I am currently designing a circuit to control a traffic light intersection for my railway modelling hobby. The PCB layout is nearly finished, but I have a question about my power input which I was made aware of could have issues.
My question is about the AC/DC (bottom right) screw terminal, where I plan to use this one https://cdn-reichelt.de/documents/datenblatt/X200/1725656.pdf
The maximum input voltage will be 16V AC and the maximum current draw of the circuit will not be higher then 100mA. The input voltage is not line voltage, but generated from a transformer which is used to power parts of the railway model (230 Volt Transformer. 32 VA. | Märklin)
The datasheet itself states that the screw terminal could handle the voltage and current, but is the clearance between the pads of the terminal enough or should I go with a bigger screw terminal and with it a wider spacing?
Hello @Strece, welcome in the club of Kicad designers. This connector seems fine for 16V/100mA and Mrs. Reichelt ist lucky if you order some. Maybe the big annular ring of the pads is fine for hand soldering but does not have 0,2mm clearance from pad to pad. You may use rectangular pads to maintain pad to pad clearance or going to a 3,81 or 5,12mm pitch model. I cannot see this on the screen copy but make sure what clearance it is inside the PCB editor and your pcb manufacturer is able to produce it. As a rule of thumb, I take the 7,5mm pitch connectors for mains. Using one higher pin count MSTB model connector with male and female part allows to swap your PCBs much more easy in case of maintenance.
Btw: Your steam engine in the screen print looks nice but I doubt the PCB manufacturer can print that small negative line wides of wheels and other engine components.
Hallo,
die Schraubklemmen sind i.O. Wichtig sind die Lötpads und die Leiterbahnen.
Nimm den PCB- Rechner, da kannst Du die Breite der Leiterbahn berechnen lassen. Ist ein prima Tool.
Die Pads an der Schraubklemme würde ich auch vergrößern.
die Pads an den Schraubklemmen gehen nicht größer weil sie sowieso schon zu wenig Abstand haben. Bei einem so einfachen Layout ist es völliger Quatsch an das produktionstechnisch erlaubte Minimum der Abstände und Restringe zu gehen. Ich nehme an, daß die selbst angelegt sind (?) Da wird vermutlich der DRC des Leiterplattenätzers ebenso wie bei der Lokomotive im Bestückdruck ansprechen. An den beiden Ampelausgängen J2+3 scheint noch ein gemeinsammes Plus als Rückleitung nützlich zu sein aber ich will mich hier nicht ins Design einmischen. (Ansonsten würde dieser Beitrag auch besser ins Projekte Kapitel des Forums passen da es ja gar nicht direkt um Kicad geht)
@janvi
Danke fĂĽr dein Feedback, also aktuell ist der Abstand zwischen den Pads (von Kupfer zu Kupfer) 0,34mm
Ich könnte die Pads etwas kleiner machen um einen Abstand von ca. 0,7mm zu bekommen, wäre das ausreichend oder sollte ich lieber folgende Terminals verwenden https://cdn-reichelt.de/documents/datenblatt/C100/1729128.pdf. Die hätten ein Rastermaß von 5,08 und natürlich einen größeren Pad/Pad Abstand.
Bestellen wĂĽrde ich bei JLCPCB und ich glaube die haben einen Minimum Abstand von 0,2mm.
@BerndHF
Danke auch für das Feedback, ja größer machen kann ich die Pads nicht mehr da die schon sehr eng zusammen liegen.
Und sorry wenn ich die falsche Kategorie ausgewählt habe.
I can’t see what is the clearance at your picture.
Until we not have human safety in mind if remember well 1kV can jump over 1mm (in typical conditions). So to jump over 0.2mm 200V is needed.
What is the capacity of C1?
I think C5 is not needed. Each IC will be happy having small ceramic capacitors (C3, C6) close to its power pins, but one electrolytic capacitor (C4) at one net should be enough.
Up to 12V I use 0.2mm clearance. For 24V I use 0.4mm. So 0,34 is in my opinion enough.
I asked only C1 capacitance…
Too small value if you want to supply it from AC 50Hz and take from it 100mA.
Q=I*t=C*U.
U=I*t/C = 100mA * 10ms / 100uF = 10V (estimated peak-peak ripple).
Right.
I only said that C5 is not needed and not that interferes with anything.
Thanks for clearance advice and also for the capacitor advice, going to change C1 with a matching capacity for a lower peak-peak ripple, I think 8V peak-peak should be good to still support the voltage regulator.
Having high ripple voltage have only one advantage - lowers the power dissipated in regulator.
Have in mind that electrolytic capacitance has big tolerance and will decrease over time so if you want to design long working device don’t design it with too small margins.
@janvi
Right, should have added some informations to my post.
@Piotr
Input voltage of the circuit is 16V AC and output voltage of the regulator is 5V. Thats why I think 8V peak-peak ripple should work under the assumption that the 7805 needs at least 7V (from datasheet) to output a stable 5V, but you’re right should not use the minimal possible capacitor to give me some buffer.
