I'm in the process of building a dual purpose power supply. The supply will have two outputs. One will be 24VAC rated at 4.0 A. The load on this supply will probably never exceed 2.0 A. The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. This filtered DC will then be connected to a small surplus 12V regulator board and heat sink assembly which by the looks of it can handle 5A or better. I plan on mounting this regulator in the cabinet and providing a terminal strip for the 12V output. The DC load will probably never exceed .500 - .750 A.
Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. The regulator uses a ua723, a TO3 and a smaller TO transistor as well a whole bunch of discrete components. I have no specs on this regulator, but it is well built, appears to be commercial grade, and although it might handle it fine I'd feel a lot better hitting it with something like 18VDC instead of
- I would hate to blow it up trying to see if it would work on the higher input.
I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. So I was thinking about employing a voltage divider at the output of the filter. The resistance ratio would be easy to figure out, however I'm just not sure how to determine the optimum resistor values. Does this seem like a viable plan, or perhaps someone my have other thoughts as to how to address this? If someone could please help me with this I would be very grateful. Thanks, Lenny