Efficiency Calculator

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Overview

Generating the Efficiency Calculator report involves three basic steps:

1. In the first step, you use the menu Tools ▶ Efficiency Calculator ▶ 1. Add Power Probes to Schematic to place a minimum of two probes -- one on the input source and one on the output load. The algorithm then calculates the power delivery efficiency from the source(s) to the load(s).
   
   The fixed power probes must be placed on the terminals of each symbol. It does not matter to which pin the probe is attached as long as no other device is attached to that pin.
   
   The efficiency-calculation algorithm produces an additional section that details the loss breakdown for all probes, assuming that each power probe represents a loss element in the design; therefore, for the most comprehensive report, place a fixed power probe on each lossy component on your schematic.
   
   
2. In the second step, you use the menu Tools ▶ Efficiency Calculator ▶ 2. Define Inputs and Outputs to specify which probes are assigned to inputs and which are assigned to output loads. Note: All power probes not assigned as inputs or outputs are considered losses.
   
   
3. In the third step, you use the menu Tools ▶ Efficiency Calculator ▶ 3. Calculate Efficiency to run the report which appears in a dialog and in the command shell window.

The efficiency-calculation algorithm reads the "Mean" measurements of the fixed power probes on the schematic and reports the efficiency to the command shell window. To calculate efficiency, the algorithm assumes the following:

• The circuit has entered into a steady state.
• The waveform viewer has an integral number of periodic cycles of data.

Although a SIMPLIS POP analysis always meets these two requirements, you must ensure that a SIMetrix simulation circuit has entered into a steady state. The efficiency-calculation algorithm uses numerical integration over the total number of simulation points; therefore, the simulation must have a high number of data points to ensure that the efficiency calculation is accurate.

To specify the number of SIMetrix simulation points, follow these steps:

1. From the Schematic Editor, select menu Simulator ▶ Choose Analysis...
2. At the bottom of the Transient tab, click Advanced Options...
3. In the Advanced Options dialog, set the Max time step to 100ns or less. Note: In some converters, the value may be 1ns or less. Some experimentation may be necessary. If the efficiency data appears noisy, the most likely cause is an insufficient number of plot points.

1. From the Schematic Editor, select menu Simulator ▶ Choose Analysis...
2. Click on the Transient tab.
3. Set the Number of plot points to at least 10k. Note: In some converters, the value may be 100k or greater. Some experimentation may be necessary. If the efficiency data appears noisy, the most likely cause is an insufficient number of plot points.

Step1: Place Power Probes

The menu Tools ▶ Efficiency Calculator ▶ 1. Add Power Probes to Schematic, allows you to place multiple fixed power probes on the current schematic. To place the power probes on your schematic, close the hint window and then follow these steps:

1. Position the power probe circle on a component pin, and then click the left mouse button. Note: To zoom in while placing the power probes, hold down the Control key and scroll the mouse wheel to pan up and down. To pan left and right, hold down the Alt key while you scroll the mouse wheel.
2. Repeat the previous step until you have placed all the power probes.
3. To stop placing power probes, click the right mouse button.

• Tools ▶ Efficiency Calculator ▶ Add Power Probes to Schematic
• Tools ▶ Efficiency Calculator ▶ Delete all Power Probes

Step 2: Define Input and Output probes

The menu, Tools ▶ Efficiency Calculator ▶ 2. Define Inputs and Outputs..., allows you to specify which probes are assigned to input sources and which are assigned to output loads. The overall Efficiency is calculated from the Input Probes and Output Probes selected at the bottom of the Efficiency Calculator dialog. The probes remaining in the upper box are considered lossy elements in the design. You can use any of the following methods to move probes from the All Power Probes box to either the Input Probes or Output Probes box.

• Click to select a single probe, and then click the appropriate Add to ... button
• Hold down the Control key, click on multiple probes, and then click an Add to... button
• With your mouse, draw a box around adjacent probes and then click an Add to... button

To define the input and output probes, follow these steps:

1. In the upper box, select the probe(s) to assign to the input sources and then click Add to Inputs
2. Select the probe(s) to assign to the output loads and then click Add to Outputs
3. Click Ok

Step 3: Calculate Efficiency

The menu, Tools ▶ Efficiency Calculator ▶ 3. Calculate Efficiency, generates the efficiency report from existing data and displays the report in a dialog and in the command shell window.

Note: If no data exists, you will be prompted to select input and output probes before the report can run. After assigning the input and output probes, you must again select menu Tools ▶ Efficiency Calculator ▶ 3. Calculate Efficiency.