Since LM317 is a linear regulator it will get very hot when i try to draw around 1 amp @1.25v with a 24v input. The transformer i have at home have these taps:
24v
12v
5v
Is it possible to add some kind of relay to make the transformer switch tap when the voltage gets over/under a specific voltage? I would prefer that the transformer automaticly switches tap. But if that is too advanced for me i can go with a manual a way (a switch) that changes the tap.
Thanks!
Best Answer
simulate this circuit – Schematic created using CircuitLab
Figure 1. Transformer tap selector.
This isn't a complete answer but will give you some ideas to work on. Whatever electronic solution you come up with is going to need a steady voltage to work with. This makes it awkward to derive from the transformer as you have a full-wave bridge rectifier on it. A commercial product would add an auxiliary winding to the transformer to give, for example, a 12 V supply that doesn't change with the tap selector. Since this is a one-off project we can add a second transformer (ex wall-wart) to generate this.
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Comments
The circuit is messy. Some hysteresis may be required to prevent the relays switching back and forward when close to the transition points. Vaux will droop every time a relay picks and this will upset the reference, etc.
All these problems can be designed out but a switching regulator solves them all with far less complexity.