A DC-DC converter includes a transformer with two oppositely-wound primary windings, one on each side of a center tap, and at least one secondary winding connected to a load having a given capacitance. A reference voltage source is connected to the center tap of the transformer via an inductor so that the transformer is driven by a current source. Two switching devices are each connected in the return path of the reference voltage and in series with a respective primary winding. A control unit alternately and periodically connects the return path for the reference voltage to one or other of the primary windings. The control unit includes an oscillator generating squarewave signals has two complementary outputs connected directly to a control terminal of a respective switching device. The frequency of the oscillator is substantially equal to the resonant frequency of a circuit comprising the secondary inductance of the transformer and the capacitance of the load.
In the DC-DC converter according to the present invention, an intermediate tap is provided in the free-wheel inductor; the free-wheeling current goes out through the tap. The switch at the main switch side is driven by an N-channel FET (NPN transistor) and a pulse transformer, or the switch constitutes a P-channel FET (PNP transistor), so that the driving circuit at the rectifying side can be made simple. Further, the DC-DC converter includes loss-less snubber circuits or a soft switching circuit having a sub-switch in order to absorb and recover the surge energy from a leaked inductance, which is generated by the addition of the intermediate tap. Moreover, the driving circuit for the soft switching circuit is also simplified.
A two-switch, two-inductor boost converter achieves output-voltage regulation in a wide input-voltage and load-current range using a constant-frequency by employing an auxiliary transformer to couple current paths of the two boost inductors so that both inductors carry the same current. By forcing the current through the boost inductors to be the same, the energy in both inductors is forced to change in unison, i.e., both inductors increase the energy when both switches are turned on simultaneously and decrease (transfer) energy when either of the converter's two switches is turned off. As a result, the stored and transferred energy of both inductors can be controlled in a wide input-voltage and load range using a constant-frequency control by controlling the time duration that the two switches are simultaneously on.
In a power supply apparatus which supplies a high-tension alternating voltage to a load, field-effect transistors (N-MOS) are disposed between both ends of a converter transformer having a center tap and the ground respectively, and a field-effect transistor (P-MOS) is disposed between the center tap and a power supply. In an ordinary operation, a transistor connected to the center tap is being on and transistors at the both ends of the converter transformer are alternately switched at the same frequency by a converter transformer driving circuit, thereby generating the high-tension alternating voltage on the side of a secondary winding of the converter transformer. When the generation of the high-tension alternating voltage is stopped, the driving circuit is controlled to cause the transistor connected to the center tap to be off and cause the transistors at the both ends of the converter transformer to be on, thereby preventing an unstable output voltage generated when output oscillation is stopped.
In a switching power source, by alternately turning on first and second MOS transistors, a switching current flows to a primary winding of a transformer, and an alternate current is transferred to a secondary side. The alternate voltage caused in a secondary winding is full-wave rectified by first and second diodes. Resonance elements (capacitor and coil) are connected to a tertiary winding coupled to an isolation transfer, thereby enabling the primary side to be set into a resonated state and to be set to a current resonance type switching power source. Since a leakage inductance of the transformer is not set to a resonance element, an interval between the windings of the isolation transformer can be closely coupled. Since a resonance current is not directly turned on/off, a peak value of the primary current is decreased and switching loss and loss due to an on-resistance can be decreased. The efficiency of a current resonance type switching power source is thus improved.
The invention relates to a continuous voltage converter with soft switching, comprising a transformer (Np, Ns) whose primary is particularly of the type with a half-bridge mounting and is adapted to be connected to a source of input voltage (Ve) by means of two electronic switches (INT1, INT2) and whose secondary, of the mono-alternating type, is adapted to be connected to a load by means of an inductance in series (L2) and means (1 to 3, G1, G2) to control alternatingly the two switches, at fixed frequency, according to a regulation by modification of the pulse width as a function of the output voltage (Vo), so as to provide to said primary a switching at zero voltage, said converter being characterized in that said secondary comprises moreover a resonant circuit (L1, C1) so as to provide for said secondary a quasi-resonant switching at zero current.
