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'[PIC] PICKIT2 High Voltage - Should I be worried?'
2009\06\27@220521 by solarwind

picon face
I've been getting more voltage-conscious ever since I got that
dsPIC33F. Anyway, the PICKIT2 program likes to default to 3.3 V (or so
it says) for programming the dsPIC33Fs. However, when I actually
measure the voltage using a multimeter, I get 0.5 V higher voltage. So
I turned the voltage down to 2.7 V and now the multimeter shows 3.3 V.

Is this a bad/dangerous thing for the PIC? I mean - when the PICKIT2
is set to 3.3 V, it's spitting out around 3.7 - 3.8 V. Will this
damage the PIC? Nothing has been damaged so far, but I'm just curious
why the voltage output on the PICKIT2 is not regulated and way higher
than what I'm setting it at.

I opened it up and found a few coils inside. I'm guessing it's a "transformer".

-- [ solarwind ] -- http://solar-blogg.blogspot.com/

2009\06\27@224454 by solarwind

picon face
On Sun, Jun 28, 2009 at 3:05 AM, solarwind<spam_OUTx.solarwind.xTakeThisOuTspamgmail.com> wrote:
> I've been getting more voltage-conscious ever since I got that
> dsPIC33F. Anyway, the PICKIT2 program likes to default to 3.3 V (or so
> it says) for programming the dsPIC33Fs. However, when I actually
> measure the voltage using a multimeter, I get 0.5 V higher voltage. So
> I turned the voltage down to 2.7 V and now the multimeter shows 3.3 V.
>
> Is this a bad/dangerous thing for the PIC? I mean - when the PICKIT2
> is set to 3.3 V, it's spitting out around 3.7 - 3.8 V. Will this
> damage the PIC? Nothing has been damaged so far, but I'm just curious
> why the voltage output on the PICKIT2 is not regulated and way higher
> than what I'm setting it at.
>
> I opened it up and found a few coils inside. I'm guessing it's a "transformer".

Hmm, just found the calibration button in the PICKIT2 program. The
voltage seems to be calibrated now.

2009\06\27@225141 by Funny NYPD

picon face
There are two possible reasons:
1. For every single PC, the USB voltage varies, even for the same PC, the +5V USB power supply can change when USB load changes (USB spec allows a minimum operating voltage of 4.4V in USB 2.0, and 4V in USB 3.0. ).
2. Make sure the Vdd of your PICKit 2 has been software calibrated as this step by step tutorial:
http://www.auelectronics.com/Q4.htm

For more info, you can refer to this tutorial on understanding PICKit 2 hardware:
http://augroups.blogspot.com/2009/05/understanding-microchip-pickit-2-rev.html

To overcome this issue, we have designed some enhanced version of PICKit 2, the BB0703+ family, which includes buck/boost circuits to secure a "+5V Vusb supply" to the system at all Vusb inputs. Two editions are available: BB0703+128K and BB0703+256K.

Fore more info, please check at our web site and on-line store:
www.auelectronics.com/products/system/bb0703.html
http://www.auelectronics.com/System-PICkit2.htm


Funny N.
Au Group Electronics, http://www.AuElectronics.com
http://www.AuElectronics.com/products
http://augroups.blogspot.com/




________________________________
From: solarwind <.....x.solarwind.xKILLspamspam@spam@gmail.com>
To: PICLIST <piclistspamKILLspammit.edu>
Sent: Saturday, June 27, 2009 10:05:00 PM
Subject: [PIC] PICKIT2 High Voltage - Should I be worried?

I've been getting more voltage-conscious ever since I got that
dsPIC33F. Anyway, the PICKIT2 program likes to default to 3.3 V (or so
it says) for programming the dsPIC33Fs. However, when I actually
measure the voltage using a multimeter, I get 0.5 V higher voltage. So
I turned the voltage down to 2.7 V and now the multimeter shows 3.3 V.

Is this a bad/dangerous thing for the PIC? I mean - when the PICKIT2
is set to 3.3 V, it's spitting out around 3.7 - 3.8 V. Will this
damage the PIC? Nothing has been damaged so far, but I'm just curious
why the voltage output on the PICKIT2 is not regulated and way higher
than what I'm setting it at.

I opened it up and found a few coils inside. I'm guessing it's a "transformer".

-- [ solarwind ] -- http://solar-blogg.blogspot.com/

2009\06\28@101337 by olin piclist

face picon face
solarwind wrote:
> but I'm just curious
> why the voltage output on the PICKIT2 is not regulated and way higher
> than what I'm setting it at.

The schematic I looked at of the PICKit2 a while ago didn't contain a
absolute voltage reference of its own.  It used the USB power voltage, which
it assumed was 5.0 volts, when in reality it can vary over quite a range and
still be legal USB.  If I remember right, the lowest valid USB power voltage
is somewhere around 4.2 or 4.3 volts.  That means the PICKit2 in those cases
can't even supply the 4.5V minimum required for Vdd during programming by
many PICs.

This was a couple of years ago.  Maybe this has been fixed and newer
versions contain a voltage reference.  In any case, you have to keep in mind
that the PICKit2 is a "hobby" level programmer optimized for price.  It does
that very well and works fine the vast majority of the time.  Unfortunately
sometimes people try to use it in a production or time=money or
success=reputation situations and get into trouble.  In your case I wouldn't
worry about it.  There is probably enough margin in all the various specs
(and possibly your voltmeter), that it will all continue to work fine.  Just
don't try to get away with the same thing when you want to build 1000 of
these things on a production line.

> I opened it up and found a few coils inside. I'm guessing it's a
> "transformer".

Very unlikely.  They are most probably normal 2-terminal inductors.  Those
would be cheaper, smaller, and more efficient than transformers for the same
voltage and current handling.  Transformers can be used in switching power
supplies too, but you generally put up with the added disadvantages only
when the isolation a transformer provides is required.  Since the PICKit2,
the computer, and the target circuit are all connected to the same ground,
there is no reason for transformers in this case.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

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