Stabilizing power source apparatus

Abstract: A stabilizing power source apparatus provides a DC output and an AC output voltage. A transformer (T1) has a primary winding (Np), first secondary windings (Ns1, Ns2) and a second secondary winding (Ns3). The switching device (Q2, Q3) is connected to the first primary winding (Np) and switches a direct voltage to supply a switched voltage to said primary winding. A driving winding (Nd) of the transformer is connected to the primary winding for controlling the switching of the switching device (Q2, Q3). Saturable reactors (Ls1, Ls2) are connected to the first secondary windings to control the ON time of currents flowing through those first secondary windings. A rectifying/smoothing circuit (D1, D2, D3, L1, C1) rectifies and smooths the outputs of the saturable reactors to generate the DC output voltage. The AC output voltage appears across the second secondary winding (Ns3). The DC output voltage is compared with a reference voltage (Vr) and is used to reset the reset value of the saturable reactors to cancel variations in the DC output voltage in accordance with the comparison result.

Description: The present invention relates to a multiple output type stabilizing power source apparatus for generating stabilized AC and DC voltages. A typical conventional multiple output type stabilizing power source apparatus as shown in Fig. 2 supplies a stabilized DC voltage to a DC load such as electronic equipment and a stabilized AC voltage to an AC load such as a fluorescent lamp. Referring to Fig.2, the stabilizing power source apparatus has inverters at the primary and secondary winding sides. A reference symbol V₀ denotes a DC voltage; Q₁, a switching transistor; and T₁, an inverter transformer. The inverter transformer T₁ has a primary winding N P and a secondary winding N S . Reference symbols D₁ and D₂ denote rectifying diodes, respectively; L₁, a choke coil; and C₁, a smoothing capacitor. A reference symbol A₁ denotes a differential amplifier for comparing a reference voltage V R with a DC output V₁ from the secondary winding N S and generating a signal corresponding to the difference. A reference symbol OSC denotes an oscillator for generating a triangular wave signal; and PM , a pulse width modulator for converting the triangular wave from the oscillator OSC to pulses of the same frequency as that of the triangular wave and for changing a pulse width of the converted pulses in accordance with a shift of a crossing point between the triangular wave from the oscillator OSC and the signal from the differential amplifier A₁. A reference symbol DR denotes a driver for amplifying the pulses from the pulse width modulator PWM and for supplying an amplified signal to the base of the transistor Q₁. A reference symbol INV denotes an inverter for receiving the DC voltage V₁ from the secondary winding N S and for generating an AC voltage upon switching; T₂, a voltage transformer for transforming the AC voltage from the inverter INV; C F , a waveshaping capacitor; and R L , an AC load for receiving an AC output V₂. It should be noted that a resistor R S detects a current flowing through the AC load R L , and the inverter INV is switched to keep the current constant in response to the detection signal. In the conventional stabilizing power source apparatus having the structure described above, a rectangular wave current obtained upon switching of the transistor Q₁ is rectified by the diodes D₁ and D₂ connected to the secondary winding N S . The rectified current is smoothed by the choke coil L₁ and the capacitor C₁ to provide the DC output V₁. The DC output V₁ is supplied to the differential amplifier A₁ and is compared with the reference input voltage V R . The differential amplifier A₁ provides a signal corresponding to the difference to the pulse width modulator PWM. In the pulse width modulator PM , the triangular wave from the oscillator OSC is converted to the pulses of the same frequency as that of the triangular wave. In this case, the pulse width is varied in accordance with the crossing point between the leading ramp of the triangular wave and the output from the differential amplifier A₁. The pulse is amplified by the driver DR, and the amplified pulse is supplied to the base of the transistor Q₁. The duty factor of the transistor Q₁ is thus controlled in response to the output from the differential amplifier A₁. Therefore, the DC voltage V₁ is kept constant. On the other hand, the stabilized DC output V₁ is supplied to the inverter INV and is converted to the AC voltage upon its switching. The AC voltage is boosted by the transformer T₂. The boosted voltage is then smoothed by the capacitor C F , and the smoothed output is supplied to the AC load R L . When the AC load R L such as a discharge lamp is driven by the stabilizing power source apparatus described above, an AC voltage which is 3 to 5 times that in normal operation is required to start discharge. Since the capacitor C F is inserted at the output side of the transformer T₂ and the output voltage at the transformer T₂ drops to provide the normal operation voltage for the load R L , no voltage drop occurs across the capacitor C F at the start of discharge when no current flows through the load R L . Thus, a high AC voltage is applied to the load R L . In the conventional stabilizing power source apparatus, however, since the switching circuits are arranged at the primary and secondary sides of the transformer, the circuit arrangement is complicated. Furthermore, since the rectangular wave voltage is supplied to the primary winding N P of the inverter transformer T₁, an AC ripple is generated by capacitive couplings between the primary and secondary windings N P and N S . This ripple has the same phase as that of the normal signal component, so that the ripple is fed back to the primary winding N P through the ground line at the secondary winding N S . Therefore, common mode noise including a comparatively high frequency component is generated. In the conventional apparatus of this type, a large line filter must be inserted at the input side to reduce such noise. US-A-4,451,876 discloses a stabilizing power source apparatus having a DC output voltage. This power source apparatus has a transformer having a primary winding and a secondary winding. A switching device is connected to the primary winding to supply a switched direct current to the primary winding. The secondary winding is connected through a saturable reactor to a rectifying/smoothing circuit which generates the DC output voltage. US-A-3,777,248 discloses a stabilizing power source apparatus having a DC output voltage. The power source apparatus has a transformer having a primary winding, a secondary winding and a driving winding. A switching device is connected to the primary winding for switching a direct current voltage to supply the switch device to the first winding and is controlled by the driving winding. The secondary winding is connected to a rectifying/smoothing circuit which generates the DC output voltage. It is an object of the present invention to provide a stabilizing power source apparatus with low-level common mode noise. It is another object of the present invention to provide a stabilizing power source apparatus which has a simple circuit structure and low manufacturing cost. According to the present invention, there is provided a stabilizing power source apparatus having a DC output voltage and an AC output voltage comprising: a transformer, having a primary winding, a first secondary winding, and a second secondary winding; a switching device, connected to said primary winding, for switching a direct current voltage to supply the switched voltage to said primary winding, a resonant capacitor connected in parallel to said primary winding of said inverter transformer, a driving winding, magnetically coupled to said primary winding, for controlling the switching of said switching device; a saturable reactor connected to said first secondary windings, for controlling ON time of currents flowing through the first secondary windings; a rectifying/smoothing circuit, for rectifying and smoothing the output of said saturable reactor to generate a DC output voltage, a circuit, for comparing the output voltage of said rectifying/smoothing circuit with a reference voltage, and controlling the reset value of said saturable reactor to cancel the variations in said DC output voltage in accordance with the comparison result; and a wave shaping circuit, having a capacitor or a choke coil and connected to said second secondary winding, for outputting said alternating current output voltage to an AC load. An embodiment of the present invention will now be described with reference to the accompanying drawings: - Fig. 1 is a circuit diagram of a stabilizing power source apparatus according to the present invention; and Fig. 2 is a circuit diagram of a conventional stabilizing power source apparatus. Fig. 1 is a circuit diagram of a stabilizing power source apparatus according to an embodiment of the present invention. Referring to Fig. 1, a reference numeral V₀ denotes an input DC voltage; L P , a choke coil; Q₂ and Q₃, switching transistors which are alternately turned on/off; and T₁, an inverter transformer. The inverter transformer T₁ has primary windings N P1 and N P2 . A reference symbol N D denotes a drive coil connected to the bases of the transistors Q₂ and Q₃. A reference symbol C P denotes a resonant capacitor inserted in parallel with the primary windings N P1 and N P2 . The switching transistors Q₂ and Q₃ comprise bipolar transistors, respectively, in the above arrangement, but can be replaced with other switching elements such as MOSFETs, GTO thyristors, normal thyristors. When thyristors are used, a waveshaper must be inserted between the coil N D and the two terminals of the switching element. In the case of thyristors, a commutating circuit must be added to turn off the thyristors. The above arrangement constitutes a resonant inverter for generating a sinusoidal wave voltage across the primary windings N P1 and N P2 . The switching operation of the two transistors is called push-pull operation. Reference symbols N S1 and N S2 denote secondary windings of the inverter transformer T₁; L S1 and L S2 , saturable reactors connected in series with the secondary windings N S1 and N S2 , respectively; D₁, D₂ and D₃, rectifying diodes; L₁, a choke coil; and C₁, a smoothing capacitor. A reference symbol N S3 denotes an AC output secondary winding; C F , a waveshaping capacitor; and R L , an AC load. A reference symbol A₁ denotes a differential amplifier for comparing a reference voltage V R with the DC voltage V₁ and generating a signal representing the difference therebetween. A reference symbol Q₄ denotes a transistor, the base of which is connected to the differential amplifier A₁ to receive the difference signal as a base current, the collector of which is connected to saturable reactors L S1 and L S2 respectively through the diodes D₄ and D₅ and the emitter of which is connected to the DC voltage V₁. The transistor Q₄ comprises a bipolar transistor, but can be replaced with another output current control element such as a MOSFET. The operation of the stabilizing power source apparatus having the arrangement described above will be described hereinafter. When the input DC voltage V₀ is supplied to the apparatus, a current flows in the bases of the transistors Q₂ and Q₃ through the resistors R₁ and R₂, so that one of the transistors Q₂ and Q₃ is turned on (it is indefinite which transistor is turned on first). Assume that the transistor Q₂ is turned on first and the voltage V₀ is supplied to the primary winding N P1 of the inverter transformer T₁. In this case, a voltage obtained by dividing the DC input voltage V₀ in accordance with the number of turns is induced at the drive coil N D magnetically coupled to the primary winding N P1 . The base-emitter path of the transistor Q₃ is reverse-biased, and the transistor Q₃ is kept off. In this case, the voltage generated at the primary winding N P1 is a sinusoidal wave. A self-excited angular frequency ω is given as: ω = 1/ L H (C P ′ + C F ′) where L H is the inductance of the primary winding N P1 of the inverter transformer T₁, C P ' is the capacitance for the primary winding N P1 based on the resonant capacitor C P , and C F ' is the capacitance for the primary winding N P1 based on the waveshaping capacitor C F . When the sinusoidal wave voltage at the primary winding N P1 transits to the negative polarity through a zero-crossing point, the induction voltage at the drive coil N D changes likewise. The induction voltage at the drive coil N D which has been supplied as the reverse-bias voltage to the base of the transistor Q₃ is then forward-biased. The transistor Q₂ is now reverse-biased to turn on the transistor Q₃ and turn off the transistor Q₂. As a result, the self-excited resonance is set in the negative half cycle. The transistors Q₂ and Q₃ are alternately turned on/off to generate the sinusoidal wave current at the primary windings N P1 and N P2 . The current is then extracted at the secondary windings N S1 and N S2 . If the saturable reactors L S1 and L S2 are not arranged, the sinusoidal wave current is full-wave rectified by the diodes D₁ and D₃. The rectified current is smoothed by the choke coil L₁ and the capacitor C₁ to provide the DC voltage V₁. In this case, the DC voltage V₁ still varies in accordance with variations in the input DC voltage V₀. In order to stabilize the output voltage V₁, the saturable reactors L S1 and L S2 are connected in series with the secondary windings N S1 and N S2 , respectively, thereby performing phase control. In this embodiment, the saturable reactors are used to reduce noise at the secondary windings of the transformer. The saturable reactors serve as elements for controlling ON time of currents flowing through the coils and may be replaced with switching elements such as transistors. The saturable reactors L S1 and L S2 are arranged such that the phase control angles representing the present saturation timings are determined by the reset values of the magnetic flux. When the reset values are increased, the phase control angles are increased, and thus the output voltages are decreased. The DC voltage V₁ is compared by the differential amplifier A₁ with the reference input voltage V R , and the difference signal from the differential amplifier A₁ is supplied to the base of the transistor Q₄. In this case, since the collector of the transistor Q₄ is connected to the saturable reactors L S1 and L S2 , the reset values of the saturable reactors L S1 and L S2 are controlled to cancel the variations in the DC voltage V₁. The DC voltage V₁ is kept constant. The AC voltage from the secondary windings N S3 is supplied to the AC load R L through the waveshaping capacitor C F . The transistors Q₂ and Q₃ have conduction times. The transistors Q₂ and Q₃ are simultaneously turned on when the sinusoidal wave voltages at the primary windings N P1 and N P2 are set to 0. In this case, the choke coil L P is arranged at the DC input side to limit the short-circuiting current. In the above embodiment, the capacitor C F is used as the waveshaping element of the AC output secondary winding N S3 . However, a choke coil may be inserted in place of the capacitor C F . In this case, the self-excited angular frequency ω' is given as: ω' = 1/ (L P //L F ′)C P ′ where L F ' is the inductance of the choke coil L F which is figured out on the basis of the primary winding N P1 , and L P //L F ' is the total inductance of the inductance of the choke coil L P and the inductance L F '. In the stabilizing power source apparatus described above, the sinusoidal wave voltage is applied in the collector-emitter paths of the transistors Q₂ and Q₃, and the voltages at the transistors Q₂ and Q₃ are substantially zero at the turn on/off timing, thereby decreasing the switching loss. Since the sinusoidal wave signal is supplied to the primary winding of the inverter transformer T₁, only low-level harmonic waves are generated as compared with the case wherein a rectangular wave voltage is supplied to the primary winding of the inverter transformer T₁. Since the common mode AC current flowing in the secondary windings through the coupling capacitance C S between the primary and secondary windings is decreased, the line filter at the input side need not be large in size. Since the switching loss is decreased as described above, the switching frequency can be increased, and the inverter transformer T₁ can be made compact. According to the present invention, the stabilizing power source apparatus has a single switching circuit, so that the number of components is decreased and the manufacturing cost is decreased. In addition, the apparatus is made small as a whole, and its reliability is improved. According to the present invention, the sinusoidal wave is supplied to the primary windings, so that the conduction noise is decreased, and the circuit arrangement can be simplified. Furthermore, since the switching frequency can be increased, the transformer can be made compact and the apparatus as a whole can be made compact. The number of transformers can be decreased, and the insulated portion between the primary and secondary windings is decreased, thereby simplifying insulation design.

Claims: A stabilizing power source apparatus having a DC output voltage and an AC output voltage comprising: a transformer (T1), having a primary winding (Np), a first secondary winding (Ns1, Ns2), and a second secondary winding (Ns3); a switching device, connected to said primary winding (Np), for switching a direct current (DC) voltage to supply the switched voltage to said primary winding (Np), a resonant capacitor (Cp) connected in parallel to said primary winding (Np) of said inverter transformer (T1), a driving winding (Nd), magnetically coupled to said primary winding (Np), for controlling the switching of said switching device (Q2, Q3); a saturable reactor (Ls1, Ls2) connected to said first secondary windings (Ns1, Ns2), for controlling ON time of currents flowing through the first secondary windings (Ns1, Ns2); a rectifying/smoothing circuit (D1, D2, D3, L1, C1), for rectifying and smoothing the output of said saturable reactor (Ls1, Ls2) to generate a DC output voltage, a circuit (A1, Q4), for comparing the output voltage of said rectifying/smoothing circuit (D1, D2, D3, L1, C1) with a reference voltage, and controlling the reset value of said saturable reactor (Ls1, Ls2) to cancel the variations in said DC output voltage in accordance with the comparison result; and a wave shaping circuit (CF), having a capacitor (CF) or a choke coil and connected to said second secondary winding (Ns3), for outputting said alternating current (AC) output voltage to an AC load. A stabilizing power source apparatus according to claim 1, characterized in that said switching device has at least two transistors to complete push-pull operation. A stabilizing power source apparatus according to claim 1, characterized in that said saturable reactor (Ls1,Ls2) has means for reducing noise at the first secondary winding of said transformer (T1). A stabilizing power source apparatus according to claim 1, characterized in that said driving winding (Nd) has means for outputting sinusoidal wave voltage to said switching device (Q1, Q2), said outputted voltage being substantially zero at the turn on/off timing of said switching device (Q1, Q2) to decrease the switching loss.

Inventors: OKOCHI SADAO, OKOCHI, SADAO, Okochi, Sadao, c/o Patent Division
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1985
Main classification: H02M3
IPC codes: H02M3