## What do you mean, "The power bus is oscillating!"?

The impedances of sources and loads in any system are very important to know and understand.  Taking appropriate meaurements is critical in knowing the behavior complex impedances.  Whether we are looking at interacions between an input filter and the modulator,  or  the impedance of a power bus and the total of serveral indepedent power supplies, conditions can exist that will actually cause unwanted (and ususally destructive) oscillations.  Being able to view impedances versus frequency (Bode plot) and operate on them mathematically permits the engineer to have a deeper understanding.  With this knowledge, one can implement appropriate design measures.

## System Performance

#### Measure Input/Output Impedance Under Load

The Input/Output Impedance Measurement Set enables the engineer to perform input impedance and output impedance measurements on systems while the systems are under operational power.  In this fashion, the true behavior of the system is revealed.

#### Measure Conducted Susceptibility/PSRR

Venable's Input/Output Impedance Measurement Set allows engineers to characterize a power supply's ability to reject noise. Such tests are commonly refered to as Conducted Susceptibility or Power Supply Rejection Ratio.

#### Measure PFC Impedance

Many, if not most, power supplies incorporate power factor correction.  PFC circuits certainly affect the input impedance of power supplies that have power factor correction (not to mention that PFCs have their own stability issues).

#### Measure 3 Phase Impedance

Understanding three phase impedance is critical in large power systems.  Venable Instruments is the only FRA provider that provides the instrumentation to measure three phase impedance.

# What Causes These Systems to Oscillate?

Distributed power systems can oscillate, especially when driving one power supply with another power supply. The input and output impedances of a power supply can predict this oscillation. Before looking at the specific details of the oscillation criteria we will review the basics of impedance.