JPH0223105Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of the invention] The invention relates to a so-called DC-DC converter that applies a DC voltage and obtains a desired DC voltage. The present invention relates to a flyback type DC-DC converter that outputs a voltage to the secondary side during the opening operation of the switching means.

[Technical background of the invention and its problems] Figure 1 shows the circuit configuration of a conventional DC-DC converter (separately excited type). In the figure, V _io is an input DC voltage, and this input DC voltage V _io is connected to the primary winding N ₁ of the transformer T via a switching means such as a transistor _Tr .
is connected so as to apply it. Further, the control means 1 outputs a control signal to control the opening/closing operation (switching) of the transistor T _r , and the frequency of the control signal is changed depending on the output signal of the error amplification means AMP. ing. When the transistor T _r starts opening and closing operations in response to a control signal of a predetermined frequency output from the control means 1, an input DC voltage V _io is intermittently applied to the primary winding N ₁ . By intermittent application of this input DC voltage V _io ,
A voltage develops in the secondary winding _N2 of the transformer T. This 2
The voltage generated in the next winding _N2 is rectified by a rectifying means such as a diode _D1 , smoothed by a smoothing means such as a capacitor _C1 , and then applied to a load _Ld as a DC voltage _V0 . . Further, this DC voltage V ₀ is compared with a reference voltage _VR in the error amplification means AMP, and the comparison result is inputted to the control means 1. The control means 1 controls the transistor according to the output signal of the error amplification means AMP.
By changing the switching operation frequency of T _r , the output DC voltage
Feedback control is performed to stabilize V ₀ at a desired voltage value. Error amplifier in this way
The AMP and control means 1 are collectively referred to as feedback control means. The above configuration, particularly the polarity relationship between the primary and secondary windings of the transformer and the connection relationship of the rectifying and smoothing means consisting of diodes and capacitors, are well-known as those of the flyback type.

Incidentally, the output voltage V ₀ is not actually a complete DC voltage, but includes a ripple component as shown in FIG. 2b. As is clear from the waveform of the ripple component included in this output voltage V ₀ when the transistor T _r is turned on (conducting state), the voltage drops when the transistor T _{r is turned on (conducting state), as is clear from the comparison with figure a, which shows the opening/closing timing of the transistor T r} . It has a waveform.

However, if a waveform that falls when the transistor T _r is ON is applied to the error amplifying means AMP, the control means 1 which controls the opening and closing operation of the transistor T _r in accordance with the output of the error amplifying means AMP is There is a risk of unstable operation and abnormal oscillation. In such a case, stabilization of the output voltage V ₀ cannot be expected at all, which has been a problem in conventional DC-DC converters.

The present invention has been developed in view of the above circumstances, and an object of the present invention is to provide a DC-DC converter that can perform stable operation regardless of the ripple component contained in the output voltage.

[Summary of the invention] The outline of the invention for achieving the above object is to control the voltage applied to the primary winding of a transformer intermittently by the switching operation of switching means, and to control the voltage applied to the primary winding of the transformer to In a flyback type DC-DC converter that outputs the voltage generated in the line, compares this voltage with a reference voltage, and controls the opening/closing operation of the switching means according to the comparison result to obtain a stable output. excitation voltage detection means connected between the means and ground and configured to detect a voltage proportional to the current flowing through the primary winding based on the voltage applied intermittently to the primary winding of the transformer; One end of the winding is grounded via the excitation voltage detection means.

[Embodiment of the invention] An embodiment of the invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram showing the configuration of the DC-DC converter according to the present invention. Components having the same functions as those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. The DC-DC converter according to the present invention is different from the conventional DC-DC converter shown in _{FIG .}
For example, a resistor _R1 is provided as an excitation voltage detection means for detecting a voltage proportional _to and a point where one end of the secondary winding _N2 of the transformer T (the side to which the diode _D1 is not connected) is grounded via the voltage detection means R1. The rest of the configuration is almost the same as that in FIG.

Hereinafter, the operation of the DC-DC converter according to the present invention will be explained with reference to FIG. 4. When the transistor T _r starts opening and closing operations in response to a control signal of a predetermined frequency output from the control means 1, an input DC voltage V _io is intermittently applied to the primary winding N ₁ of the transformer T. Due to the intermittent application of this DC voltage V _io (this is called the "excitation voltage"), an excitation current I _c flows through the primary winding N ₁ of the transformer T, and this excitation current I _c causes a voltage to be applied across the resistor R 1 . (part of the excitation voltage) is generated. The waveform of the voltage generated across this resistor R1 is shown in FIG. 4c. The waveform of the voltage generated across this resistor R1 is, as is clear from comparison with Figure a, which shows the opening/closing timing of the transistor _Tr , as follows:
The waveform is such that the voltage gradually increases when the transistor T _r is turned on. Therefore, in this way, a voltage (pulse voltage) with a waveform in which the voltage increases when the transistor T _r is turned on is applied to one end of the capacitor C ₁ , and this capacitor C ₁ causes the transformer T
When the voltage generated in the secondary winding of is smoothed after being rectified by the diode _D1 , the waveform of the ripple component included in the DC output voltage _V0 becomes the waveform shown in FIG. 4d. This means that the waveform shown in Figure 4c is added to the waveform shown in Figure 2b, and the waveform shown in Figure 4c is added to the waveform shown in _Figure 2b.
The voltage of the secondary winding not only rises only when it is OFF, but also continues to rise even when the transistor T _r is turned ON. As a result, the waveform becomes such that the voltage gradually increases both when the transistor T _r is turned on and off.

In this way, if the waveform of the ripple component included in the output voltage V ₀ is a waveform in which the voltage gradually increases both when the transistor _Tr is turned on and off, then when focusing only on this ripple component, the control means 1 , which acts in the direction of lowering the switching frequency of the transistor _Tr , so that feedback control for obtaining stable output can be performed stably.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, but can be modified and implemented as appropriate within the scope of the gist of the present invention.

For example, in the above embodiment, one capacitor _C1 was used as the smoothing means, but a plurality of capacitors and chiyoke coils (or resistors) were used, and π
A type smoothing circuit may also be considered. Even in such a case, by applying a part of the excitation voltage to one end of the capacitor, the same effects as in the embodiment described above can be achieved.

In addition, the DC-DC converter includes an oscillation winding N ₀ of the transformer T and a resistor R ₂ , as shown in FIG.
There is also a so-called self-excited DC-DC converter in which an oscillation circuit is configured based on a capacitor C ₂ and the oscillation frequency is controlled by an oscillation control means (CNT) 2. Even in such a DC-DC converter, if the voltage generated across the resistor R1, which is the excitation voltage detecting means provided on the emitter side of the transistor T _r , is applied to one end of the capacitor _C1 , the same effect as in the above embodiment can be achieved. It is possible to achieve the following effects.

[Effects of the invention] According to the invention described above, it is possible to easily change the waveform of the ripple component included in the output voltage, thereby eliminating abnormalities in the feedback control means that have been a problem in conventional DC-DC converters. Since oscillation can be prevented, it is possible to provide a DC-DC converter that can operate stably regardless of the waveform of the ripple component included in the output voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a conventional DC-DC converter, FIG. 2 is a waveform diagram for explaining the operation of the DC-DC converter shown in FIG. 1, and FIG. 3 is a DC-DC converter according to the present invention. A circuit diagram showing the configuration of the DC converter, Fig. 4 is a waveform diagram to explain the action of the DC-DC converter shown in Fig. 3, and Fig. 5 shows a modification of the DC-DC converter shown in Fig. 3. It is a circuit diagram. 1...Control means, 2...Oscillation control means (CNT), _Vio ...Input voltage, _Tr ...Transistor (switching means), T...Transformer, _N1 ...Primary winding,
N ₂ ... Secondary winding, N ₀ ... Oscillation winding, R1 ...
Resistor (excitation voltage detection means), C ₁ ... capacitor (smoothing means), V _R ... reference voltage, AMP ... error amplification means, D ₁ ... rectification means (diode).

Claims (1)

[Scope of utility model registration request] The voltage applied to the primary winding of the transformer is controlled intermittently by the switching operation of the switching means, and the voltage applied to the primary winding of the transformer is
In a flyback type DC-DC converter that outputs the voltage generated in the next winding, compares this voltage with a reference voltage, and controls the opening/closing operation of the switching means according to the comparison result to obtain a stable output, Excitation voltage detection means is connected between the switching means and the ground and detects a voltage proportional to the current flowing through the primary winding of the transformer based on the voltage applied intermittently to the primary winding of the transformer, A DC-DC converter, characterized in that one end of the secondary winding is grounded via the excitation voltage detection means.