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12VDC to 5VDC

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Monisyst

New Member
Hi

I'm trying to design a DC to DC converter for use with a car battery of 12VDC to output 5VDC with 3.0A.

Could someone point me in the direction of a schematic or a general idea of what parts I should be using? I was thinking a LM7805 regulator would be a good start but I am an amateur and wondered if anyone had any better ideas?


Thanks
 

indulis

New Member
You could try:

**broken link removed**

On the right side of the page, just enter your numbers and it will lead you through the rest of the design (schematic, BOM and simulation)
 

peterbrown

New Member
NI is fine. But if you want to find a cheapter one, LM2575 might be your right choice. The useage is the same with 7805, but two or three cap/inductor inside as filter.
I used it couple of time in audio products.
if you not worry much about the noise, switching regular might be the other cheap choise. like: IT34063
 
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indulis

New Member
Monisyst wanted 12Vin to 5V @ 3A out...

The LM2575 is only good for 1A, the IT34063 can only do 1.5A, and you won't get 3A from a linear 7805 either [(12V-5V)*3A= 21watts that it would have to dissipate].
 

Monisyst

New Member
Monisyst wanted 12Vin to 5V @ 3A out...

The LM2575 is only good for 1A, the IT34063 can only do 1.5A, and you won't get 3A from a linear 7805 either [(12V-5V)*3A= 21watts that it would have to dissipate].

Oh I was recommended that by a friend... I mean currently I have a circuit doing that job that I bought but I'm not entirely sure what it is other than it is 7 pin and uses the metal enclosure as a heat sink.
 

indulis

New Member
Oh I was recommended that by a friend... I mean currently I have a circuit doing that job that I bought but I'm not entirely sure what it is other than it is 7 pin and uses the metal enclosure as a heat sink.

What circuit doing "that job"??? 7 pin???

You asked about a 12V to 5V @ 3A DC-DC converter. this is not a "linear" regulator like the 7805, it is a switching power supply.

What are your exact power requirements?
 

Monisyst

New Member
What circuit doing "that job"??? 7 pin???

You asked about a 12V to 5V @ 3A DC-DC converter. this is not a "linear" regulator like the 7805, it is a switching power supply.

What are your exact power requirements?

Well what I require is a step down DC to DC converter that takes in a 12VDC input from a car battery and out puts 5VDC at 3A to power a portable video recording device. I've been researching it in terms of what parts because what I have is something that I payed a company to build me several years ago but they no lionger exist and I'd like to build my own for cheapness and ease of repair ect.
 

mneary

New Member
That looks pretty good exactly what I want assuming it'll work; Thank you.

What would I have to change to get that circuit to work with a 24VDC input instead of 12VDC?
I just did a WebBench simulation, and it appears that the circuit given will work up to 40V with no changes. (40V is the max for the chip.)

You can easily run your own WebBench simulations.
 

Hero999

Banned
Does it have to ba a switching regulator?

If efficiency isn't important then you could go with linear but I wouldn't recommend it for 24V, at which point a switching regulator probably becomes cheaper.

A linear regulator such as the LM7805 can be boosted to supply 3A.
 

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Monisyst

New Member
Right I think I've got the design down now... turns out I don't need 3A after all I was informed that I can use 1A with no ill effects.

I've added a diode (although not entirely sure what type to use) in to protect the circuit from the batteries being connected the wrong way round.

I've added in a 0.01uF capacitor for protection against spikes will that be sufficient?
 

Hero999

Banned
I would recommend using more than 0.01µF (10nF), I wouldn't recommend using anything less than 100nF.
 
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