Switching power supply capable of ac to dc conversion

• US 20030063479A1
• Filed: 09/26/2002
• Published: 04/03/2003
• Est. Priority Date: 09/28/2001
• Status: Active Grant

• Current Assignee: Sanken Electric Company Limited
• Original Assignee: Sanken Electric Company Limited
• Inventors: Yamagishi, Toshiyuki, Morita, Koichi
• Granted Patent: US 6,600,670 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A switching power supply capable of translating a.c. voltage of sinusoidal waveform into d.c. voltage, comprising a rectifier circuit connected to a pair of a.c. input terminals for rectifying the incoming commercial a.c. voltage. A first main switch is connected between the pair of outputs of the rectifier circuit via a main inductor. A smoothing capacitor is connected in parallel with the first main switch via a rectifying diode. A second main switch is connected in parallel with the smoothing capacitor via the primary winding of a transformer. The first and the second main switch are each provided with a soft-switching capacitor connected in parallel therewith. A first and a second ancillary inductor, electromagnetically coupled respectively to the main inductor and to the transformer primary, are connected in parallel with the first and the second soft-switching capacitor, respectively, via an ancillary switch. A switch control circuit is connected to the main switches for on-off control thereof at a repetition frequency higher than the frequency of the input a.c. voltage, and to the ancillary switch for on-off control thereof at such a repetition frequency, and with such conducting periods, as to assure soft turn-on of the main switches.

Claims

1. A switching power supply capable of translating a.c. voltage of sinusoidal waveform into d.c. voltage, comprising:

(a) a pair of a.c. input terminals for inputting a.c. voltage having a known frequency;

(b) a rectifier circuit connected to the pair of input terminals for rectifying the input a.c. voltage, the rectifier circuit having a first and a second output for providing a rectifier output voltage;

(c) a main inductor connected to the first output of the rectifier circuit;

(d) a first main switch connected to the first output of the rectifier circuit via the main inductor on one hand and, on the other hand, to the second output of the rectifier circuit;

(e) first soft-switching capacitance means associated with the first main switch;

(f) a rectifying diode;

(g) a smoothing capacitor connected in parallel with the main switch via the rectifying diode and having a first terminal and a second terminal;

(h) a transformer;

(i) a second main switch connected to the first terminal of the smoothing capacitor via a primary winding of the transformer on one hand and, on the other hand, to the second terminal of the smoothing capacitor;

(j) second soft-switching capacitance means associated with the second main switch;

(k) a rectifying and smoothing circuit connected to the transformer for providing output d.c. voltage;

(l) a first ancillary inductor connected to the main inductor and electromagnetically coupled thereto;

(m) an ancillary switch connected to the main inductor via the first ancillary inductor on one hand and, on the other hand, to the second output of the rectifier circuit;

(n) a first reverse-blocking diode connected in series with the first ancillary inductor;

(o) a second ancillary inductor electromagnetically coupled to the primary winding of the transformer and having one extremity connected to a junction between the second main switch and the smoothing capacitor, and another extremity connected to the ancillary switch;

(p) a second reverse-blocking diode connected in series with the second ancillary inductor; and

(q) a switch control circuit connected to the first main switch for on-off control thereof at a repetition frequency higher than the frequency of the input a.c. voltage, to the second main switch for on-off control thereof in order to cause d.c. voltage to be intermittently applied from the smoothing capacitor to the primary winding of the transformer, and to the ancillary switch for on-off control thereof at such a repetition frequency, and with such conducting periods, as to assure soft turn-on of the first and the second main switch.

2. The switching power supply of claim 1 wherein the switch control circuit is adapted to drive the first and the second main switch at the same repetition frequency.

3. The switching power supply of claim 2 wherein the switch control circuit is adapted to turn the first and the second main switch at the same moment.

4. The switching power supply of claim 1 wherein the switch control circuit comprises:

(a) first voltage detector means for detecting an input voltage or an output voltage of the rectifier circuit;

(b) second voltage detector means for detecting a voltage across the smoothing capacitor;

(c) third voltage detector means for detecting the output voltage of the rectifying and smoothing circuit;

(d) current detector means for detecting a current through the rectifier circuit;

(e) a periodic wave generator for generating a periodic voltage wave with a frequency higher than the frequency of the input a.c. voltage;

(f) first tentative conducting period determination means connected to the first and the second voltage detector means and the current detector means and the periodic wave generator for determining tentative conducting periods for the first main switch in order to hold the voltage across the smoothing capacitor at a desired value and to cause the input current of the rectifier circuit to approximate a sinusoidal waveform;

(g) second tentative conducting period determination means connected to the third voltage detector means and the periodic wave generator for determining tentative conducting periods for the second main switch in order to hold the output voltage of the rectifying and smoothing circuit at a desired value;

(h) a timer connected to the periodic wave generator for determining conducting periods for the ancillary switch in synchronism with the periodic wave;

(i) conducting period limitation means for providing a conducting period limitation signal that is in a prescribed state for a prescribed period of time from the beginning of each conducting period of the ancillary switch;

(j) a first logic circuit having inputs connected to the first tentative conducting period determination means and the conducting period limitation means for nullifying the tentative conductive periods for the first main switch as long as the conducting period limitation signal is in the prescribed state; and

(k) a second logic circuit having inputs connected to the second tentative conducting period determination means and the conducting period limitation means for nullifying the tentative conductive periods for the second main switch as long as the conducting period limitation signal is in the prescribed state.

5. The switching power supply of claim 4 wherein the conducting period limitation means comprises a timer connected to the periodic wave generator for providing the conducting period limitation signal in synchronism with the periodic wave.

6. The switching power supply of claim 1 wherein the switch control circuit comprises:

(a) first voltage detector means for detecting an input voltage or an output voltage of the rectifier circuit;

(b) second voltage detector means for detecting a voltage across the smoothing capacitor;

(c) third voltage detector means for detecting the output voltage of the rectifying and smoothing circuit;

(d) current detector means for detecting a current through the rectifier circuit;

(e) a periodic wave generator for generating a periodic voltage wave with a frequency higher than the frequency of the input a.c. voltage;

(f) first tentative conducting period determination means connected to the first and the second voltage detector means and the current detector means and the periodic wave generator for determining tentative conducting periods for the first main switch in order to hold the voltage across the smoothing capacitor at a desired value and to cause the input current of the rectifier circuit to approximate a sinusoidal waveform;

(g) second tentative conducting period determination means connected to the third voltage detector means and the periodic wave generator for determining tentative conducting periods for the second main switch in order to hold the output voltage of the rectifying and smoothing circuit at a desired value;

(h) a timer connected to the periodic wave generator for determining conducting periods for the ancillary switch in synchronism with the periodic wave;

(i) first conducting period limitation means for providing a first conducting period limitation signal that is in a prescribed state for a first prescribed period of time from the beginning of each conducting period of the ancillary switch;

(j) second conducting period limitation means for providing a second conducting period limitation signal that is in a prescribed state for a second prescribed period of time from the beginning of each conducting period of the ancillary switch;

(k) a first logic circuit having inputs connected to the first tentative conducting period determination means and the first conducting period limitation means for nullifying the tentative conductive periods for the first main switch as long as the first conducting period limitation signal is in the prescribed state; and

(l) a second logic circuit having inputs connected to the second tentative conducting period determination means and the second conducting period limitation means for nullifying the tentative conductive periods for the second main switch as long as the second conducting period limitation signal is in the prescribed state.

7. The switching power supply of claim 6 wherein the first conducting period limitation means comprises a timer connected to the periodic wave generator for providing the first conducting period limitation signal in synchronism with the periodic wave, and wherein the second conducting period limitation means comprises another timer connected to the periodic wave generator for providing the second conducting period limitation signal in synchronism with the period wave.

8. The switching power supply of claim 1 wherein the switch control circuit comprises:

(a) first voltage detector means for detecting an input voltage or an output voltage of the rectifier circuit;

(b) second voltage detector means for detecting a voltage across the smoothing capacitor;

(c) third voltage detector means for detecting the output voltage of the rectifying and smoothing circuit;

(d) current detector means for detecting a current through the rectifier circuit;

(e) a periodic wave generator for generating a periodic voltage wave with a frequency higher than the frequency of the input a.c. voltage;

(f) first tentative conducting period determination means connected to the first and the second voltage detector means and the current detector means and the periodic wave generator for determining tentative conducting periods for the first main switch in order to hold the voltage across the smoothing capacitor at a desired value and to cause the input current of the rectifier circuit to approximate a sinusoidal waveform;

(g) second tentative conducting period determination means connected to the third voltage detector means and the periodic wave generator for determining tentative conducting periods for the second main switch in order to hold the output voltage of the rectifying and smoothing circuit at a desired value;

(h) a timer connected to the periodic wave generator for determining conducting periods for the ancillary switch in synchronism with the periodic wave;

(i) first main switch voltage detector means for detecting voltage across the first main switch;

(j) second main switch voltage detector means for detecting voltage across the second main switch;

(k) means for providing a first and a second reference voltage;

(l) a first comparator connected to the first main switch voltage detector means and to the providing means for comparing the voltage across the first main switch with the first reference voltage;

(m) a second comparator connected to the second main switch voltage detector means and to the providing means for comparing the voltage across the second main switch with the second reference voltage;

(n) first conducting period limitation means connected to the first comparator for providing a first conducting period limitation signal that is in a prescribed state from the beginning of each conducting period of the ancillary switch to the moment when the voltage across the first main switch becomes less than the first reference voltage;

(o) second conducting period limitation means connected to the second comparator for providing a second conducting period limitation signal that is in a prescribed state from the beginning of each conducting period of the ancillary switch to the moment when the voltage across the second main switch becomes less than the second reference voltage;

(p) a first logic circuit having inputs connected to the first tentative conducting period determination means and the first conducting period limitation means for nullifying the tentative conductive periods for the first main switch as long as the first conducting period limitation signal is in the prescribed state; and

(q) a second logic circuit having inputs connected to the second tentative conducting period determination means and the second conducting period limitation means for nullifying the tentative conductive periods for the second main switch as long as the second conducting period limitation signal is in the prescribed state.

9. The switching power supply of claim 1 wherein the transformer has a secondary winding, and wherein the rectifying and smoothing circuit is connected to the secondary winding of the transformer.

10. The switching power supply of claim 9 wherein the rectifying and smoothing circuit comprises:

(a) a rectifying diode connected to one extremity of the secondary winding of the transformer, the rectifying diode being so oriented as to become conductive in response to a voltage developing across the transformer secondary during the nonconducting periods of the second main switch; and

(b) a smoothing capacitor connected in parallel with the transformer secondary via the rectifying diode.

11. The switching power supply of claim 9 wherein the rectifying and smoothing circuit comprises:

(a) a rectifying diode connected to one extremity of the secondary winding of the transformer, the rectifying diode being so oriented as to become conductive in response to a voltage developing across the transformer secondary during the conducting periods of the second main switch; and

(b) a smoothing circuit connected in parallel with the transformer secondary via the rectifying diode.