JPH0210668B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an isolated switching regulator that combines a chopper circuit and an inverter circuit.

[Prior art] Conventionally, this type of switching regulator has a sixth
The devices shown in Figures 9 through 9 were known. Of these, the one in Figure 6 is the DC power supply 1
A series circuit of the primary winding 3 of the transformer 2 and the switching transistor 4 is connected between both ends of the transformer 2, and
A series circuit of a damping resistor 5 and a capacitor 6 is coupled in parallel with the primary winding 3, and a secondary winding 7 is connected in parallel with the primary winding 3.
A load 10 is coupled through a rectifier diode 8 and a smoothing capacitor 9, and the so-called 1
It is a stone on/off type.

In the one shown in FIG. 7, a series circuit consisting of a reset winding 11 and a diode 12, which are magnetically coupled to a transformer 2, is coupled to both ends of the DC power supply 1, and the device 8 shown in FIG. 1 is connected to the secondary side. , 9, a flywheel diode 13 and a chiyoke coil 14 are added, and it is a so-called one-stone on/off type.

The one in Fig. 8 has the primary winding 3 of the transformer 2,
The collectors of the transistors 15 and 16, which are opened and closed alternately, are coupled together, and the base and emitter of the transistors 15 and 16 are coupled via a diode 18 to an auxiliary winding 17 wound around the transformer 2. A starting resistor 23 is coupled between them, and
The secondary winding 7 includes two rectifier diodes 8, 1.
9. A transistor 20 is coupled via a capacitor 9, the base of this transistor 20 is grounded via a Zener diode 21, and the emitter
A resistor 22 is inserted between the bases, and the emitter is coupled to the load 10 via a capacitor 32, which is a so-called one-transformer inverter series regulator connected in series.

In the circuit shown in FIG. 9, a switching transistor 24, a flywheel diode 27, an inductor 28, and a capacitor 29 forming a chopper circuit are inserted between the DC power supply 1 and the transformer 2 in the circuit shown in FIG. A pulse width control circuit (hereinafter referred to as PWM) 25 and an oscillator 26 are connected to the base of the transistor 24, and the PWM 25 is formed by connecting the connection point of resistors 30 and 31, and is a so-called chopper type one-transformer converter. be.

[Problems to be solved by the invention] The so-called one-stone on/off type shown in Fig. 6 is
Since there is only one transistor 4, transformer 2
poor core utilization and large core shape;
The damping resistor 5 generates a large amount of heat, so if it is housed in a small case, the reliability will be lowered, and since the transformer 2 requires an insulating space distance, there is a limit to miniaturization.

Since the one shown in Fig. 7 is an on/off type, it has the advantage of being smaller because the core shape is half that of the on/off type shown in Fig. 6, but since it is one stone,
The reset winding 11 is required to be almost the same as the primary winding 3 and requires space, the rectifier circuit on the secondary side requires a chain coil 14, and the transformer 2 requires an insulating space distance. There were drawbacks such as a limit to miniaturization.

The so-called series regulator using a one-transformer inverter shown in Fig. 8 is extremely complex and expensive because if it has multiple outputs, the number of regulators on the secondary side of transformer 2 must be increased accordingly. There were flaws.

The so-called tipper type one-transformer converter shown in Figure 9 can easily handle multiple outputs, does not require a tipper coil on the output side, reducing costs, and has a high core utilization rate for transformer 2, making it compact. It has advantages such as being able to However, there was a drawback that there was a lot of noise because the frequencies of the tipper and the inverter were different.

The present invention aims to solve all of the above-mentioned problems.

[Means for solving the problem] A chopper circuit and a self-excited inverter circuit are sequentially coupled to the DC power supply, and the transformer of the inverter circuit provides insulation from the load coupled to the secondary winding. In the switching regulator,
A control winding for detecting changes in the output from the inverter circuit is wound around the transformer, and this control winding is coupled to the chopper circuit via a waveform shaping circuit, a pulse width conversion circuit, and a drive circuit. It is something.

[Operation] When the chopper circuit is turned on, one of the transistors forming the inverter circuit is turned on, and current flows through this transistor. When this current flows and saturates the transformer, one transistor is turned off and the other transistor is turned on. In this way, the two transistors are turned on and off alternately. The on and off times at this time correspond to the output of the inverter circuit, so
Compare this on/off detection waveform with the reference waveform,
The pulse width is converted and the pulse width converted signal is sent to the chopper circuit via the drive circuit to control the opening/closing time of the chopper circuit.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. Note that the same parts as in FIGS. 6 to 9 are given the same reference numerals.

FIG. 1 is a block diagram showing the basic principle of the present invention. In this figure, 1 is a DC power supply, and a chopper circuit 33 and a self-excited inverter circuit 34 are sequentially coupled to this DC power supply 1. A control winding 35 is coupled to the inverter transformer 2 of this inverter circuit 34, and this control winding 35 is coupled to one input side of a pulse width conversion circuit 37 via a waveform shaping circuit 36, and the other input side is coupled to the inverter transformer 2 of the inverter circuit 34. A reference voltage circuit 38 is coupled to the side. This pulse width conversion circuit 37 is coupled to the chopper circuit 33 via a drive circuit 39.

The secondary winding 7 of the inverter transformer 2 is coupled to a load 10 via rectifying diodes 8 and 19 and a smoothing capacitor 9.

FIG. 2 shows the specific electric circuit of FIG. 1. In FIG. 2, the chopper circuit 33 is composed of a switching transistor 24, a flywheel diode 27, an inductor 28, and a smoothing capacitor 29. The inverter circuit 34 has two switching transistors 15 and 16 coupled in a push-pull type, and also includes an inverter transformer 2 and a starting resistor 23.
The inverter transformer 2 also includes a primary winding 3, a secondary winding 7, a base winding 17, and a control winding 35. This control winding 35 is 3
It is coupled to the negative side input terminal of a pulse width conversion circuit 37 consisting of an operational amplifier via a waveform shaping circuit 36 consisting of a diode 40 and a capacitor 41 for shaping a comparison voltage waveform such as a square wave, and also serves as the reference voltage circuit. The cathode side of the Zener diode 38 is coupled to the positive input terminal. The output side of this pulse width conversion circuit 37 is coupled to the base of a transistor 39 as a drive circuit, the collector of this transistor 39 is coupled to the base of the switching transistor 24 via a resistor 42, and the emitter is connected to the DC power source 1. is connected to the negative side of Note that 43 is a dropper resistor for driving the pulse width conversion circuit 37.

Next, the operation of the present invention will be explained.

When the DC power supply 1 is turned on, a constant reference voltage Vz is obtained by the resistor 43 and the Zener diode 38, and the positive input side of the pulse width conversion circuit 37 is fixed by this voltage. At this point, the inverter circuit 34 is not oscillating, so the negative input side of the pulse width conversion circuit 37 is 0V, so the output of this pulse width conversion circuit 37 appears and turns on the transistor 39 as a drive circuit. However, when this transistor 39 is turned on, the transistor 24 of the chopper circuit 33 is also turned on. This transistor 2
4 turns on, the starting resistor 23 and the base winding 17
Current flows to the bases of transistors 15 and 16 via. When one of them turns on, the other base windings become reverse voltage and turn off. It operates as a push-pull inverter circuit representing a so-called Royer circuit.

For example, if the transistor 15 is turned on first, then the base winding 17 allows current to flow so that the transistor 15 is saturated, and the current flows until the transformer 2 is saturated (Fig. 4a,
f).

When transformer 2 saturates, the collector current of transistor 15 begins to decrease, creating a reverse voltage in base winding 17 and turning on the other transistor 16. (Figure 4 b, f). In this way, the saturation of the transformer 2 is used to turn on and off the transistors 15 and 16 alternately.

A high frequency pulse is generated in the secondary winding 7 of the transformer 2 by turning on and off the transistors 15 and 16, and this is rectified and smoothed to obtain a DC output voltage Eo.

Here, the control winding 35 is connected to the solid line A ₁ in FIG.
As shown by the dotted line _A2 , a pulse that changes according to input fluctuations and load fluctuations is obtained, and by controlling the chopper circuit 33 using this pulse, a constant output voltage Eo can be obtained. This will be explained in more detail with reference to FIG.

The solid line in FIG. 3 obtained by the control winding 35
A pulse like _A1 is generated by the waveform shaping circuit 36.
It becomes a triangular wave like a ₁ .

Now, assuming that the voltage Ei of the input power supply 1 has increased, the pulse generated in the control winding 35 will also increase as indicated by the dotted line in Figure 3.
The waveform rises as shown in A ₂ , and therefore the peak value of the triangular wave also rises as shown in a ₂ . Therefore the zener voltage
The intersection with Vz also changes from point X ₁ to point X ₂ .
That is, as the input voltage Ei increases, the output pulse width of the pulse width conversion circuit 37 narrows from W ₁ to W ₂ , so the on period of the transistor 39 and the on period of the transistor 24 also become narrow. Therefore, the output voltage of the chopper circuit 33 decreases, and the output voltage Eo is kept constant. Conversely, when the input voltage Ei decreases, the pulse width becomes wider, increasing the output of the chopper circuit 33 and keeping the output voltage Eo constant.

Next, FIG. 5 shows another embodiment of the present invention. That is, in the example of FIG. 2, a PNP type transistor is used as the transistor 24 of the chopper circuit 33, but in the example of FIG. 5, an NPN type transistor 24 is used. In this case, a resistor 44 is inserted between the emitter and the base, and the reference voltage Vz from the Zener diode 38 is supplied to the negative input side of the pulse width conversion circuit 37, and the voltage to be compared is supplied to the positive input side. The operation in such a configuration is substantially the same as in the case of FIG.

[Effects of the Invention] Since the present invention is configured as described above, it has the following effects.

(1) By using the self-excited oscillation of the inverter circuit as the oscillator of the chopper circuit, the frequency becomes the same and noise generation can be prevented.

(2) Cost reduction is possible because an oscillator for the chopper circuit is not required.

(3) For example, in the case of a television receiver, conventionally the pulse of a flyback transformer was used as the oscillator of the chopper circuit, making the entire system complicated, but with the present invention, the system can be integrated only with the power supply section. It is possible to downsize the device.

(4) Since the saturated inverter transformer is used, or the method of driving the base current of the transistor allows inversion even if the core is unsaturated, it is not necessary to use the EI iron core for transformer insulation. For example, a ring core can be used without using a ring core, and insulation can be achieved in a compact form.

(5) Even if there are multiple output systems, only the rectifier circuits need to be connected, so the circuit configuration is simple and can be provided at low cost, with fewer failures.

(6) The circuit that controls the chopper circuit is formed by a control winding wound around a transformer, a waveform shaping circuit consisting of a diode and a capacitor, a pulse width conversion circuit consisting of an operational amplifier, and a drive circuit. , the configuration of the circuit that controls the chopper circuit can be simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the switching regulator according to the present invention, FIG. 2 is a specific electric circuit diagram of the present invention, FIG. 3 is an explanatory diagram of waveforms during pulse width conversion, and FIG. 4 5 is a specific electric circuit diagram of another example of the present invention, and FIGS. 6 and 7 are waveform diagrams of each part.
8 and 9 are electrical circuit diagrams of different examples of conventional switching regulators, respectively. 1...DC power supply, 2...Inverter transformer,
3...Primary winding, 7...Secondary winding, 8, 19...
Rectifier diode, 9...Smoothing capacitor, 1
0...Load, 24...Switching transistor, 27...Flywheel diode, 28...
...Inductor, 29 ... Smoothing capacitor, 33
... Chopper circuit, 34 ... Self-excited inverter circuit, 35 ... Control winding, 36 ... Waveform shaping circuit,
37... Pulse width conversion circuit, 38... Reference voltage circuit (Zener diode), 39... Drive circuit (transistor), 40... Diode, 41...
capacitor.

Claims (1)

[Claims] 1. In a switching regulator in which a chopper circuit and a self-excited inverter circuit are sequentially coupled to a DC power source, and the load coupled to the secondary winding is insulated by the transformer of the inverter circuit, A rectifier circuit that connects the secondary winding of the transformer and the load, a control winding that is wound around the transformer and detects changes in the output pulse of the inverter circuit, and a diode and a capacitor that detects with the control winding. a waveform shaping circuit that shapes the pulse into a triangular wave; a pulse width conversion circuit that includes an operational amplifier and compares the output of the waveform shaping circuit with a reference voltage and outputs a pulse signal controlled to a predetermined pulse width; A switching regulator comprising: a drive circuit that controls the opening/closing time of the chopper circuit based on the pulse signal output from the pulse width conversion circuit.