JPH02131361A - Switching regulator - Google Patents

Abstract

PURPOSE:To enable designing an apparatus easily by comparing the signal of an output detector circuit and a primary side current signal and by controlling the ON time of a switching part according to the comparison results. CONSTITUTION:A control circuit 40 voltage-compares a primary side current signal (f) and a voltage control signal (d) and controls the ON the OFF of a switching transistor 12 on the basis of results of the voltage comparison. When, e.g., a load becomes lighter, a DC voltage (b) rises and the voltage control signal (d) lowers accordingly. That is, a threshold vale for the primary side current signal (f) lowers and the ON time of the switching transistor 12 shortens in the control circuit 40. This is directed to lowering of the DC (b) and even if the load varies as a result, the DC voltage (b) is restored to the original state quickly. Thus, even an apparatus with different electric characteristics can be designed easily.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a switching regulator used as a DC stabilized power supply.

Conventional technology> Switching regulators, which have the advantages of small size, light weight, and high efficiency, are becoming more and more important because they match the trend of the times of lighter, thinner, shorter, and smaller sizes. Among them, RCC (
Although the ringing choke converter type is suitable for small capacity, it requires a relatively small number of parts and is widely used as an inexpensive switching power supply.

The circuit configuration of a conventional RCC switching regulator will be explained with reference to FIG.

The ringing choke converter 1o, which is a main component of the switching regulator, is a self-help DC-DC converter circuit that generates a DC voltage b by varying the voltage level of a DC voltage a generated by a rectifier circuit (not shown). hand,
During the half cycle in which the switching transistor 12 is in the ON state, the energy supplied from the primary side is stored in the converter transformer 14, while in the subsequent half cycle in which the switching transistor 12 is in the OFF state, the energy stored in the converter transformer 14 is transferred to the rectifier circuit 15. The voltage is transferred to the electrolytic capacitor 152, and a DC voltage b is generated across the electrolytic capacitor 152 during this switching process.

Next, the basic principle of switching by the switching transistor 12 will be explained. First, when the DC voltage a is applied, a base current flows to the switching transistor 12 through the starting resistor 13 on the N1 winding side and the base resistor 16 on the N2 winding side of the converter transformer 14, and this quickly turns on. However, due to the inductance of the converter transformer 14, the primary current C that is the object of control of the switching transistor 12 does not rise instantaneously but increases like a ramp function. Then, at the same time as the switching transistor 12 is turned on, the converter transformer 1
While the positive base current generated on the g side of the N2 winding of No. 4 flows, when the primary side current C increases to a certain extent, the switching transistor 12 switches from the on state to the off state due to the characteristics of the transistor. When the switching transistor 12 is turned off, the converter transformer 1
The energy stored in 4 is released to the rectifier circuit side, and at the timing when this energy release ends, the switching transistor 12 becomes forward biased again and turns on, and the same operation is repeated thereafter.
A switching transistor 12 is configured to perform switching. This is the basic principle by which the ringing choke converter 10 automatically oscillates, but in order to prevent the DC voltage b from fluctuating greatly even when the load condition changes, the output connected to the output stage of the ringing choke converter 10 is The on period of the switching transistor 12 is adjusted by the detection circuit 20 and the like.

The output detection circuit 20 is a circuit consisting of a resistor 21, a resistor 22, a shunt regulator 23, and a photocoupler 24. The DC voltage b is divided by the resistor 21 and the resistor 22, and the divided voltage h is compared and controlled by the shunt regulator 23. , the photocoupler 24 is operated by controlled current. A DC voltage generated by rectifying the voltage generated in the N2 winding in a rectifier circuit 61 is applied to the secondary side of this photocoupler 24, and a switching transistor 12 is applied to the output stage of this photocoupler 24. A transistor 62 is connected to bypass the base current flowing to the base side of the transistor. That is, the photocoupler 24 and the transistor 62 are operated according to the magnitude of the DC voltage b, and the base current of the switching transistor 12 is adjusted to decrease, thereby making the on-period variable. This stabilizes the DC voltage b. Moreover, the primary side current C is detected by a shunt resistor 17 connected to the emitter side of the switching transistor 12, and if this indicates an abnormality, the switching transistor 12 is forcibly turned off, and the switching transistor 12 is prevented from overcurrent.
etc. are designed to protect them.

Problems to be Solved by the Invention> However, in the case of the above conventional example, a configuration is adopted in which the base current of the switching transistor 12 is adjusted by a transistor circuit including the transistor 62, etc.; Since each component is intricately intertwined and has a structure that performs a predetermined operation as a whole, when determining component constants at the design stage, repeated trials and errors such as experiments are required for each switching regulator. There is a drawback that it is indispensable. Furthermore, since there are large variations in the component parts, particularly in the current amplification factors of each transistor, there is a drawback that variations are likely to occur in the switching regulator itself, and adjustment is difficult. Moreover, if you take this variation into account when designing, you will have no choice but to use switching transistors with a somewhat large capacity.
Another drawback is that the cost of the Swiss regulator is high. In other words, these drawbacks can be a huge problem for manufacturers who must timely manufacture and develop switching regulators with different electrical characteristics such as current capacity and output voltage.

The present invention was devised in view of the above circumstances, and an object of the present invention is to provide a switching regulator that can be easily designed even if the electrical characteristics such as current capacity and output voltage are different. shall be.

<Means for Solving the Problems> A switching regulator according to the present invention includes a switching section, a starting circuit, and a converter transformer, and includes a ringing choke converter that converts input direct current into alternating current, and an output of the ringing choke converter. a primary-side current sensing circuit that generates a primary-side current signal having the same waveform as the primary-side current based on the primary-side or secondary-side coil voltage of the converter transformer; and a detection of the output detection circuit. It has a comparator that compares the signal with the primary side current signal, and a control circuit that varies the on time of the switching section according to the comparison result.

<Operation> The on-period of the switching section is made variable according to the output of the converter transformer and the magnitude of the primary current.

Embodiment> Hereinafter, an embodiment of a switching regulator according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the switching regulator, and FIG. 2 is a timing chart showing voltage waveforms of the main parts to explain the operation of the switching regulator.

A DC voltage a generated by a rectifier circuit (not shown) is applied to a ringing choke converter 10, which is a main component of a switching regulator.

The ringing choke converter 10 is composed of an electrolytic capacitor 11, a switching transistor 12 (switching section), a converter transformer 14, a rectifier circuit 15, etc., and generates a DC voltage b by varying the voltage level of the energized DC voltage a. This is an automatic DC-DC converter circuit. To explain in more detail, the switching transistor 12 connected to the N1 winding on the primary side of the converter transformer l4 is a switching element that controls the primary side current C of the converter transformer 14, and is turned on by a control circuit 40 to be described later. Although the period is regulated, switching is performed using the same principle as before. And in this switching process,
During the half cycle in which the switching transistor l2 is in the on state, the energy supplied from the primary side is stored in the converter transformer 14, while in the subsequent half cycle in which the switching transistor l2 is in the off state, the energy stored in the converter transformer 14 is transferred to the rectifier circuit 15. The voltage is transferred to the electrolytic capacitor 152, so that a DC voltage b is generated across the electrolytic capacitor 152. The base current k of the switching transistor 12 is supplied via a starting resistor 13 (starting circuit) connected to the N1 winding side and a base resistor 16 connected to the N3 winding side of the converter transformer 14. It has become. Further, the rectifier circuit 15 is connected to the N3 winding on the secondary side of the converter transformer 14, as described above, and the primary side current sensing circuit 30, which will be described later, is connected to the N2 winding. The secondary coil voltage e generated in the N2 winding is (N2/Nl) times the primary voltage h applied to the N1 winding due to the winding ratio.

An output detection circuit 20 for detecting DC voltage b is connected to the output stage of the ringing choke converter 10 having such a configuration.

The output detection circuit 20 is a circuit consisting of a resistor 21, a resistor 22, a shunt regulator 23, a photocoupler 24, etc., and the shunt regulator 23 compares and controls the divided voltage obtained by dividing the DC voltage b by the resistors 21 and 22. At the same time, the photocoupler 24 is operated by a controlled current,
As a result, the configuration is such that the magnitude of the DC voltage b is detected and outputted as the voltage control signal d. However, the voltage control signal d is an inverted output signal of the voltage value of the DC voltage b.

On the other hand, the primary current sensing circuit 30 includes an integrating circuit 31 that has a resistor 311 and a capacitor 312 and integrates the secondary coil voltage e, a transistor 321 and a diode 3.
22 and a reset circuit 32 for discharging the charge of the capacitor 312.
It is designed to generate a primary side current signal f having the same waveform as . That is, instead of directly detecting the primary current C flowing through the ringing choke converter 10, the primary current signal f is generated using the secondary coil voltage e as an input, so that the primary current C is indirectly detected. It has become. This primary side current signal f is guided to a control circuit 40 (such a primary side current sensing circuit 30
(The principle behind the ability to generate the primary current signal f having the same waveform as the primary current C will be described later).

The control circuit 40 mainly includes a comparator 41 that compares the voltages of the primary current signal f and the voltage control signal d, and is configured to forcibly turn off the switching transistor 12 based on the result of this voltage comparison. ing. In more detail, the output stage of the primary current sensing circuit 30 is connected to the positive input of the comparator 41, while the output stage of the output detection circuit 20 and a resistor 42 are connected to the negative input of the comparator 41. , 43, 44, and a Zener diode 45 are connected to a reference voltage generation circuit.

The reference voltage d' generated by this reference voltage generation circuit depends on the permissible upper limit value of the primary side current C since the maximum value of the voltage control signal d is regulated, but this will be described later. In addition, the output side of the comparator 41 is connected to a resistor 4.
6. It is pulled up to the secondary voltage e via the diode 47 and is also connected to the base side of the transistor 49. That is, the switching state of the transistor 49 changes according to the control signal g generated by the comparator 41, thereby bypassing the base current k flowing through the N2 winding of the converter transformer 14 and the pace resistor 16. It has become. Note that 47 shown in the figure is a protection diode when the transistor 49 is in a reverse bias state.

Next, the principle by which the primary side current C can be indirectly detected by the primary side current sensing circuit 30 will be explained with reference to FIGS. 1 and 2.
This will be explained with reference to the figures.

First, the DC voltage a is the ringing choke converter 10
When the switching transistor 12 is energized and a starting current j flows through the base of the switching transistor 12, the switching transistor 1
2 is turned on. At this time, the N1 winding of the converter transformer 14 is energized with ■1 as the primary voltage h, and the primary current C of the ramp wave flows. That is,
When the switching transistor 12 is on, the primary current C increases with a time function expressed as (Vl/L)t. After that, when the energy of the converter transformer 14 stored during the period when the switching transistor 12 is in the on state is discharged to the rectifier circuit side, the primary side voltage h becomes -■1 and the switching transistor 12 becomes reverse biased and turned off. state, and the primary side current C becomes zero. However, v1 is the voltage across the electrolytic capacitor 11, and L is the inductance of the N1 winding of the converter transformer 14.

Further, the primary current sensing circuit 30 is supplied with a secondary coil voltage e which is (N2/Nl) times the primary voltage h, and when the switching transistor l2 is on, the integrating circuit 3l Capacitor 31 in
2 increases with a time function expressed as (v2/R-C)t, while the polarity of the secondary coil voltage e is reversed when the switching transistor 12 is in the off state. As a result, the transistor 321 of the reset circuit 32 is turned on and the charge in the capacitor 312 is discharged, and as a result, the primary current signal f, which is the voltage across the capacitor 312, has the same waveform as the primary current C. becomes. However, v2 is the peak value of the secondary coil voltage e, R is the resistance value of the resistor 311, C is the capacitance value of the capacitor 312, and (v2/R - C)
Assume that there is a relationship of ccV 1/L.

Next, the functions of the switching regulator configured as described above will be explained.

First, during the period To, the primary current C at a normal level commensurate with the load size is flowing, and at the timing when the primary current signal f becomes larger than the voltage control signal d, the control circuit 4o The generated control signal g
becomes active, and in the sense that the on-period of the switching transistor 12 is regulated, the maximum level of the primary current C is stabilized together with the DC voltage b.

It is also assumed that during the period T1, the load condition changes and becomes almost a short circuit, so that the output voltage b becomes almost zero and the primary current C becomes abnormally large.

Then, as the output voltage b decreases, the voltage control signal d tries to rise, but is regulated by the reference voltage d' and saturates, while the primary current signal r becomes thicker and thicker. Then, at the timing when the primary side current signal f becomes larger than the reference voltage d", that is, at time t1, the control signal g becomes active and the switching transistor 12 is forcibly turned off. In other words, the DC voltage b
Even if the primary current C increases due to a short circuit, its maximum level is limited to a value commensurate with the magnitude of the reference voltage d', thereby protecting the switching transistor 12 and the like from overcurrent. That is, in the control circuit 40, the reference voltage generation circuit including the Zener diode 45, resistors 43, 44, etc. is a circuit necessary for determining the maximum permissible level of the primary side current C.

Thereafter, when the load state returns to the original state in period T2, the same control as in period To is performed, but the load state becomes lighter during period T3. Then, the DC voltage b increases and the voltage control signal d decreases accordingly. In other words, the threshold value for the primary current signal f in the control circuit 40 decreases considerably, and the switching transistor 1
The on time of 2 is shortened. This is a direction in which the DC voltage b is lowered, and as a result, even if the load condition changes, the DC voltage b is quickly returned to its original value.

Effects of the Invention> As described above, in the case of the switching regulator according to the present invention, the component constants can be easily determined at the design stage, and the switching regulator can be easily determined even if the switching regulator has different electrical characteristics such as current capacity and output voltage. However, it can be easily designed.

Moreover, the circuit configuration is such that variations in component parts do not have a large effect on the function of suppressing the primary side current within a predetermined range, so even if inexpensive components are used, the switching regulator There is no large variation in itself, and adjustments can be easily made.

In particular, when outputting the same capacitance as the conventional method, a switching transistor with a small capacitance can be used. Therefore, there is a great advantage that an inexpensive and high-performance switching regulator can be obtained.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams for explaining one embodiment of the switching regulator according to the present invention.
The figure is a circuit configuration diagram of a switching regulator, Figure 2 is a timing chart showing voltage waveforms of main parts to explain the operation of a switching regulator, and Figure 3 is a first diagram to explain a conventional switching regulator. FIG. 12・ ・ 13・ ・ 14・ ・ 15・ ・ 20・ ・ 30・ ・ 31・ ・ 32・ ・ 40・ ・ a, b C φ Conflict d ・ ・ e ・ f ・ ・ g ゛ ゛ ゛゜Switching transistor starting resistance converter Transformer rectifier circuit output detection circuit Primary current sensing circuit Integrator circuit Reset circuit Control circuit...DC voltage Primary current Voltage control signal Secondary coil voltage Primary current signal Control signal Patent applicant Tabuchi Electric Co., Ltd.

Claims (1)

[Claims] (1) A ringing choke converter that includes a switching section, a starting circuit, and a converter transformer and converts input DC into AC, an output detection circuit that detects the output of the ringing choke converter, and a primary or secondary side of the converter transformer. It includes a primary current sensing circuit that generates a primary current signal having the same waveform as the primary current based on the secondary coil voltage, and a comparator that compares the detection signal of the output detection circuit and the primary current signal. A switching regulator comprising: a control circuit that varies the on-time of the switching section according to the comparison result.