diode D3 and set this in line

const diode=0.730 'measured drop on input diode to calibrate input voltage


Rerun the program and then change line

const VIN_CAL=10.0 'set to calibrate input voltage measurement


until the displayed input voltage exactly matches the input voltage measured with your multimeter....


Presume that with a bit of effort a "Semi Self Calibrating" routine, or a "Wizard", could be created, where various multimeter readings could be inputted for the code to calculate the required calibration constants.
 
Spacedementia87
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Posted: 12:15pm 05 Aug 2016
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  matherp said  
  Quote  Does the Zener diode need a power rating? Would a 500mW be too small?


It is probably not needed at all. It is just to protect the uP if something goes wrong with the current limit detection. 500mW would be fine


Ahh brilliant thanks. I thought as much

With D3 someone said 1N4004. However that seems to have a max current of 1A.

Would this not be an issue if drawing currents higher than 1A?

If it can cope with 1.2A with a 1V drop (1.2W) that would have the diode operating at 140°C. Pretty close to the max temp.

Is this a problem?
 
centrex

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Joined: 13/11/2011
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Posted: 03:30pm 05 Aug 2016
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if you are worried use a 1N5408 or similar, good for 3 amps.
This diode is to protect against reverse polarity of the input supply.
In my board I use the 1N4004 as I am never likely to want more than 1 Amp
Cliff
 
bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2949
Posted: 05:01pm 05 Aug 2016
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All,

Has anyone created a full Bill of Materials list yet?

Kind Regards,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
Spacedementia87
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Joined: 03/08/2016
Location: United Kingdom
Posts: 26
Posted: 10:34pm 05 Aug 2016
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Thanks for all the help.

bigmik, I am creating a BOM as I am working through it.

Though I am only a Newbie!
 
Spacedementia87
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Posts: 26
Posted: 09:38am 08 Aug 2016
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Hi sorry me again!

I am trying to make sense of how the setting of the voltage works.

The max output from the pic32 is 5v right?

If so how can it feed greater than 5v to the set pin of the lm3080?
 
matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10216
Posted: 09:13pm 08 Aug 2016
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  Quote  If so how can it feed greater than 5v to the set pin of the lm3080?


The opamp Ua has a gain of 10 and is powered by the input voltage
 
Spacedementia87
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Posted: 11:48pm 08 Aug 2016
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Ahh ha!

Sorry I am very new at this and I am using this as a project to help me learn!

Amazing work. Thank you.
 
Spacedementia87
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Posted: 12:27am 17 Aug 2016
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  Quote  set the output voltage to be the same as the input voltage (make sure that you are using an input of 12V or less to match the power resistor)


My laptop supply brick is 24V.

I can get another lower voltage supply for this step, does it matter that I do some steps of the calibration using a different input voltage to the one intend to use as standard?
 
Spacedementia87
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Posted: 07:14am 22 Aug 2016
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I have made a BOM here:

BOM

I have left of specific part numbers because it is not linked to a specific PCB and you may wish to use different package typesEdited by Spacedementia87 2016-08-23
 
bigmik

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Joined: 20/06/2011
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Posts: 2949
Posted: 06:25pm 22 Aug 2016
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Thanks SapceDementia,

That will come in handy.

Kind Regards,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
Spacedementia87
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Joined: 03/08/2016
Location: United Kingdom
Posts: 26
Posted: 07:03pm 04 Sep 2016
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  Spacedementia87 said  
  Quote  set the output voltage to be the same as the input voltage (make sure that you are using an input of 12V or less to match the power resistor)


My laptop supply brick is 24V.

I can get another lower voltage supply for this step, does it matter that I do some steps of the calibration using a different input voltage to the one intend to use as standard?


Any word on this. I am quite stuck!
 
matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10216
Posted: 10:27pm 04 Sep 2016
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You can use any voltage. All this step is doing is calibrating the voltage drop so that it warns you if you are trying to set an output voltage that is not achievable given the input voltage
 
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