Multiple Switching power supplies Problem?

[magudaman]

I have an amp requiring 24 volts at 6 amps DC. I can get the small laptop surplus power supplies pretty cheap is there any problems if run 2 or 3 of them in parallel to get the necessary current.

 

[N-Channel]

I have an amp requiring 24 volts at 6 amps DC. I can get the small laptop surplus power supplies pretty cheap is there any problems if run 2 or 3 of them in parallel to get the necessary current.

Magudaman,

There might be a problem with doing that. It's not simply a matter of paralleling them to get the necessary current, like in linear power supplies, or even batteries. You also need to synchronize them to the exact same frequency to eliminate beat frequencies.

This situation occurs when you connect two or more switchers of the same (but not exact) frequency together. Say one is calculated to run at 50kHz, and actually clocks in at 49.99kHz, and the other one, also calculated to run at 50kHz, clocks in at just over 50kHz. The difference between these two is a sweeping variable frequency that can cause a whole mess of noise filtration problems and feedback loop compensation problems, as well.

Locking the two PWM ICs to the same frequency (and phase) lets each module run at its own level, while eliminating the beat frequencies, and limiting the noise to a predictable set of variables.

The other problem is, if any of the three supplies' output voltages are off from the others by even a few millivolts, then the one with the highest output voltage will take most of the load, while the others just "idle" along for the ride.

Getting back to reality, since you're more than likely not going to have easy access to the insides of the units, much less working schematics of them, you're almost better off just building one yourself. There's more than enough help in this forum for help.

Are you wanting to run this off the AC line? If so, then you can take an old AT or ATX power supply and modify its output section to give you the voltage(s) you need. Since you need 24V @ 6A, any 200W or more AT or ATX box should more than do. In that case, there are several threads in this forum, and several articles on the web on how just to do this.

Hope this helps.

Steve