JP3468162B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device that performs DC / DC conversion after rectifying a commercial power supply,
For example, the one used as a power source for a printer is targeted.

[0002]

2. Description of the Related Art A switching regulator (hereinafter referred to as a switching power supply device) is widely used as a power supply for various electric devices because it can downsize a transformer.

In a switching power supply device, a commercial power supply is once converted into a direct current voltage by a rectifier circuit, and then this direct current voltage is converted into an alternating current voltage by a switching transistor and supplied to a primary side winding of a transformer, and the secondary side of the transformer is supplied. The AC voltage induced in the winding is converted into a DC voltage by a rectifier circuit and supplied to the load.

A starting circuit for starting the switching transistor is indispensable for the switching power supply device. As a conventional start-up circuit, Japanese Patent Laid-Open No. 2-106161 discloses an example in which a start-up resistor R11 is provided at a stage subsequent to a rectifier circuit 102 for rectifying a commercial power supply 101 as shown in FIG.
As shown in FIG. 4, an example in which a starting resistor R11 is connected to the live (L) side of the commercial power source 101 to reduce the loss of the starting resistor R11 is disclosed.

With the circuit configuration shown in FIG. 3, a voltage substantially equal to the voltage of the smoothing capacitor C1 for rectification of the commercial power source 101 is applied to the starting resistor R11 even after starting, as shown in FIG. 5 (a). Since it continues, there is a problem that the power loss is large.

Smoothing capacitor C1 for rectification of commercial power source
Smooths the input AC voltage, the voltage across it is
The voltage becomes close to the AC peak voltage, and when expressed as an effective value,
It is expressed by equation (1).

[Equation 1] Therefore, power loss in the starting resistor R11 of FIG. 3, V ² /
R11 = 2 × (AC voltage effective value) ² / R11.

On the other hand, when the circuit configuration as shown in FIG. 4 is used, an AC half-wave voltage is applied to the starting resistor R11 as shown in FIG. 5B, so that the voltage applied to the starting resistor R11 is an effective value. Is expressed by the equation (2).

[Equation 2] Therefore, power loss in the starting resistor R11 in FIG. 4, V ² /
R11 = (1/2) × (AC voltage effective value) ² / R11, and the power loss is reduced to 1/4 in FIG.

[0008]

However, in the circuit of FIG. 4, the voltage applied at the time of start-up is AC half-wave voltage.
Since no voltage is applied to the start-up resistor, the start-up characteristic becomes worse than in the case where the start-up resistor R11 is connected to the latter stage of the smoothing capacitor C1 as shown in FIG. Especially when the output voltage is large, the output voltage drops during the half cycle when the power is not supplied,
The rising waveform of the output voltage may be in the shape of a saw blade as shown in FIG. 6, and the stability at the time of start-up will be poor.

Further, EMI (electromagnetic immunit)
y) As a filter component to suppress noise,
Live side route of commercial power supply and Neutral (Neut
The line bypass filter 10
3 is mounted, and further, a discharge resistor R12 is mounted in parallel with the line bypass filter 103 for the purpose of complying with the standard requirements for preventing the risk of electric shock at the time of plugging and unplugging the outlet. This discharge resistor R12 is necessary both when the starting resistor R11 is connected to the latter stage of the smoothing capacitor C1 as shown in FIG. 3 and when it is connected to the AC single pole side as shown in FIG. Since an AC voltage is constantly applied to the discharge resistor R12, there is a problem that a power loss of a value represented by (AC voltage effective value) ² / R12 always occurs.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a switching power supply device having excellent starting characteristics and stability at the time of starting.

[0011]

In order to solve the above-mentioned problems, the invention of claim 1 is a transformer, a first rectifying circuit for rectifying a commercial power source, and rectification by the first rectifying circuit. A second rectifier circuit connected to the secondary winding of the transformer; and a second rectifying circuit connected to the secondary winding of the transformer. A switching power supply device that supplies a voltage rectified by a rectifier circuit to a load is provided with two impedance elements provided corresponding to the live side and the neutral side of a commercial power source, and one end of each impedance element is the above-mentioned. It is connected to the gate terminal or the base terminal of the switching element, the other end of one impedance element is connected to the live side terminal of the first rectifier circuit, and the other impedance element It is connected to the neutral terminal of the first rectifier circuit.

In the present invention, since impedance elements are provided corresponding to the live side and the neutral side of the commercial power source, regardless of whether the commercial power source voltage is positive or negative,
There is no fear that the starting characteristics will deteriorate.

Further, the live side terminal and the neutral side terminal of the first rectifying circuit for rectifying the commercial power supply are connected through the first and second impedance elements, so that the first
Also, the second impedance element can be used as a discharge resistor.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a switching power supply device according to the present invention will be specifically described with reference to the drawings. Below, a switching power supply device used as a power supply for an inkjet printer will be mainly described.

The switching power supply device according to the present invention is characterized in that starting resistors R1 and R2 are provided on the live (L) side path and the neutral (N) side path of the commercial power source, respectively.

FIG. 1 is a circuit diagram of an embodiment of a switching power supply device according to the present invention, showing a circuit configuration of a ringing choke inverter system. The switching power supply device shown in FIG. 1 is an EMI connected to a commercial power supply 101.
A rectifier circuit 3 comprising a filter circuit 1, a diode bridge 2 and a smoothing capacitor C1 for rectifying the commercial power supply 101 and converting it into a DC voltage; a transformer (transformer) 4;
A switching transistor Q1 that generates an AC voltage supplied to the primary winding 4a of the transformer 4, a capacitor C2 and a resistor R2 that are connected in series between the gate terminal of the switching transistor Q1 and the auxiliary winding 4b of the transformer 4. , A transistor Q2 for controlling ON / OFF of the switching transistor Q1, a resistor R4 and a Zener diode D1 connected in series between both ends of the smoothing capacitor C1, and a rectifier connected to the secondary winding 4c of the transformer 4. It includes a diode D2 and a capacitor C3, and a voltage detection circuit 5 and a load 6 connected across the capacitor C3.

The voltage detection circuit 5 has a photocoupler 7 for controlling ON / OFF of the transistor Q2, a Zener diode D3, and a resistor R5.

In addition to this, the switching power supply device of FIG.
Starting resistor R connected to the live side path of the commercial power source 101
1 and a starting resistor R2 connected to the neutral path.

Next, the operation of the flyback type switching power supply device shown in FIG. 1 will be described. When a main switch (not shown) is turned on, the AC input voltage from the commercial power source 101 is converted into a DC voltage by the rectifier circuit 3 and then the starting resistor R
1 to the gate terminal of the switching transistor Q1.

As a result, the switching transistor Q
1 starts to be turned on, the primary winding 4a of the transformer 4 is excited, and a positive feedback voltage is generated across the auxiliary winding 4b. The positive feedback voltage drives the switching transistor Q1 to turn on further. Along with that, the exciting current of the primary winding 4a also increases, and the positive feedback voltage across the auxiliary winding 4b increases, so that the switching transistor Q1 is rapidly turned on completely.

When the switching transistor Q1 is completely turned on, its drain current linearly increases due to the inductance of the transformer 4, and as a result, the drain-source voltage rises and conversely the voltage of the primary winding 4a. And the positive feedback voltage across the auxiliary winding 4b also decreases.
By continuing such an operation, the switching transistor Q1 is rapidly turned off.

When the switching transistor Q1 is turned off, the primary winding 4a and the secondary winding 4 of the transformer 4 are turned on.
The polarity of c is reversed, and the current starts to flow from the secondary winding 4c to the load side via the rectifying diode. This current gradually decreases until it finally reaches zero.

As a result, a counter electromotive force is generated in each winding of the transformer 4, the polarity of each winding of the transformer 4 is inverted, and a positive feedback voltage is applied between the auxiliary windings 4b in the direction of turning on the switching transistor Q1 again. Then, the switching transistor Q1 is turned on again. The series of operations described above is repeated.

FIG. 2A is a voltage waveform diagram of the starting resistor R1, and FIG. 2B is a voltage waveform diagram of the starting resistor R2. As shown in the figure, a half-wave current alternately flows through the starting resistors R1 and R2. That is, regardless of whether the AC input voltage is positive or negative, a current flows through either of the starting resistors R1 and R2, so that the starting resistor R1 is provided only on the live side as shown in FIG.
The start-up characteristics are improved as compared with the case of connecting. Therefore, there is no possibility that the output voltage waveform has a saw-tooth shape as shown in FIG.

Voltage V applied to each starting resistor R1, R2
And loss power V ² / R1, V ² / of each starting resistor R1, R2
R2 is the same as the starting resistor R11 shown in FIG. 3, and is represented by the equations (3), (4), and (5), respectively.

[Equation 3] ^{V 2 / R1 = (1/2)} × (AC voltage effective ^{value) 2 / R1 ... (4)} V 2 / R2 = (1/2) × (AC voltage effective value) ² / R2 ... (5)

When the two starting resistors R1 and R2 and the starting resistor R11 in FIG. 4 are the same resistance, the two starting resistors R
The total loss power of 1 and R2 is represented by (AC voltage effective value) ² / R1, which is larger than the case where the starting resistor R11 is connected to only one side of the commercial power source 101 as shown in FIG. , Compared with the case where the starting resistor R11 is connected after the smoothing capacitor C1 on the AC input side as shown in FIG.
become.

In the case of the power supply device shown in FIG. 1, the commercial power supply 1
Since the two starting resistors R1 and R2 are connected in series between the live side of 01 and the neutral side, these starting resistors R1 and R2 are connected in series.
1 and R2 can also serve as a discharge resistance. Therefore, it is not necessary to provide a separate discharge resistor, power consumption can be reduced, and component cost and circuit scale can be reduced.

Further, EMI (electromagnetic immunit)
y) In order to suppress noise, it is desirable to connect the starting resistors R1 and R2 to the latter stage side of the EMI filter circuit, that is, the side away from the AC input side. Starter resistor R after the diode 2 for
Since 1 and R2 are connected, EMI noise can be efficiently suppressed.

In the above-described embodiment, an example of using it as a power source for an ink jet printer has been described.
The switching power supply device of the present invention can be used as a power supply for various electric devices.

[0030]

As described in detail above, according to the present invention, the first and second impedance elements serving as start-up resistors are provided on the live side and the neutral side of the first rectifying circuit for rectifying the commercial power source. Since they are connected to both sides, there is no fear that the startup characteristics will deteriorate regardless of whether the commercial power supply waveform is positive or negative.

Further, since the live side terminal and the neutral side terminal of the first rectifier circuit are connected via the first and second impedance elements, they can serve as a discharge resistance and a separate discharge for exclusive use. It is not necessary to provide a resistor, the cost of parts can be reduced, and the device can be downsized.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a switching power supply device according to the present invention.

2A is a waveform diagram of a voltage flowing through a starting resistor R1, FIG.
(B) is a waveform diagram of the voltage flowing through the starting resistor R2.

FIG. 3 is a circuit diagram showing an example in which a starting resistor is provided in a subsequent stage of a rectifier circuit that rectifies a commercial power source.

FIG. 4 is a circuit diagram showing an example in which a starting resistance is connected to the L side of a commercial power source to reduce the loss of the starting resistance.

5A is a diagram showing a voltage waveform applied to a starting resistor, and FIG. 5B is a diagram showing a voltage waveform applied to a starting resistor.

FIG. 6 is a diagram showing a rising waveform of an output voltage.

[Explanation of symbols]

1 EMI filter circuit 2 diode bridge 3 rectifier circuit 4 transformers 5 Voltage detection circuit 6 load 101 Commercial power supply C1 smoothing capacitor D1, D2 diode R1 to R5 resistance

Claims (4)

(57) [Claims] 1. A transformer, a first rectifier circuit for rectifying a commercial power source, and a switching circuit for converting the voltage rectified by the first rectifier circuit into an AC voltage and supplying the AC primary voltage to the primary winding of the transformer. A switching power supply device that includes an element and a second rectifier circuit connected to a secondary winding of the transformer, and supplies a voltage rectified by the second rectifier circuit to a load. Two impedance elements provided corresponding to each of the live side and the neutral side are provided, one end of each impedance element is connected to the gate terminal or the base terminal of the switching element, and the other end of one impedance element is It is connected to the live side terminal of the first rectifier circuit, and the other end of the other impedance element is connected to the neutral side terminal of the first rectifier circuit. Switching power supply device according to claim. 2. The switching power supply device according to claim 1, wherein the two impedance elements are also used as discharge resistors. 3. The switching power supply device according to claim 1, further comprising an EMI filter circuit connected between an input terminal of a commercial power supply and the first rectifier circuit. 4. The switching power supply device according to claim 1, wherein the switching power supply device comprises a ringing choke converter system circuit.