Power supply design issues.
I recently had some boards made and I am using a LM1084 regulator for the power supply. (24VDC to 5VDC)·I am switching some LEDs and a 5VDC coil relay with a BS2. The relay is being switched through a 2N4401 transistor. The LEDs work fine but when the relay output goes HIGH the voltage regulator gets very very hot. I have already fried 2 BS2's here and I'm getting frustrated. Are there any existing power supply schematics available? I have attached my schematic for review.·I would greatly appreciate any feedback and patience as I am still learning here...
Rob
Rob
tif
![](/plugins/FileUpload/images/file.png)
2M
Comments
·
Using a Linear regulator and going from 24V to 5V is going to generate some heat...· Even if your 5V circuit is only drawing 100mA the Regulator will need to dissipate about 1.9 Watts of heat with the 19 Volt difference.· If you can you would be better off using a lower voltage supply, or have a secondary regulator in a cascade design similar to how it has been done with the Propeller so that you·spread the heat load out a bit.
·
i.e.
·
Supply the 24V into a 15 Volt regulator, and then supply the 15V into the 5V regulator.· In this scenario each regulator will need to dissipate 1 Watt of heat rather than 2 Watts for a single regulator.
·
·
Alternatively a switch-mode regulator will be more efficient and not run as HOT, but it might end up costing more in additional components.· Here is an alternative that might work.· http://cache.national.com/ds/LM/LM2679.pdf
·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.