Specifications

016-538-B0-002 Rev. B

Fig. 1-3, Ferroresonant ‘Tank’ Circuit and Resulting Output Waveform

The base APX-100W unit contains a ferroresonant transformer, resonant circuit capacitor,

and an input/output terminal block.

The APX-100W uses ferroresonant transformer technology to provide line conditioning and

voltage regulation. The primary and secondary windings of the transformer are physically

isolated from each other by a large steel core which greatly reduces the capacitive coupling

of spikes and noise to the secondary winding. This provides a regulated, current-limited

output with excellent isolation and noise attenuation: 120dB in common mode; and 60dB in

transverse mode.

An oil-ﬁ lled resonant capacitor is connected to the resonant (secondary) winding of

the transformer forming a tank circuit. This provides the resonant circuit function which

contributes to the voltage regulation of the supply. The advantage of this type of transformer/

capacitor design is the ability of the ferroresonant transformer to regulate its output voltage

over a wide range of input voltages and output loading. Typical output voltages may vary +

3% to 5%, with input voltage variations of + 15% of nominal line voltage, and output loading

of 20% to 100%. This tight regulation is advantageous in cable television applications as the

active devices are protected from dangerous voltage ﬂ uctuations.

Another unique feature of the ferroresonant transformer is its ability to provide current limiting

in the event of a short circuit. This effect is called foldback. The transformer’s output current

can typically reach 150% of the nameplate output current rating for a short period of time

without damage to the transformer. When the transformer reaches the saturation point, the

output current will decrease (foldback on itself) to a minimum value, and thereby provide

current limiting. Designs based on a ferroresonant transformer are extremely rugged and

reliable, and offer many years of trouble-free operation.

1.0 Introduction, continued

1.1 Operating Principle

A true RMS voltmeter must be used to correctly measure the output voltage of the APX-100W .

NOTE:

Ferroresonant Transformer and

AC Capacitor

Clean Output Waveform

Noisy Input Waveform