JPS6321425B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a DC-DC converter.

A conventional DC-DC converter is shown in Figure 1. This DC-DC converter is a unidirectional drive type for the transformer 3, and when the switching transistor 4 is turned on, the voltage E of the power supply 1 is applied to the transformer 3 and simultaneously sent to the output side. The excitation energy stored in the inductance L is released (reset) when the winding voltage of the transformer 3 is reversed while the switching transistor 4 is off, causing current to flow through the flow path shown at i in Figure 1. The input power source 1 is then regenerated (charged). Here, the secondary side terminal of transformer 3
The smoothing circuit 6 disposed between AB and CD is similar to the capacitor shown in FIG. 2 in terms of releasing (resetting) excitation energy.

This circuit utilizes the fact that the winding voltage of the transformer 3 is inverted while the switching transistor 4 is off to transfer the flow path to the reset diode 2 and release the accumulated excitation energy. , the inductance L of the transformer 3 is reduced in order to complete the discharge in the off period and to obtain time margin.
It is necessary to set the voltage to a small value, and as a result, the initial voltage rise in the off period becomes steep as shown in FIG. 3, which has the disadvantage of becoming a source of noise.

It is well known that spike noise in a power supply is generated by the mechanism in which the voltage variation dv/dt is transformed into a longitudinal current via the equalization capacitance between the windings of a transformer. Therefore, the smaller the voltage variation, the smaller the power supply noise. However, the conventional circuit described above has the disadvantage of generating a lot of noise due to its steep rise.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC-DC converter that achieves low noise by reducing the amount of voltage change in the off period.

In the present invention, when setting the inductance of the transformer to a large value, it is determined by the switching period of the main switch, the inductance of the transformer, the line capacitance of the transformer, the junction capacitance when a transistor is used as the main switch, etc. In relation to the free resonance state, in order to reset the excitation energy stored in the transformer when the main switch is turned off, no reset circuit is provided in the first inversion period due to the above free resonance state, and the inductance L of the transformer is increased. A state of free resonance is established, and this state is connected to the next inversion section (that is, in phase with the on section), and during the free resonance process within the next inversion section, a reverse flow path is created by a diode set in parallel with the main switch. By discharging excitation energy and regenerating (charging) the power supply, the amount of voltage change in the off section is minimized and the excitation energy is reset, thereby realizing a low-noise power supply.

The present invention will be explained in detail below with reference to embodiments shown in the drawings.

FIG. 4 shows a circuit diagram of an embodiment of the present invention.
The figure shows the terminal voltage waveform of the switch circuit and its current waveform. In FIG. 4, the switch circuit is constructed by connecting a switching transistor 4 and a diode 2 in parallel, with flow paths in opposite directions being ensured, and switching is performed by connecting a transformer 3 and a power supply 1 in series. Power is transmitted to the output side by switching on transistor 4. When the switching transistor 4 is switched off, the sixth inductance is determined by the inductance L of the transformer 3, which is set to be relatively large, and the stray capacitance such as the line capacitance of the transformer 3 and the junction capacitance of the switching transistor 3.
The diode 2 passes through the first inversion section with the free resonance showing the gentle voltage change shown in the figure, and is in phase with the on section at the next inversion, and the induced voltage of the transformer 3 is larger than the voltage of the power supply 1. The reset current operates to charge the power supply 1. The waveforms of the terminal voltage e and current i of the switch circuit at that time are shown in FIG. According to experimental confirmation by the inventors, the total stray capacitance of the circuit shown in Figure 4 is 275 _P F.
It was confirmed that the inductance of transformer 3 could be increased to 230mH.
Obtain a free resonant frequency of 20KHz. Therefore, if the off period of the switching transistor 4 is 30 μsec, the above first inversion period will be 25 μsec.
The next inversion section can be in phase with the on section. Note that the terminals F, G, and
The switch circuit with H is the FET shown in Figure 5,
Of course, the same operation can be obtained even with a diode inherent in the structure.

As explained in detail above, according to the present invention, the amount of voltage change during switching is 1/10 compared to the conventional example.
Therefore, the amount of spike-like noise that appears in the input/output can be reduced to about 1/100, and the DC-DC converter according to the present invention has a great effect as a power supply in the field of digital transmission where noise is averse. It is something that can be demonstrated.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional DC-DC converter; FIG. 2 is another circuit diagram of the smoothing circuit of FIG. 1; and FIG. 3 is a waveform diagram for explaining the operation of FIG. 4 is a circuit diagram of one embodiment of the DC-DC converter according to the present invention, FIG. 5 is a circuit diagram of another embodiment of the switch circuit used in FIG. 4, and FIG. 6 is a circuit diagram of another embodiment of the switch circuit used in FIG. FIG. 4 is a waveform diagram for explaining the operation of the embodiment. 1: power supply, 2: diode, 3: transformer,
4: Switching transistor.

Claims (1)

[Claims] 1. In a DC-DC converter that drives the transformer in one direction, in order to reset the energy accumulated in the transformer when the switch is turned on, a distribution means is provided to regenerate it to an external power source or to dissipate it in an external element, and to reduce the inductance of the transformer. and that the direction of the voltage induced in the windings of the transformer in the distribution section by the free resonance frequency based on the line capacitance of the transformer is configured to be in phase with the direction when the switch conducts and transmits energy to the output. Characteristic DC-DC converter.