Well, I have been trying for sometime to get a fairly smooth PWM on LEDs and motors with my lab power supply which works fine when switched up providing both +5V and +12V supplies without any hassles.
However, it is when I used two +9V batteries (in series) along with a 7812 and 7805 to power up my PIC16F877A circuit when it all started falling apart.
Individually, the 7812 and 7805 ICs are able to power up my 12V and 5V rails pretty well but when I short the input pins of both to the battery supply, it all goes haywire. The 7805 starts putting out about 7-8V and the 12V supply falls to 3V or so. The battery levels also start draining rapidly. All of it points to a short somewhere but I am not able to locate it. The power circuit is pretty standard and I am quite sure I connected the pins correctly.
The thing that bothers me is if they can work ok separately why can't the regulators work properly in tandem?
However, it is when I used two +9V batteries (in series) along with a 7812 and 7805 to power up my PIC16F877A circuit when it all started falling apart.
Individually, the 7812 and 7805 ICs are able to power up my 12V and 5V rails pretty well but when I short the input pins of both to the battery supply, it all goes haywire. The 7805 starts putting out about 7-8V and the 12V supply falls to 3V or so. The battery levels also start draining rapidly. All of it points to a short somewhere but I am not able to locate it. The power circuit is pretty standard and I am quite sure I connected the pins correctly.
The thing that bothers me is if they can work ok separately why can't the regulators work properly in tandem?