PE-iLAB - Help - Hardware: DSP- and Buck/Boost board
1. Introduction
The PE-iLAB is an educational system consisting of hardware and software to teach students the basic operation of switching converters as well as their digital control. The supplied hardware (see picture) consists of the DSP controller board and the Buck/Boost power stage board which are explained in this help file.
Figure 1: Picture of Hardware and Description
2. Quick start guide
This section shows the basic steps needed to run the converter using the interface software:- Make sure the jumpers on the DSP board are set up for operation with power board (see section "Using with power board")
- Plug in DSP board into Buck/Boost board
- Connect the DSP board to the PC using the supplied USB cable
- Connect the source and load to the Buck/Boost board (see section "Connecting to source and load")
- Connect the oscilloscope probes to the test points as needed (see section "Probing test points")
- Adjust the voltage of the source to the correct level (see section "Electrical Specifications") and turn it on
- Start the interface software and select the COM port the DSP board is connected to from the combo box (see section "Connecting software to COM port")
- Check if the interface software is receiving data ("Receiving" in the bottom right hand corner has a red background)
- Set parameters in the interface and run converter
Note: The source and load might be equipped with a voltage and current measurement, in this case the shown multimeters are not needed.
3. Equipment for testing
The following is a list of the minimum needed equipment for doing all the experiments with the PE-iLab system:- DC source (60V/5A)
- DC load (60V/5A) or resistor load box (300W)
- Oscilloscope
- PC (Windows)
- differential probes
- multimeters (if source and/or load not equipped with voltage and current measurements): 2 voltmeters, 2 amperemeters
4. DSP controller board
The DSP board interfaces to the PC and the power stage. The DSP is programmed to communicate with the PC interface software and to control the power stage.
4.1 Connecting USB cable / Installing driver
A USB cable is supplied with each DSP board to connect to the PC. After plugging it in, Windows will find a new USB device and ask for the driver. Select the manual installation method and the directory with the supplied driver to install it. Windows will then create a virtual COM port which will show up in the Windows Device Manager under Ports (COM & LPT1).4.2 Connecting software to COM port
Once the installation is finished, the PC interface can be started and the just created COM port needs to be selected from the COM port combo box. If everything was done correctly, the PC interface will show "Receiving" with a red background in the bottom right hand corner which means that it is receiving data from the DSP.4.3 Using as a stand-alone board
The DSP board can operate as a stand-alone unit and take its power from the USB port of the PC. Therefore the 2 jumpers (see picture) need to be set to connect across the isolation barrier. This setup is helpful while becoming familiar with the DSP and interface software and to verify correct operation.
Figure 2: Jumper setup in stand-alone operation
4.4 Using with power board
When the DSP board is plugged into the power stage board, the 2 jumpers (see picture) need to be changed to be in parallel with the isolation barrier. Thus the DSP will get its power from the power stage board once an input voltage is applied to it. With this setup the power stage can be operated and the connection to the PC is completely isolated which guarantees a safe operation independent of the used source and load.
Figure 3: Jumper setup in system
Warning: Do NOT plug DSP board into the power board when the jumpers are set up for stand-alone operation!
4.5 LED's and Reset
There are 3 LED's close to the USB connector with the following meanings:- one red LED: the USB side is powered up
- two blinking LED's: birectional commmunication to the PC is functional
- 1st LED: the DSP is powered up
- 2nd LED: converter is running
5. Buck/Boost power stage board
The power stage is able to be used as a Buck or Boost converter depending on which pins the input voltage is applied to and which mode the DSP controller code and PC interface are supporting.
5.1 Electrical specifications
The converter is designed for the following operating conditions:- input voltage range in Buck operation: 15V .. 60V
- input voltage range in Boost operation: 15V .. 30V
- maximum load current: 5A
5.2 Connecting to source and load
There is a small drawing on the board which shows how to connect the power wires for the source and load depending on whether Buck- or Boost mode is used (see picture).
Figure 4: Connection of source and load
Warnings:
- Do NOT use only one ground wire to connect to both source and load!
- Do NOT reverse the polarity of the wires for the source and load!
5.3 Plugging in the DSP board
Plug in the DSP board with the power supply turned off and the USB cable disconnected. Make sure that the jumper settings for the power supply of the DSP board are right (see detailed description of the DSP board).5.4 Probing test points
Several test points are located on the board to be able to probe the most important signals. They have small labels on them with the following meanings:| Name | Description | Measure in reference to (without differential probes) | Measure in reference to (with differential probes or ONE regular probe) |
|---|---|---|---|
| IN+ | positive input voltage in Buck mode (positive output voltage in Boost mode) | GND | IN- |
| IN- | negative input voltage in Buck mode (negative output voltage in Boost mode) | - | - |
| OUT+ | positive output voltage in Buck mode (positive input voltage in Boost mode) | GND | OUT- |
| OUT- | negative output voltage in Buck mode (negative input voltage in Boost mode) | - | - |
| PGND | power ground | - | - |
| GATELOW | low-side gate voltage | GND | PGND |
| SW | switch node: middle point between the low and high-side MOSFET | GND | PGND |
| GATEHIGH | high-side gate voltage | see Notes | SW |
| VCC | +5V supply to the DSP board | GND | GND |
| GND | signal ground | - | - |
| AGND | analog ground | - | - |
| I_L | sensed inductor current | GND | AGND |
| I_in | sensed input current for Boost mode (output current for Buck mode) | GND | AGND |
| I_out | sensed output current for Boost mode (input current for Buck mode) | GND | AGND |
| V_in | sensed input voltage for Buck mode (output voltage for Boost mode) | GND | AGND |
| V_out | sensed output voltage for Buck mode (input voltage for Boost mode) | GND | AGND |
Notes:
- IN-, OUT-, PGND, GND and AGND are not directly connected to each other and therefore can NOT be used as one common ground for the oscilloscope ground clips
- the table shows the reference points for each signal if differential probes are available or not
- for most accurate measurements use differential probes or ONE regular probe at a time
- if signals with different reference points need to be probed at the same time, differential probes need to be used
- the high-side gate voltage needs to be probed in reference to the switch node; if no differential probes are available, only use ONE regular probe for that signal
Figure 5: Testpoints for input and output voltage
Figure 6: Testpoints for switching signals
Figure 7: Testpoints for sensed signals
5.5 Scaling of sensed voltages and currents
The real voltages and currents calculate from the sensed test points as follows:- inductor current (A) = [I_L(V) - 2.5V] × 5
- input current (A) = [I_in(V) - 2.5V] × 2.5
- output current (A) = [I_out(V) - 2.5V] × 2.5
- output voltage (V) = [V_out(V) - 1V] × 20
- input voltage (V) = [V_in(V) - 1V] × 20
- inductor current (A) = I_Lmeas(mV) × 50
6. Hardware troubleshooting
| Problem | Possible failure | Suggested solution |
|---|---|---|
| Converter doesn't run and doesn't consume any input current | Input fuse blown | Replace with fuse (125V/5A) |
| No output current when converter is running and loaded | Output fuse blown | Replace with fuse (125V/5A) |
| Interface software cannot connect to hardware | USB cable unplugged | Close interface, plug in USB cable, reopen interface and select the COM port from the drop-down list |
| DSP board connected to power board: power board not powered up | Apply voltage to power board according to specifications | |
| stand-alone DSP board: jumpers are not set right to power up from USB port of PC | Fix jumper settings |
7. Appendix
Figure 8: Test setup for buck (left) and boost (right) operation
Figure 9: Schematics of a non-synchronous (left) and synchronous (right) buck converter
Figure 10: Schematics of a non-synchronous (left) and synchronous (right) boost converter
Figure 11: Schematics of test points