JPH02269472A - Ac-dc both output power circuit - Google Patents

Abstract

PURPOSE:To miniaturize the title power circuit, and to improve the stability of output voltage by connecting an AC voltage generating circuit generating AC voltage from the node of a bleeder resistor and a current control circuit to the output section of a rectifying smoothing circuit. CONSTITUTION:Rectifying smoothing circuits D1, C1 rectify and smooth the electromotive voltage of the secondary winding N3 of a transformer, and generate DC voltage. On the other hand, an AC voltage generating circuit 1 is composed of a bleeder resistor R5, a current control circuit Q3 controlling currents flowing through the bleeder resistor R5 and a ZD, and a switch control circuit 4 transmitting a changeover signal alternately changing over currents flowing through the bleeder resistor R5 in binary modes over the current control circuit Q3 and the ZD, and the AC voltage generating circuit 1 is connected to the output sections of the rectifying smoothing circuits D1, C1, thus generating AC voltage from the node of the bleeder resistor R5 and the current control circuit Q3 and the ZD. Accordingly, DC voltage and AC voltage can be generated substantially from the single secondary winding.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a switching regulator that generates an alternating current voltage as well as a direct current voltage.

(b) Prior Art FIGS. 3 and 4 show circuit diagrams of a conventional switching regulator that generates both direct current and alternating current. In both figures, N1 is the primary winding of the transformer, N2 is the feedback winding, and the primary winding current of the transformer is interrupted by the automatic oscillation operation of the switching transistor Q1. N3 and N
4 is a winding on the secondary side of the transformer, and in the example shown in Fig. 3, a diode D1 rectifies the electromotive voltage of the winding N3, a capacitor C1 smoothes it, and a predetermined DC is applied to the first output terminal 0UT1. Generates voltage. Also, capacitor C2 is connected to winding N4
The electromotive force is shaped into a waveform, and an alternating current voltage is generated at the second output terminal 0UT2.

In the example shown in FIG. 4, a predetermined DC voltage is generated at the output terminal 0UTI by rectifying and smoothing the electromotive force of the winding N3 using Dl and C1, and a part of the winding N3 is shared to output the voltage at the output terminal 0UTI. AC voltage is generated at OUT2.

(C1 Problems to be Solved by the Invention However, the above-mentioned conventional switching regulator had the following problems.

As shown in Figure 3, a circuit in which separate windings N3 and N4 are provided on the secondary side of the transformer for DC voltage generation and AC voltage generation, respectively, requires a transformer with a large number of windings and is therefore large. It has the disadvantage of high cost and low cost. Although the circuit shown in FIG. 4 does not have this drawback, it does have the drawback that the output voltages vary depending on the state of the loads connected to the output terminals 0UTI and 0UT2. Furthermore, in both of the circuits shown in FIGS. 3 and 4, the output voltage is controlled on the primary side of the transformer, so that the DC voltage output control and the AC voltage output control are only applied at the same time. For this reason, it has been impossible to independently control, for example, the frequency or duty ratio of the alternating current voltage. Furthermore, there was also the drawback that the stability of the output voltage was low due to the influence of mutual induction occurring between the secondary windings via the transformer.

In order to eliminate the above-mentioned problems, it is necessary to separate the transformer and the control circuit, which poses an obstacle in terms of space and cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide an AC/DC side output power supply circuit that eliminates the various problems of the prior art by generating DC voltage and AC voltage from a single secondary winding of a transformer.

(Means for Solving Problem d1) This invention provides a switching circuit in the primary winding of the transformer to intermittently interrupt the current flowing through the primary winding, and In a switching regulator connected to a rectifying and smoothing circuit that rectifies and smoothes the electromotive force of the winding to generate a DC voltage, there is a bleeder resistor, a current control circuit that controls the current flowing through the bleeder resistor, and a current control circuit that controls the current flowing through the bleeder resistor. an alternating current voltage generating circuit that includes a switch control circuit that supplies a switching signal that alternately switches between two values to the current control circuit, and generates an alternating current voltage from a connection point between the bleeder resistor and the current control circuit! It is characterized by being connected to the output section of the

(e) Function In the AC/DC side output power supply circuit of the present invention, the rectifying and smoothing circuit rectifies and smoothes the electromotive force of the secondary winding of the transformer to generate a DC voltage. On the other hand, the AC voltage generation circuit includes a bleeder resistor, a current control circuit that controls the current flowing through the bleeder resistor, and a switch control circuit that provides the current control circuit with a switching signal that alternately switches the current flowing through the bleeder resistor between two values. The AC voltage generating circuit is connected to the output part of the rectifying and smoothing circuit, so that AC voltage is generated from the connection point between the bleeder resistor and the current control circuit.

In the AC voltage generating circuit, since the AC voltage is output through the bleeder resistor, a voltage drop occurs depending on the current flowing through the bleeder resistor.

Due to the action of the current control circuit and the switch control circuit, the current flowing through the bleeder resistor is alternately switched between two values, so that an alternating current voltage that changes periodically with a certain amplitude is generated.

In this way, the DC voltage is generated using the electromotive force of the secondary winding of the transformer, and the DC voltage is used as a power source to separately generate the AC voltage. A side output power supply circuit can be configured.

(f) Embodiment FIG. 1 shows a circuit diagram of an AC/DC side output power supply circuit according to an embodiment of the present invention.

In FIG. 1, Ql is a switching transistor, and transformer windings N1. N2, resistor R2R3, and capacitor C3 constitute an automatic oscillation circuit. Q2 is a transistor that controls the base current of Ql, and is controlled by the output of comparator 2. A rectifier diode D1 and a smoothing capacitor c are connected to the secondary winding N3 of the transformer.
1, and generates a DC voltage at the first output terminal 0UTI via the current limiting resistor R1.

The voltage at the output terminal 0UTI is fed back to the comparator 2 via the resistor R4. The comparator 2 compares the output voltage of the terminal 0UTI with the voltage of the reference voltage circuit 3 as a reference, performs negative feedback control, and stabilizes the output voltage. The circuit 1 connected to the output part of the rectifying and smoothing circuit is an AC voltage generating circuit, and generates an AC voltage at the second output terminal 0UT2.

In the AC voltage generation circuit 1, the resistor R5 is a bleeder resistor, and the transistor Q3 and Zener diode ZD
are connected in series. Also, bias resistors R6, R7, and R8 are connected between the collector, base, and ground of Q3. The resistor R8 is a variable resistor, and the switch control circuit 4 is connected in parallel. Here Q3. ZD, R6, R
7 and R8 constitute a current control circuit according to the present invention,
Controls the current flowing through the bleeder resistor R5.

The AC voltage generating circuit 1 shown in FIG. 1 has a circuit configuration of a so-called shunt regulator, and has a Zener diode Z.
The voltage drop caused by the bleeder resistor R5 is controlled based on the Zener voltage of D.

However, since the base bias voltage of Q3 is switched, a voltage that fluctuates with a constant amplitude is obtained at the output terminal 0UT2.

Specifically, the switch control circuit 4 includes a switch element that selectively shorts/opens both ends of the variable resistor R8, and a control circuit that turns the switch element on and off at regular intervals.

The voltage Vo generated at the terminal 0UT2 when the variable resistor R8 is opened and shorted by the switch control circuit 4 is as follows.

<When open> Vo (R7+R8)/ (R6+R7+R8)=VZ
+VIE ”■O= (Vz +Vmt) (R6+R7+R8
)/(R7+R8) <When shorted> V o-R7/ (R6+R7) =Vz +Vsi;
, V o = (VZ + VIE) (R6 + R7)
/R7 Here, ■2 is the Zener voltage of the Zener diode ZD, and ■□ is the voltage drop between the base and emitter of the transistor Q3.

In this way, the voltage generated at the terminal 0UT2 can be switched by the switch control of the switch control circuit 4, and the voltage generated when the switch is opened can be adjusted by the value of the resistor R8. FIG. 2 shows the voltage waveforms occurring at terminals 0UTI and 0UT2. Voltage from 0UTI■
A DC voltage of 1 is generated, and a voltage of V is generated at a constant period at 0UT2.
An alternating voltage that switches from a to Vb is generated. However, 0U
Since the voltage generated at T2 has a constant DC bias applied to it, when it is used as a pure AC voltage, it can be used through a DC cut capacitor.

The AC/DC re-output power supply circuit shown in FIG. 1 can be used, for example, as a high voltage generation circuit in an electrophotographic copying machine or a laser beam printer. Corona discharge is caused and the alternating current voltage generated at terminal 0UT2 can be supplied to other loads. If this AC medium voltage is lower than the DC high voltage that occurs at 0UTI, it can generate a stable AC voltage regardless of voltage fluctuations in the DC high voltage, and is not affected by the DC high voltage load and changes in frequency and The duty ratio can also be controlled independently. In addition, DC high voltage can be turned off in a pseudo manner by lowering the voltage below the corona discharge voltage, and even in that case, AC medium voltage can still be generated, so DC voltage and AC voltage are independent. remote control is possible. In addition, although the circuit in the example generates a positive DC voltage,
The present invention can be similarly applied to circuits that generate negative voltages.

(Effects of the Phantom Invention According to this invention, since it is possible to substantially generate DC voltage and AC voltage from a single secondary winding using a single transformer, miniaturization and cost reduction can be achieved. In addition, a stable voltage can be supplied without being mutually influenced by the conditions of the DC load and AC load.

Furthermore, it is also possible to independently control the frequency and duty ratio of the AC voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an AC/DC output power supply circuit according to an embodiment of the present invention. FIG. 2 is a diagram showing the output voltage waveform of the same power supply circuit. 3 and 4 are circuit diagrams of the main parts of a conventional AC/DC side output power supply circuit. 1-AC voltage generation circuit, 2-Comparator, 3-Reference voltage generation circuit, 4-Switch control circuit. R5 - bleeder resistance, (Dl, C1) - rectifier/smoothing circuit, (C3, ZD, R6, R7, R8) - current control circuit,

Claims (1)

[Claims] (1) A switching circuit is provided in the primary winding of the transformer to intermittent the current flowing through the primary winding, and the electromotive force of the secondary winding is rectified and smoothed to create a DC voltage in the secondary winding of the transformer. A switching regulator is connected to a rectifying and smoothing circuit that generates a bleeder resistor, a current control circuit that controls the current flowing through the bleeder resistor, and a switching signal that alternately switches the current flowing through the bleeder resistor between two values. AC/DC dual output, comprising a switch control circuit for supplying the circuit, and an AC voltage generation circuit that generates an AC voltage from a connection point between the bleeder resistor and the current control circuit, and connected to an output part of the rectification and smoothing circuit. power circuit.