Hi S143,
Hi spec thanks for the info.I will do like it.
One last problem here.
When I use a 24V transformer it will produce DC 34V.when I apply this voltage to the input of the regulator it generates heat and voltages are messed up.It wont maintain 1.25V across R1.so i changed my transformer back to a 12V one.Is there any way to get 24V from this regulator using a transformer?what value transformer it supports maximum?
The LM317 has over temperature protection built in that reduces the current if the LM317 case temperature gets too high. Typically LM317 temperature protection would not operate with an LM317 power dissipation under 1W, if the LM317 were not mounted on a heatsink. Strangely enough, an LM358 would be exactly the same. This means that, without a heat-sink, an LM317 or LM358 will only provide a relatively low current.
The power dissipation in the LM317 is the voltage between the LM317 input and output terminals (Vio) multiplied by the current being sourced by the LM317 (Iout) at its output terminal. So if the input voltage were 30V and the output voltage were 12V, Vio would be 30V-12V = 18V. So, in this instance the LM317 could only supply a maximum current of 1W/18V = 0.056 Amps.
To get a higher current you would need to mount the LM317 on a heatsink, the bigger the better, to keep the LM317 case temperature down. The heatsink does not necessarily need to be a bought heatsink. It can be the chassis of your equipment or even a sheet of aluminum.
Even if you use an external power transistor, the external power transistor would still need to be mounted on a substantial heatsink.
Just a general note. It is not normally practical to get much more than 1A from an LM317, even though the LM317 is rated at 1.5A. And the 1A would only be possible with a fixed output voltage and an optimum transformer, rectifiers and reservoir capacitor.
A far better approach, to meet your requirement, would be to build a power supply from transistors or a high specification power supply using an opamp and transistors.
spec