One of the most common questions I get when I am out on the road meeting with engineers and distributors is: "How can I add something to the schematic that is created by WEBENCH® Power Designer?" My response until now has been "We are working on a way to do that, but not right now..." Many times this leads into a discussion of the how's and why's of WEBENCH® Power Designer or the challenges facing both novice and more experienced design engineers. Both are valuable discussions, but so far, this hasn't helped them edit a schematic. Until now...
With the introduction of TI's WEBENCH® Schematic Editor, I can now answer the question by saying, "Just click on the 'Edit this Design' link and start modifying your circuit!" You can follow my example below or watch a video here. In this case, I am designing a very common power supply, 1.8V, 2A out, 11-13V input.
WEBENCH Power Designer creates over 200 designs that will meet these requirements. You can sort the designs by any of the columns and you can also search the list with the search window if you know which part or which set of parts you would like to use.
I pick a solution using the LM3150 (which has simulation enabled) and click on "Open Design". The design is created and the dashboard fills the screen with all of the usual WEBENCH Power Designer features and tools. Once the design is created, you will notice a link in "Your Complete Design" section:
Yes, there it is. The "Edit this Design" link... I modify the design first, changing the components as I normally would to get the best solution. I optimize the design, as usual, to get to the best solution. Up to this point, I have used WEBENCH Power Designer as I always had, then I click the link to edit the schematic. The existing design is saved and a duplicate copy is created. I add some notes to the convenient pop-up window to document the design and click on the "Edit This Design" button.
WEBENCH Schematic Editor fills up the window, with a tool bar on top, a BOM list to the left, and the circuit ready to be edited. As I hover over devices they become active and I can make the same changes I could from the BOM previously. The tool bar has resistors, capacitors, inductors, and diodes that may be added. There is a wiring tool, a rotate button, a select tool, a grab tool, and copy and paste tools, as well. Under the "Place Part" tab, there are instruments that can be added (various sources for current or voltage) as well as links to the passives.
I want to add a ripple filter and simulate the results. I click on the lines to delete (holding CTRL down allows you to select multiple objects) so I can add my filter and move my load out of the way:
I place an inductor, click on "Select Alternate Part" and choose from one of the plethora of inductors built into the WEBENCH library. Next, I add the capacitor and its associated part and reconnect the load, yielding the new edited schematic. The wiring tool takes a little bit of practice. It will continue wiring unless you hit "ESC" after you are finished with each wiring run. The nodes are marked with the red symbol making connections a little bit easier and allowing you to line up the wires.
I have added two components to the schematic. I could also add additional output capacitors, additional board parasitics, or additional components to better represent a complete solution. While simply editing the schematic, adding to the BOM and documentation are nice features, I can also now confirm that the changes made have the desired effect by simulating the new schematic. Click on the Sim button (the red sine wave) and I can now run the startup simulation for the new circuit. Clicking on "Start New Simulation" (green button) launches the simulation and the simulation completes in about a minute and a half. I can now choose the waveforms I want to see using the node voltages or currents listed:
The node numbers are listed on the schematic for easy reference. Click on the waveforms you want to see and they will be displayed in the waveform window. In this case, I click on the "V5" and "V6" (the output node before and after the filter). The full waveform and zoomed portion are shown below.
As you can see, the filter did reduce the ripple from more than 15mV to less than 10mV. You will also note the voltage dropped significantly due to the DCR of the additional inductor. Choosing a lower DCR inductor will reduce the change in output voltage, however, I may need to slightly adjust the targeted output voltage, depending on the design tolerances. The simulation is run again and the previous waveforms are plotted with the new simulation waveforms.
In this case, I do not need to adjust the output voltage target and I am happy with the solution. I can now create the documentation for the updated design and send it to a colleage (or share the design in WEBENCH). I can also export the schematic to one of several CAD tools. These are all features of the WEBENCH Power Designer that will help create power supply solutions faster.
I am just very happy now that I can answer the original question with, "Well, let me show you how to modify the schematic by using WEBENCH Schematic Editor..." Give it a try here and let me know how it goes? We'll be demonstrating this new feature in TI’s booth #805 at the Applied Power Electronics Conference (APEC) in Fort Worth, Texas, next week, March 17-19. If you are attending, swing by the booth and let us show you a demonstration.