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Jim's FAQ's

January 2010
jhayden
0

            The “Volt-Ampere” is the measure of “apparent power” and is used primarily in circuits using alternating current (AC).  The Volt Ampere (VA) consists of 2 components, the first is the real power known as Watts, while the other is the reactive power known as VAR (Volt-Amps-Reactive).  The following equation shows how the 3 terms are related:  VA = (W2 + VAR2)1/2.  In DC circuits, the VAR term drops to 0 since reactive power doesn’t show up in DC.  More information on this topic can be found here

 

A common graphical representation of the relationship between these three components is the power triangle.  The real power (Watts) makes up the adjcent leg, reactive power (VAR) makes up the opposite leg, and the apparent power (VA) is the resulting hypotenuse.

534 Views 0 Comments Permalink Tags: power, va, volt_amps, watts, var, real_power, reactive_power
jhayden
0

            While op-amps are designed to reject noise and other disturbances in the supply rails, shifts in the supply voltage can affect the output of the op-amp.  Just how much the op-amp may be affected depends on a number of factors (noise, frequency, temperature, degree of change in voltage, etc). The op-amp’s power supply rejection ratio (or PSRR) can give a good estimation of how much an output can be affected by noise or changes in the supply rail.  The PSRR is frequency dependant so its value will change under different circumstances. The voltage delivered to the op-amp’s supply pins should be kept constant, within the manufacture’s specifications, and as noise free as possible.

624 Views 0 Comments Permalink Tags: output, op_amp, supply_rail, supply_voltage, psrr, power_supply_rejection_ratio
jhayden
0
     Many op-amps can work off of a range of voltages; however, some characteristics of the op-amp may behave differently at different supply voltages.  Check the manufacture’s datasheet for details on the working specifications for the device at the voltage you want to run it at. The supply voltage should not exceed the specifications given by the manufacture and should remain constant.  Special considerations may apply to particularly low voltage levels.
363 Views 0 Comments Permalink Tags: op_amp, supply_rail, supply_voltage, powering
jhayden
0
Having a coax connector that doesn’t match a coaxial cable’s characteristic impedance can lead to reflections, attenuation, and other signal problems.  Since many coaxial connectors come in 50 & 75 ohm versions, many manufactures list the RG cable rating individual connectors are compatible with.  Matching the RG cable rating will ensure that not only will the impedance match but the connector’s physical size will match the cable as well.
467 Views 0 Comments Permalink Tags: sma, bnc, cable, impedance, coax, n_type, coax_cable, tnc, impedance_matching
jhayden

jhayden

 Member since: Dec 3, 2008

Answers to various technical inquiries received over the years.

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