Help with this circut

[NTRR]

I would like to know what I need to do to make this run off of 5 or 12 volts from the pc's power supply. I am just getting started so this will be my first project.

http://www.electronics-lab.com/projects/motor_light/009/index.html



Thanks

 

[Mysterae]

I'd forget using 5V for this circuit, use the 12V.

To step down the 12V to 9V you have a few options:

1. Use a 9V voltage regulator at the 12V source
2. A zener diode of the correct rating in series with the source
3. A resistor in series with the source, the rating of which will depend on the power drawn from the supply (1W, 2W or more)

The voltage reg is the more elegant solution. I'd imagine you would want an on/off switch too and remove the charging point from the circuit.

 

[Mister X]

Other then adding a heatsink to the 5 volt regulator I don't see any reason why it won't work at 12 volts as is.

 

[Mysterae]

Yeah good thinking Mister X. After a quick look at the datasheet for the LM3915, it accepts over 20V at the supply.

However, it does say the supply to the LEDs should be kept below 7V to limit the IC's power dissaption, or else a limiting resistor should be fitted to take the heat (R9 of the circuit the OP linked too). He may have to change R9 depending on the load of the circuit.

 

[Mister X]

Roger that but R16 instead of R9?

 

[Mysterae]

Doh! Yeah R16 i meant. I can't read this morning....

 

[Mister X]

Not to worry.....Some of us have that problem every morning.

 

[NTRR]

Thanks guys when/if I get this built I'll let you know how it works.

 

[RancidWAnnaRIot]

I'd forget using 5V for this circuit, use the 12V.

To step down the 12V to 9V you have a few options:

1. Use a 9V voltage regulator at the 12V source
2. A zener diode of the correct rating in series with the source
3. A resistor in series with the source, the rating of which will depend on the power drawn from the supply (1W, 2W or more)

The voltage reg is the more elegant solution. I'd imagine you would want an on/off switch too and remove the charging point from the circuit.

i'd only suggest method #1

method #3 is retarded no offense... you don't use resistors to regulate voltage.. it's impossible.. only if the circuit draws a constant amount of current... IMO it has a slim chance of working well.