Power Supply ("4 wires 3 phase" to "5V")

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PILOTIK

Joined: 22 Sep 2002
Posts: 13

15 Jan 2003 0:22 Power Supply ("4 wires 3 phase" to "5V")

Hi!

Somebody can helps me?
I'm trying to design subj without transformer (low cost).
The AD7752 (this power supply for it) "eats" 17mA+5mA for LED and Counting Mechanism = ~25-30mA.
My current PowerSupply uses all 3 phases but if i disconnect 2 phases the device works pnly half of the period (50Hz).
I need scheme which use 3 phases too, but works with only one of them without stopings for a halfperiod.
More over This power supply must haven't any transformers Sad

Can U help me?

Thanx.
WBR

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flatulent

Joined: 19 Jul 2002
Posts: 4875
Helped: 324
Location: Middle Earth

15 Jan 2003 0:35 Safety problems

You are getting into serious safety problems if you draw power from the utility mains without any transformer between. The only way to overcome this is to have your circuit totally cased in insulating material of two independent layers (double shielding). The minimum power supply would be one transformer between one phase and neutral. The output would have a bridge rectifier and a large enough capacitor that the current drawn by your circuit between power line cycles would be small. You calculate this by first deciding the voltage droop. Then you calculate the charge drawn by your circuit Q=I x t. Where t is the time between half cycles of the power line. Then you calculate the capacitor C = Q/voltage droop. I have seen circuits where the power line voltage is reduced with voltage dividers, but this still has the safety problem.