Dome Node

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.

About the neopixel chipset supply over CANBUS. As it’s 24v it may cause problems as reading the sm regulator component specs they seem to top out at 15 to 20 volts. Probably need a switched mode pre regulator stage unless a D^2T package regulator is used. I did purchase 2x 5v LT323AT regulators for the main microcontroller psu. For the 30v AC rms supply the VMA404 module regulators need their input decoupling capacitor upgraded as it’s only 35v rated. Most of the components now in Dome Node box at the Boiler Room except the LT323AT regulators. Possibly arrange visit to where I live to pick the components outstanding up. I also downloaded the ON semiconductor specs about the switching regulator from Velleman mainly because it shows a different pcb layout using a more substantial heatsink. Whether this could be used for the node module CANBUS supply using any HVT suffixed switching regulator.
About the boosted linear regulator circuit is that it is strange to see no limiting resistor on the booster transistor’s base connection. On non current protection circuits I’ve always seen a 10 ohm 1 - 2 watt resistor directly connected to the transistor. Considering a higher voltage capable example a HVT version of the variable 317 regulator can be substituted though it’s a hassle of getting an exact voltage output. Been on Jaycar’s website for a tapped transformer. I didn’t find that much with a 2 amp or slightly greater rating.

Psu for Dome Node.Esr Components/Quasar Electronics now stock the Ceebek 5v and 12v switched mode regulated supply module boards. These do have a far larger heatsink than the Velleman VMA404 modules. Only breakpoint is the price - just under £22.
For the regulator overload protection either refer to the regulator’s datasheet or the following circuit suggestion.
There’s also a 2 transistor analogue circuit that has been used in battery charger circuits in the past. It’s action tends to be a cyclic on/off (to several MHz) as the current limit figure is reached. A capacitor can be placed between the 2 transistors (across the driver transistor C-B junction) to suppress high frequency interference. Have seen this circuit referred to as an electronic current limit. A disadvantage is that this current regulator drops some voltage as well.
Found a 100VA sub-minature 12/15 volt tapped transformer on Jaycar’s website. Have purchased for a power tool battery charger. Import duty was heavy though.

Been browsing websites for switched mode psu’s. Esr Components where I’ve got the Velleman modules also have the Cebek modules of various voltages 5, 12, and 24 volt. Comes on a fairly large 87.5mm by 72mm pcb board with through hole components. Decide on which voltage is required for the Dome Nodes on the CANBUS system 12 or 24 volts. Not sure what voltage the Node’s logic runs on. With the higher 24 volt there’s only the LD/LT 108x series lo- dropout regulators which will withstand the 24 volt input, 30/32 volts maximum.

As a further reply about the Ceebek DC to DC modules, the 24v and 12v do have an extra transistor on the pcb. This is not however present on the 5v module. I do wonder whether this extra transistor is involved with any protection circuit.

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