24v will power a TDA7498 Class-D 100Wx2 Stereo Digital Power Amplifier @ 4Amp max.
12v will run a preamplifire. 500mA max.
5v will run an Arduino Pro mini, 20x4 LCD and a real time clock module. I would say max of 500mA. Currently 7805 runs a bit warm (not hot).
Issue I'm facing is,
When I switch-on with "SW", I see +12v and +5v rails power spikes way above there intended values.
E.g.: +12v rail max peak around 20v and 5v rail max peak around 8v.
I had issues with many Arduino pro mini boards where it stopped working and some, I had to bun boot loader again to function.
So any thoughts to why I get high voltage spikes, even with liner regulators and please, if my design is not correct, I'm open for suggestions to fix and improve.
That's not a standard topology for a power supply, in particular the heavy pulse currents at switch on could lead to brief reverse-biasing of the L7812 and L7805 (you can't assume the secondary voltages are what you expect during these pulses).
I'd add a diode from centre-tap to these regulators.
The peak voltage of a sine wave is about 1.4 times the RMS voltage and the capacitors charge-up to the peak. Then there is about a 1.4V drop across the diode bridge.
Good!
But back to your original scope pictures.
The second, switch off, shows you are picking up stray environmental noise. Do you have any wires connected to the 5 volt output? Looks like it.
The first picture, switch on, shows inductance limiting the charging of the capacitors. Likely because of what is connected to the 5 volt line.
Paul
There's only one orientation of a diode that makes sense for the regulators - it will protect them from negative spike (which can easily destroy a 780x regulator).
ON the diagram there is a 100nF before and after both regulators but on the pcb the 2 electrolytic caps (according to the size probably around 100uF) is not in the diagram.
With the regulators been able to supply up to 1A should the output Caps not be closer to 1000uF?
