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Switched Mode Power Supply Examples

In this section we show three different levels of modeling switched mode power supplies. In the fourth section various implementations per converter type are available for download


Open Loop


In the open loop simulations, the duty cycle of the switching Mosfets is constant. Only a few components are required and the open loop is merely to justify component size and voltage, current and power levels.

The basic circuit elements are found in the components/circuit section. The scope and ground symbol are selected from the bottom button-bar. It is suggested to start a new simulation example by first adding the ground symbol on your schematic, so the ground node is included.
Notice that the gate of the Mosfet and IGBT are system nodes, they can directly be connected to the system control blocks as well as the constant duty-cycle blocks. <br>Click to close the image

Since we are simulating open loop, there is no need for control, only a block giving a constant duty-cycle. Notice that he output of these blocks are system nodes, so they directly connect to the gates of the Mosfet and IGBT selected from Components/Circuit/Semiconductor.
There are various blocks for single ended, dual ended and synchronous PWM, as well special blocks for interleaved PWM and phase shifted control signals as required for Full Bridge and Dual Active Bridges. The constant PWM blocks are found in Components/Library/PowerConverters/SMPS/PWM. <br>Click to close the image

The coupled inductors are found in Components/Library/PowerConverters/SMPS/CoupledInductors/Ideal. <br>Click to close the image










 

Closed Loop


Connecting to Mosfet with system node gate

The feedback is implemented using the generic control blocks for SMPS. Here we can choose if we want to use the ideal circuit mosfet model with system control node or if we are going to use the mosfet models with an electric gate connection. If you quickly want update the open loop examples, the blocks from the section Components/Library/PowerConverters/SMPS/Control/CurrentMode and Components/Library/PowerConverters/SMPS/Control/VoltageMode as can be seen on the right side of the figure below. Als the opamps(with electric circuit connections) and comparator with system output Components/Library/PowerConverters/SMPS/Control/Opamp connect directly to the system node gate of the Mosfet.

Connecting to Mosfet with electric node gate

If you would like to connect the system output to a more detailed mosfet model or a mosfet model with electric circuit node gate connection, the drivers from the section Components/Library/PowerConverters/SMPS/Driver should be used.

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Generic control blocks

In the Closed Loop example section we will only use the generic control blocks and gate driver blocks that have an electrical circuit node output and therefore (via an external gating resistor) connect to the electrical gate node of the mosfet model.

The generic models are especially designed to make fast closed loop simulations since they have a build-in oscillator. Therefore the simulation step size dt can still be relative large. The single ended model is for the Buck, Boost, BuckBoost and flyback converters. The double ended model is for Push-Pull converters. The GateDriverSyn block can be used for a synchronous buck and the more general GateDriver block is intended for the Half and Full Bridge as well as the Dual Active Bridge.

The generic blocks are on the Components/Library/PowerConverters/SMPS/Control/Generic section.

Control components such as opamps, comparators, opto-couplers and a voltage regulator can be found in the Components/Library/PowerConverters/SMPS/Control/Opamp, Components/Library/PowerConverters/SMPS/Control/OptoCoupler and Components/Library/PowerConverters/SMPS/Control/TL431 section.

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Mosfets and BJTs

Semiconductor switches like mosfets, and bipolar transistors can be found in the semiconductor Components/Library/PowerConverters/Semiconductors/Mosfet and Components/Library/PowerConverters/Semiconductors/BJT section. The MosfetLevel0 model only has the gate capacitance modeled, the MosfetLevel1 also includes two parasitic inductors with value LLead at the Drain and Source connections as well as the output capacitance Cds.

Miscellaneous

Several other components can be found in the Library/PowerConverter/SMPS section such as EMI common mode filters and bridge recifiers.

 

Detailed semiconductor models


When the closed control loop is being verified by simulation, the next step is to add more detail in the simulation. This is done in multiple ways

The detailed models include the complete control IC models as well as more detailed semiconductor models. Care has to be taken to specify the correct parameters for each device.

Semiconductors

For the Mosfet the MosfetLevel0, MosfetLevel1 and VDMOS are pin compatible. The VDMOS has a thermal node on the right side and the parameters can be given via the model node. The BJT is more or less ideal except for its miller capacitance which influences the bandwidth of the device. The JFET is only a static device, but capacitance can be added externally. <br>Click to close the image

Gate drivers

The gate drivers have internally delay and losses and therefore give a better result when it comes to switching times of the mosfets. Also the charge pump can be added for the high-side driver, to simulate the procedure for charging the bootstrap capacitor. <br>Click to close the image

Breadboard components

To get a more realistic view of the circuit, breadboard components can be used. Internally they are equal to the models in semiconductor/IC. <br>Click to close the image

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