power supply to 1,5v (clock) AND 3v (LED)?

[eddie_meltzer]

hey!
this is my very first post,so be nice to me.=)
im looking to install a LED in my desk clock. the mechanism currently running on a 1,5v battery, but id very much like it to run on a power supply together with the led filament im adding. the best voltage for the led is 3v,iv found, due to the brightness being to much with anything higher that 3v.
my plan is to run it all on a laptop type power supply, i have several.

what would be the easiest configuration for 1,5v and 3v?
do amps matter?

i dont even know if im asking the right question.
please help an ignorant fool out.

thanks in advance.

 

[Martaine2005]

Hi Eddie and welcome to EP.
There are many ways to do this but a laptop style power supply is completely OTT for your project.
Let’s start at the beginning. LEDs can have a forward voltage as low as 1.6V. Have you tried any?.
If it’s to illuminate the clock, trying different LEDs in the dark will give you a better idea. Most people want to dim their devices LED.
Current in this instance will be very low. A clock can work for a couple of years on a single AA 1.5V battery.

A 5V USB phone charger would be a good start rather than a laptop type.
Better still, a rechargeable shaver power supply or toothbrush supply from a secondhand shop (thrift).
You can then use a DC-DC buck converter for the clock and a single current limiting resistor for the LED.

Martin

 

[bertus]

Hello,

What are the current requirements for the clock and led?
As @Martaine2005 said, an USB charger might be a better start, as the voltage drop is much smaller.

Bertus

 

[Martaine2005]

FYI Eddie, I have several Remington shaver/trimmer power supplies from car boot, family, friends etc.
Ranging from 5V @1000mA and 3.2V @ 1500mA.
The beauty of these are they come with over 2.5 meters of flex and a DC jack. They’re also very safe unlike Chinese cheap phone chargers.

Martin

 

[kpatz]

Is this an analog quartz movement clock (with hands) or a digital LCD display?

Considering the clock uses such a minuscule amount of current, you could use a 5V USB power supply (phone charger or similar), a simple voltage divider to power the clock and a current limiting resistor for the LED.

It's not the most efficient method, since you'd waste power to heat in the voltage divider but with the correct resistors this can be minimized, but it is the simplest circuit wise, and you'd only need 3 resistors... two for the divider and one for the LED, plus a capacitor to buffer the voltage to the clock, I'd say 10-25μF should do the trick.

For example, a 10K+4.7K resistor divider would give you 1.6V to the clock and up to 500 μA of current, plenty to power the clock, and you'd waste ~340 μA of current in the divider, which isn't a lot. As for the LED, you probably only need 1mA at the most to it since you don't want it real bright, which for a 1.7V typical voltage drop LED would be (5-1.7)/0.001 = 3.3k.

Here's another approach I found in an instructables here: https://www.instructables.com/Quartz-Clock-Power-Supply-Hack-AA-battery-to-AC-p/ This one uses 3 diodes in a series shunt to create a voltage drop, plus a 1K resistor and two 22μF capacitors. This circuit will waste more power but will give a more steady 1.5-1.8V supply to the clock movement for analog movements where the current draw varies. Just add the LED+resistor to the 5V side to get your light.

 

[Externet]

+5 V -------------------|>|----|>|----|>|-----------------3V------------------|>|----|>|---------------1.5V

Feed the 5V from a USB supply adapter to series of plain diodes as 1N400x to obtain 3 and 1.5 Volts.

 

[Audioguru]

The LED must have a series current-limiting resistor.

 

[Harald Kapp]

Got a question about driving LEDs?

You can also buy LEDs with integrated series resistor, suitable for direct operation from 5 V (example). Imho the easiest solution here.

And here is a dead simple 5 V to 1.5 V converter circuit.

 

[eddie_meltzer]

ok,this is a lot to take in.
the clock is an analog mechanism with hands.and the led is one of those filaments that go into a bulb.
theres not room for anything else in the front,where i need the led to be,so no cobs.
i have a few chargers from 5v and upwards.

i need the same supply to power both the 1,5v clock and the 3v(nothing above 3v) led.the whole thing will be placed inside the housing(wood and brass),behind the dial.
what is the absolutely simplest and safest way to get this done?
and please,dont post stuff someone else already posted(it confuses things more than necessary)+nothing a 10 yo wouldnt understand.
i apologize if i make it too difficult to help me.

thanks.

 

[bertus]

Hello,

When there is no space in the clock, you could use a multi wire cable to get from the poser sources to the clock.
An old phone wire already has 4 wires in it.
One could be the common gound, one the 3 Volts and one the 1.5 Volts.

Bertus

 

[Audioguru]

What color is the LED?
I think a tiny little SOT-223 surface-mounted LM317 (plus a couple of ceramic capacitors) can make the 1.5V and a resistor can light the LED.

 

[Ferotn22]

I were using SOT-223 with ceramic capacitors and it worked well

 

[eddie_meltzer]

so no one can help me?
thats fine,i can find another forum.
thanks.

 

[Martaine2005]

so no one can help me?
thats fine,i can find another forum.
thanks.

I count 7 people who responded and tried to help.
Maybe ‘Dora the explorer’ forum has better ideas for the under 10 year olds.
Just sayin’...

Martin

 

[bertus]

Hello,

The led requirements are not clear yet.
Could you post details on the led to be used?
Perhaps a picture of the led.
The maximum size for pictures is about 300 kB.

Bertus