If you can explain the diffrences that would be great.
What is the spec for the SMPS should be? Should 5v 60A SMPS do? (It is being used on another ptoject at present, I can compenscate it for this project for a moment.
But, what spec SMPS be better?
Thanks.
I'd go for at least 80A@5V, 100A would be better - that gives you some overhead, seeing as each diode will need nearly 40A, that puts you at nearly 80A total. Two 40A @ 5V supplies would work too, although you might be cutting it a little close if you want to run the diodes at full power.
Linear supplies dissipate the excess energy as heat, much like a resistor in series with a load would. So if you have a load that needs 1A with a resistor in series, 1A will still flow through the resistor (Components in series see the same current!). Say you have a 10 ohm resistor and you have 1A going to your load through the resistor, that's a voltage drop 10V across the resistor, which means you are dissipating 10W as heat. I didn't add the calculations but the formulas used are P=IV and V=IR.
Switching supplies generally act more like a transformer. Many are basically transformers with an intermediate stage that rectifies the high voltage AC from the wall into high voltage DC then converts it into high frequency high voltage AC which allows the use of a much smaller/lighter transformer to drop the voltage to what is required, then rectifies the output again back to DC at the desired output voltage. Instead of dropping the excess voltage as heat they convert the voltage directly to what you need. So say your load needs 100W of power at 10VAC (That's 10A current [P=IV]). You provide 100VAC to a transformer which converts the voltage to 10VAC. Power must remain equal on both sides of the transformer, so if your load is consuming 100W your input to the transformer must be 100W. But instead of being at 10V it's at 100V.
Using P=IV we can see that the Current (I) is equal to 100W/100V, which is 1A@100V on the input vs 10A@10V on the output. In theory there is no energy wasted here, you put in 100W and you get out 100W at the desired voltage. Unlike the above linear example where you'd need to put in 110W to get 100W out, thus using 1.1A input instead of 1A input.
Switching supplies can also use PWM (pulse width modulation) with an inductor and capacitor instead of AC and a transformer with a rectifier to achieve the same result. See the faucet analogy below for a basic explanation of the PWM system.
An analogy:
You can think of a linear supply as a sink with a faucet and a drain in which faucet flows at a constant rate, and the drain drains at a constant rate, but the flow of the faucet is greater than the flow of the drain. In order for this arrangement to work, you have to dump excess water somewhere; in the case of a linear power supply, the excess is turned into heat.
You can think of a switching power supply as a sink with a faucet and a drain in which the faucet can be rapidly turned on and off. The drain still doesn't flow as fast as the faucet does, but by toggling the faucet on and off you can make sure you don't overflow the sink.
I hope that wasn't too much for you ... you do need a basic understanding of electrical theory to understand it really, and I'm not so good with my words, so that doesn't help.
