Oft Posed Queries

We recogize it can be challenging to find quick answers, so this will help.

Q:  Do I need Bode Boxes (injection transformers or isolation transformers)?

A:  No, not with Venable's current line of laboratory grade instruments.  They all feature isolated/floating channel inputs and oscillator output rated to 600Vpk.  Older instruments genarally do not have this isolation built in, so Bode Boxes are required to protect the instrument.  There are instances, such as very high voltage power supplies, or impedance loading reduction where a Bode Box is handy.

 

Q:  Can I automate my FRA?  I want to add it to my ATE rack.

A:  Yes, the Venable FRAs support IEEE-488 and USB 2.0 PC interfaces, and the Command Controls are available by request.  Venable can also provide a "rack ear" kit for mounting in an 19" rack system.

 

Q:  What is the difference between the Venable Stability Analysis™ Software Version 5.5 and Version 6?

A:  Venable's latest Stability Analysis Software Version 6 is a significant change that brings an upgraded graphical environment to the user experience.  Version 6 also uses the off the shelf Windows USB drivers (GPIB driver support goes away, see above).  FRAs that ship with V6 can still run V5.5, but older FRAs may not operate with V6. Learn more on our Software Downloads page.

 

Q:  What is the difference between a frequency response analyzer and an oscilloscope?

A:  A major difference between Venable Frequency Response Analyzers (FRAs) and oscilloscopes is that FRAs evaluate circuits as a function of frequency, while oscilloscopes evaluate as a functions of time.  FRAs stimulate a circuit with a signal and evaluate the response.  Oscilloscopes evaluate circuits passively.

 

Q:  What is the K-Factor Analysis?

A:  In a nutshell, it is a method of evaluating a plant (modulator) transfer function, and determining the appropriate phase boost needed to compensate the plant.  In Venable's Stability Analysis Software, all you have to do is specify a desired crossover frequency and phase margin, and the Venable software will generate component values for your compensation circuit.  You are also able to model the compensation, combine it with the measured modulator transfer function and see the resulting overall loop gain.

 

Q: What crossover and phase margin does my power supply need?

A: That depends, but two rules of thumb provide a good starting place. The crossover frequency should be a decade less than the switching frequency (if fs is 250kHz, then fc should be about 25kHz). This keeps switching noise out of the loop. Sixty degrees of phase margin should provide decent transient response with minimal overshoot. Again, this is just a starting place, your mileage may vary.

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