Push-pull, resonant type switching power supply circuit

• US 5,548,502 A
• Filed: 08/29/1994
• Issued: 08/20/1996
• Est. Priority Date: 08/27/1993
• Status: Expired due to Term

• Current Assignee: Hamamatsu Photonics KK
• Original Assignee: Hamamatsu Photonics KK
• Inventors: Kosugi, Mitsuo
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US08/297,044
• Time in Patent Office: 722 Days
• Field of Search: 363/15, 363/22, 363/23, 363/24, 363/25, 363/133, 363/134, 323/223, 323/247, 323/251, 323/282, 323/285
• US Class Current: 363/22
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/337 in push-pull configuration H02M3/33576 takes precedence; with self-oscillating arrangements H02M3/3382, H02M3/3385
• 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

To provide a resonant switching power supply switch with a simple structure and little noise, a push-pull resonant switching power supply circuit includes a transformer 104, a capacitor 105, two transistors 106a and 106b (bipolar transistors or field-effect transistors), and a bias circuit 201. The transformer 104 has a rectification circuit 340 connected to its secondary winding. The capacitor 105 forms a parallel resonant circuit in combination with the transformer 104. The transistors 106a and 106b are push-pull connected to the primary winding of the transformer 104 and the bases of which are connected to a feedback winding 104 of transformer. The bias circuit 201 applies a variable bias voltage to the base of the transistors.

Claims

1. A switching power supply circuit comprising:

a transformer including a primary winding having an inductance, a feedback winding, and a secondary winding, said primary winding and said feedback winding being located at a primary side of said transformer, said secondary winding being located at a secondary side of said transformer, and said feedback winding having a first terminal and a second terminal;

a capacitor having a capacitance and connected in parallel to said primary winding to form a resonance circuit in combination with said primary winding, said resonance circuit resonating at a frequency determined by the capacitance of said capacitor and the inductance of said primary winding;

a rectifying circuit, connected to said secondary winding, rectifying a voltage developed across said secondary winding and producing a rectified voltage;

a transistor pair connected across said primary winding in push-pull configuration, said transistor pair including a first transistor having a control electrode connected to the first terminal of said feedback winding, and a second transistor having a control electrode connected to the second terminal of said feedback winding; and

a bias circuit connected to the control electrodes of said first and second transistors and applying a bias voltage thereto, said bias circuit including means for varying the bias voltage;

wherein said bias voltage varying means comprises means for generating a reference voltage, and comparison means for comparing the rectified voltage produced from said rectifying circuit with the reference voltage and for outputting a comparison result, the bias voltage being varied based on the comparison result.

2. A switching power supply circuit according to claim 1, wherein said reference voltage generating means comprises means for varying the reference voltage.

3. A switching power supply circuit according to claim 2, wherein said feedback winding comprises a single winding.

4. A switching power supply circuit comprising:

a transformer including a primary winding having an inductance, a feedback winding, and a secondary winding, said primary winding and said feedback winding being located at a primary side of said transformer, said secondary winding being located at a secondary side of said transformer, and said feedback winding having a first terminal and a second terminal;

a capacitor having a capacitance and connected in parallel to said primary winding to form a resonance circuit in combination with said primary winding, said resonance circuit resonating at a frequency determined by the capacitance of said capacitor and the inductance of said primary winding;

a rectifying circuit, connected to said secondary winding, rectifying a voltage developed across said secondary winding and producing a rectified voltage;

a transistor pair connected across said primary winding in push-pull configuration, said transistor pair including a first transistor having a control electrode connected to the first terminal of said feedback winding, and a second transistor having a control electrode connected to the second terminal of said feedback winding;

a bias circuit connected to the control electrodes of said first and second transistors and applying a bias voltage thereto, said bias circuit including means for varying the bias voltage;

an RC filter composed of a resistor and a capacitor, said RC filter being connected to said rectifying circuit to remove ripple components contained in the rectified output and output a d.c. voltage; and

voltage division means, connected to the output of said RC filter, for producing a divided voltage of the d.c. voltage;

wherein said bias voltage varying means comprises means for generating a reference voltage, and comparison means for comparing the divided voltage of the d.c. voltage with the reference voltage and for outputting a comparison result.

5. A switching power supply circuit according to claim 4, wherein said reference voltage generating means comprises means for varying the reference voltage.

6. A switching power supply circuit according to claim 5, wherein said feedback winding comprises a single winding.

7. A switching power supply circuit according to claim 6, further comprising a resistor interposed between the control electrode of said first transistor and said bias circuit, and wherein the bias voltage is applied to the control electrode of said second transistor through said feedback winding.

8. A switching power supply circuit according to claim 7, further comprising a power supply supplying a voltage, and wherein said primary winding has a center tap separating said primary winding into two segments, said power supply being connected to the center tap of said primary winding to apply the voltage thereto.

9. A switching power supply circuit according to claim 8, further comprising a winding connected between said power supply and said center tap of said primary winding, wherein an inductance of said winding is greater than an inductance of said primary winding.

10. A switching power supply circuit comprising:

a transformer including a primary winding having an inductance, a feedback winding, and a secondary winding, said primary winding and said feedback winding being located at a primary side of said transformer, said secondary winding being located at a secondary side of said transformer, and said feedback winding having a first terminal and a second terminal;

a capacitor having a capacitance and connected in parallel to said primary winding to form a resonance circuit in combination with said primary winding, said resonance circuit resonating at a frequency determined by the capacitance of said capacitor and the inductance of said primary winding;

a rectifying circuit, connected to said secondary winding, rectifying a voltage developed across said secondary winding and producing a rectified voltage;

a transistor pair connected across said primary winding in push-pull configuration, said transistor pair including a first transistor having a control electrode connected to the first terminal of said feedback winding, and a second transistor having a control electrode connected to the second terminal of said feedback winding;

a bias circuit connected to the control electrodes of said first and second transistors and applying a bias voltage thereto, said bias circuit including means for varying the bias voltage; and

voltage division means, connected to said rectifying circuit, for producing a divided voltage of the rectified voltage, and wherein said bias voltage varying means comprises means for generating a reference voltage and a differential amplifier having a non-inverting input terminal applied with the reference voltage and an inverting input terminal applied with the divided voltage of the rectified voltage, said differential amplifier producing an amplified differential output of the reference voltage and the divided voltage of the rectified voltage.

11. A switching power supply circuit according to claim 10, wherein said reference voltage generating means comprises means for varying the reference voltage.

12. A switching power supply circuit according to claim 11, wherein said feedback winding comprises a single winding.

13. A switching power supply circuit according to claim 12, further comprising an RC filter composed of a resistor and a capacitor, said RC filter being connected to said rectifying circuit to remove ripple components contained in the rectified out, and wherein said voltage division means is connected to said RC filter.

14. A switching power supply circuit according to claim 13, further comprising a resistor interposed between the control electrode of said first transistor and said bias circuit, and wherein the bias voltage is applied to the control electrode of said second transistor through said feedback winding.

15. A switching power supply circuit according to claim 14, further comprising a power supply supplying a voltage, and wherein said primary winding has a center tap separating said primary winding into two segments, said power supply being connected to the center tap of said primary winding to apply a voltage thereto.

16. A switching power supply circuit according to claim 15, further comprising a winding connected between said power supply and said center tap of said primary winding, wherein an inductance of said winding is greater than an inductance of said primary winding.