DC Power Supply (5V 10A) - Questions

[Dr.Ehsan]

Hello,
I'm planning to design a circuit for a DC Motor with these parts:
1* 7805
2 * 2N2955 (paralleling two transistors to increase current)
plus some capacitor and resistors.
(the circuit image is attached)
Here is my question:
If I use a 12volts-6Ampere transformer ( 12V * 6A = 72W), does it provide enough power to have 5V-10A as output?
theoretically: 72W/5V = 14.4Ampere


Thanks,

 

[DemonicSandwich]

That math would be somewhat accurate if you were building a switching (SMPS) circuit.
This circuit however is linear. It regulates by bleeding the excess energy off as heat.
Another words, to get 10A output, you need 10A input regardless of supply voltage.


Since your transformer can only supply 6A at 12V, 6A (30Watts) is all you're gonna get without overtaxing the transformer.

The regulator and pass transistors will dissipate (12V-5V) * 6A = 42Watts of heat.

 

[Dr.Ehsan]

Thanks, as far as I knew, designing a switching (SMPS) circuit is a little hard and needs many parts.
Is there any simple switching circuit to bu used?

 

[audioguru]

The regulator and pass transistors will dissipate (12V-5V) * 6A = 42Watts of heat.

Your math is also wrong. The 12V transformer has a peak voltage of 17V, not 12V. The rectifier and pass transistors will dissipate (17V - 5V) * 6A = 72W of heat.
The motor uses additional power so the transformer is much too small and this one has a voltage that is much too high.

 

[bountyhunter]

Transformer current rating is far too low. In a linear power supply using a full wave bridge, the transformer secondary RMS current is about 1.6 - 1.8 times the DC load current. You would need a transformer rated for at least 16A secondary. Voltage rating would need to be about 7VAC ballpark. The peak AC voltage is not 1.414 X the secondary voltage rating when running at at rated current since the voltage waveform is not a true sine wave any more (there is flattening on the tops of the waveform where the current flows). You also have to allow for the ripple voltage on the filter cap, and at least 2.5V of drop for the regulator pass transistors: in your circuit it would be more like 3.5V because you added external transistors to the reg. At 10A load, ripple voltage will be significant and you will need a huge filter cap as well as a huge heatsink for the power transistors. This is why the good Lord invented switchers.....

 

[Dr.Ehsan]

There's a simple switching circuit (including LM2576), which has 5V - 3A output.
(the circuit image is attached)
Datasheet: https://www.electro-tech-online.com/custompdfs/2011/11/LM2576.pdf
Question: Is it possible to increase its current by power transistors?

 

[Diver300]

There's a simple switching circuit (including LM2576), which has 5V - 3A output.
(the circuit image is attached)
Datasheet: https://www.electro-tech-online.com/custompdfs/2011/11/LM2576-1.pdf
Question: Is it possible to increase its current by power transistors?

If you want more current from a switch mode regulator, you would probably be best to use one that is rated to 10 A or more.

**broken link removed**

 

[bountyhunter]

The other option is to go for a controller IC designed to drive high current FETs.

 

[bountyhunter]

If you want more current from a switch mode regulator, you would probably be best to use one that is rated to 10 A or more.

**broken link removed**

That part can only handle a VIN maximum of about 5.5V, you can't build a 5V out design with it..

 

[Diver300]

That part can only handle a VIN maximum of about 5.5V, you can't build a 5V out design with it..

Ooops! You're quite right, it wouldn't work.

I think this one would, and several can be shared for more current.

**broken link removed**

 

[Reloadron]

Starting with the transformer if you go the linear route you are looking at about $30 USD, followed by about maybe $5 USD for a full wave bridge rectifier, followed by maybe another $5 USD for filter capacitors before we even worry about regulation. Then comes building or making a board to put the components on plus a box for the power supply to call home. Now I am not knocking home brew or the benifits of building a power supply yourself but given a choice why not consider finding a home computer ATX form factor power supply? For about $20 USD I can buy a plain Jane PSU that will deliver:

+3.3V@24A; +5V@30A; +12V1@12A; +12V2@13A; -12V@1.5A; +5VSB@2.5A.

Used units in scrap computers flood tree lawns in the US daily and can be had for free. Again, if there is a specific reason to build I can understand but for a quick and simple 5 volt 10 amp solution to drive a motor I would just find a cheap or free ATX PSU and use it. I doubt the motor will care and it is already in a nice little metal can all packaged.

Just My Take
Ron

 

[Dr.Ehsan]

Starting with the transformer if you go the linear route you are looking at about $30 USD, followed by about maybe $5 USD for a full wave bridge rectifier, followed by maybe another $5 USD for filter capacitors before we even worry about regulation. Then comes building or making a board to put the components on plus a box for the power supply to call home. Now I am not knocking home brew or the benifits of building a power supply yourself but given a choice why not consider finding a home computer ATX form factor power supply? For about $20 USD I can buy a plain Jane PSU that will deliver:

+3.3V@24A; +5V@30A; +12V1@12A; +12V2@13A; -12V@1.5A; +5VSB@2.5A.

Used units in scrap computers flood tree lawns in the US daily and can be had for free. Again, if there is a specific reason to build I can understand but for a quick and simple 5 volt 10 amp solution to drive a motor I would just find a cheap or free ATX PSU and use it. I doubt the motor will care and it is already in a nice little metal can all packaged.

Just My Take
Ron

Thank you dear,
Finally I'm using a home computer ATX power supply.

 

[Reloadron]

They are cheap and for the most part they work. If you need help with how to set it up and get it going just ask. Remember, it was only a suggestion.

Ron