JPS63274367A - Switching power circuit - Google Patents

Abstract

PURPOSE:To stabilize an output voltage efficiently by respectively providing the error amplifier of a control circuit with a resistance determining a feedback gain and a control current output part with an output current limiting resistance. CONSTITUTION:A switching power circuit is composed of a main transformer 1, a self-oscillated feedback circuit controlling the ON-OFF state of a switching element by its feedback winding and others to obtain a DC output voltage Vout by making the output voltage of a transformer secondary winding L2 go through a magnetic amplifier MA, rectification and smoothing and the like. Then, a control current corresponding to the output voltage Vout is caused to flow through the magnetic amplifier MA by a control circuit 10. Said control circuit 10 is composed of an error amplifier 11 and a control current output part 12 and said error amplifier 11 is provided with a resistance R5 deciding a feedback gain. Also in a control current output part 12, a resistance R4 for limiting an output current is connected between the emitter of a transistor Tr2 and the positive side F point of said output voltage Vout. Thus, said feedback gain can be varied so as to be capable of operating within the most efficient range.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a switching power supply circuit used as a stabilized power supply, and particularly to a switching power supply circuit that stabilizes the output voltage of a switching converter by the action of a magnetic amplifier and its control circuit. This invention relates to a switching power supply circuit.

[Summary of the invention]

This invention includes a magnetic amplifier inserted between the secondary side of a switching converter and a rectifier circuit that rectifies and outputs a pulsed output voltage, and a control current that is applied to the magnetic amplifier according to the output voltage of the rectifier circuit. In a switching power supply circuit equipped with a control circuit that stabilizes the output voltage by flowing the output voltage, the control circuit is configured to include an error amplification section that detects an error of the output voltage with respect to a reference voltage, and a switching power supply circuit that responds to the error detected by the error amplification section. A control current output section that outputs a control current is provided in the error amplifier section, and a resistance that limits the output current is provided in the control current output section. The purpose is to provide a compact, highly stable, and high-performance regulated power source that fully brings out the control characteristics.

[Conventional technology]

In general, switching power supply circuits are superior to dropper-type stabilized power supply circuits in that they are smaller, lighter, more efficient, and can handle a wider range of input voltage and load fluctuations.

However, there are problems such as the complexity of one circuit and the high cost, and there is a need to reduce costs by integrating components and miniaturizing components by increasing the switching frequency.

By the way, circuit systems for switching power supplies that have a voltage control function that can handle a wide range of input voltage and load fluctuations include circuits that use separately excited pulse width control (PWM) switching converters, and circuits that use self-excited ringing converters. A choke converter (RCC) type circuit is mainly used.

In particular, self-excited RCC type switching power supply circuits, which have a relatively simple circuit configuration, a small number of parts, and are inexpensive, are often used in small-capacity power supplies incorporated in general electronic devices.

An example of a switching power supply circuit of this type will be briefly described with reference to FIG.
~ D14 and the Zener diode ZD form a self-oscillation feedback circuit (ringing choke circuit) that controls on/off of the switching element 2, and the main transformer 1
By intermittent current flowing through the primary winding, the voltage generated in the secondary winding L2 is rectified and smoothed by the diode D1 and the capacitor C1, resulting in a substantially stabilized output voltage V.
out is supplied to the load. In addition, Rs.
is a resistor for applying a starting pulse when the input voltage Vin is applied.

This circuit is of the "rON-OFF type" (flyback type) in which the energy stored in the main transformer 1 when the switching element 2 is ON is transmitted to the load side when it is OFF, and the switching element 2 is part of the oscillation circuit. has become,
Since a feedback loop for output control is formed within it, the circuit is simpler than the separately excited PWM method.
Difficult to start up and stabilize oscillation.

Therefore, it has been considered to reduce the burden on the switching converter by providing a magnetic amplifier on the secondary side of the main transformer 1 to stabilize the output voltage, as shown in FIG.

The switching power supply circuit converts the pulsed output voltage generated in the secondary winding L2 of the main transformer 1 into a magnetic amplifier (
After passing through MA (magamp element) MA, it is rectified by a diode D1, and smoothed by a capacitor C1 to obtain a DC output voltage V out.

When the main transformer 1 does not generate an electromotive voltage in the secondary winding L2, the control circuit 3 controls the DC output voltage Vou
A control current Is corresponding to t is passed through the magnetic amplifier MA in the direction of the arrow to generate a control magnetic flux, and then the main transformer 1
When an electromotive force is generated in the next winding L2, B of the magnetic amplifier MA
- The timing at which the voltage rises on the output side is delayed by the H loop characteristic, and the pulse width of the pulsed output voltage is controlled.

That is, when the output voltage Vout becomes high, the pulse width of the pulse voltage passed through the magnetic amplifier MA is controlled to be small as shown in FIG. 8(b) to lower the effective value.
When the output voltage Vout decreases, its pulse width changes as shown in the figure (
As shown in a), the effective value is increased by controlling it to be large, so that the DC output voltage V out is always constant.

In this way, R
Although it is possible to reduce the load on the CC circuit and obtain a stable output voltage with a relatively simple circuit, it is possible to reduce the switching frequency by using a high-performance magnetic amplifier whose core is made of amorphous metal material such as an amorphous alloy. By increasing the frequency of , some miniaturization becomes possible.

[Problems to be solved by the invention] However, in a switching power supply circuit that combines such a switching converter and a magnetic amplifier,
The amplifier is nothing more than a control element, and requires a control circuit with good characteristics in order to make full use of its characteristics. Furthermore, in order to lower the cost of power supplies, there is a strong demand for lower cost of the control circuit itself.

However, in the past, in order to obtain high performance, an expensive IC (integrated circuit) was used for this control circuit, or a low-mounted feedback amplifier was used. However, there was a problem in that the magnetic amplifier could not be used effectively and an excessive control current was passed through the magnetic amplifier, causing heat generation and reducing efficiency.

The present invention solves these problems and makes full use of the excellent characteristics of a magnetic amplifier at low cost.

The purpose is to provide a highly efficient and high performance switching power supply circuit.

[Means for solving problems]

In order to achieve the above object, the present invention includes a switching power supply circuit as described above, in which a control circuit that causes a control current to flow through a magnetic amplifier is replaced with an error amplification section that detects an error of a DC output voltage with respect to a reference voltage.

and a control current output section that outputs a control current according to the error detected by the error amplification section, and a resistor that determines a feedback gain in the error amplification section.

Each control current output section is provided with a resistor that limits the output current.

[For production]

According to the switching power supply circuit configured in this way, the control current can be varied within the range in which the feedback gain by the control circuit can operate the magnetic amplifier most efficiently, and the upper limit of the control current output by the control current output section can be set. It can be limited within the maximum value at which the magnetic amplifier does not saturate.

As a result, it is possible to fully bring out the excellent characteristics of the magnetic amplifier and to efficiently stabilize the output voltage, and it is also possible to increase the switching frequency.

【Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an embodiment of the present invention, and is a circuit diagram of only a portion corresponding to the secondary side of a switching converter in the switching power supply circuit of FIG. 7, and parts corresponding to those in FIG. 7 have the same reference symbols. It is attached. In addition, the primary side is the 7th
Since this is the same RCC circuit as shown in the figure, illustration and explanation thereof will be omitted.

In this embodiment, the control circuit 101 and the error amplification section 11
and a control current output section 12.

In the error amplification section 11, R1 and R2 are voltage dividing resistors for output voltage detection, and when the output voltage Vout is a desired value, the voltage Va at the point A is kept constant by the Zener diode ZD1, and the reference voltage vb at the point B is set. The resistance ratio of Ro and R2 is determined so that it is higher than the sum of the base-emitter voltage of the transistor Tr1 by a predetermined value.

Then, due to Va-Vb corresponding to the error of the output voltage Vout with respect to the reference voltage, the transistor TrL becomes the transistor Tr of the control current output section 12.

control the base current of

A predetermined operating current is set by the Zener diode ZD and resistor R1. R6 is a resistor that determines the feedback gain;
C2 is a capacitor connected to improve the frequency characteristics of the system.

The control current output section 12 includes a transistor Tr2 whose base is grounded between the collector and emitter of the transistor Tr and via a Zener diode ZD□, and the positive side of the output voltage V out (the output side of the rectifier circuit using the diode D2). ) and a diode D3 connected between the collector and point E on the output side of the magnetic amplifier MA.

Then, the base current of the transistor Tr of the control current output section 12 is controlled by the transistor Tr of the error amplifier 11, and the control current I according to the output voltage Vout is controlled.
s to the magnetic amplifier MA through the diode D.
The control current is caused to flow in the direction of the arrow (when no electromotive force is generated in the secondary winding L2 of the main transformer 1).

Therefore, even when the desired output voltage Vout is obtained, the control circuit 10 causes the magnetic amplifier MA to flow a predetermined control current Is to operate near the center of the control range, and then the output voltage Vout When t becomes high, the control current Is increases to increase the actance of the magnetic amplifier MA, and when the output voltage Vout becomes low, the control current Is decreases to reduce the actance of the magnetic amplifier MA. .

Generally, in the case of negative feedback control, control accuracy improves as the feedback gain is increased, but it is known that the system tends to become unstable, so the feedback gain must be set appropriately for the output voltage accuracy. There is.

In this embodiment, the resistor R6 serves to determine the feedback gain of the error amplification section 11, and the resistor R4 serves to determine the feedback gain of the control current output section 12, and both determine the gain of the entire feedback system to an appropriate value. do.

In addition, as a result of various experiments, when using a magnetic amplifier,
It has been found that if a large control current is applied and the magnetic amplifier is used at its maximum control capability, the magnetic amplifier generates more heat, resulting in a decrease in the amount of magnetic flux and a loss of control power.

Therefore, the operating point of the magnetic amplifier is determined by the maximum control current Isma in the control current-control magnetic flux characteristic curve shown in FIG.
It is desirable to use the control current at a position of 1/2 of x.
The control current Is should be set so as not to exceed a certain appropriate value, for example Ismax.

Therefore, in this embodiment, the resistor R4 inserted in the emitter circuit of the transistor Tr of the control current output section 12 has a function of limiting the output current, that is, the control current Is, and the control current Is is actually intermittent. Even considering that Ismax in FIG. 2 is a DC value, the minimum value of the resistor R4 is defined so that the control current Is does not exceed ('IIsmax).

On the other hand, the maximum value of this resistor R4 can be set freely, but if the control function is taken into consideration, the control current value will be (1/2) I
It is necessary to regulate it to about smax.

Therefore, the setting range of R1 is (2Vout/Is
max)≧R4≧(Vout/fTr smax).

Here, when I smax is about 30 mA and the desired output voltage Vout is 16 V, the resistance value of the resistor R4 is set to, for example, 1Ω.

Furthermore, in the above setting range, it is possible to set the resistance value of the resistor R4 to a value of several hundred ohms or more, so the input impedance of the control current output section 12 becomes as high as several tens of kilohms or more, and the gain of the feedback system increases. depends mostly on the resistor R6.

In this embodiment, the resistance value of the resistor Rs is set to 1.5Ω, for example.
In this case, the gain of the error amplifying section 11 is approximately 100.

Further, by utilizing the high input impedance of the control current output section 12, the feedback frequency characteristics can be freely set by the capacitance of the capacitor C.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment as well, the secondary side of the switching converter is the first
Since it is substantially the same as the embodiment shown in the figure, a description thereof will be omitted, but a choke coil CH is inserted in the smoothing circuit, and a diode D2 is connected to absorb the surge current when the smoothing circuit is turned off.

This switching power supply circuit is configured to cause a switching converter to self-oscillate using a saturable reactor having a core made of an amorphous metal material.

That is, one end of the primary winding L□ of the main transformer 1' is grounded through the source and drain of the switching element 5 made of MOS-FET, and the alternating current from the commercial power supply of AC30 to 270 cm is passed through the full-wave rectifier circuit 4. rectify with capacitor C
The primary winding L□ according to the input voltage Vin smoothed by
By switching on and off the current flowing through the secondary winding II Lz by the switching element 5, an electromotive voltage is generated in the secondary winding II Lz in an ON-〇N manner.

This main transformer 1' is provided with a feedback winding Lb, which is connected to a diode D4 and a coupling capacitor C,
, C4 and a coupling resistor R1 (change the constant depending on the direction of the current to improve the linearity of ON time change) to the primary winding of the saturable transformer 6 to form a loop circuit,
One end of the secondary winding of the saturable transformer 6 is grounded, and the other end is connected to the gate of the switching element 5 via a coupling capacitor C9 to form a self-oscillation feedback circuit.

Further, a Zener diode ZD is connected between the gate of the switching element 5 and the ground, and a resistor Rs for obtaining a starting pulse is connected between the positive power supply line and the switching element 5.

A capacitor C1 for releasing residual energy is connected in parallel to the primary winding L1 of the main transformer 1'.

FIG. 4 shows a schematic diagram of the B-H loop characteristics (hysteresis characteristics) of this saturable transformer 6.

The primary side current of this saturable transformer 6 generates an excitation magnetic field H, and due to the change in the magnetic flux φ, a voltage of
2 is generated (V, ccdφ/dt).

When the saturable core becomes saturated, the magnetic flux φ does not change, so the voltage v2 on the secondary side becomes O.

Therefore, in the embodiment shown in FIG. 3, when the input voltage Vin is applied, a starting trigger is applied to the gate of the switching element 5 through the resistor Rs, and this switching element 5 is turned on, and one of the main transformers of the main transformer 1' is turned on. Volume #IL1
A current flows to generate an electromotive voltage in the secondary winding L2.

At the same time, an electromotive voltage is generated in the feedback winding Lb of the main transformer 1', and a current corresponding to the electromotive voltage is generated on the primary side of the saturable transformer 6 through the coupling capacitor C3, the diode D4, and the coupling resistor R1. flows. As a result, the voltage v2 is generated on the secondary side as described above and is applied to the gate of the switching element 5 through the coupling capacitor C9, so that the switching element 5 maintains the ON state.

After that, when the core of the saturable transformer 6 becomes saturated,
The secondary voltage becomes 0, the charge in the capacitor C6 is discharged, and the gate potential of the switching element 5 decreases, turning it off.

Then, due to the residual energy of the main transformer 1', a reverse voltage is generated in the feedback winding Lb, and the coupling capacitor C1
The saturable core of the saturable transformer 6 is magnetized in the opposite direction through the capacitor C, and the voltage generated on the secondary side thereby
Charge 6 in the opposite direction. During this time, the switching element 5 remains in the OFF state.

When the voltage charged in the capacitor C8 exceeds the zener voltage of the zener diode ZD1, a current flows at that moment, and this triggers a resonant ringing voltage due to the inductance, capacitance, and resistance in the feedback loop. , becomes a trigger pulse to re-ignite the switching element 5, and the switching element 5 is turned on again.
It becomes N state. Thereafter, similar oscillation operations are repeated.

The ON time of oscillation at this time (the time during which the switching element 5 is turned on and current flows through the primary winding L1 of the main transformer 1') is the time until the core of the saturable transformer 6 reaches saturation. From this, if the coupling resistor R1 and coupling capacitors C, C4 are set to appropriate values, the main transformer 1
' varies depending on the magnitude of the electromotive voltage of the feedback winding Lb.

That is, when the input voltage increases or the load decreases, the electromotive voltage of this feedback winding Lb increases, the exciting current of the saturable transformer 6 also increases, and the saturable core saturates faster, causing O
N time is shortened and the energy transmitted to the secondary side of the main transformer 1' is reduced.

Conversely, when the input voltage decreases or the load increases, the electromotive force in the feedback winding Lb of the main transformer 1' decreases, and O
As the N time increases, the energy transmitted to the secondary side of the main transformer 1' increases.

The OFF time (the time during which the switching element 5 is OFF) is influenced somewhat by fluctuations in the input voltage and load, but it is determined mainly by the release route of the residual energy of the main transformer 1', so it remains approximately constant. .

Therefore, when the input voltage is high and the load is light, the ON duty is small as shown in Figure 5 (a), and when the input voltage is low and the load is heavy, the ON time and OFF time are as shown in Figure 5 (b). The ON duty increases. As can be seen from this figure, as the ON duty increases, the oscillation frequency decreases.

Thus, according to this embodiment, the main transformer 1'
The primary side converter absorbs large input fluctuations and load fluctuations, and on the secondary side, the output voltage is further stabilized by the action of the magnetic amplifier MA.

Further, in this embodiment, an amorphous alloy core with excellent high frequency characteristics is used for the saturable transformer 6 and the mag-amp element MA, and a MOS-FE capable of high-speed operation is used for the switching element 5.
By using T, it is possible to increase the switching frequency, and it operates stably even at 300 KHz or higher.

Note that if the switching frequency does not need to be so high, a bipolar transistor or the like may be used as the switching element.

The embodiments in which the present invention is applied to a switching power supply circuit using a self-excited switching converter using an RCC method and a saturable transformer have been described above, but the present invention is not limited to this, and other self-excited or separately excited switching converters may be used. Of course, the present invention can also be similarly applied to switching power supply circuits.

〔Effect of the invention〕

As explained above, the switching power supply circuit according to the present invention can control feedback gain and maximum control using a simple circuit without using an expensive integrated circuit for the control circuit of a magnetic amplifier that stabilizes the secondary output voltage of a switching converter. The current can be set freely and the excellent control characteristics of the magnetic amplifier can be fully utilized to efficiently cope with and stabilize output voltage fluctuations due to load fluctuations, improving performance and reliability. be able to.

Furthermore, it is easy to increase the switching frequency,
This also makes it possible to achieve further miniaturization and lower costs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a main part of a switching power supply circuit showing an embodiment of the present invention, and FIG. 2 is a characteristic curve diagram of control current versus control magnetic flux amount of a magnetic amplifier. FIG. 3 is a circuit diagram showing another embodiment of the invention. Fig. 4 is a schematic diagram of the characteristics of the B-H loop of the saturable transformer, Fig. 5 is an explanatory diagram of the switching operation in the embodiment of Fig. 3, and Figs. 6 and 7 are respectively the conventional self-excited ringing
A circuit diagram showing a different example of a choke converter (RCC) type switching power supply circuit. FIG. 8 is a waveform diagram for explaining the action of the magnetic amplifier MA in FIG. 7. 1.1'...Main transformer 2.5...Switching element 4...Full wave rectifier circuit 6...Saturable transformer 10...Control circuit 11...Error amplification section 12
...Control current output section MA...Magnetic amplifier

Claims (1)

[Scope of Claims] 1. A magnetic amplifier is inserted between the secondary side of the switching converter and a rectifier circuit that rectifies and outputs the pulsed output voltage, and the magnetic amplifier is provided with an output voltage corresponding to the output voltage of the rectifier circuit. In a switching power supply circuit including a control circuit that stabilizes an output voltage by flowing a control current, the control circuit includes an error amplification section that detects an error of the output voltage with respect to a reference voltage, and an error amplification section that detects an error of the output voltage with respect to a reference voltage. and a control current output section that outputs a control current according to the error that is detected, and the error amplification section is provided with a resistor that determines a feedback gain, and the control current output section is provided with a resistor that limits the output current. Features a switching power supply circuit.