6V Voltage Regulator Circuit

[rcb1976]

Hello -

Wondering if anyone has any information or help with this circuit. I have a variable input of 10-20VDC. I would like to regulate this down to 6VDC with a max of 1amp draw. This load on the system fluctutes. I have tried a 7806 but I am getting 10VDC out when I test the circuit with a 12VDC power supply attached to the imput. It gets very hot even with no load on the system. Any Ideas on what I can do to regulate this to the 6V with a fluctuating or constant input.
Any help would be great

 

[zeitghost]

It shouldn't be getting hot with no load on it!

Check that you have connected it up correctly.

It sounds like you have the terminals mixed up, which is very easy to do with some packages.

What package is the 7806 in?

78 series regulators require bypass capacitors to ensure stability (not oscillating).

The 78xx datasheet shows a 0.33uF capacitor on the input and a 0.1uF capacitor on the output.

A 10uF 10V electrolytic on the output will also help.

rgds
Zeit.

 

[rcb1976]

Thank you Zeit- The package is LM340T-6 3 pin package. I will go back and verify the arrangment again. This is all very new to me. I have tried the .33uF and .10uF caps on the input and output as in the datasheet. I'll also try that 10uF on the output. I will post my results. Thanks for the help.
Rob

 

[ScottyUK]

Failing that, and if the 6V is not a very tight tolerance, you can use a standard 78*05 regulator with a couple of forward-biased signal diodes - 1N4148s or similar - connected in the common leg to raise the output to 6.1V. The 78*05 regulators are very common in most supplier's catalogues, while the 78*06 is less common, in Europe at least.

The hot IC without any load sounds like either oscillation or incorrect connection. Good advice above re. capacitors local to regulator IC.

 

[BrianR]

Generally a lightly loaded 3-terminal regulator getting hot when it is correctly connected and serviceable means it's oscillating at high frequency. Connect those capacitors very close to the in and out pins on the chip.

 

[felixc]

Aside from your "no-load" problem, If you output one amp at six volts with an input of 20 volts, your regulator is going to get damn hot, absolutely requiring a heat sink.
You may want to check at the "Simple Switchers" made by National Semiconductor, The LM2676 would fit you bill nicely, would just get warm to a finger touch, and is not so complicated to build. The web site provides temperature simulation, and even a list of components to make your switcher, as per your design parameters. The temperature simulation even shows a PCB layout. I've been using it several times: it works! It will probably end up being smaller than your linear and its heat sink.