Dome Node

I have both the 12v and the 24v 78S series linear regulators. There is a method of increasing the current by the use of an external PNP pass transistor (TIP36C). A circuit also exists with 2 external transistors with one used for current protection (in this case a TIP42C). However this may increase the dropout voltage to nearly 6-7 volts as the datasheet shows a 3 ohm power resistor in series with the regulator. Current is set by an extra resistor in series with the TIP36C transistor. Maybe marginal with 15v AC rms supply. Possibly ok with 30v AC rms supply for 24v. Have a 200VA 15 volt dual wound transformer and 2 8amp in line bridge rectifier components. Also have UF54 series and SB5100 ultra fast/ Schottky barrier diodes for switched mode regulator module line isolation. Think these switched mode modules could do with an extra capacitor across the module’s input. I noticed a discrepancy between values given in the module’s schematic and what’s actually supplied/fitted. Pdf info vma404- schematic.pdf. Components now at Boiler Room. Could bring HD instrument case , unfortunately non IP rated, to house this circuit and finally clear bench. For a reduced overload current a 7824 regulator could used instead of the S series for 1 to 1.5A. In the overall circuit an overload would cause the TIP42C to conduct raising the voltage on the TIP36C’s base turning it off reducing the current. Not sure if this action would occur in a cyclic fashion giving rise to possible RFI as with a twin back to back transistor current regulator. Wonder if a strategically placed capacitor would solve this potential problem.

For the microcontroller psu, can 2 switched mode buck converter modules be cascaded with line isolation diodes. If not a slight downgrade in current output would be a buck converter module and the 78S05 2A regulator. Specs say 170uV of noise. There’s also the buck module and the LT323AT regulator, but at over £4 and only 1 to 2 suppliers I’ve not choosen this option. 17/1/20 Delivered forementioned components to the Guildford Boiler Room except the 78S05 regulator. Components are now with the displays in the Dome Node box.

Decided on the buck converter linear voltage regulator option. Set the buck converter output to 9v then feed the 5v and 3v3 regulators from it’s output. Hope the 3v3 regulator would still operate. Seems like isolation diodes have been used between the switched mode and linear/ lo-drop regulators and this will be still the case.