English: Simplified block diagram of a Pulse Step Modulator (PSM) used e.g. in high power AM modulators and short wave radio transmitters
The PSM consist of N series-connected modules. In the block diagram only four modules in different colors shown, for simplicity. Typical PSM modulators consist of 32 up to 64 modules in series.

Each module consisting of

• A floating DC voltage source U
• Switching element S. In real systems this switch is a IGBT transistor or high power MOSFET.
• Free wheeling Diode D
• control logic (not shown in the diagram)

The output voltage U_Rl is equal on all modules. With switch S the voltage per module can be switched to the output or not. If switch S in a module is open, the diode D provides a current path for the output current of the other modules in series with a closed switch S.

The output voltage U_Rl can be controlled stepwise, shown on the right side in the colorized timing diagrams. In the optimized version (bottom on the right) with equal load on all modules the module with the longest on time (for example the yellow module) is switched off first.

For accurate output voltage control a PWM is superimposed on the switching control, not shown, with an additional low pass output filter stage.