JP2003092881A - Power supply for control circuit in power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply for control circuit of power supply unit capable of suppressing power consumption at low voltage close to required voltage for a control circuit in a boost half-bridge type (BHB type) power supply unit. SOLUTION: In a boost half-bridge type (BHB type) switching power supply unit, there is provided a rectifying circuit consisting of four diodes connected to a tertiary winding of a transformer. Smoothing is conducted by a choke coil and a capacitor to form a power supply for the control circuit. As a result, power can be supplied at low voltage close to required voltage for the control circuit, thus the highly efficient power supply unit can be provided, which is capable of suppressing power consumption in the control circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the efficiency of a boost half bridge type (BHB type) switching power supply and reducing the size and cost of a power supply device.

[0002]

2. Description of the Related Art Conventionally, a boost half bridge type (BHB type) switching power source suitable for an on-board power source in a wide input voltage range has been used, and this method is a circuit in which a boost chopper circuit and an asymmetric control half bridge circuit are integrated. It is possible to drive a self-driven synchronous rectification MOSFET in a wide input range, and it is a high efficiency DC input power supply that uses a low withstand voltage and low on-resistance MOSFET as a main switch element and a synchronous rectification element. An example of this circuit diagram is shown in FIG.

The BHB type power supply device is a switching power supply device which the applicant has previously proposed as a high efficiency power supply device. (JP-A-11-262263) In a conventional BHB type switching power supply, a power supply for a control circuit is generally provided with a tertiary winding on a transformer, and a capacitor is connected to the tertiary winding via one diode, The voltage generated in the capacitor is used.

FIG. 4 is a diagram showing the characteristics of the power supply voltage for the control circuit according to the conventional method. T1 is a period during which Q2 is on, and T2 is a period during which Q1 is on. See also T
s is the switching cycle of Q1 and Q2. Therefore, assuming that the input voltage is Np, the number of primary windings of the Vin transformer, the number of tertiary windings is Nt, the voltage between terminals of the capacitor C2 is Vc2, and the voltage between terminals of the capacitor C4 is Vc4, the following equation is established.

[Equation 1]

[Equation 2]

[Equation 3] From Equation 3, it can be seen that in the conventional circuit, Vc4 changes at the same rate as the input voltage changes. Therefore, in the power supply whose input voltage changes, it is necessary to set the tertiary winding Nt so that Vc4 becomes equal to or higher than the minimum operating voltage of the control circuit when the input voltage is the lowest voltage.

In order to maintain the power supply voltage of the control circuit at a constant voltage or more in a wide variation range of the input voltage, a large voltage with a considerable margin with respect to the voltage required by the control circuit is used in the transformer. It had to be generated in the next winding.

Therefore, there has been a problem that the power consumption of the control circuit is increased and the power efficiency of the power supply device is also lowered.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a control circuit for a boost half bridge type (BHB type) power supply device. By supplying a voltage that is higher than the voltage but is as low as possible, it is possible to provide the power supply for the control circuit of the power supply device that can reduce the power consumption.

[0008]

The invention set forth in the claims for attaining the above object makes use of the effectiveness of a BHB type switching power supply, and can be applied to a highly efficient power supply device. A power supply for a control circuit of the device is provided.

That is, the BHB type switching power supply is provided as a DC input high-efficiency power supply suitable for an on-board power supply in a wide input voltage range, but its control circuit power supply supplies a stable voltage at a low voltage. The power consumption of the control circuit is reduced, and a highly efficient and stable output is provided as a power supply device.

The BHB type switching power supply is a boost half-bridge type switching power supply in which a boost converter and a half-bridge converter are combined, and an AC voltage is applied to the primary winding of the transformer, and the secondary winding of the transformer and An AC voltage corresponding to the number of turns is induced in the tertiary winding, and the voltage induced in the tertiary winding is rectified by providing a rectifying circuit composed of four diodes, thereby utilizing the full wave of the AC waveform. It is possible.

By providing a rectifier circuit consisting of four diodes connected to the tertiary winding of the transformer, smoothing it with a choke coil and a capacitor, and using it as a power supply for the control circuit, the voltage required by the control circuit is adjusted. Electric power can be supplied at a low voltage close to that, and it is possible to avoid supplying unnecessary voltage and lowering the efficiency of the power supply device.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a semiconductor switching device according to the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same members are designated by the same reference numerals,
A duplicate description will be omitted.

FIG. 1 shows an embodiment of the present invention, and FIG. 1 is a circuit diagram thereof. This circuit diagram is obtained by replacing the conventional BHB power supply device shown in FIG. 3 in which one diode is connected to the output terminal of the tertiary winding with four diodes.

Each of the four diodes is connected to two output terminals of the tertiary winding, two anodes and two cathodes of the diode are connected, and the opposite terminals of the diode are two cathodes and two anodes, respectively. Connect the two as output terminals, and connect the choke coil to one of the diode terminals, connect the other end of the choke coil and the other diode terminal to the capacitor, and supply the voltage across the capacitor as the power supply for the control circuit. To be done.

By combining the diodes as described above, the voltage of the lower capacitor on the input side is applied to the primary winding of the transformer while the lower switching element on the primary side is on, The voltage converted by the winding ratio of the line and the tertiary winding is generated in the tertiary winding, and conversely, the voltage of the upper capacitor is the primary voltage of the transformer while the upper switching element on the primary side is on. An AC voltage is applied to the winding to generate an AC voltage in the tertiary winding, which makes it possible to supply power to the capacitor in positive and negative cycles.

FIG. 2 is a diagram showing the characteristics of the power supply voltage for the control circuit according to the method of the present invention shown in FIG. In the circuit of the present invention, the voltage Vp at point P has a waveform obtained by rectifying the voltage generated in the tertiary winding Nt as shown in FIG. 3, and Vc5 is averaged between L5 and C5.

[Equation 4] On the other hand, the output voltage of the main circuit is expressed by the following equation.

[Equation 5] From number 4 and number 5

[Equation 6] Here, since Vout is made constant by the control circuit, Vc5 is also indirectly made constant and its voltage becomes constant. Therefore, Vc5 can be set close to the minimum operating voltage of the control circuit, this voltage does not change, and power loss in the control circuit can be reduced.

[0017]

EFFECTS OF THE INVENTION In a BHB type switching power supply, a rectifier circuit consisting of four diodes connected to the tertiary winding of a transformer is provided, smoothed by a choke coil and a capacitor, and used as a power supply for a control circuit. It is possible to provide a high-efficiency power supply device that can supply power at a voltage that is higher than or equal to the voltage required by the control circuit and that is as close as possible to that voltage and that is low in power consumption in the control circuit.

[0018]

[Brief description of drawings]

FIG. 1 is an example of a power supply for a control circuit of a BHB type power supply device showing an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of a power supply voltage for a control circuit according to the method of the present invention.

FIG. 3 is a diagram showing a power supply for a control circuit of a conventional BHB type power supply device.

FIG. 4 is a diagram showing a characteristic of a power supply voltage for a control circuit according to a conventional method.

[Explanation of symbols]

1, input 2, loads C1 to C5, capacitors D1 to D4, diodes Q1 to Q4, switch elements L1, L2, L5, inductance T, transformer Np, transformer primary winding Ns, transformer secondary winding Nt, transformer 3 Output voltage Va of bridge circuit by secondary winding Vp and diodes D1 to D4, voltage Vb of transformer secondary winding when Q2 is turned on, voltage T1 of transformer secondary winding when turned on, Q2 Period T2, Q1 is on, switching period 6 of Q1 and Q2, control circuit

Claims (2)

[Claims] 1. A boost half-bridge type switching power supply in which a boost converter and a half-bridge converter are combined, a tertiary winding is provided in a transformer, and four diodes are bridge-connected to the tertiary winding of the transformer. For smoothing the output voltage of the rectifier circuit and using it as a power source for the control circuit. 2. The power supply device according to claim 1, wherein the output terminal of the rectifier circuit consisting of four diodes connected to the tertiary winding of the transformer has a voltage of the input side capacitor when the switch element is on. A power supply for a control circuit of a power supply device, characterized in that a voltage converted by a winding ratio of a primary winding and a tertiary winding of a transformer is generated and smoothed by a choke coil and a capacitor.