In many applications a voltage regulator is required to provide a voltage within a predetermined range formed from a voltage source having a different voltage level. Some circuits are subject to uncertain and undesirable functioning and even irreparable damage if an input power falls outside a certain range.
A prior art regulated power apparatus 10 is shown in FIG. 1. The apparatus 10 is a boost-boost-isolated power converter. The apparatus 10 generally includes an AC input 12, also known as an AC to DC converter, coupled with an input converter 14. In the exemplary embodiment shown, the input converter 14 comprises a power factor correction (PFC) front-end. The input converter 14 is able to be configured as a boost converter. The input converter 14 is coupled with an intermediate regulator 16 comprising another boost regulator which is coupled with an output converter 18, in this case a DC-DC converter. The output converter 18 is configured as a isolation stage. A regulation circuit 20 is coupled between the intermediate regulator 16 and the output converter 18.
The AC input 12 is coupled to receive an AC signal VAC and to generate an unregulated direct current (DC) coupled as an input to the input converter 14. Typically, the input converter 14 receives the unregulated direct current from the AC input 12 and generates a boosted or increased voltage. The increased voltage is a DC voltage. The intermediate regulator 16 receives the increased voltage and generates a regulated voltage. The regulated voltage comprises a voltage that is boosted higher than a minimum output voltage of the input converter. The output converter 18 receives the regulated higher voltage and generates an output voltage that is bucked down or lower than the higher regulated voltage. The regulation circuit 20 senses a power drop and power increase in Vout and controls a duty cycle of a regulation switching element within the intermediate regulator 16 to supply a compensating power to correct the power increase or power drop in Vout.
There are many inherent drawbacks associated with the apparatus 10. The apparatus 10 generates high surge current at start-up. Secondary components of the output converter 18 undergo high stress and the apparatus is exposed to high noise levels from the surge current. Additionally, the primary components of the output converter 18 also endure a high voltage stress. The apparatus 10 being a boost-boost-isolation power converter, is bulky and inefficient.
Another prior art power regulator similar to the apparatus 10 uses a buck type PFC front end, followed by a buck converter coupled with a buck type down converter. This other prior art has an inherent drawback of low power factor correction at low input AC line and has symptoms of discontinued input current requiring large filters to smooth out a switching ripple current. Further, this other prior art suffers from the buck PFC front end running at a relatively low efficiency compared to a boost type of front end. Also, this buck-buck-isolation configuration suffers from a high RMS current requiring high copper loss on the primary side due to a relatively low voltage coming from the two buck converters upstream.
Accordingly, it is desirable to create a regulated power converter to greatly increase the efficiency and decrease the cost of such power converters.