• Electronic Laboratories

DC POWER SUPPLY

Electronic Laboratories manufactures CVT types ferro-resonant DC power supplies. These are inherently very reliable. Main input current waveform is nearly sinusoidal with low harmonic content. The output has no series element for output voltage control. The ferro-resonant transformer converts the input voltage to a quasi square-waveform. This waveform helps in converting to DC voltage and the ripple is filtered by means of inductor and/ or capacitor input filter. The output is current limited and the supply is short-circuit proof if all the components are properly rated. Multiple DC outputs are possible. This power-supply eliminates to and fro noise from the main input because: i) the construction of the ferro-resonant transformer is some-what like that of ultra-isolation transformer. The primary and secondary are physically separated and have very low capacitance between them. ii) The equivalent circuit of the transformer is in effect, a low-pass filter. iii) The secondary is tuned to mains frequency, presenting low impedance to others and the low frequency transformer core presents higher losses at higher frequencies. This power-supply has very fast response to changes in input voltage, and the load-change response is also good. It is subject to output voltage variation linearly proportional to the input frequency change due to its ferro-resonant nature. The overall temperature rise can be controlled by proper design. Studying the advantages and disadvantages of this reliable DC power supply, it becomes obvious that though it is not usable for some applications, where weight matters. eg, stationary control panels, inductive and switching loads like relays, solenoids, etc.