JPS6260469A - Power unit - Google Patents

Abstract

PURPOSE:To miniaturize a unit, and to reduce cost by integrally forming positive and negative power circuits and selecting the direction of conduction to a primary winding by an electronic switch. CONSTITUTION:A power unit is constituted of a transformer T1, a primary winding l1 thereof has an intermediate tap TP, a transistor (hereinafter called Tr) Q3 for switching, Trs Q1, Q4-Q6 shaping an electronic switch for changing over output polarity and a controller consisting of a micro-computer 1, etc. The Tr Q3 is driven by switching pulses from a PWM control circuit 5, and DC voltage is acquired through secondary windings l2-l3, etc. for the transformer T1. In this case, a polarity changeover circuit 3 is changed over through the Tr Q1 in order to obtain desired polarity voltage, and either of the Tr Q5 or the Tr Q6 is selected and conducted. Accordingly, the direction of conduction of the primary winding l1 is used as desired polarity and the Tr Q1 is turned ON-OFF, and load 7 is supplied with positive or negative desired polarity DC voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device, and more particularly to a power supply device that supplies high-voltage DC power with both positive and negative polarities.

[Prior Art] When performing negative development and positive development in devices such as microfilm and electronic copying machines, a positive power supply voltage and a negative power supply voltage are required as high-voltage DC power supply voltages for charging. .

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

[Problems to be Solved by the Invention] In the conventional power supply device, since two circuits are provided separately as described in L, there are problems in that the number of parts is large and the entire device becomes large. Furthermore, since the conventional device switches the output of high voltage, there is a problem in that a large amount of noise is generated at that time.

The present invention has been made to solve these problems.

[Means for Solving the Problems J] In order to solve the problems described above, the power supply device of the present invention includes a transformer having a primary winding and two secondary windings,
The direction of the DC applied to the primary winding from the power supply circuit is 1.
an electronic switch that switches in both directions with respect to the winding direction of the next winding, a switching circuit that turns on and off the direct current, and the on.

The currents generated in each of the secondary windings when turned off are rectified and smoothed with opposite polarities, and the outputs of the two rectifying and smoothing circuits whose outputs are connected in series and the outputs of the two rectifying and smoothing circuits are connected. A configuration consisting of means for controlling the output voltage or output current of the power supply device obtained as a sum to a predetermined value ψ was adopted.

[Sakukawa 1] In the configuration shown in FIG. 3, transistors Q5, . A positive DC voltage Vcc is applied from a power supply circuit (not shown) to either terminal C or F of the primary winding 11 of the transformer T1 via either one of the terminals C and F of the primary winding 11 of the transformer T1. The direct current flowing from the selected terminal toward the intermediate tap TP is turned on and off by turning on and off the switching transistor Q3, thereby driving the transformer Tl.

The switching pulse that turns on and off the transistor Q3 is outputted from the PWM control circuit 5 and is input to Q3- as an inverted version via the transistor Q2.
In this case, since the duty ratio is made sufficiently small, the on time T1 of Q3 is made sufficiently shorter than the off time T2.

When transistor Q1 is turned off, Q5 is turned off,
When Q6 is turned on, the operation is as follows.

By turning on and off the transistor Q3, the direct current flowing from the terminal C to the terminal E of the primary winding 11 is turned on and off.
2 in the next winding. ) 3, a forward voltage El is generated when it is on, and a flyback voltage -E with the opposite polarity when it is off.
2 occurs, and due to the difference in polarity between diodes D2 and D3, for example, El is charged to capacitor C5, and -E
2 is charged to capacitor C4. and the voltage smoothed by both capacitors, i.e. two rectifiers.

The voltage of the sum of the outputs of the smoothing circuit becomes the output voltage HVout of the output terminal 6. Here, T I +T2, and since TI<(T2), HVout becomes a negative voltage.

Here, in order to control the output voltage HVout to a desired level with high precision, the polarity of the divided voltage of HVout by the resistors R11 and R12 is inverted to positive via the polarity switching circuit 3, and the polarity is inverted to the inverting input terminal of the error amplifier 4. is input. A reference voltage (plus) related to the target output voltage to be obtained is given to the non-inverting input terminal of the error amplifier 4 from the microcomputer via the D/A converter 2, and the error amplifier 4 uses this reference voltage. The difference between the partial voltages is determined, amplified, and outputted to the PWM control circuit 4. The PWM control circuit 4 changes the duty ratio of the switching pulse of Q3 by changing the duty ratio of the pulse output to the transistor Q2 according to the above-mentioned difference voltage, and adjusts the ratio of the on time Tl and off time T2 of Q3. change. Through such feedback, the output voltage 1 (Vout) is controlled to a target negative voltage.

On the other hand, when transistor Q1 is turned on, Q5 is turned on and Q6 is turned off, direct current flows from terminal F to E in primary winding 11, with respect to the winding direction of primary winding 1i [1]. Since the flow is in the opposite direction to the above case, 2
Next winding J22. )3, the polarity of the forward voltage and flyback voltage generated at
It becomes E2. Then, the output voltage HVout becomes ・T1+T2, which becomes a positive voltage. Then, the same feedback as described above is performed, and the HVout is controlled to the target positive voltage to be obtained.

As described above, in the configuration in which the positive power supply circuit and the negative power supply circuit are integrated, positive and negative outputs can be obtained. It also allows constant voltage control of the output.

[Embodiments] Hereinafter, details of embodiments of the present invention will be described with reference to the attached drawings.

1 above ±11 FIG. 1 is a circuit diagram showing the configuration of a power supply device according to a first embodiment of the present invention.

What is indicated by the symbol T1 is a transformer, and the intermediate tap TP
A primary winding with l and two secondary windings 122, 12
It has 3.

Terminals F and C at both ends of the primary winding are connected to smoothing capacitors C2 and C3, current limiting resistors R7 and RIO, and transistor Q5. Predetermined DC voltage Vcc via Q6
It is connected to a power supply circuit (not shown) that supplies power.

Transistor Q5. Q6 connects the DC voltage Vcc to the primary winding J
The electronic switch which switches the output polarity of the power supply device 15 by selectively applying voltage to either terminal F or C of 21 is configured together with the transistors Ql and Q4 described below, and the base of Q5 is Resistor R for current limiting
4, the base of Q6 is connected to the collector of transistor Q1 via an inverter circuit composed of transistor Q4 and resistors R1, R2 and R3. The emitter of the transistor Q1 is grounded, and the control output signal of the microcomputer 1 that controls the power supply device is inputted to the base. That is, transistor Q5. The on/off of Q6 is controlled so that either one is turned on by the on/off of the transistor Q1, and the on/off of Q1 is controlled by the microcomputer.

In addition, the terminal E of the middle tap TP of l in the primary winding turns on and off the direct current applied to the primary winding 11, and turns the transformer T1
It is connected to the collector of the switching transistor Q3 that drives the transistor Q3.

A switching pulse generated from a PWM (pulse width modulation) control circuit to be described later and inverted and amplified via transistor Q2 is input to the base of Q3. Q3 has its emitter grounded, and a resonance capacitor CI and damper diode DI are connected between the collector and emitter.
are connected in parallel.

On the other hand, both ends of the first secondary winding 2 of the transformer T1 are connected to a rectifying and smoothing circuit consisting of a series connection of a diode D2 and a capacitor C4, and a load 7 is connected to the connection point between the diode D2 and the capacitor 04. is connected to the output terminal 6 of the power supply device.

Further, both ends of the second secondary winding 13 are connected to a rectifying and smoothing circuit consisting of a diode D3 having a polarity opposite to that of the diode D2, and a grounded capacitor C5 connected in series. The connection point between capacitors 05 is the first secondary winding 12. It is connected to the connection point between capacitors 04.

That is, the outputs of two rectifying and smoothing circuits that rectify and smooth the current generated in each of the secondary windings 112 and 123 with opposite polarities are connected in series and connected to the output terminal 6.

Furthermore, the output terminal 6 has an output voltage HVou of the output terminal 6.
A voltage divider consisting of a series connection of a resistor R11 and a grounded resistor R12 is connected to detect the partial voltage of t.
The connection point between the resistors R11 and R12 is connected to an inverting input terminal of an error amplifier 4 via a polarity switching circuit 3 that switches the polarity of the divided voltage at the connection point.

The polarity switching circuit 3 switches (inverts) the polarity of the input divided voltage, or outputs it to the operational amplifier 4 as is, depending on the level of the control input signal caused by turning on or off the transistor Q1. , here Ql
Switching is performed when the switch is off, and not when it is on.

Further, the error amplifier 4 determines the difference between the above-mentioned divided voltage applied to the inverting input terminal and the reference voltage applied to the non-inverting input terminal, amplifies the difference, and outputs the result. The above-mentioned reference voltage is a reference voltage related to the absolute value of the target output voltage that the power supply bag should obtain, and the value is given to the D/A converter 2 in digital form from the microcomputer 1, and the value is given to the D/A converter 2 in analog form by the D/A converter 2. The signal is converted into and applied to the error amplifier 4.

In this case, the reference voltage is given as an absolute value, for example, a positive value, regardless of the polarity of the target output voltage. Further, the output of the error amplifier 4 is connected to the input of the PWM control circuit 5.

The PWM control circuit 5 is a known one that compares a triangular wave or sawtooth wave of a predetermined frequency with the input voltage, and outputs the pulse by changing its duty ratio. It is inverted and amplified via Q2 and input as a switching pulse to the base of transistor Q3.

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

During operation, a predetermined positive DC voltage Vcc is applied from the power supply circuit.
is applied to the emitter of the transistor Q5゜Q6 of the electronic switch, and the transistor Ql is turned on or off by the control signal of the microcomputer 1 depending on the output polarity to be obtained from the power supply. Only one of them is turned on, and DC voltage Vcc is applied to either terminal C or F of the primary winding. In this case, Vcc is the capacitor C2 or C3.
It is smoothed and applied by .

At the same time, a switching pulse is introduced to the base of the switching transistor Q3, which turns Q3 on and off, turning on and off the direct current applied to the primary winding 11, and driving the transformer TI.

The above switching pulse is inputted to the base of the transistor Q3 as an inverted version of the one output from the PWM control circuit 5 via the transistor Q2, and its duty ratio is made sufficiently small, and as described later, the switching pulse is inputted to the base of the transistor Q3. It is controlled according to the magnitude of the absolute value of the voltage.

Here, the operation when the transistor Ql is turned off by the control signal of the microcomputer 1 is as follows.

When transistor Ql is turned off, transistor Q5 is turned off, and when Q4 is turned off and Q6 is turned on, DC voltage Vcc is applied to one terminal C of primary winding j21.

Here, when the switching transistor Q3 is turned on, a current flows from one terminal C in the primary winding Jl toward the terminal E of the center tap, and a current flows in the secondary winding Jl according to the winding ratio. A predetermined so-called forward voltage E1 is generated at No.3.

This is the diode D2. This is because, due to the difference in polarity of D3, for example, diode D2 is turned off and D3 is turned on, so that forward voltage E1 is not applied to capacitor C4, but is applied to capacitor C5 and charged across it.

Next, when the transistor Q3 is turned off, the current in the primary winding 11 is cut off, so that a so-called flyback voltage -E2 having a polarity opposite to the forward voltage E1 when the transistor Q3 is turned on is generated in the secondary windings 122 and 123.

This is because the diode D2 is turned on and D3 is turned off due to the reversal of the 1-generated voltage, and only the capacitor C4 is charged with the flyback voltage -E2. - The forward voltage El previously charged to the capacitor C5 and the flyback voltage -E2 charged to the capacitor C4 are smoothed by both capacitors and become the output voltage HVout at the output terminal 6. That is: The voltage of the sum of the outputs of the two rectifying and smoothing circuits becomes the output voltage HVout, and the on-time of the transistor Q3 (forward voltage E1
If the off time (time of occurrence of flyback voltage E2) is T1, and T2 is the off time (time of occurrence of flyback voltage E2), then as mentioned above, the duty ratio of the switching pulse is sufficiently small, that is, TI((T2 Therefore, the output voltage HVout becomes a negative voltage.

Note that when the transistor Q3 is off, a resonant circuit is formed by the resonant capacitor C1 and the inductance L between the terminals C and F of the primary winding J21, voltage resonance occurs, and a negative voltage is generated in the inductance L. , the above-mentioned turn-off becomes more reliable and switching loss is reduced. Further, in this case, since current flows through the damper diode D1, the efficiency becomes higher.

On the other hand, in order to control the absolute value of the output voltage HV out to a predetermined value with high precision, the output voltage HV out
The voltage ut is divided by resistors R11 and R12, and the divided voltage -vl is input to the polarity switching circuit 3.

In the polarity switching circuit 3, since the transistor Ql is off in this case, the polarity switching (inversion) of the above-mentioned partial voltage -Vl is performed as described above, and in this case, the partial voltage -Vl becomes +Vl.
The signal is inverted and output to the inverting input terminal of the error amplifier 4.

Then, in the error amplifier 4, as described above, the differential voltage VO-Vl of the above-mentioned divided voltage with respect to the reference voltage vO corresponding to the target output voltage is determined, amplified, and outputted to the PWM control circuit 5.

The PWM control circuit 5 sets the duty ratio of the pulse output to the transistor Q2 based on the input difference voltage vo-v.
It is changed depending on the polarity and size of i.

For example, if the differential voltage vo-vt is positive, that is, if the absolute value of the actual output voltage VHout corresponding to the divided voltage Vl is smaller than the absolute value of the target output voltage corresponding to the reference voltage vO, the output Increase the pulse duty ratio. In other words, Q3 obtained by inverting with transistor Q2
Reduce the duty ratio of the switching pulse.

As a result, the on time TI of Q3 mentioned above changes to the off time T2.
As a result, the output voltage f (Vout) is controlled to the desired output voltage.

Further, when the differential voltage VO-Vl is negative, the output voltage HVout is controlled to the desired output voltage by doing the opposite to the above.

Due to the above feedback, the output voltage HVout
is controlled to a predetermined negative voltage.

On the other hand, when the transistor Ql is turned on by the control signal from the microcomputer I, the operation is as follows.

When transistor Ql is turned on, transistor Q5 is turned on, while Q4 is turned on and Q6 is turned off, so that 1
In the secondary winding) l, the current flows from the terminal F to the terminal E, and since it flows in the opposite direction to the winding direction of the primary winding as in the above case, the secondary winding j22° is turned on and off by turning on and off the transistor Q3. The polarities of the forward voltage and flyback voltage generated at 13 are opposite to those described above, and are -El and +E2. Then, the forward voltage -El is charged to the capacitor C4 and the flyback voltage E2 is charged to the capacitor C5 in the reverse operation as described above. Due to smoothing by both capacitors, the output voltage of output terminal 6 HVout
Since TI<<72, a predetermined positive voltage is obtained.

Then, in the same way as in the previous case, the output voltage HVoutc
7) The divided voltage 13 by the resistors R11 and R12 is guided to the polarity switching circuit 3, but in this case, since the transistor Ql is off, polarity switching is not performed, and the divided voltage is applied to the error amplifier 4 as it is.

Then, in the same manner as described above, the duty ratio of the output pulse of the PWM control circuit 5 is controlled according to the output voltage of the error amplifier 4, so that the output voltage HVout is controlled to a positive voltage of the desired value ψ. .

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 transistor Ql of the electronic switch.

Q4. Q5. By selecting the direction of the direct current applied to the primary winding 11 via Q6 in either direction with respect to the winding direction of the primary winding, a positive or negative output can be obtained.

Also, microcomputer 1. D/A converter 2, polarity switching circuit 3. The magnitude of the output voltage can be controlled to a desired value via a control circuit composed of an error amplifier 4 and a PWM control circuit 5.

In the first embodiment of the present invention, the output voltage HV is
The connection point between the secondary windings 3 and 05, which was grounded in the configuration shown in Figure 1, was
As in the second embodiment of the present invention shown in the figure, the resistors R11, R1
By connecting to the connection point between the two, constant current control of the output current can be performed.

In this case, load 7. The output current flowing through R12 is
A voltage is detected at both ends of the polarity switching circuit 12, and this voltage is led to the polarity switching circuit 3 and below, and the above-described control is performed accordingly, whereby the output current is controlled to be a constant current.

[Effects of the Invention] As is clear 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, thereby reducing the number of parts, downsizing the device, and Manufacturing costs can be reduced. Furthermore, since the output polarity is switched by switching the input side with a low voltage (absolute value), noise generation can be prevented by 1F. Also, constant voltage control or constant current control of the output can be performed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the structure of a power supply device according to a first embodiment of the present invention, and FIG. 2 is a circuit diagram showing the structure of a power supply device according to a second embodiment. 1...Microcomputer 2...D/A converter 3...Polarity switching circuit 4...Error amplifier 5...
PWM control circuit 6...Output terminal 7...Load
T1...Transformer 11-...Primary winding,
, d2, 1.3... Secondary winding Ql-Q6... Transistor D1-D3... Diode R1-R12... Resistor Cl-C5... Capacitor

Claims (1)

[Claims] 1) a) a transformer having a primary winding and two secondary windings; b) direct current applied to the primary winding from a power supply circuit; an electronic switch that switches in both directions with respect to the winding direction, c) a switching circuit that turns on and off the direct current, and d) rectifies the current generated in each of the secondary windings by turning on and off with opposite polarity to each other. two rectifying and smoothing circuits whose outputs are connected in series; e) controlling the output voltage or output current of the power supply device obtained as the sum of the outputs of the two rectifying and smoothing circuits to a desired value; A power supply device comprising means for: 2) The power supply device according to claim 1, wherein the on-time of the direct current is sufficiently shorter than the off-time.