JPH0368632B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a switching power supply circuit used as a stabilized power supply, and in particular to a self-oscillation type switching power supply circuit.
Related to what constitutes a DC-DC converter circuit.

[Summary of the Invention] The present invention provides a switching power supply circuit that includes:
A feedback winding is provided in the main transformer that generates an output voltage on the secondary side by intermittent power supply on the primary side. By forming a self-oscillation feedback circuit that controls the switching element that intermittents the current on the side, the output voltage is stable even over a wide range of input and load fluctuations, and it is easy to increase the frequency. This circuit can be provided at low cost.

[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 complicated circuits and high costs, and there is a need to reduce costs by integrating components and miniaturizing components by increasing the switching frequency.

As described above, the conventional 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 a separately excited pulse width control (PWM) circuit as shown in Figure 8. A self-excited ringing converter (RCC) circuit as shown in FIG. 9 is mainly used.

The separately excited PWM type switching power supply circuit shown in FIG. The voltage generated in diode D ₁
The output voltage obtained by _rectifying with
Supply Vout to the load. Note that the diode _D2 is for absorbing surge current by the choke coil CH.

Then, this output voltage Vout is divided by the resistors R ₁ and R ₂ and amplified by the feedback amplifier 11, and the oscillation/pulse width modulation circuit 12 is controlled by the voltage, and the switching element 13 is turned on. - The off duty is now controlled.

This circuit uses the "ON-ON method" which transmits energy to the load when the switching element 13 is ON.
(forward method), the switching circuit, oscillation/pulse width modulation circuit, and feedback amplifier are each independent, so the oscillation is stable, and there are advantages such as a high degree of freedom in circuit design, but the circuit is complicated. However, there are problems such as a large number of parts and a high price.

On the other hand, the self _- excited RCC type switching power supply _{circuit shown} in FIG _.
D ₁₄ and the Zener diode ZD form a self-oscillation feedback circuit (ringing circuit) that controls the on/off of the switching element 23, and the voltage generated on the secondary side of the main transformer 20 is passed through the diode D _3. It is then rectified and smoothed by capacitor _C2 and supplied to the load.

Note that Rs is a resistance for applying a starting pulse when the input voltage Vin is applied.

This circuit is an "ON-OFF method" (flyback method) in which the energy stored in the main transformer 20 when the switching element 23 is ON is transmitted to the load side when it is OFF, and the main switching element 23 is part of the oscillation circuit. Since a feedback loop for output control is formed within it, the circuit is simpler than the separately excited PWM system, but it is difficult to stabilize startup and oscillation.

Therefore, this RCC type circuit has the following problems compared to the "ON-ON type" (forward type) circuit shown in FIG. 8, which is commonly used in separately excited type.

(b) In order to avoid saturation of the main transformer, it is necessary to make the main transformer larger and provide a gap to adjust the output.

(b) The ripple current of the output capacitor is large.

(c) When a regulator using a magnetic amplifier is added to the secondary side of the main transformer or an inductive load such as a motor is connected, oscillation tends to become unstable due to sudden load fluctuations.

(d) When multiple outputs are used, cross regulation between outputs is large (easily affected by fluctuations in other outputs).

(e) Difficult to start up at low temperature due to power outage input.

(f) When using a MOS-FET as a switching element, it is difficult to start up and stabilize oscillation, so high frequency switching of 200KHz or higher cannot be performed with low loss (bipolar transistors have a limit to high frequency) .

[Problem that the invention seeks to solve]

In this way, the commonly used separately excited pulse width control (PWM) type switching power supply circuit has the advantages of stable oscillation and a large degree of freedom in circuit design, but the circuit is complicated. However, although self-excited RCC switching power supply circuits are simple and inexpensive, they are difficult to stabilize startup and oscillation compared to separately excited systems. There are various problems listed in (a) to (f) above, such as difficulty and problems with increasing the frequency.

The present invention solves these conventional problems in self-excited oscillation type switching power supply circuits, has a simple circuit, can handle a wide range of input and load fluctuations, has stable startup and oscillation, and can operate at high switching frequencies. The purpose is to make it possible to

[Means for solving problems]

In order to achieve the above object, the present invention rectifies and smoothes the voltage generated on the secondary side by using a switching element to intermittent the current flowing through the primary side of the main transformer according to the input voltage. A switching power supply circuit that obtains an output voltage includes a feedback winding in the main transformer, a saturable transformer, and a coupling circuit that couples the primary side of the saturable transformer and the feedback winding, and the output of the feedback winding A self-oscillation feedback circuit for controlling the switching element is formed on the secondary side of the saturable transformer, and the coupling circuit is connected to a series circuit of a parallel circuit of a first capacitor and a first resistor, and a diode. The second capacitor and the second resistor are respectively connected in parallel.

[Effect]

The switching power supply circuit according to the present invention combines a main transformer with a switching element connected to the primary side and a saturable transformer through a feedback winding and a coupling circuit to form a self-oscillating feedback circuit, and a saturable The switching element is turned off by utilizing the saturation of the transformer.

Therefore, as the output of the feedback winding of the main transformer changes in response to input or load fluctuations, the current on the primary side of the saturable transformer changes,
As the magnitude of the excitation magnetic field changes, the time it takes for the saturable core to reach saturation also changes, and as a result, the secondary output of the saturable transformer changes, changing the time to turn on the switching element, and changing the switching pulse width. increases and decreases to absorb fluctuations in the input or load, and control is performed to automatically maintain a constant output voltage, and the constant of the coupling circuit changes depending on the direction of the current, so that the on-state The linearity of time change is improved and stable oscillation can be obtained.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention, and parts corresponding to those in FIG. 8 are given the same reference numerals.

This switching power supply circuit connects one end of the primary winding L ₁ of the main transformer 1 to ground via the source and drain of the switching element 3 formed by a MOS-FET, and connects the primary winding L ₁ to the ground in accordance with the input voltage Vin. By intermittent the flowing current by switching element 3, the voltage generated in secondary winding _L2 is rectified by diode _D1 , and the output voltage Vout smoothed by chiyoke coil CH and capacitor _C1 is loaded. supply to.

The main transformer 1 is provided with a feedback winding Lb, which is connected to the first capacitor _C3 and the first resistor.
In the parallel circuit of R ₃ and the series circuit with diode D ₄ ,
Second capacitor C ₄ as well as resistor R ₄ and variable resistor VR
and a second resistor formed of a series circuit connected in parallel to the primary winding of the saturable transformer 2 to form a loop circuit,
One end of the secondary winding of the saturable transformer 2 is connected, and the other end is connected to the gate of the switching element 3 via a parallel circuit of capacitor C ₅ and resistor R ₅ to form a self-oscillation feedback circuit. is forming.

In addition, a Zener diode ZD ₁ is connected between the gate of the switching element 3 and the ground, and a resistor Rs for obtaining a starting pulse is connected between the positive input terminal and the switching element 3.
A capacitor _C6 for residual energy absorption is connected in parallel to the primary winding _L1 of the main transformer 1.

Before explaining the operation of this embodiment, the characteristics and operation of the saturable transformer 2 will be explained.

Figure 2 shows only this saturable transformer, and the third
The figure shows a schematic diagram of the B-H loop characteristics (hysteresis characteristics) of the saturable core.

An excitation magnetic field H is generated by the primary current I ₁ of this saturable transformer, and a voltage E ₂ is generated on the secondary side due to a change in the magnetic flux φ. That is, E ₂ ∝dφ/dt.

As I ₁ increases in the positive direction from 0 at the start, a positive voltage is generated as E ₂ until H passes from 0 through the course shown by the dashed line and reaches point A.
Furthermore, when H exceeds point A, the saturable core becomes saturated, and after H reaches point B, I ₁ decreases and H
Even if moves from point A to point C, φ does not change, so E ₂ becomes 0.

Thereafter, E ₁ is reversed, I ₁ increases in the negative direction, and when H passes point D, a negative voltage is generated as E ₂ . Further, when I ₁ starts to decrease after H reaches the Ea point due to the value of I ₁ <0, for example, H starts to return from the Ea point along the course shown by the broken line and E ₂ becomes 0.

Next, when I ₁ becomes positive again, a positive voltage is generated as E ₂ while H passes point Fa and reaches point A, and A
After passing the point, E ₂ becomes 0. Below, loop every time E ₁ reverses polarity (A → B → C → D → Ea → Fa → A)
The cycle of is repeated, and the secondary voltage E ₂ becomes as shown in FIG. 4a.

As a result, the switching element 3 shown in FIG. 1 is controlled to turn on and off as shown in FIG. 1b.

Here, if the value of I ₁ < 0 is small, the loop (A→
B→C→D→Eb→Fb→A) cycle, I ₁ <0
If the value of is large, a loop (A→B→C→D→Ec→
As a result of repeating the cycle Fc→A), the OFF time in FIG. 4b is mainly determined by the value of I ₁ <0. Further, the ON time changes depending on the length of F→A determined by the value of I ₁ <0 and the value of I ₁ >0.

In this way, the saturated/unsaturated state of the core of a saturable transformer can be used as a switch for energy transfer, and by using an amorphous alloy as the core material of this saturable transformer, a rapid B -H loop characteristics are obtained, and high frequency switching is possible with a small excitation current.

Therefore, the operation of the embodiment shown in FIG. 1 will be explained.

When the input voltage Vin is applied, a starting trigger is applied to the gate of the switching element 3 through the resistor Rs, this switching element 3 is turned on, current flows through the primary winding L ₁ of the main transformer 1, and the 2 An electromotive voltage is generated in the next winding _L2 .

At the same time, the feedback winding Lb of this main transformer 1
A positive electromotive voltage is generated at the second resistor R ₄ , VR, capacitor C ₄ and diode of the coupling circuit 15.
A current corresponding to the electromotive voltage flows to the primary side of the saturable transformer 2 through D ₄ , the capacitor C ₃ , and the resistor R ₃ .

As a result, as described above, a voltage is generated on the secondary side and is applied to the gate of the switching element 3 through the capacitor _C5 and the resistor _R5 , so that the switching element 3 maintains the ON state.

After that, when the core of saturable transformer 2 becomes saturated, its secondary voltage becomes 0, and the capacitor
The charge on _C5 lowers the gate potential of the switching element 3, turning it off.

Then, a reverse voltage is generated in the feedback winding Lb due to the residual energy of the main transformer 1, which causes the saturable core of the saturable transformer 2 to move in the reverse direction through the second resistor R ₄ , VR and capacitor C ₃ of the coupling circuit 15. The negative voltage thereby generated on the secondary side charges the capacitor C ₅ in the forward and reverse direction through the Zener diode ZD ₁ . During this time, the switching element 3 remains in the OFF state.

When the secondary voltage becomes 0 again, capacitor C ₅
At the moment the voltage charged in the Zener diode ZD ₁ exceeds the Zener voltage of the Zener diode ZD 1, a current flows, and this triggers a resonant ringing voltage due to the inductance, capacitance, and resistance in the feedback loop, which causes the switching element to This becomes a trigger pulse to re-ignite the switching element 3, and the switching element 3 is turned on again.

Thereafter, similar oscillation operations are repeated.

ON time of oscillation at this time (switching element 3
The time it takes for the current to flow through the primary winding L1 of the main transformer ₁ after turning ON is the time it takes for the core of the saturable transformer 2 to reach saturation, so the capacitors _C3 and C of the coupling circuit 15 ₄ , the resistor R ₃ , the second resistor R ₄ , and VR are set to appropriate values, which vary depending on the magnitude of the electromotive force in the feedback winding Lb of the main transformer 1.

That is, when the input voltage increases or the load decreases, the electromotive voltage of this feedback winding Lb increases,
The excitation current of the saturable transformer 2 also increases, the saturable core saturates faster, the ON 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 voltage of the feedback winding Lb of the main transformer 1 decreases, the ON time increases, and the energy transmitted to the secondary side of the main transformer 1 increases. .

The OFF time (time during which the switching element 3 is OFF) is affected to some extent by fluctuations in the input voltage and load, but mainly due to the electromotive force in the feedback winding Lb due to the residual energy of the main transformer 1 and the capacitor _C4. Since it is determined by the values of the second resistor R ₄ and VR, it is approximately constant.

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

As described above, according to this embodiment, the primary side converter section of the main transformer 1 absorbs large input fluctuations and load fluctuations, so the output voltage is simply rectified on the secondary side of the main transformer 1. By simply smoothing the voltage, an output voltage Vout with small voltage fluctuation can be obtained.

Furthermore, if the constants of the capacitors C ₃ and C _{4 and the resistor R 3 and} the second resistor R ₄ and VR of the coupling circuit 15 are set to appropriate values, the system can quickly respond to fluctuations in the power supply voltage and load and become stable. Although oscillation can be obtained, the allowable range of each constant is small compared to the variation of components.

However, by changing the values of the second resistor R ₄ and VR, stable oscillation can be obtained by largely absorbing variations in other constants.

Therefore, as in this embodiment, the second resistor is composed of a fixed resistor _R4 and a variable resistor VR, and
By adjusting VR, there is no need to adjust each constant individually, and the adjustment of the coupling circuit 15 is extremely simple.

However, this second resistor can also be composed of only a fixed resistor or a variable resistor, or can also be composed of both resistors connected in parallel.

FIG. 6 shows another embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals, and their explanation will be omitted.

In this embodiment as well, the converter part based on the self-oscillation feedback circuit is the same as the embodiment shown in FIG. rectifier, capacitor
_C7 to obtain the DC input voltage Vin, and the main transformer 1' is wound with three secondary windings _L2 , _L3 , _L4 , and the output circuits 5,
6 and 7 are formed to obtain three types of output voltages V ₁ to V ₃ .

The output circuit 7 is the same as the output circuit in the embodiment shown in FIG. 1, and outputs a substantially stabilized quasi-stabilized DC voltage _V3 by absorbing input and load fluctuations in the converter section as described above. .

The output circuit 6 is provided with a commonly used dropper type stabilization circuit 8 on the output side of a rectification/smoothing circuit similar to the output circuit 7, to generate a stabilized DC voltage V ₂ with improved stability against load fluctuations. get.

The output circuit 5 is the secondary winding of the main transformer 1'
The pulsed output voltage generated at _L2 is passed through mag-amp element MA, rectified by diode _D5 , and smoothed by chiyoke coil CH and capacitor _C8 to obtain a stabilized DC voltage _V1 . Note that the diode _D6 is for absorbing surge voltage by the choke coil CH.

9 is a feedback amplifier for mag-amp control, which outputs a control current Is according to the magnitude of the output voltage V ₁ via the diode D ₇ , and the main transformer 1' is turned OFF.
When no electromotive force is generated in the secondary winding L ₂ in the state,
The control current Is is passed through the mag-amp element MA in the direction of the arrow to generate a control magnetic flux, and then when the main transformer 1' is turned on and an electromotive force is generated in the secondary winding _L2 , the mag-amp element MA The pulse width of the pulsed output voltage is controlled by delaying the timing at which the voltage rises on the output side due to the B-H loop characteristics.

In other words, when the output voltage V ₁ increases, the pulse width of the pulse voltage passing through the mag-amp element MA increases
As shown in Figure b, the pulse width is controlled to be small to lower the effective value, and when the output voltage V ₁ becomes low, the pulse width is controlled to be increased as shown in Figure a to increase the effective value. so that the output voltage V ₁ remains constant.

In this way, in order to obtain a more stable output voltage than the embodiment shown in FIG. However, since the input voltage is substantially stabilized, the burden on each stabilizing circuit is small, and the circuit can be made smaller and have lower losses.

Here, the value of each resistor and the capacitance of the capacitor constituting the coupling circuit 15 in this embodiment are set in the following range under conditions of, for example, an output of 20 W and a switching center frequency of 150 KHz.

1KΩ≦R ₃ ≦5KΩ 1KΩ≦R ₄ +VR≦5KΩ 0.01μF≦C ₃ ≦0.1μF 1000PF≦C ₄ ≦5000PF Furthermore, in this example, the saturable transformer 2 and the mag-amp element MA are made of amorphous material with excellent high frequency characteristics. By using a high-quality alloy core and using a MOS-FET capable of high-speed operation for switching element 3, it is possible to increase the switching frequency to 300KHz.
It works stably even above.

Note that if it is not necessary to make the switching frequency so high, a bipolar transistor or the like may be used as the switching element.

Further, in any of the embodiments, since the control operation is performed in principle by the magnetic response of the saturable transformer 2, the response to fluctuations is fast and stable even during high frequency operation.

Therefore, together with the simple circuit, the power supply can be miniaturized,
It is easy to reduce weight and cost.

In particular, when a mag-amp system is used to control the output of the secondary side of the main transformer, the higher the input voltage in this circuit, the higher the switching frequency. For example, the control range can be expanded according to the frequency, and the core can be made smaller accordingly.

Furthermore, the switching power supply circuits of the above embodiments are superior in the following points as compared to conventional switching power supply circuits using converters of other types.

() Although it is self-excited, it operates stably even with sudden load fluctuations and input fluctuations, is easy to start, and operates even at low voltage input. In particular, even if an inductive load such as a mag-amp element on the secondary side of the main transformer is connected, startup and oscillation operations are stable.

() The switching drive circuit including the saturable transformer absorbs a portion of the residual energy when the main transformer is turned off, reducing the burden on the snubber circuit.

() Switching drive circuits that include saturable transformers can be made smaller due to higher frequencies, and can be constructed using only passive components other than the switching elements, so they are less susceptible to external noise than other types of ICs, such as PWM control ICs. It is strong, reliable, and responds quickly.

() The primary converter part of the main transformer has fewer parts and fewer expensive active elements, so
It can be constructed at a lower cost than other self-excited oscillation circuits that have a control function.

() The coupling circuit for obtaining stable oscillation does not require particularly high-precision components, and its adjustment is extremely simple.

〔Effect of the invention〕

As explained above, the switching power supply circuit according to the present invention can configure a constant voltage power supply circuit that supports a wide range of inputs with a simple circuit, is highly stable against fluctuations in input voltage and load, and is compatible with high frequency switching frequencies. It is also possible to reduce the size, weight, and cost of the power supply.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a switching power supply circuit showing an embodiment of the present invention, FIGS. 2 to 5 are explanatory diagrams for explaining the operation of the embodiment of FIG. 1, and FIG. A circuit diagram showing another embodiment, FIG. 7 is a waveform diagram illustrating pulse width control using the mag-amp element, and FIG. 8 is an example of a conventional separately excited pulse width control (PWM) type switching power supply circuit. FIG. 9 is a circuit diagram showing an example of a conventional self-excited linking converter (RCC) type switching power supply circuit. 1, 1'...Main transformer, 2...Saturable transformer, 3...Switching element, 4...Full-wave rectifier circuit, 5-7...Output circuit, 8...Dropper type stabilization circuit, 9... ...Feedback amplifier for mag-amp control, 15...Coupling circuit, L ₁ ...Primary winding, L ₂
~ _L4 ...Secondary winding, Lb...Feedback winding, _C3 ...First capacitor, _R3 ...First resistor, _C4 ...Second capacitor, _R4 , VR... Second resistor, D ₄ ...
…diode.

Claims (1)

[Claims] 1. An output voltage is obtained by rectifying and smoothing the voltage generated on the secondary side of the main transformer by intermittent current flowing through the primary side of the main transformer according to the input voltage using a switching element. The switching power supply circuit includes a feedback winding in the main transformer, a saturable transformer, and a coupling circuit that couples the primary side of the saturable transformer to the feedback winding, and the output of the feedback winding. A self-oscillation feedback circuit for controlling the switching element is formed on the secondary side of the saturable transformer, and the coupling circuit is formed into a series circuit of a parallel circuit of a first capacitor and a first resistor, and a diode. A switching power supply circuit characterized in that it is configured by connecting a second capacitor and a second resistor in parallel. 2. The switching power supply circuit according to claim 1, wherein at least a part of the second resistor is a variable resistor.