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3.3v drops in programming ckt.

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mandar_mahajan

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I have made the programming circuit for programming p89lpc936 using MAX232, & 74HCT02N for flash programmerby NXP.
But the 3.3V drops as soon as i connect my controller in the circuit. & the flash magic fails to read the device signature.

I don't know what's the problem. Plz help.
Any kind of help is appriciated!!!!
 

Naturally there lies some path which is dropping the voltage. But to guess where, posting your schematic will be highly beneficial. Cheers
 

check your supply lines, they might be interchanged.
also check your IL lines for short.

hock
 

posting the schematic. I have connected pin 13 of 74hc02 directly to reset pin of controller.
 

Shouldn´t T1 be a NPN and not PNP transistor as posted?
 

About the transistor mentioned in the schematic:
The notch on the body indicates emitter, so whether the body is also a emitter.

If this is the case, then i have connected the transistor reversed.......

reply urgent.
 

The transistor shown is a PNP according to your diagram. It should be a NPN type (a BC548 maybe).
 

Hi pauloynski!
I think it should be pnp only, but as u said i will change it & will see the results. ARE U SURE ABT THIS????.

ALSO ANSWER THE QUESTION FROM THE EARLIER POST...
 

If Vdd is +3.3V (connected to the collector of T1) then the transistor must be a NPN. I suppose Vdd is an input. Am I right?
 

YES ITS VDD FOR CONTROLLER. IDONT KNOW WHAT WILL BE THE RESULT , BUT I AM REPLACING NP WITH NPN AS PER U, & WILL POST THE RESULT.
MEANWHILE ANSWER MY QUERY:
The notch on the body indicates emitter, so whether the body is also a emitter.????
 

If the Vdd is the output that you want then the transistor is right (PNP) and the problem resides in your logic. If it is an input and the output is the emiter of the transistor T1 then it should be a NPN.
 

As the schematic shows, it is a A92 transistor which is PNP and is fine as per the schematic. But the pins are opposite when compared to a BC548 transistor. Mean If you are facing the name side of the transistor, left pin is the emitter, centre is the base and right pin is the collector. Confirm the transistor is connected in this configuration in your HW. Hope it helps you. Cheers
 

Hi param,
When i connect my com port for programming, the voltage is 0.
which is correct. & when i read the device signature, the supply of controller is 2.4v.
I think it should be 3v. Is this is the problem??? Is it because the 47k res at the base of the transistor???
The controller is not detected & i am unable to load my program in it.....

Can u put some focus on this issue.........
 

If the emitter is connected to 3volts, it is natural that the collector will give out 2.4 volts due to the junction drop. If you expect to get 3 volts at the collector, the emitter should be supplied with 3.6volts to compensate the drop. Cheers
 

Hi param,I modified my power supply as u suggested & now i am getting 3v.
But still the microcontroller is not recgnosied by the flash programmer.
I am suspecting now on controller itself. Clearly don't know what the problem is???
Frustrated & confused....
Anyways thanks for ur valuable suggestions, i am debugging the kit & will post u the results ...

Regards
Mandar
 

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