JPH0650935B2 - Power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power supply device, and more particularly to a power supply device for supplying a high voltage DC power supply of positive and negative polarities.

[Prior Art] A positive power supply voltage and a negative power supply voltage are required as a high-voltage DC power supply voltage for charging when performing negative development and positive development in devices such as microfilm, electronic copying machines, and laser beam printers. Is.

In the conventional power supply device used in such a case, a positive power supply circuit and a negative power supply circuit are separately provided and these two circuits are switched and used by a relay or the like.

[Problems to be Solved by the Invention] In the conventional power supply device, since the two circuits are separately provided as described above, there are problems that the number of components is large and the entire device becomes large. Further, the conventional device has a problem that a large noise is generated at that time because the high voltage output is switched.

The present invention has been made to solve such a problem.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a transformer having a primary winding and two secondary windings, and a switching for turning on / off the direct current are provided. Circuit and rectifying and smoothing the currents respectively generated in the secondary windings by turning them on and off with mutually opposite polarities, and turning on and off two rectifying and smoothing circuits whose outputs are connected in series and the switching means. A configuration in which a means for controlling the output by changing the duty ratio is provided is adopted.

[Operation] With the above configuration, since the output ratios of the two rectifying / smoothing circuits having different polarities can be changed by the duty ratio of the switching means, the polarities of the total output obtained from the two rectifying / smoothing circuits connected in series. And the output value can be controlled as desired.

[Examples] Hereinafter, details of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing the configuration of the power supply device according to this embodiment.

Reference numeral T3 indicates a transformer, which has a primary winding l1 having an intermediate tap and two secondary windings l2 and l3.

A predetermined positive DC voltage Vcc is applied to the intermediate tap TP of the primary winding l1 from a power supply circuit (not shown). Again 1
Terminals C and F at both ends of the next winding are manually operated changeover switches SW1 for switching the polarity of the output of the device.
Is connected to each of the contacts A and B, and is connected to the collector of the switching transistor Q1 via the changeover switch SW1. The emitter of the transistor Q1 is grounded, and the output of the monostable multivibrator 2 is connected to the base. The output of the oscillator 1 is connected to the input of the monostable multivibrator 2.

On the other hand, the terminals G and H at both ends of the first secondary winding 12 of the transformer T3 are connected to a rectification / smoothing circuit composed of a diode D1 and a capacitor C4 connected in series, and the diode D
1 and the capacitor C4 are connected to the output terminal 6 of the power supply device.
It is connected to the.

Further, the terminals I and J at both ends of the second secondary winding 13 are connected to a rectifying / smoothing circuit composed of a series connection of the diode D1 and a diode D2 having a reverse polarity and a grounded capacitor C5. , The connection point between the capacitors C5 is connected to the connection point between the first secondary winding 12 and the capacitor C4.

That is, the outputs of the two rectifying / smoothing circuits for rectifying and smoothing the currents generated in the secondary windings 12 and 13 with opposite polarities are connected in series and connected to the output terminal 6.

Next, the operation of this embodiment configured as described above will be described.

In operation, the monostable multivibrator 2 first transmits a pulse having an ON / OFF ratio of about 1: 1 at a predetermined frequency, that is, a clock pulse having a duty ratio of about 0.5.
To enter.

The monostable multivibrator is triggered by the above pulse, and outputs a pulse with a sufficiently small duty ratio to the transistor Q.
1 and the transistor Q1 is turned on / off to perform switching. That is, the on-time of the transistor Q1 is sufficiently shorter than the off-time.

On the other hand, the DC voltage Vcc is applied to the intermediate tap TP of the primary winding 11 of the transformer T3, and the movable contact piece of the changeover switch SW1 is switched to either of the contacts A and B. A current flows toward one of the terminals C and F at both ends of the line l1. Then, this current is turned on by the switching of the transistor Q1,
It is turned off and the transformer T3 is driven.

Here, when the changeover switch SW1 is changed over to the contact A side, the operation is as follows.

When the transistor Q1 is turned on, a current flows from the terminal E of the intermediate tap toward the one terminal C side in the primary winding l1, and a predetermined so-called forward voltage E1 is generated in the secondary winding l3 according to the winding ratio. . This is the secondary winding 12,
In the terminals G to J at both ends of l3, for example, the terminals G and I sides are positive, the terminals H and J sides are negative, and the diode D1 is turned off due to the polarity of the diode, and D2.
Is turned on, no voltage is applied to the capacitor C4,
On the other hand, the forward voltage E1 is charged to both ends of the capacitor C5.

Next, when the transistor Q1 is turned off, the current in the primary winding l1 is cut off, so that a so-called flyback voltage −E2 is generated in the secondary winding l2 with a polarity opposite to that of the forward voltage when it is on.

This is because the polarities of the terminals G to J are opposite to those at the time of turning on, so the diode D1 turns on, D2 turns off, and only the capacitor C4 is charged with the flyback voltage -E2 this time.

The forward voltage E1 previously charged in the capacitor C5 and the flyback voltage −E2 charged in the capacitor C4 are smoothed by both capacitors, and the sum thereof becomes the output voltage of the output terminal 6.

As described above, the on time of the transistor Q1 (T
1) is sufficiently shorter than the off time (T2) and the generation time of the forward voltage E1 is sufficiently shorter than the generation time of the flyback voltage E2. Becomes a predetermined negative voltage.

On the other hand, when the changeover switch SW1 is switched to the contact B side, the current flows in the secondary winding l1 from the terminal E to the terminal E, which is the reverse of the above case with respect to the winding direction of the primary winding l1. Since the current flows in the direction, the polarities of the forward voltage and the flyback voltage generated in the secondary windings 12 and 13 by turning on and off the transistor Q1 are opposite to those in the above case, and are -E1 and + E2. Then, by the operation reverse to the above, the forward voltage −E1 is charged in the capacitor C4 and the flyback voltage E2 is charged in the capacitor C5. The output voltage of the output terminal 6 is smoothed by both capacitors C4 and C5. Therefore, the output voltage becomes a predetermined positive output voltage due to the magnitude relationship depending on the generation time described above.

As described above, according to this embodiment, in the configuration in which the positive power supply circuit and the negative power supply circuit are integrated, the direction of the low-voltage input current applied to the primary winding of the transformer is set to the winding of the primary winding. Switch SW for both directions
By switching through 1, positive and negative outputs can be obtained.

In the above configuration, a power supply circuit (not shown) that supplies the DC voltage Vcc may be connected to the changeover switch SW1 and the collector of the transistor Q1 may be connected to the intermediate tap of the primary winding l1.

As can be understood from the above embodiments, the polarity change of the total output not only changes the polarity of the voltage applied to the primary winding but also changes the ON time T1 and the OFF time T of the transistor Q1.
It can be seen that the duty ratio of 2 can be used by reciprocal. That is, if the on-time T1 and the off-time T2 are interchanged, an output of opposite polarity can be obtained when the switch SW1 is on the A side. Also, the transistor Q1
It is obvious that the output voltage value can also be controlled by changing the duty ratio of the on time / off time. That is, the polarity and output value can be controlled as desired by changing the duty ratio within the range of 0 to 1.

FIG. 2 shows an embodiment in which output control is performed by the duty ratio of the transistor Q1 as described above. Here, the transformer T3 has only a single winding l1 (equivalent to when the switch SW1 in FIG. 1 is switched to the A side with terminals C and E), and the secondary side has the configuration shown in FIG. Is the same.

The output duty ratio of the monostable multivibrator 2 can be changed by the control circuit 3. The control circuit 3 changes the output pulse width by changing the time constant of the monostable multivibrator 2. In the case where only the polarity needs to be changed as in the case of FIG. 1, the monostable multivibrator 2 is composed of a TTL element or the like having a complementary output, and the control circuit 3 simply selects the complementary output. You may comprise from the switch which outputs.

With the above configuration, the polarity of the output voltage from the terminal 6 can be changed depending on whether the on-time T1 and the off-time T2 of the transistor Q1 are T1 << T2 or T1 >> T2, and the windings of the windings l2 and l3 can be changed. Appropriately T1, T2 depending on the ratio
It is also possible to control the output voltage to a desired value by adjusting the duty ratio of.

According to the above embodiment, there is an advantage that the transformer T3 is further downsized and the degree of freedom of output control is greatly improved as compared with the configuration of FIG.

[Effect] As is apparent from the above description, according to the configuration of the power supply device of the present invention, the positive power supply circuit and the negative power supply circuit are integrally configured to reduce the number of parts, downsize the device, and reduce the manufacturing cost. Can be reduced. Further, since the polarity of the output is switched by switching the duty ratio on the input side having a low voltage (absolute value), the generation of noise can be prevented.

[Brief description of drawings]

1 and 2 are circuit diagrams respectively showing configurations of power supply devices according to different embodiments of the present invention. 1 ... Oscillator 2 ... Monostable multivibrator 3 ... Pulse width control circuit Q1 ... Transistor T3 ... Transformer SW1 ... Changeover switch D1, D2 ... Diode C4, C5 ... Capacitor 6 ... Output terminal

Claims (1)

[Claims] 1. A transformer having a primary winding and two secondary windings, a switching circuit for turning on / off the direct current, and a current generated in each of the secondary windings by turning on / off the direct current. Are rectified and smoothed with mutually opposite polarities, and two rectification and smoothing circuits whose outputs are connected in series, and by changing the duty ratio of the on time and the off time of the switching means, A power supply device comprising means for controlling the polarity or output value of the serial output.