Pic behaving abnormaly @ 6.5V suply

Bare in mind that the one you need is LM2940-5 as there are a few types of LM2940s with different output voltage.

Gayan Soyza said:

Now only we got another point that you don't have enough space to keep your transformer also.

Click to expand...

I thought he is using nokia charger?

mvadu said:

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..

Click to expand...

Hi,
Looking again at your first post, you said the chager output was 6.5V, was this measured without the battery connected to the charger? [ie: no load]

The fact that you have connected the 7805 reg and its dropped to 5.2V suggests that 7805 is loading the charger, so you are getting the same voltage value as you would if a battery was connected.

If the charger was designed to charge a 4.8V battery, then these are the voltages 'off load' and 'on load' you would expect.

Try connecting a 100R or 47R resistor across the output of the charger and check the voltage across the resistor. [use a 0.5Watt resistor]
No other loads connected except the 100R or 47R

Lets know what you measure

bananasiong said:

I thought he is using nokia charger?

Click to expand...

Due to space problems he is using Nokia charger to insert into the table Clock enclosure.

For MVADU

To work this circuit properly it needs 3W (onwards) LED’s. With some small 5mm ones cannot take the real effect to mix the colors. Because it was happened to me earlier by placing small LED’s. After that I shifted to bigger ones (5W ones).

For higher wattage LED’s it needs large current. In the original link he has used 3W 350mA LED’s.

So the Charger can or cannot supply the current required for the LED’s is a doubt.

If MVADU is satisfied then it’s OK.

hi mvadu,

I have posted a pix of a shunt regulator.

Looking at what Gayan has just posted, is it possible that you can confirm WHAT you are trying to use the charger for???

Post a circuit or description.

Just because I love Ti so much, check out the PTH08080 adjustable switching regulator. It can (according to the datasheet) output 5v from voltages as low as 6.1v, and it handles 2.25A.

Hi ericgibbs, what is the purpose of the npn transistor in your attachment?

Thanks

just use 3AA batteries. or 4 rechargeable ones. and no regulation is needed.

Gayan Soyza said:

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?

Click to expand...

Gayan Soyza said:

Due to space problems he is using Nokia charger to insert into the table Clock enclosure.

For MVADU

To work this circuit properly it needs 3W (onwards) LED’s. With some small 5mm ones cannot take the real effect to mix the colors. Because it was happened to me earlier by placing small LED’s. After that I shifted to bigger ones (5W ones).

For higher wattage LED’s it needs large current. In the original link he has used 3W 350mA LED’s.

So the Charger can or cannot supply the current required for the LED’s is a doubt.

If MVADU is satisfied then it’s OK.

Click to expand...

Hi Gayan,

I think I confused some people out there..
I stated specs about my power supply just to tell you that I have a seperate power suply like the one you have.. where in I can test my PIC projects.. . Once I have the project working on breadboard powered by this power supply I usually build a PCB with its own power source.. (with the small transformer capable enough to power the circuit)..

For this project as space was my concern.. and I had a old Nokia charger lying arround I thought of using it (it was rated @5.3V 900mA) and designed my PCB like that. Since the female pin of Nokia charger can't be plugged in to the bread board i could not test it before hand

Yes.. I am using 3W RGB LED (each rated @359mA) and with PWM and the resistor values I have, it won't cross 900 mA.

And about the enclosure.. its a table clock cum lamp with a umbrella like diffuser, powered by 220V 10W lamp. I removed the lamp and fixed my LED with a small heat sink.. on the back of the clock mechanism i am fixing the PCB.. No space for a transformer inside the enclosure..

Since it was raining heavily over the weekend here and power was down.. so could not test Mike's zener method..

Any way I have ordered samples for LM2940-5 from National.com. Have to wait for them to arrive..

bananasiong said:

Hi ericgibbs, what is the purpose of the npn transistor in your attachment?

Thanks

Click to expand...

hi bananasiong,
Not knowing what his current loading may be and not knowing what power rating of zener diode he could get,
I show a transistor capable of sinking quite a bit of current.

Its just a way of using a low power zener to drive a power/shunt sink.

Is this what you mean?

Regards

Since seeing his latest post, it appears we have ALL been wasting our time.

If had told us clearly in his OP, what he was really doing, instead of talking about PIC problems,
it would have saved us wasting our time!! ****

So You can directly apply your charger to your Circuit.Its rated at
(it was rated @5.3V 900mA).no need regulators.

So You can directly apply your charger to your Circuit.Its rated at
(it was rated @5.3V 900mA).no need regulators.

The Nokia charger is obviously not regulated which is not unusual for some of the cheaper small switched mode power supplies.

All that's required is a 5V 1A regulator regulator with a drop-out voltage of less than 0.3V which is a bit of a tall order but possible. I know circuit that will do this or you can have a look at Linear's and National Semiconductor's websites.