Phil Langhorst, a St. Louis power supply design consultant has an unusual Christmas present request: an EDA program that can simplify the design of a power supply p.c. board. Langhorst says, “I need a way to input information about voltage and current into a schematic and have that information drive the design rules and the schematic format. I have checked a dozen different board layout programs and none have provided the desired results. Most of these EDA programs are intended for digital systems and they don't provide the necessary degree of automation for power supply circuit boards.”
Here are his recommended specifications for the EDA program:
- The first step is to produce the schematic for the circuit, which then becomes the source for further information.
- The designer should be able to enter the current handled by each connection, not just each node. The designer would enter the current being carried by each connection and the program makes the required adjustments. That information automatically adjusts the width of the schematic trace (so high current traces look fat), and the width of the copper etch.
- Based on the relative current in the traces being widened, the program provides a copper fill routine that's smart enough to increase the trace width up to the spacing rules.
- After completing a node, the designer should be able tell the program its group (class) in terms of a name like “flyback collector” or “hot logic.” That information produces specific colors for all the nodes in a given class.
- Next, the designer tells the program the voltage between the classes in a matrix format. The voltage information then automatically determines the creepage rule as dictated by a voltage to spacing table or rule.
- Voltage-to-spacing tables should be selectable, so the designer can choose to layout a board for Europe, UL840, automotive, with or without conformal coat, etc.
Langhorst says he has yet to find a design program that can do this. Finding such a program has also proved to be very time consuming. “If you ask an EDA salesman, the inevitable answer is ‘oh yeah, we can do that’ but its only after you load a demo and spend two days, do you discover it can't be done.”
He would like to know if there has ever been an EDA program written by an electrical engineer? And, why the words “voltage” and “current” are absent from the tool bars and menus? What he is asking for must be child's play compared with transmission characteristics, propagation delay, etc. that are available. He doesn't need a $100,000 package that can handle a 100-pin BGA and 47-layer p. c. boards. Most power boards are only two-sided, and use low pin count IC's.
Do any of our readers have any suggestions? He would also like to see a comparison of EDA packages based on “power friendliness.”
