JPH0239186B2 - CHOKURYUDENATSUHENKANKAIRO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an improvement of a DC voltage conversion circuit.

[Prior art and its problems]

For example, when powering an electronic device such as a telephone exchange from a DC power source such as a battery, a DC voltage conversion circuit converts the DC power supply voltage to the required DC voltage before powering the electronic device. .

FIG. 1 is a circuit diagram showing a conventional example of such a DC voltage conversion circuit. In the figure, 1 is a DC power supply,
2 is a first transistor, 3 and 4 are diodes, 5 is a second transistor, 6 is a transformer,
6a is its primary winding, 6b is its secondary winding, 7,
8 is a rectifier diode, 9 is a reactor, 1
0 is a capacitor, and 11 is a load.

This circuit operates so that during the period when each of transistors 2 and 5 are both conducting, the primary winding 6 of transformer 6 is
The voltage of the DC power supply 1 is applied to a, and the voltage induced in the secondary winding 6b of the transformer 6 is rectified by the diode 7, and then smoothed by the reactor 9 and capacitor 10. This is to obtain the required power supply voltage. Note that during the period when both transistors 2 and 5 are in a non-conducting state, the magnetization state of the transformer 6 is changed by feeding back the excitation current of the transformer 6 to the DC power supply 1 via the diodes 3 and 4. Perform a reset.

In such conventional DC voltage conversion circuits, there is a period in which current and voltage cross each other when a transistor is turned on or turned off, which causes switching loss. This switching loss is influenced by the turn-on time or turn-off time of the transistor.

When using a transistor with a large current capacity in order to increase the output capacity of a DC voltage conversion circuit, generally only transistors with long turn-on and turn-off times can be obtained, which increases switching loss and reduces heat generation. As a result, the cooling fins become larger, causing problems such as the inability to make the DC voltage conversion circuit smaller and lighter, or the conversion efficiency decreasing.

In addition, the operating frequency of this type of DC voltage conversion circuit is limited by the characteristics of the transistor, such as turn-on time, storage time, and fall time. However, it has the disadvantage that it cannot operate at high frequencies.

[Purpose of the invention]

The present invention has been made in order to solve the problems and drawbacks of the prior art as described above, and therefore, an object of the present invention is to reduce switching loss, reduce size, reduce weight, and improve efficiency. The object of the present invention is to provide a DC voltage conversion circuit that is capable of increasing the operating frequency.

[Key points of the invention]

The main point of the present invention is that in the conventional DC voltage conversion circuit as shown in FIG.
The third transistor is connected in parallel to perform transient switching.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing one embodiment of the present invention. In this figure, the same elements as in FIG. 1 are given the same reference numerals.

The circuit configuration shown in FIG. 2 differs from that shown in FIG.
2 is connected in parallel to the transistor 5.

Next, the circuit operation will be explained. First, transistor 2
When a drive signal is supplied to the base of the transistor 2 by means not shown, the transistor 2 starts conducting. After transistor 2 is fully conductive, transistor 1
Applying the same drive signal to the base of 2, the voltage of DC power source 1 is applied to the primary winding 6a of transformer 6 through transistors 2 and 12, thereby
The voltage generated in the next winding 6b is rectified by a diode 7, smoothed through a smoothing reactor 9 and a capacitor 10, and then supplied to a load 11.

At this time, a current that transiently increases flows through transistors 2 and 12, but the voltage applied to the transistor elements is shared by transistor 12, which becomes conductive after transistor 2, so that the switching voltage, which is the product of current and voltage, is Loss will mainly occur in transistor 12.

Immediately after transistor 12 becomes completely conductive, when a drive signal is applied to the base of transistor 5, the current flowing through transistor 12 is transferred to transistor 5, which has a lower on-voltage. Hereinafter, power is supplied to the load 11 using a circuit including a DC power supply 1, a transistor 2, a transformer 6, and a transistor 5.

Next, when the power supply from the DC power supply 1 to the load 11 is cut off, the transistor 5 is cut off first, and immediately after the current transfers to the transistor 12, the transistor 12 is cut off. Switching is performed by After the transistor 12 is disconnected, it is necessary to immediately disconnect the transistor 2 to prevent the excitation current of the transformer 6 from flowing through the diode 3 and the transistor 2.

After the transistor 2 is turned off, the excitation current of the transformer 6 is fed back to the DC power supply 1 through the diodes 3 and 4, and the magnetization state of the transformer 6 is reset.

In FIG. 3, transistors 2 and 5 in FIG.
and 12 drive signal waveforms, and FIG. 4 shows a drive signal generation circuit for realizing the drive signal waveforms shown in FIG. 3, respectively.

Regarding FIG. 3, there is no need to explain it any further.

In FIG. 4, 20 is a pulse oscillator, 21-
23 each is a monostable multivibrator (mono multi), 32 and 33 are each an integrating circuit, 34
36 are buffer circuits, and 37 to 39 are pulse transformers.

FIG. 5 is a waveform diagram of various signals in FIG. 4.

The circuit operation will be explained with reference to FIGS. 4 and 5. The output pulse I of the oscillator 20 is inputted to the monostable multivibrators 21, 22 and 23 as a common trigger pulse. The output pulse widths T ₁ , T ₂ and T ₃ of each of the monostable multivibrators 21, 22 and 23 are adjusted by R and C of the time constant circuit in each vibrator so that T ₁ > T ₂ > T ₃ .
Let's decide.

The respective outputs of the monostable multivibrators 22 and 23 are input to integration circuits 32 and 33, respectively, and are waveform-shaped. The time constants R ₁ and C ₁ of the integrating circuit 32 are set smaller than the time constants R ₂ and C ₂ of the integrating circuit 33, and the buffer circuit 3 has a threshold level Th.
4, 35, and 36 respectively, the fifth
The drive signal waveforms shown in Figures B, C, and D are obtained from the output sides of the pulse transformers 37, 38, and 39. It goes without saying that these drive signal waveforms are the same as the signal waveforms shown in FIG.

In the embodiment shown in FIG. 2, the transistor 12, which operates at high speed and has a high on-state voltage, may be connected in parallel to the transistor 2 instead of the transistor 5. In this case, the order of conduction and disconnection is as follows. , it is needless to explain that transistors 5 and 2 are interchangeable.

〔Effect of the invention〕

As explained above, high-voltage, high-power transistors generally have long storage times and fall times, and the losses caused by these are large, which reduces switching efficiency. However, it was difficult to reduce the weight. Generally, high-power transistors that switch quickly have a high saturation voltage and a large main current loss.

Therefore, in the present invention, a high-speed transistor is connected in parallel to a high-power transistor, and transient switching is performed by this transistor, and the high-power transistor does not perform switching, but allows the main current to flow, thereby solving the problem. Ivy.

Therefore, the high power transistor used here may be a transistor with slow switching and low saturation voltage. In addition, high-speed transistors connected in parallel only need to perform transient switching;
Since no main current flows, a transistor with small collector loss is sufficient. The faster the switching speed of the high-speed transistors connected in parallel, the smaller the collector loss, and the smaller the transistor capacity is required. FET and SIT are high-speed transistors.
etc. can also be used.

In this way, switching loss can be reduced by flowing the switching current through the high-speed transistor and the main current through the large-current transistor, thereby reducing the size of the heat dissipation fin and improving efficiency. The present invention is particularly effective for highly efficient, compact, and lightweight DC conversion circuits that perform large-capacity power conversion.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional example of a DC voltage conversion circuit, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a waveform diagram showing drive signal waveforms of each transistor in FIG. 2. 4 is a circuit diagram showing a drive signal generation circuit for generating the drive waveform shown in FIG. 3, and FIG. 5 is a waveform diagram showing waveforms of various signals in FIG. 4. Explanation of symbols, 1... DC power supply, 2... First transistor, 3, 4... Diode, 5... Second transistor, 6... Transformer, 7, 8... Rectifier diode, 9... Reactor , 10... Capacitor, 11... Load, 12... Third transistor (FET, SIT, etc.), 20... Oscillator, 21, 22,
23...monostable monomulti, 32,33...integrator circuit, 34,35,36...buffer circuit, 3
7, 38, 39...Pulse transformer.

Claims (1)

[Claims] 1. The primary winding of the transformer is connected in series between the emitter of the first transistor and the collector of the second transistor, and the collector of the first transistor and the emitter of the second transistor are connected in series. A DC power supply is connected between the emitter of the first transistor and the second transistor.
A diode is connected between the emitter of the transistor and between the collector of the first transistor and the collector of the second transistor so that the current direction is opposite in polarity to that of each of the transistors. When conducts,
In the DC voltage conversion circuit which obtains an output voltage by rectifying and smoothing the voltage generated in the secondary winding of the transformer, a third transistor having a faster switching speed than each of the first and second transistors is connected to the first transistor; Second
are connected in parallel to one of the transistors, and when turned on, the transistor to which the third transistor is not connected in parallel, the third transistor, and the transistor to which the third transistor is connected in parallel. When the transistor is turned off, the third transistor is connected in parallel, the third transistor is turned on, and the third transistor is not connected in parallel in that order. 1. A direct current voltage conversion circuit characterized in that the third transistor performs transient switching by controlling conduction and disconnection of each transistor so as to turn on and off.