need 5V and 12V Dc for CD rom

[Anish_anirudh]

Hello all,

Please can anybody tell me how to make one power supply for using the normal cd rom for playing music cd by connecting the power supply from a transformer . If possible the compnent level discription also the circuit dia.

5 v dc and 12 V dc

and also how can we connect from the CAR battery to convert to 5 and 12 volt respectively for this cd rom if we are using this CD ROM for using in CAR for playing music cd

Anticipating reply

Anish Anirudhan

 

[dipal_z]

Please do not cross post.
======================

You can use LM7805 and LM7812 to get 5V DC and 12V DC supply from any unregulated power supply. They don't need any other components except Decoupling/filtering capacitors at input and output.

You can construct the unregulated power supply using transformer and full wave or bridge rectifier. Refer to datasheets of LM7805 and LM7812 for details on connecting them.

Have a look at this circuit for reference.

You can use the same circuit to power it from car battery as well.

 

[jrz126]

Doesnt the lm7812 require a much higher voltage (~15V) for it to regulate properly?

 

[panic mode]

that's true but they have 18VAC source. the circuit above can work if stuff after S2 is removed. 1N4007 diode and SK100 would create way too big voltage drop. for poweing CDROM drive you would have to check power requirement. I'm pretty sure that 500mA transformer is not enough.

 

[jrz126]

The O.P. specified car battery usage though.

 

[dipal_z]

Doesnt the lm7812 require a much higher voltage (~15V) for it to regulate properly?

Yes they do but only advantage is they are low cost and easily available. Also the link I have given is for reference only and OP needs to modify it as per his requirements.

 

[lord loh.]

78xx series have a dropout voltage of 2.5v max and their current capacity is 100mA.

See the absolute maximum ratings in the attached datasheet.

 

[Nigel Goodwin]

78xx series have a dropout voltage of 2.5v max and their current capacity is 100mA.

That's the 78Lxx, not the 78xx, the 78xx is 1A.

 

[Anish_anirudh]

Hello,

Thanks all for their guide lines.

One more thing to be discussed in this matter.
How do we make conection form a CAR battery (12V DC) to 5VD and 12 VD with reduced amp to connect this power to play the CD ROM.

DO we can make one power supply like that?

Regards


Anish Anirudhan

 

[panic mode]

Hi anish,

you need to specify power requirement, something like
1.5A @ 12VDC and 0.5A @ 5V.
getting 5V can be done using 7805 regulator. the excess voltage
(assuming battery voltage is in 12-15V range, it could be 12-5=7V or 15-5=10V) and required current (say 0.5A) will create some heat.
so 7V*0.5A=3.5W or 10V*0.5A=5W. This means that you probably need heatsink for this regulator. 5V is used for electronics of the drive and probably has to meet TTL standard for 5V power source (4.75-5.25V) which is easily done with the good old 7805.
12V rail is used to power motors in the drive and it doesn't have to be quite so precise as 5V. You might want to try taking it directly from car battery or maybe drop it a bit with two diodes for example since the average battery voltage is usually a bit higher than 12 anyway.
diodes would have to meet current requirement of the drive's 12V side.
I mentioned 1.5A as an example. in such case it would be good idea to forget 1A diodes such as 1N4001-1N4007 and go for something bigger such as 3A versions 1N5401-1N5407.

 

[kinjalgp]

You can use Low Dropout Regulators (LDO) which has near 0.5V drop across it. National manufacturers wide range of LDO's.
Another thing you can use is flyback switching regulator which will be perfect for car applications. See this **broken link removed**