JPS5911775A - Switching regulator - Google Patents

Abstract

PURPOSE:To reduce the cost of a switching regulator which is inserted into the primary side circuit of a DC converter by performing the drive of the regulator at the power source energizing time by the primary side circuit itself, thereby simplifying the structure. CONSTITUTION:When a power source switch S is closed, the condenser C1 at the output side of a rectifier 4 is charged. When the charging voltage becomes a value or higher, a switching transistor Q1 is conducted. As a result, a DC converter 2 is energized, and an AC is generated at the output coils N2-N7 of an inverter transformer T1. The AC generated at the coil N6 is converted by a diode D2 and a condenser C3 into a DC. This DC holds the transistor Q1 in conductive state. Then, the duty of the transistor Q1 is controlled so that the current of a fluorescent lamp is always equalized to the set value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator, and particularly to a switching regulator.
This invention relates to a tsupa-type switching regulator.

More specifically, the present invention relates to a switching regulator type power supply device with a dimming function suitable as a power supply for an exposure light source of an electronic copying machine.

2. Description of the Related Art Conventionally, a switching regulator type power supply device having a dimming function has been commonly used as a power supply for an exposure light source (for example, a fluorescent lamp) of an electronic copying machine.

FIG. 1 is a circuit diagram showing an example of a conventional switching regulator type power supply device.

When the power switch S is turned on, the control circuit 3 is energized via the auxiliary transformer T2, and supplies a pulse current of constant tenity to the primary winding of the pulse transformer T3. The switching transistor Q1 is turned on and off at the constant duty by a pulse signal generated in the secondary winding of the pulse transformer T3.

On the other hand, as is clear from the figure, the switching transistor Ql has one pole and one pole of the DC output terminal of the rectifier circuit 4, and D
It is connected in series with one end of the primary winding of the C converter 2. Therefore, when the power switch S is turned on, the DC
Converter 2 is energized and its inverter transformer T1
A high voltage is generated in the secondary winding of.

Said voltage is applied to the fluorescent lamp 1. At start-up, since the relay switch R8 is closed, both filaments fl and f2 of the fluorescent lamp 1 are connected in series and are preheated by the output of the secondary winding of the inverter transformer T1. After a suitable period of time has elapsed, relay switch R8 is opened and fluorescent lamp 1 is turned on.

The output current of the secondary winding of the inverter transformer T1 is detected by the current transformer CT, and the detected output is divided by the HJ variable resistor VR and the load resistor R and input to the control circuit 3.

In the control circuit 3, the voltage of the reference power supply 5 adjusted according to the current setting value is compared with the detection voltage appearing across the load resistor R, and the pulse current whose duty changes according to the difference is performed. is generated. This pulse current is supplied to the primary side of the pulse transformer T3, as described above.

With the above configuration, the duty of the switching transistor Ql, that is, the output current of the DC converter 2 on the secondary side is controlled to a predetermined value by adjusting the reference power supply or the variable resistor VR. Therefore, the preheating current and discharge current of the fluorescent lamp 1 can be controlled to preset values, and a scheduled amount of light can be generated with a scheduled rise characteristic.

However, in the conventional device shown in FIG. 1, the switching transistor Q1 is started by the output of the control circuit 3 at the time of starting, so a power source and a pulse transformer for energizing the control circuit are required, and the structure is complicated. This method has drawbacks such as complication and high cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching regulator, particularly a chopper-type switching regulator, that does not require a separate power supply or pulse transformer for control circuit monitoring.

In order to achieve the above object, in the present invention, when the DC converter is started, the switching transistor is made conductive by the secondary power supply circuit, and after the start-up, the switching transistor is made conductive through the attached winding added to the inverter transformer. 1. Further, in the present invention, the output current adjustment after startup is performed by making the switching transistor conductive.
This is achieved by controlling the duty of the switching transistor based on the deviation of the output current from the reference value.

9 below, the invention will be described in detail with reference to the drawings.

FIG. 2 is a circuit diagram of an embodiment in which the present invention is applied to a power source for an exposure light source of a copying machine, and the same reference numerals as in FIG. 1 represent the same or equivalent parts.

When the power switch S is turned on, the output side of the rectifier circuit 4 (
The capacitor CI on the DC side) is charged to the polarity shown. The charging voltage exceeds a certain value.

Then, a current flows through the circuit of capacitor C1 → resistor R1 → zener diode ZDI to ZD3 → resistor R2 → diode D1 → base/emitter of switching transistor Ql → capacitor C1, and this causes the circuit of capacitor C1 to is conductive.

As a result, the DC converter 2 can enjoy power. That is,
As is well known, the capacitor (:2 and the inverter transformer T
At a resonant frequency determined by the inductance of the input winding of transistors Q, 2. Q3 is alternately conductive, thereby generating an alternating current in the output windings N2-N7 of the inverter transformer T1.

The friend current generated in winding N6 is converted to direct current by diode D2 and capacitor C3.

The direct current is supplied to the base of the switching transistor Q1 through the circuit of capacitor C3 → resistor R2 → diode resistor 1 → base/emitter of switching transistor Q1 → capacitor C3, and is supplied to the base of switching transistor Q1 to keep the transistor Q1 in a conductive state. .

When DC converter 2 starts up, the inverter transformer T
When the conduction of the switching transistor Q1 is maintained by the output from the winding N6 of 1, the terminal voltage of the capacitor C1 changes to
Nosenar voltage ■The value after subtracting the sum of ZD1 to VZD3 is
The output DC voltage of winding @N6 also becomes smaller. Therefore, current flows through the path of the resistor R1 and the Zener diodes ZDI to ZD3.

When the circuit is started, the relay switches R8I and R82 are connected to the side pressure shown in the drawing by a relay (not shown), and the fluorescent lamp 1 is in a preheated state. That is, winding N4
→ Filament f1 → Relay switch R8I, R8
2 → filament f2 → winding N5 → winding N2 → winding N4
A circuit is formed and a preheating current is supplied to filaments f1 and f2.

When preheating is completed, relay switches R8I and R82 are switched to the opposite side as shown in the diagram by the operation of the relay.
Each of the filaments fl and f2 of the fluorescent lamp 1 is supplied with power from the windings N4 and N5 of the inverter transformer T1, respectively.

At the same time, a high voltage is applied between the filaments fl and f2 by the winding N2, so that the fluorescent lamp 1 is lit. Note that 7 is a starting auxiliary electrode provided adjacent to the fluorescent lamp 1, which serves to assist the initial discharge of the fluorescent lamp 1 and ensure lighting.

The preheating current and the discharge current are detected by the current transformer CT and compared with the reference power supply 5 in the control circuit 3, as in the conventional example shown in FIG.

The output of the current transformer CT and the reference power source 5 can be compared using any appropriate method, but an example is as follows: 1. The peak value is determined according to the voltage of the reference power source 5. The triangular wave (3rd
A) in the figure is generated, and its voltage level is compared with the voltage level generated across the resistor R, that is, the voltage level representing the current of the fluorescent lamp 1. , this level is shown in Figure 3 as t, three straight lines.

Straight line C corresponds to when the current of fluorescent lamp 1 is equal to the current setting value, straight line C corresponds to the case when the current setting value is greater than the current setting value, and straight line 2 corresponds to the case when the current setting value is also smaller than the current setting value. shall be taken as a thing.

While the level of the triangular wave A is lower than the fluorescent current level, the control circuit 3 produces an output and supplies current to the light emitting diode of the photocoupler 8, causing it to emit light. Therefore,
The light-receiving transistor of the photocoupler 8 becomes conductive, thereby making the bypass transistor Q4 conductive.

Therefore, the pace emitter circuit of the switching transistor Q"1 is short-circuited by the bypass transistor Q4, and said switching transistor Q1 is cut off. As a result, the DC converter 2 temporarily stops working and the fluorescent pair 1 is switched off. On the other hand, when the level of the triangular wave A is greater than the fluorescent lamp current level, the control circuit 3 produces no output and the photocoupler 80
Light emitting diodes do not emit light1. Therefore, as described above, the base current of the switching transistor Q1 is supplied from the winding N6 through the capacitor C3 and the resistor R2 to maintain the conductive state. This energizes the DC converter 2 and supplies current to the fluorescent pair 1.

FIGS. 3(b) to 3(d) show changes in the duty of the switching transistor Q1 when the fluorescent lamp current fluctuates relative to the set value. Figure (b) shows the case when the fluorescent lamp current is equal to the set value, (C) shows the case when it is larger than the set value, and (d) shows the case when it is smaller than the set value. As is clear from the comparison in d), when the fluorescent lamp current becomes larger than the set value, the duty of the switching transistor Q1 decreases, reducing the fluorescent lamp current.

On the other hand, when the fluorescent lamp current becomes smaller than the set value, y'-1 of the switching transistor Q1 becomes a dog;
Increase fluorescent lamp current. In this way, the fluorescent lamp current is always controlled to be equal to the set value;
In the above embodiment, a zener diode Z is connected in series with the resistor R1.
DI-ZD3 is connected, but its purpose is to connect resistor R1
This is to reduce power consumption in the system, and is not necessarily necessary.

Although the present invention has been described above as being applied to a power source for an exposure light source of a copying machine, it is clear that the present invention is not limited to this and can also be applied to a general C converter.

According to the present invention, in order to control the output of the I)C converter, the switching transistor inserted in the primary side circuit of the I)C converter is driven not by the control circuit but by the - Since the side circuit itself is used (7), there is no need for an additional power supply device or pulse transformer to drive the control circuit, simplifying the configuration and reducing costs.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a DC converter device as a power source for the exposure light source of a conventional copying machine, Fig. 2 is a circuit diagram of an embodiment of the present invention, and Fig. 3 is a time chart for explaining its operation. be.

Claims (3)

[Claims] (1) A DC converter, its driving DC power supply,
A switching try inserted in series between one end of the primary winding of the DC converter and one pole of the DC power supply
a switching transistor energizing winding wound around an inverter transformer of a DC converter; a means for rectifying the output of the switching transistor energizing winding to supply a forward base current to the switching transistor; connecting means for supplying a forward base current from the DC power supply to the switching transistor; , and means for comparing the reference value with a reference value and controlling the duty of the switching transistor according to the deviation. (2) A patented regulator characterized in that the connection means for connecting the other pole of the DC power supply to the base of the switching transistor comprises a series circuit of a resistor and a Zener diode. (3) The switching regulator according to claim 1 or 2, wherein the means for controlling the duty of the switching transistor is energized by an auxiliary winding wound around an inverter transformer.