PICKIT2 won't supply power?

MrDEB

Well-Known Member

• Jul 24, 2013

• #1

It was working or maybe so it seemed?
Have an externally powered circuit with a 7805 on board voltage reg. Pickit2 programmed the pic just fine.
Connected to a u-powered development board with some leds connected to ports. No power?Connected an led across Grd and V+ no led lights up.
Connect battery and pic works. The power led on the PICKIT2 lights but the TARGET led never lights.
Looked at Pickit2 help files but??

 

mvs sarma

Well-Known Member

• Jul 24, 2013

• #2

I always try to use 3mm high bright LEDs,change the series resistors to 1K or 1.5K from the original design of 470 ohms, thus reduce the USB load. Check the orientation of the target LED.

 

absf

Active Member

• Jul 25, 2013

• #3

The +5V from USB is not directly connected to the Vdd of the target board. It was switched through 2 mosfets controlled by the PIC on the pickit2. See the attached schematic and it is very clear there..

Allen

 

Attachments

• pickit2_scheme.pdf

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mvs sarma

Well-Known Member

• Jul 25, 2013

• #4

Even here
1. Vdd adj section would pose issues , in the absence of rail to rail op amp.
2. I was suggesting to use 1K or 1.5K for R4, R6 and R7 and manage with good 3mm LEDs instead of wasting the power from USB.
3. Values of R28, R29 and R30 are high compared to original 33 ohms.

Microchip themselves advise at times to power the target externally or power the USB of PIC from a externally powered socket.

 

be80be

Well-Known Member

• Jul 25, 2013

• #5

The pickit2 doesn't supply power if its not turned on in software you can't just hook it up and the chip runs..

 

JonSea

Well-Known Member

Most Helpful Member

• Jul 26, 2013

• #6

As Burt said, you have to enable Vdd, and possibly adjust the voltage.

Just to be sure....you know a 7805 requires around 7 volts on the input to get 5 on the output? If you supply 5 volts to a board that has a regulator, it's not going to work.

Also, if a board has a regulator, you can't just ignore it and supply 5 volts from the PICkit to the ICSP connector. Most regulators won't tolerate voltage on the output with nothing on the input.

 

JonSea

Well-Known Member

Most Helpful Member

• Jul 30, 2013

• #7

It would be really nice to have some feedback on this. Problem resolved? Operator error? USB hub issue?

Otherwise, the time spent answering seems kind of pointless.

 

blueroomelectronics

Well-Known Member

• Jul 30, 2013

• #8

As an aside, the PICKit2 checks the target for power and short circuit. Big filter caps on the target will appear as a short and it won't supply VDD.

 

JonSea

Well-Known Member

Most Helpful Member

• Jul 30, 2013

• #9

blueroomelectronics said:

As an aside, the PICKit2 checks the target for power and short circuit. Big filter caps on the target will appear as a short and it won't supply VDD.

Click to expand...

Good point Bill. It should be noted that if the PICkit does detect a short, it must be disconnected from USB and the GUI closed and restarted to restart it.

 

dr pepper

Well-Known Member

Most Helpful Member

• Jul 30, 2013

• #10

The pickit will also measure its o/p voltage so you can confirm there is juice going to your chip, dont forget to click on the update button to re read the voltage.
If you overload the pickit current wise it'll shutdown, usually opening up a error message.