Buck converter

Switched step-down chopper (transistor and freewheeling diode); fire drives the transistor.

  • Boolean
  • electrical
  • Modelica Standard Library
  • 5 ports
  • 2 parameters
BlockBuck converterKindbuckConverterLibraryConverters

Description

The switches of a step-down (buck) chopper: a transistor from dc_p1 to dc_p2 and a freewheeling diode from dc_n1 (anode) to dc_p2 (cathode). dc_n1 and dc_n2 are the same node.

The block has no inductor or capacitor. Add a series inductor and a capacitor after dc_p2 to form the converter.

Example

DC-DC converters Buck, boost, and bidirectional half-bridge converters switching at 10 kHz with 50 % duty.

Duty A 0.5PWM 10 kHzC A 100 µFLoad A 10 Ωv out A24 VGround (buck)BuckL 1 mHDuty B 0.5PWM 10 kHz (boost)C B 100 µFLoad B 50 Ωv out B12 VGround (boost)L 1 mH (boost)BoostDuty C 0.5PWM 10 kHz (half-bridge)C C 100 µFLoad C 50 Ωv out C12 V (half-bridge)Ground (half-bridge)L 1 mH (half-bridge)Half-bridge
In Gradara, select a Buck converter block and press F1, then choose Open example. It opens as a new model in My models, ready to run.

Also in this example:DC voltageVoltage sensorConstantGroundResistorCapacitorInductorBoost converterBuck-boost converterPWM generator

Ports

Inputs 1

  • firefire_pBoolean

    Transistor gate (Boolean). True turns the transistor on.

Conserving terminals 4

  • in+dc_p1electrical

    Input positive terminal.

  • in−dc_n1electrical

    Input negative terminal, connected internally to dc_n2.

  • out+dc_p2electrical

    Output positive terminal: the switch node where transistor and diode meet.

  • out−dc_n2electrical

    Output negative terminal, connected internally to dc_n1.

Parameters

  • Transistor on resistanceRonTransistor0.00001 Ω

    ≥ 0

    On resistance of each transistor, in ohms. 0 or more.

  • Diode on resistanceRonDiode0.00001 Ω

    ≥ 0

    On resistance of each freewheeling diode, in ohms. 0 or more.

Equations

Modelica
fire_p true: dc_p2 follows dc_p1 (through RonTransistor)
fire_p false: the diode carries the inductor current from dc_n1 to dc_p2
Continuous conduction, duty cycle d: mean(v2) ≈ d · v1

Implementation

Modelica Standard Library 4.1.0Modelica.Electrical.PowerConverters.DCDC.ChopperStepDown
MSL documentation

Assumptions and limitations

  • Ideal switches: transistors are GTO-type switches that conduct only forward, and diodes switch at 0 V. Off conductance is fixed at 10 µS and knee voltages at 0 V. No switching times, reverse recovery, or conduction voltage drop beyond the on resistance.
  • Power flows only from input to output.

Tips

  • Drive fire_p from the fire output of a PWM generator.

See also

Select a block in Gradara and press F1 to open its page offline.