JPH0340078Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a ringing chain type DC-DC converter (DC-DC converter). [Prior Art] Generally, the above-mentioned DC-DC converter includes a self-excited transistor oscillation circuit that oscillates when an input DC voltage is applied, which includes a switching transistor and an oscillation transformer, and a self-exciting transistor oscillation circuit that oscillates when an input DC voltage is applied, and a It consists of a rectifier circuit provided. FIG. 2 shows an example of a circuit of a conventional DC-DC converter of this type, in which one end of the primary winding N1 of an oscillation transformer T is connected to the collector of a switching transistor Q. The other end of N1 is connected to one end of the secondary winding N2 of the transformer T and to the DC positive voltage input terminal E. The other end of the secondary winding N2 is connected to the base of the transistor Q via the base current limiting resistor R1, and a bias resistor R2 is connected in parallel between the base and the emitter of the transistor Q. Connection point is DC negative voltage input terminal F
It is connected to the. The self-excited transistor oscillation circuit 1 is configured as described above, and a DC power source Eb is connected between the input terminals E and F. Further, the anode of a diode D is connected to the connection point between the primary winding N1 of the oscillation transformer T and the collector of the transistor Q, and a smoothing capacitor C1 is connected between the cathode of the diode and the emitter of the transistor Q. , a rectifier circuit 2 is configured. A DC positive voltage output terminal U and a DC negative voltage output terminal V are drawn out from both ends of the capacitor C1, and a load L is connected between these output terminals U and V. In the above DC-DC converter, the DC current flowing through the primary winding N1 of the oscillation transformer T is intermittently caused by the on/off operation caused by a predetermined change in the base potential of the switching transistor Q in the self-excited transistor oscillation circuit 1. be done. The excitation energy accumulated in the primary winding N1 of the transformer T during the period when the transistor Q is on charges the capacitor C1 via the diode D during the period when the transistor Q is off. As described above, the DC output voltage Eo obtained by converting the input DC voltage from the DC power source Eb is obtained from both ends of the capacitor C1 and is supplied to the load L. In the circuit operation described above, the diode D is biased alternately in the forward and reverse directions due to the rapid voltage changes accompanying the on/off operation of the transistor Q, resulting in high-frequency ringing caused by the reverse recovery time of its function. Noise occurs. This noise component is fed back to the base of the transistor Q via the transformer T, and the noise is further amplified. Figure 3 shows an example of the output voltage waveform of the oscillation circuit 1 accompanied by this noise. In the figure, Vp is the maximum amplitude of the ringing noise, t1 is the switching period, t2 is the period of the noise component, and t3 is the is the noise duration. Normally, the period t2 of the noise component is considerably shorter than the switching period t1. The above-mentioned high-frequency noise components are radiated into the air and adversely affect radio interference and the operation of electronic devices that handle minute signals, so measures to prevent this type of noise are required. Conventionally, as a measure to prevent this noise, a surge absorber consisting of a series-connected circuit of a resistor and a capacitor was connected in parallel to the transistor Q or the diode D. This surge absorber reduces the rise and fall speed of the current flowing through transistor Q or diode D through the action of a capacitor, and consumes the energy charged in the capacitor through a series resistor, thereby suppressing ringing noise components. It acts as an absorber. [Problem that the invention attempts to solve] However, the above method does not solve the problem of switching
Since the surge absorber is connected to a location with a large amount of energy, there is a drawback that power loss increases and DC conversion efficiency decreases. An object of the present invention is to provide a DC-DC converter that prevents ringing noise from occurring without reducing DC conversion efficiency. [Means for Solving the Problems] The configuration of the present invention for solving the above problems will be described below with reference to FIG. 1 showing a circuit diagram of an embodiment. In the DC-DC converter of the present invention, the current in the primary winding N1 of the oscillation transformer T is interrupted by the switching transistor Q, which is turned on and off by a predetermined change in the base potential, and the current in the primary winding N1 of the oscillation transformer T is a self-excited transistor oscillator circuit 1 configured such that a signal from line N2 is fed back to the base of the switching transistor Q, and oscillates at a predetermined frequency when an input DC voltage is applied;
In a DC-DC converter equipped with a rectifier circuit 2 provided on the output side of the self-excited transistor oscillation circuit, a filter circuit is connected between the secondary winding N2 of the oscillation transformer T and the base of the switching transistor Q. A low-pass filter 3 consisting of a resistor R3 and a capacitor C2 is provided, and a base current limiting resistor R1 is connected between the connection point between the filter resistor R3 and the capacitor C2 and the base. [Operation of the device] In the DC-DC converter configured as described above, the ringing noise component fed back from the rectifier circuit 2 side to the base side of the switching transistor Q via the oscillation transformer T is passed through the low-pass filter 3. It is erased by . As a result, the transistor Q can be effectively driven only by the regular switching signal, and the ringing noise output is significantly reduced. Furthermore, since the low-pass filter 3 is inserted at a location where switching energy is relatively small, power loss is small and DC conversion efficiency does not decrease. In particular, in this invention, the connection point between the filter resistor of the low-pass filter and the capacitor is not directly connected to the base of the transistor, but is connected via the base current limiting resistor, so that the capacitance of the low-pass filter capacitor is It is possible to eliminate ringing noise components without increasing the value. Note that if a base current limiting resistor is not used, the capacitance of the low-pass filter capacitor must be increased, and if the capacitance of this capacitor is increased, the waveform of the fundamental oscillation component will be blunted and the DC conversion efficiency will decrease. do. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. In FIG. 1, the same parts as in the circuit diagram of FIG. 2 are given the same reference numerals. That is, 1 is a self-excited transistor oscillation circuit, Q is a switching transistor that is turned on and off by a predetermined change in base potential, T is an oscillation transformer, R1 is a base current limiting resistor, and R2 is a bias resistor. R3 is a filter resistor inserted and connected between the secondary winding N2 of the oscillation transformer T and the above-mentioned resistor R1, and C2 is a capacitor connected in parallel to the series connection circuit of the above-mentioned resistors R1 and R2. A low-pass filter 3 is constituted by a resistor R3 and a capacitor C2.
2 is a rectifier circuit similar to that shown in FIG. 2, which is composed of a diode D and a capacitor C1. In this embodiment, the ringing noise component fed back from the diode side to the base side of the switching transistor Q via the oscillation transformer T is eliminated by the low-pass filter 3.
As a result, transistor Q is driven only by the regular switching signal, and the output of ringing noise is significantly reduced. Table 1 shows numerical examples of this noise reduction, and compares and contrasts cases with and without the low-pass filter 3 regarding the maximum noise amplitude Vp and noise duration t3 mentioned above.

[Table] As seen in the above table, the reduction in noise in this example is clear. [Effect of the invention] As mentioned above, according to the invention, switching
In a DC-DC converter equipped with a self-excited transistor oscillation circuit including a transistor and an oscillating thyristor, a low-pass transistor is connected between the secondary winding of the oscillating transformer and the base of the switching transistor.
Since the filter is inserted, the noise component fed back from the output side of the transistor oscillation circuit to the base side of the switching transistor via the oscillation transformer can be eliminated by the low-pass filter. Thereby, ringing noise included in the output of the DC-DC converter can be significantly reduced. In addition, the above low-pass
Since the switching energy at the insertion point of the filter is relatively small, the power loss due to the filter is small and the DC conversion efficiency does not decrease. In particular, in the present invention, the connection point between the filter resistor and the capacitor of the low-pass filter is not directly connected to the base of the transistor, but is connected via the base current limiting resistor.
This has the advantage of being able to eliminate ringing noise components without increasing the capacitance of the filter capacitor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a conventional DC-DC converter,
FIG. 3 is a waveform diagram showing an example of the output voltage waveform of the self-excited oscillation circuit in the converter. 1...Self-excited transistor oscillation circuit, Q...Switching transistor, T...Oscillation transformer,
2... Rectifier circuit, 3... Low pass filter.

Claims (1)

[Claims for Utility Model Registration] The current in the primary winding of the oscillation transformer is interrupted by a switching transistor that operates on and off in response to a predetermined change in base potential, and the signal from the secondary winding of the oscillation transformer is A self-exciting transistor oscillator circuit configured to feed back to the base of the switching transistor and oscillating at a predetermined frequency when an input DC voltage is applied; In the DC-DC converter equipped with a rectifier circuit, a low-pass filter consisting of a filter resistor and a capacitor is provided between the secondary winding of the oscillation transformer and the base of the switching transistor, and the filter resistor A DC-DC converter, characterized in that a base current limiting resistor is connected between a connection point between the capacitor and the base and the base.