Pic behaving abnormaly @ 6.5V suply

[mvadu]

Hi,
I designed a RGB moodlight with PIC 16F628. I am using TMR0 interrupt for PWM and Pin B1-B3 for output. I thought of using a Nokia Charger for power supply. I made the PCB with the female adapter for the same. After deploying the code PIC is not working as expected. If the logic is simple as
if PinA0 is high the turn Pin B1 high then it works fine but with 3channel PWM in place it gives out voltage from all the pins..

First I trusted Nokia charger so much that I suspected PIC itself, but then some how I checked Charger output it is 6.5-6.6V. (but it is rated at 5.35V and its SMPS).

So do you think (or have prior experience) applying 6.5V to a pic will destroy it or affect the working?
Or should I again check my code only?

 

[ericgibbs]

hi,
What does the PIC 16F628 spec sheet say regarding the Vsupply?
>>
So do you think (or have prior experience) applying 6.5V to a pic will destroy it or affect the working?
Or should I again check my code only?

 

[Gayan Soyza]

Did you see a smoke? I think you have already damaged the chip.

6.5V is too high, give the supply through a 7805 regulator + decoupling capacitors.

For you refer to this mood light already made.

https://www.electronics-lab.com/projects/games/005/

 

[CanonMan75]

Did you see a smoke? I think you have already damaged the chip.

6.5V is too high, give the supply through a 7805 regulator + decoupling capacitors.

For you refer to this mood light already made.

https://www.electronics-lab.com/projects/games/005/

6.5V is too low for a 7805 to work properly, it needs at least around 2.5V more than the rated output voltage on the input pin to work properly.

 

[Gayan Soyza]

6.5V is too low for a 7805 to work properly, it needs at least around 2.5V more than the rated output voltage on the input pin to work properly.

You haven't understood the situation. I told 6.5V is too high for the PIC.

Its better use a 7805 for the PIC. with the voltage drop Then it needs about 7.5V input.

Throw that nokia charger.

 

[CanonMan75]

You haven't understood the situation. I told 6.5V is too high for the PIC.

I have understood the situation

I'd suggest the following.... use a 7.5V or 9V mains adaptor as the main power source, and then a 7805 regulator with decoupling caps close to the PIC.

 

[Pommie]

Or just use a 5.1V zener across the pics supply pins with a current limiting resistor in the 6.5V connection. The resistor should drop 1.5V at the maximum current that the pic (including any pins that source current) will take.

Mike.
Edit, you would of course power the LEDs of the 6.5V supply with the correct current limiting resistors and/or transistors. This would require that the pic I/O pins sink current.

 

[mvadu]

Guys Thanks for the replies..
No I have not seen the smoke yet
I think I will go with Pommie to add a zeener..

Actually I am doing same moodlight as mentioned by Gayan (https://www.electronics-lab.com/projects/games/005/) but with little variations.. I have 8 DIP switches.. custom software written in JAL...

I have 1K resistor on RB1-RB3 which drives transistors.

No one more confusion.. If i limit voltage across PIC VSS and VDD to +5V, my input pins will still be connected to +6.5 through a 10K resistor.. Is that a safe value or I need to increase it a bit?

 

[Pommie]

It should be fine with 10k resistors but if you want to be really safe, just connect the dip switches to the 5V zener supply. There is a pic chip that has a zener built in but I can't remember which one. It maybe worth searching for it if you need guide lines on how to use it.

Mike.

 

[mvadu]

Thanks mike

 

[Hero999]

Us an LM2936Z-5, it'll regulate properly with input voltages as low as 5.2V

 

[mvadu]

The problem is in my city I am not getting LM2936Z-5, I searched for one more project (interfacing Dallas 1621 with RS232 line) but failed to locate it. Can you suggest for any other Ultra-Low Quiescent regulator?

Edit: But this regulator should handle the current drawn from Ultrabright RGB LED, if all the colurs are ON total current will exceed 1A, (since they are driven by a PWM source this max current may last for few micro seconds)

 

[bananasiong]

How about LM2940?

 

[Gayan Soyza]

Still cannot power up your project?

I keep a separate 5V regulated power supply for PIC micro controller Circuits.

It consist of a 9V 500 mA transformer + Bridge rectifier + Smoothing capacitor + 7805 + decoupling capacitor.

For most PIC projects I'm using this power supply no more problems.

 

[mvadu]

I tried one thing.. I just connected a 7815 regulator to the Nokia charger, its output droped from 6.8V to 5.2V.. So the regulator IC is working as voltage dropper.. Do you think I can use this approch..

 

[Gayan Soyza]

You keep a seperate Power supply for your PIC circuits.

7815 is 15V.Is it comming more than 15V from a nokia charger?

you must use 7805.Your nokia charger method is not a good idea.

 

[mvadu]

Still cannot power up your project?

I keep a separate 5V regulated power supply for PIC micro controller Circuits.

It consist of a 9V 500 mA transformer + Bridge rectifier + Smoothing capacitor + 7805 + decoupling capacitor.

For most PIC projects I'm using this power supply no more problems.

Even I have such power suply..

2A (0-24V) transformer + Bridge rectifier + Smoothing capacitor
then a 7805 for 5 V supply
a 7809 for 9V , and a LM317 for 1.25V to 18V linear regulator

But the thing here is I found a nice table clock with a nice shader with enough space to fit my PCB, then i designed a PCB for mood light keeping Nokia charger in mind for Power supply...

Now I have PCB in place.. Code in place.. PIC runs the code in a bread board.. but abnormal in PCB powered by Nokia charger..

 

[bananasiong]

He said that the output voltage of the charger is only 6.8 V. A 7805 will not work well since it requires at least 7 to 7.5 V. The dropout voltage is around 2 to 2.5 V, depends on the temperature and the load current.
Sometimes my 7805 works well with the input just around 6 V, but he said that the load current is high, so this will increase the drop out voltage.
So a low drop out voltage regulator is needed.

 

[mvadu]

How about LM2940?

Specs look interesting..

Today I will look for LM2940... hope to find it..

 

[Gayan Soyza]

Now only we got another point that you don't have enough space to keep your transformer also.
Whats the progress in Pommies method the (zener diode).Did you try that?