I am trying to create a circuit in which I can use 12V power supply that is plugged into a wall socket with a transformer OR use a 9V battery if the user wants to. I simply want to power about 4 to 5 LED's, (plan on making the final circuit flash using a 555 timer with a switch to change to non-flashing). Any help would be appreciated.

 

Hi BZ,
Welcome to AAC.
What colour LED's and current rating.?
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Right now white LED's. I have that part figured out. It is the 12V OR 9V part I am not sure of. I have found circuits on how to step down 12V to 9V. Can I just add a 9V battery after the step down without damaging the battery if the circuit is plugged into 12V???

 

hi BZ,
There is this type of female connector.
Pushing the external 12VDC plug into the socket disconnects a 0V line pin, the battery negative would be connected via this pin.
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Added diagram:

 

Keep in mind a 9 volt PP3 type alkaline battery, a good quality version under a 500 mA load is good for about an hour. On average a 555 timer IC can source or sink about 200 mA and at that will likely run hot.

If you only want or need 9 VDC why not use a 9 VDC wall wart supply? If you want to run with a 12 volt source just add a 9 volt buck converter.

Ron

 

There is one vital piece of information missing before any of the above answers are valid. What current will the LEDs need?

 

There is one vital piece of information missing before any of the above answers are valid. What current will the LEDs need?

And how will the 4-5 LEDs get connected (series/parallel) combination?

 

Assume a single LED powered at 15mA on 12VDC. Assume the LED has a Vf (forward voltage drop) of 2.2V. You would need a 653Ω resistor. Assume the same conditions but on 9V. You would need a 453Ω resistor.

Now: Assume you have a 12V source with a 653Ω resistor pushing 15mA through your LED. Then you switch the voltage to 9V. Instead of 15mA you will have 10mA. The LED will be dimmer. Changing voltages changes the current. Unless you're building independent circuits, one with the 9V battery and the other with the 12V source.

Now this: We don't know what LED's you're running. We don't know what the desired current is. Therefore we don't know what answer to give you other than to give you some sort of switching mechanism. But you might not like the outcome.

There IS another approach, a constant current circuit, one that regardless of the power supply (9V or 12V) the current can be controlled. HOWEVER, under that set of circumstances you're going to be creating a lot of waste heat. And your 9V battery won't last very long. Likely less than an hour. But then again, this is also assumed because we don't know what current you wish to run your LED's at.

 

hi,
The TS has stated that the LED section is decided, he is asking for idea's regarding either battery and/or wall wart operation. Post #3.
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The TS has stated that the LED section is decided, he is asking for idea's regarding either battery and/or wall wart operation. Post #3.

Can't speak for others, but yes, I know that. I was pointing out that there will be a difference when switching from 12V to 9V. Was I ambiguous?

But you might not like the outcome.

 

hi,
The TS has stated that the LED section is decided, he is asking for idea's regarding either battery and/or wall wart operation. Post #3.
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yes, but knowing the dropout available lets us help him with switching options/dc-dc converter options if he wants a higher efficiency solution to make his 9v battery last longer.

 

Hi Salts,
I 'think' his concern is if he has 9V battery connected, and he plugs in a 12Vdc wall wart it will fry his battery.
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Can I just add a 9V battery after the step down without damaging the battery if the circuit is plugged into 12V???

 

Obviously, you add a 12V jack with a switch in it that disconnects the 9V battery when the 12V adapter is plugged in.
No schematic was posted so we do not know:
1) Each white LED needs up to 3.6V. Five LEDs in series need 18V plus a few volts in the current-limiting resistor. Leds in series/parallel each series string with its own resistor?
2) A 9V battery drops to 6V during its life. Then none of the LEDs are in series?
3) Reducing or boosting voltage and limiting current makes a lot of heat. Needs a fan?

 

hi,
The TS has stated that the LED section is decided, he is asking for idea's regarding either battery and/or wall wart operation. Post #3.
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Yes, he has decided what LEDs he will use but he still hasn't let us know the current requirements for his selection. We can only offer valid solutions when we have enough information. "White LEDs" is all the information he gave.. The current could be anything from a few mA to several amps.

 

Who knows what LEDs and components lurks in the hearts of this circuit? The Shadow knows!

That's all I got.

Ron

 

hi BZ,
There is this type of female connector.
Pushing the external 12VDC plug into the socket disconnects a 0V line pin, the battery negative would be connected via this pin.
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Added diagram:

Thank you. What is the name of this type or female connectore?
This is where I originally got the idea. I bought this as one of my first projects. For my own project I am making, I like the idea of having a 9V option because the battery is smaller than a 12V pack. I was able to assemble this but do not really understand how it all works. https://www.amazon.com/dp/B09L89Z9BY?ref=ppx_yo2ov_dt_b_product_details&th=1

 

Hi BZ,
Look here for type.
https://www.we-online.com/catalog/en/DC_THT_RIGHT_ANGLED_LOW_PROFILE_2_8_694101308002


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Thank you. What is the name of this type or female connectore?
This is where I originally got the idea. I bought this as one of my first projects. For my own project I am making, I like the idea of having a 9V option because the battery is smaller than a 12V pack. I was able to assemble this but do not really understand how it all works. https://www.amazon.com/dp/B09L89Z9BY?ref=ppx_yo2ov_dt_b_product_details&th=1

The connector is calld a DC power barrel jack. Be aware that they are available with different diameter center pins. Either make sure what your order matches the one on your power source or order the matching female connectors too.

 

The IC in the Amazon kit has its part number removed then you cannot look it up to see how it works.
A 9V battery is small then it will have a very short life. The battery drains all the time which is why they say to remove it when the light is not lighting.

 

The IC in the Amazon kit has its part number removed then you cannot look it up to see how it works.
A 9V battery is small then it will have a very short life. The battery drains all the time which is why they say to remove it when the light is not lighting.

You can't see the markings in the first picture, but it the laid out parts picture, you can see this:

It's a CD4017 decade counter.​