CALCULATING CURRENT AND POWER REQUIREMENTS OF THE BOARD
The board, if fully deployed with all eight CE lamps and the Synchronous Communications Adapter lamps, can light 170 bulbs simultaneously. With a bulb spec of 200ma steady state, that comes to 34A of current with the bulb at its peak voltage. I will use RMS voltage because the filament is fed by AC and that is the most appropriate measurement to calculate the power used. With the 1130 lamp circuit fed by 7.5VAC, the board will dissipate some 255W across its area of just over 74 square inches - a power density, if we cheat and assume even bulb spacing, of about 3.4W per square inch.
The traces between the triac and bulb socket as well as from the ground plane to the Tbulb socket need to carry 200ma, which is easily handled by the traces I drew. Signal current when lighting the lamp is around 0.63ma, thus trivial. Lamp Test mode with all 170 lamps illuminated would require about 107ma.
The remaining current to accommodate is the connection of power and ground wiring from the 1130 to the PCB. These have to handle 35A across them. Thus, if each is fed with dual terminals (17.5A load) a plated hole of 1.6 mm will be adequate. In normal practice, without Lamp Test turned on, a typical system draw is probably down around 5A to 10A. I chose to specify a 2 oz copper for the 4 layer PCB which makes this design even more conservative.
I put in about 12 hours of time drawing all the traces, placing components, composing the silkscreen text and verifying the design. One side of the 2 pin header socket that attaches to the bulbs will be connected to the 7.5VAC inside layer simply by the design tool leaving the copper of that layer in contact with the plated hole that the socket is soldered into. However, that is not visible in the normal view in the tool with all layers stacked, so I have to turn off the upper layer and observe the AC layer to ensure that an insulating hole is not reserved around that pin of the socket.
No comments:
Post a Comment