JPH0638549A - Dc-ac converter for power supply - Google Patents

Abstract

PURPOSE:To contrive improvement of safety, low cost and improvement of conversion efficiency by providing the positive feedback loop of a pair of main transistors of half-bridge construction and a transformer with first timer for delay and second timer for determining oscillation frequency. CONSTITUTION:A self-excited type DC-AC converter composed of the feedback loop of a pair of transistors 14a, 14b constituting a half bridge being a main circuit and a transformer T4, and of switching means 12a, 12b, first timers 11a, 11b for delaying and conducting these switching means and second timers 13a, 13b for interrupting the switching means 12a, 12b and determining oscillation frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input DC power supply, a main transistor pair provided with a diode, a capacitor pair, a primary winding of a transformer having a predetermined feedback winding and a secondary output winding. DC-AC (direct current-alternating current) converter for power supply, which is configured as a half bridge, and in particular, a self-excited vibration power supply DC-AC for increasing conversion efficiency by effectively driving the main transistor pair. Regarding the configuration of the converter.

[0002]

2. Description of the Related Art A DC-AC converter for a power supply, for example, rectifies a direct current obtained by rectifying a commercial power supply by using a small transformer to switch at a high frequency of several tens of KHz or more on the primary side and discharges high frequency power on the secondary side. It has become. Many proposals have been made for several decades as a method of converting this high frequency power into a direct current and using it as a power source for electronic devices.

FIG. 9 is a diagram showing an example of a DC-AC converter for a power supply according to a conventional technique (CQ Publishing "Switching Regulator Design Know-how" issued in March 1990 1
Page 45, Figure 5-9). In this figure, Vp and GND1 represent the input DC power supply terminal and its voltage. GND1 also represents the ground on the primary side. Reference numeral 1 is a drive circuit which oscillates at a predetermined frequency and emits outputs 1a and 1b having opposite phases as shown in FIGS. Reference numerals 2a and 2b are main transistor pairs provided with diodes 13a and 13b. 4a and 4b are voltage Vp
Is a pair of capacitors that divides into two. T3 is a transformer having a primary winding L31, an auxiliary power supply winding L32, and an output winding L33. The drive circuit 1 receives power from the input Vp at the time of startup,
After a certain time, it is supplied from the auxiliary power supply winding L32. The main transistor pair 2a and 2b, the capacitor pair 4a and 4b, and the winding L31 form a half bridge. CL indicates a center line.

With this configuration, the transformers T1 and T2 output 1a.
And 1b are level-converted and the main transistor pair is alternately energized with a dead time as shown in FIGS. 10 (a) and 10 (b). The dead time is set by the main transistor pair 2
This is to prevent the a and 2b from conducting at the same time and short-circuiting the input power source to destroy it. In Fig. 10 (c), the current flows through the winding L31 +
-I1 triangular wave exciting current. This is the case when there is no load on winding L33. When there is a load, the current is + -I2, which is a combination of the excitation current and the load current, as shown in FIG.

By the way, the exciting current also flows through the diodes 13a and 13b and is fed back to the input power source so that most of the loss does not occur. Therefore, the conversion unit having a half-bridge structure, which is a well-known main circuit, has high conversion efficiency. However, the conventional technique of FIG. 9 requires a complicated drive circuit 1 and two transformers for level conversion in order to provide a dead time. The method of providing the drive circuit 1 having a predetermined oscillation frequency outside is called an external excitation type.

The above is the embodiment of the DC-AC converter for power supply according to the prior art.

[0007]

However, although the above-mentioned conventional technique has a good conversion efficiency in the half bridge of the main circuit known to the public, it has a complicated drive circuit for timing generation and two transformers. There is a problem that efficiency deteriorates. In addition, there is a problem that the cost is increased due to the addition of extra components by the separately excited method.

The present invention has been made in view of these problems, and an object thereof is to improve the total conversion efficiency by reducing the number of constituent elements as compared with the self-excited type including the half bridge of the main circuit. Another object is to provide a DC-AC converter for a power supply which has a reduced cost.

[0009]

In order to solve such a problem, the power supply DC-AC converter of the present invention has a main transistor pair provided with a diode for an input DC power source, a capacitor pair, and a predetermined pair. A half bridge is composed of a feedback winding and a primary winding of a transformer having a secondary output winding, and switch means for applying a predetermined feedback winding feedback voltage to a control electrode of a main transistor pair, It is composed of a first timer that gives a signal for delaying the feedback voltage of a predetermined feedback winding to the switch means, and a second timer that short-circuits the output end of the switch means to determine the oscillation frequency. It is characterized by reducing the number of components in a DC-AC converter for a power source that emits, and increasing the overall conversion efficiency and reducing the cost.

Further, by making the setting of the time constant of the first timer approximately inversely proportional to the feedback voltage (proportional to the voltage of the input power supply), the high frequency voltage of the secondary output winding is rectified and smoothed regardless of the input power supply voltage. It has a characteristic that it is converted to a stable DC voltage.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing specific blocks and circuit configurations in the present invention.

The pair of transistors forming the half bridge are N-type field effect transistors 14a and 14b.
In addition, the transformer T4 has a primary winding L41 and feedback windings Lb1 and Lb.
It was changed to one having an output winding not shown in FIG. The black dots on the winding indicate the winding direction. Reference numerals 15a and 15b are internal parasitic diodes. The reason why the field effect transistor is used is that this diode can be apparently omitted, and high speed switching can be performed because there is no storage time unlike a bipolar transistor. However, parasitic capacitances 16a and 16b between the gate and the source,
Although not shown, since the parasitic capacitance between the drain and the gate and between the drain and the source is as large as 1500 pF, it is necessary to reduce the driving impedance. However, the use of bipolar transistors as in the past does not change the gist of the present invention. Resistors 17a and 17b, 18a and 18b
Is to divide the input DC power supply voltage and apply a bias voltage to the gates of the transistor pairs 14a and 14b to ensure the self-startability of the system. These resistors are made sufficiently large so that the time constants of the parasitic capacitances 16a and 16b are selected sufficiently larger than the oscillation period of the system. This is because it does not affect the oscillation frequency of the system after starting. The induced voltage in the feedback windings Lb1 and Lb2 is connected to the constant voltage sources 10a and 10b, the switches 12a and 12b, and the first timers 11a and 11b by the lines Fa and Fb, and the constant voltage sources 10a and 10b generate the constant voltage first. Timer 11a
And 11b and the second timers 13a and 13b, respectively. The first timers 11a and 11b delay the above-mentioned induced voltage (dead time) and give a control signal to the switches 12a and 12b. The switches 12a and 12b have a low impedance (speed up the charging of the parasitic capacitance 16) and the transistor pair 14a.
A conduction voltage is alternately applied to the gates of and 14b. When one of the transistor pairs 14a and 14b becomes conductive, the induced voltage of + V and, on the contrary, -V of the corresponding lines Fa and Fb is maintained by the positive feedback. This is cut off by the second timers 13a and 13b, and since the oscillation frequency of the system operates at a constant voltage, it is stably determined regardless of the input DC voltage. When the second timer 13 operates, the output of the switch 12a or 12b is short-circuited, and one of the transistor pairs which has been conducting is turned to the non-conducting state. The magnetic flux of the transformer T4 also decreases, and induced voltages of opposite polarities are generated in the lines Lb1 and Lb2. The reverse polarity induced voltage delays the first timer to make the other transistor pair 14 conductive. In FIG. 1, by repeating this, high frequency power having a stable frequency is emitted from the secondary winding.

Next, specific examples of the constant voltage source 10, the switch 12, the first timer and the second timer shown in FIG. 1 will be described with reference to FIG.
The constant voltage source 10 is a resistor 30 and a Zener connected in the opposite direction.
It is composed of diodes 31a and 31b. FIGS. 3A and 3B show the voltage + -V generated in the winding Lb and the output + -Vz of the constant voltage source 10.

The first timer 11 has a resistor 33 which determines a time constant.
And a capacitor 34, a transistor 32, and a diode 35. The base-emitter saturation voltage of the transistor 32 and the forward voltage of the diode 35 are set to the same V
Assuming th, the base-emitter voltage of the transistor 32 becomes a + -Vth trapezoidal wave in FIG. The + Vth portion shows the conduction period of the transistor 32. The sloped part is related to the time constant and becomes the dead time. FIG. 3D shows one ON / OFF state of the transistor pair 14. The second timer is composed of a resistor 41, a capacitor 42, a transistor 40, and a diode 43 that determine the time constant. It has the same configuration as the first timer, but has a longer time constant and determines the half cycle of the oscillation period. The base voltage of the transistor 40 is represented by a triangular wave having a peak at + V in FIG. 3 (e), and FIG. 3 (f) shows a short ON period. This ON
The period is short because the induced voltage is inverted by the positive feedback as soon as the transistor 40 is turned on. During this ON period, the transistor 40 discharges the parasitic capacitance 16. The switch 12 includes a transistor 36 and this transistor 36
And the current limiting resistance 3
9 and a base resistor 37. The current limiting resistor 39 is about several hundred ohms and the transistor 40 of the second timer.
Protect. FIG. 1 of the present invention thus configured emits high frequency power having a stable frequency. The power loss is a charge and discharge loss of the parasitic capacitance 16, a switching loss of the transistor pair 14, an iron loss and a copper loss of the transformer T4, and they are insignificant. Depending on the oscillating frequency and the electric power handled, conversion efficiency of 95% or more can be obtained, and if it is about several hundred watts, there is no need to consider heat dissipation. 80% at best with conventional technology
It was a stand. The time constants of the first and second timers are
Assuming t1 and t2, the result is as follows.

T1 = C1R1 * ln ((Vz + Vth) / (Vz-Vth)) t2 = C2R2 * ln ((Vz + Vth) / (Vz-Vth)) where C1, C2 and R1, R2 are It is the value of the capacitor and resistance of the constant circuit. In addition, ln represents the natural logarithm.

Next, another embodiment of the configuration of the first timer will be described with reference to FIG. In order to control the transistor 58, the time constant capacitor 59 is charged by the constant current source 50, and discharging is performed by switching with the base resistor 61 when the induced voltage in the transistor 60 becomes negative. Since the feedback voltage of the feedback winding Lb is proportional to the input DC voltage, if the current of the output 50b of the constant current source 50 is increased / decreased roughly inversely proportional to the feedback voltage, the dead time is modulated almost inversely proportional to the input DC voltage. To be done. By doing so, a substantially stable DC voltage can be obtained by passing the induced voltage of the secondary winding through the rectifying / smoothing circuit regardless of the input DC voltage. Further, in this case, there is a feature that the circuit load on the secondary side for further stabilizing this becomes easy.

The constitution of the constant current source 50 is such that a stable zener voltage is applied to the base of the transistor 51 by the zener diode 52 and the resistor 54, and the zener voltage and the emitter resistor 53 cause a constant current to the collector of the transistor 51. Take out. When the base of the transistor 55 is used as an input terminal and the feedback voltage is divided and connected thereto by the resistors 56 and 57, the current flowing through the transistor 55 increases in proportion to the feedback voltage. This causes the current at output 50 to decrease roughly inversely. Therefore, the time (dead time) until the capacitor 58 is charged and the transistor 58 becomes conductive becomes substantially inversely long. Since the second timer does not change, the oscillation frequency is constant, so the conduction duty of the transistor pair 14 changes. As a result, even if the input voltage changes, the product of the voltage of the output winding and the time product becomes substantially constant, and the above-described effect can be obtained. The diode 58 is the feedback winding L.
It is provided to protect the constant current source 50 when the feedback voltage of b becomes negative. Further, the modulation method corresponding to the input voltage of the first timer may modulate the voltage applied to the resistance of the time constant circuit (not shown).

FIG. 5 shows the operation waveforms of FIG.
(A) shows the change in the feedback voltage when the DC input fluctuates. In FIG. 4, the solid line waveform is the feedback voltage V1, and the dotted line waveform is V2.
Corresponding to. (B) shows the base voltage waveform of the transistor 58, which is not a negative voltage in this case. (C) shows the ON / OFF state of the transistor 58. (D) is the voltage waveform when the output winding is loaded (+ -Vs1, + -Vs
2) represents the timing. When there is no load, it becomes a square wave with almost zero state. This is because the exciting current is a triangular wave even if there is a dead time.

Next, another embodiment of the present invention in which the transistor pair 14 is made complementary in FIG. 6 will be described. 14a is an N-type transistor and 14b is a P-type transistor, and only one feedback winding Lb of the transformer T5 is required.
The circuit configuration is also substantially symmetrical to the center line CL. L51 is a primary winding of the transformer T5, and L52 is an output winding. The resistor 70 and the zener diodes 71a and 71b forming the constant voltage source may be a set. Switch 12a is the same as in FIG. 4, but switch 12b changes the polarity of the transistor and the orientation of the diode. The transistors 73a and 73b and 76a and 76b forming the first timer and the second timer are also made complementary, and the base electrode is also made common to simplify the time constant circuit.
The time constant circuit is composed of a resistor 74 and a capacitor 75, and a resistor 77 and a capacitor 78. Complementary transistors 79a and 79b having base electrodes commonly connected and a resistor 80 are not necessarily required, but OF of the transistor pair 14 is not necessary.
Make the person doing F more certain.

FIG. 7 shows the operation waveforms of FIG.
A of (a) shows the base waveform of the first timer, and B shows the base waveform of the second timer. In this case, transistor pair 7
The base-emitter saturation voltage Vth of 3,76 is the clamp voltage. Dotted lines AA and BA in the figure represent curves that become the target voltage + -Vz when not clamped. 7B and 7C show the ON / OFF states of the transistor pair 14 with dead time.

Next, another embodiment of the present invention, in which a constant current source as shown in FIG. 4 is applied to the first timer shown in FIG. 6, will be described with reference to FIG.

The constant current source 90 emits a constant current in both positive and negative directions, and a zener diodes 91a and 91b, and a constant voltage in both directions generated by the resistor 92 are connected to all electrodes of complementary transistors 93a and 93b. Lead to the base 94
With and, a constant current is taken out from the collector side of the transistor pair 93. This constant current is shunted with the charging current to the complementary transistor pair of 95a and 95b, which uses the feedback voltage divided by the resistors 96 and 97 as the base input, and the capacitor 75,
The effect similar to that of FIG. 4 is obtained by making the output voltage almost inversely proportional to the input DC voltage.

Although the embodiment of the present invention has been described above, various modifications can be considered in details.

[0024]

According to the configuration of the present invention described above, the feedback voltage of the transformer is delayed by the first timer to drive the main circuit of the half bridge, and the oscillation frequency can be determined by the second timer. The effect of making it possible to configure a DC-AC converter for power supply that is inexpensive and has high conversion efficiency is great.

[Brief description of drawings]

FIG. 1 is a diagram showing specific blocks and circuits according to an embodiment of the present invention.

FIG. 2 is a diagram showing a specific circuit of the block of FIG.

FIG. 3 is a diagram showing operating waveforms in FIGS. 1 and 2;

FIG. 4 is a diagram showing another configuration circuit of the first timer of FIG.

5 is a diagram showing operation waveforms in FIG. 4;

FIG. 6 is a diagram showing another embodiment of the present invention.

FIG. 7 is a diagram showing operating waveforms in FIG. 6;

FIG. 8 is a diagram showing another configuration circuit of the first timer applied to FIG. 7.

FIG. 9 is a diagram showing an example of a conventional technique.

FIG. 10 is a diagram showing operation waveforms in FIG. 9.

[Explanation of symbols]

4a, 4b, 34, 42, 59, 75, 78 ... Capacitors 2a, 2b, 14a, 14b, 32, 36, 40, 51, 5
5, 58, 73a, 73b, 76a, 76b, 79a, 79
b, 93a, 93b, 95a, 95b ... Transistors 3a, 3b, 15a, 15b, 35, 38, 43, 58 ... Diodes 31a, 31b, 52, 71a, 71b, 91a, 91b ... Zener diodes 10a, 10b ... Voltage source 11a, 11b ... First timer 13a, 13b ... Second timer 12a, 12b ... Switch T1, T2, T3, T4, T5 ... Transformer Vp ... DC input terminal or voltage GND1 ... Grounding on primary side CL ... Center line Fa , Fb ... Feedback line L31, L32, L33, L41, Lb1, Lb2, Lb ... Transformer winding

Claims (2)

[Claims] 1. A half bridge is composed of a main transistor pair provided with a diode, a capacitor pair, and a primary winding of a transformer having a predetermined feedback winding and a secondary output winding for an input DC power supply. DC-AC for power supply
In a (DC-AC) converter, switch means for applying a feedback voltage of the predetermined feedback winding to the control electrode of the main transistor pair, and a signal for delaying the feedback voltage of the predetermined feedback winding are sent to the switch means. A DC-AC for a power supply, which is configured by a first timer for giving and a second timer for determining an oscillation frequency by short-circuiting the output end of the switch means, and discharging high frequency power from the secondary output winding.
converter. 2. The power supply according to claim 1, wherein the time constant of the first timer is set to be substantially inversely proportional to the feedback voltage (which is proportional to the voltage of the input power supply). DC-AC converter.