What Are Pulsed Power Supplies?

Pulsed power supplies are specialized electrical power sources that store energy over a charging interval and then deliver it to a load as a brief, high-amplitude pulse with controlled voltage, current, and rise time characteristics. They differ from conventional regulated DC power supplies in that their output is inherently transient: the energy released during a single pulse may far exceed what a steady-state supply of similar average power rating could provide, because the instantaneous power is the stored energy divided by the short pulse duration. Applications that require intense but brief electrical excitation, such as driving lasers, magnetrons, plasma generators, and particle beam sources, depend on pulsed power supplies to deliver peak currents of thousands of amperes or peak voltages of hundreds of kilovolts with pulse widths ranging from nanoseconds to milliseconds.

The design of a pulsed power supply integrates four functional stages: an AC or DC primary power source, an energy storage element, a switch that controls the discharge, and a pulse-shaping network that conditions the output waveform for the load. The efficiency and repetition rate of the overall system are determined by how quickly the storage element can be recharged between pulses, which in turn constrains the average power drawn from the primary source.

Energy Storage and Charging Systems

Capacitor banks are the most common energy storage medium because capacitors support rapid charge and discharge cycles and can be manufactured in configurations that reach megajoule stored energies. High-voltage power supplies derived from resonant charging circuits transfer energy from the primary source to the capacitor bank with efficiencies above 90 percent by exploiting inductor-capacitor resonance to double the voltage from supply to capacitor in a single half-cycle. Pulse repetition rates from a few hertz to several kilohertz are achievable with appropriate thyristor or solid-state charging circuitry. Where faster energy delivery is needed at extreme current levels, inductive energy storage using superconducting coils or opening-switch topologies can provide energy densities beyond what capacitive systems achieve. The US Particle Accelerator School course materials on pulsed power engineering describe these charging topologies in detail.

Switching and Pulse Forming Circuits

Releasing stored energy into the load requires a switch that can handle high voltage in the off state and high current once triggered, transitioning from blocking to conducting in nanoseconds to microseconds. Gas-filled spark gaps and thyratrons served as the primary switch technologies through most of the twentieth century because of their ability to handle peak currents above 100 kA. Solid-state switches based on silicon carbide IGBTs and MOSFETs now compete for repetitive-pulse applications at lower current levels, offering longer service life and greater timing precision. A pulse-forming network (PFN), built from cascaded LC sections, shapes the discharge into a flat-topped rectangular pulse whose duration is set by the network's propagation delay. Pulse transformers inserted after the switch step the voltage up or down and provide isolation between the modulator and the load. Design and performance specifications for pulsed modulators used in radar and accelerator contexts are documented in IEEE Transactions on Plasma Science.

Output Characteristics and Load Matching

The load presented by a klystron, a laser head, or a plasma source is often resistive or weakly resistive, but its impedance may change during the pulse as the current through it ionizes gas or heats a conductor. Pulse-forming networks and transmission-line modulators are designed to a characteristic impedance chosen to match the nominal load resistance, maximizing energy transfer and pulse flatness. Load mismatches cause reflections that return energy to the switch and can damage components. Crowbar circuits, which short the capacitor bank if the load arcs over, protect the power supply from damage during faults. Testing and calibration of high-voltage pulsed power supplies follow guidelines maintained by the NIST Physical Measurement Laboratory for voltage and current metrology at pulsed conditions.

Applications

Pulsed power supplies have applications in a wide range of disciplines, including:

• Radar transmitter modulators for aviation and naval systems
• Particle accelerator klystron and magnetron drivers
• Excimer and CO2 laser pump circuits
• Magnetic pulse welding and metal forming
• Electroporation for food preservation and medical cell treatment
• High-power microwave source excitation for electromagnetic testing