JPH0546191B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor inverter that operates well even under load fluctuations.

The conventional example shown in FIG. 1 will be explained. The transistor inverter shown in FIG. 1 includes an AC power supply 1, a rectifier 2 that rectifies the AC power supply voltage, an oscillation transformer 7 having a pair of input windings 7a and 7b, and a resonance capacitor 4 that resonates with the oscillation transformer 7. , a chiyoke coil 3 for smoothing the output current of the rectifier 2,
The smoothed current is passed through each input winding 7a of the oscillation transformer 7,
A pair of switching transistors 5a, 5b are alternately supplied to the switching transistor 7b, and a pair of switching transistors 5a, 5b are wound around the oscillation transformer 7 and both ends thereof are connected to each switching transistor 5a, 5b.
It is of a push-pull type with a base winding 7c connected to the base of. 6 is a starting auxiliary resistance,
7d is the output winding of the oscillation transformer 7, and 11 is the load.

The transistor inverter shown in FIG. 1 further includes the following configuration. 8 is a pair of input coils 8a,
8b. The output of the output coil 8c of the current transformer 8 is supplied as a base current to each switching transistor 5a, 5b via a rectifier 9 and each base resistor 10a, 10b.

A type of LC vibration phenomenon occurs between the input windings 7a, 7b and the resonance capacitor 4 in FIG. This effect appears on the base winding 7c, causing the switching transistors 5a and 5b to become conductive alternately. here,
Taking as an example the timing when the switching transistor 5a turns off and the switching transistor 5b turns on, the operation at that time will be discussed. At this time, the oscillating voltage of the resonance capacitor 4 goes from negative to zero, and then tries to change to positive. The voltage of the base winding 7c also shows a similar tendency,
Transistors 5a and 5b are both temporarily in a conductive state.

The oscillating voltage of the resonant capacitor 4 tends to change from zero to positive polarity in accordance with the oscillation cycle. At this time, the switching transistor 5
A pulsed current circulating around a and 5b is formed. The closed circuit through which the pulsed current flows is the resonance capacitor 4 → input coil 8a → switching transistor 5a
between the collector and base of → the base winding 7c → between the base and collector of the switching transistor 5b → the input coil 8b → the capacitor 4.

FIG. 2a shows the waveform of the collector current of the switching transistor 5a. The pulsed current seen at the end of the half wave is formed as described above when the switching transistor 5a is turned off. The voltage of the resonance capacitor 4 corresponding to this is as shown in FIG. 2b. A certain width period in which the voltage of the resonant capacitor 4 is zero occurs because the voltage across the closed circuit is clipped.

The problem with the circuit shown in FIG. 1 is that the pulsed current flows into the input coils 8a and 8b of the current transformer 8.
The next step is to supply a type of base current to the switching transistor, for example 5a, which is to be turned off. The pulsed current is input to the input coil 8.
A and 8b flow simultaneously, and this acts to strengthen the excitation of the current transformer 8, giving an output current to its output coil 8c. Half or a portion of the current flows to the base of the switching transistor 5a to be turned off next when the voltage of the base winding 7c is low, causing a sudden increase in the base current. This is harmful because it prevents the residual carrier from disappearing in the switching transistor 5a, slows down its switching speed, and causes switching loss accompanied by heat generation.

An object of the present invention is to suppress a sudden increase in base current for a switching transistor to be turned off, and to increase the switching speed of the switching transistor.

In the present invention, a DC-DC converter is used that converts a direct current into a direct current according to its magnitude. This DC-DC converter is connected in series with a smoothing coil. The DC-DC converter transforms the smoothed current flowing through the chiyoke coil,
A direct current having a magnitude corresponding to the base current of each switching transistor is generated. This DC−DC
The output current of the converter is supplied as a base current to each of the transistors via a pair of base resistors.

The DC-DC converter is arranged in series with the choke coil and is located outside the closed circuit through which the pulsed current flows. Therefore, a sudden increase in base current for the switching transistor to be turned off is prevented.

The embodiment of FIG. 3 according to the present invention will be described below. Note that the component numbers in FIG. 1 are quoted as they are, and some of the overlapping explanations are omitted.

The transistor inverter in Figure 3 is an AC power source 1
, a rectifier 2 that rectifies the AC power supply voltage, an oscillation transformer 7 having a pair of input windings 7a and 7b, a resonance capacitor 4 that resonates with the oscillation transformer 7, and a rectifier 2 that smooths the output current of the rectifier 2. a pair of switching transistors 5a, 5b which alternately supply the smoothed current to each input winding 7a, 7b of the oscillation transformer 7; It is a push-pull type with a base winding 7c connected to the base. Reference numeral 6 indicates a starting auxiliary resistor, 7d indicates an output winding of the oscillation transformer 7, and 11 indicates a load. The above points are the same as those in FIG.

The transistor inverter shown in FIG. 3 further includes the following configuration. 12 is a DC-DC converter that converts direct current into a direct current according to its magnitude. The DC input current flowing between the input terminals 12b and 12c is transformed, and the output terminal 1
A DC output current is formed between 2a and 12b. The terminal 12b is a shared terminal that serves as an input terminal and an output terminal.

The DC-DC converter 12 is connected in series with the smoothing coil 3. Input side terminal 12
b and 12c are in series with the chiyoke coil 3, and transform the smoothing current flowing therethrough. The DC output current formed between the output side terminals 12a and 12b of the DC-DC converter 12 is
Each switching transistor 5 via 0b
a, 5b as a base current. Terminal 1
The tip of 2a is divided into two parts, one is the base resistor 10a
one switching transistor 5a via
and the other is connected to the base of the base resistor 10
It is connected to the base of the other switching transistor 5b via the transistor 5b.

As described above, the DC-DC converter 12 functions as a base current supply source for each switching transistor 5a, 5b. However, the base current is transferred to a pair of switching transistors 5
Since it does not have the function of a control signal source for selecting which of a and 5b to supply, the base winding 7c that selectively controls this cannot be omitted.

Terminals 12b, 12c of DC-DC converter 12
The larger the smoothed current flowing through, the larger the base current formed by transforming it. This feature suppresses wasteful base current during light loads, and supplies the necessary and sufficient base current during heavy loads to eliminate drive shortages. By the way, if the starting auxiliary resistor 6 that receives the output voltage (DC power supply voltage) of the rectifier 2 is also used for operation, and it alone covers all the base current required for inverter operation, the efficiency corresponding to load fluctuations will increase. This is not good because it is not only difficult to maintain normal inverter operation, but also the power loss of the starting auxiliary resistor 6 becomes excessive.

The above-mentioned pulsed current also flows in the case of the circuit shown in FIG. The path of the pulsed current that flows when the switching transistor 5a is turned off is from the resonance capacitor 4 → between the collector and base of the switching transistor 5a → the base winding 7c → between the base and collector of the switching transistor 5b →
This is a closed circuit of capacitor 4. The path of the pulsed current that flows when the switching transistor 5b is turned off is from the resonance capacitor 4 → between the collector and base of the switching transistor 5b → the base winding 7c → between the base and collector of the switching transistor 5a → when the capacitor 4 is closed. It is a circuit. The DC-DC converter 12 is outside these closed circuits and is not affected by pulsed currents. Therefore, a sudden increase in base current when pulsed current is generated is avoided.

Next, the embodiment shown in FIG. 4 will be described. This embodiment embodies the DC-DC converter 12 of the circuit shown in FIG. This circuit is partially different from the circuit shown in FIG. 3, but this is due to the fact that a chiyoke coil 3 is used as a control signal source for the DC-DC converter 12.

The DC-DC converter 12 in FIG. 4 includes a capacitor 1 connected in series to a smoothing coil 3.
3, a transistor 14 for controlling the discharge of the capacitor 13, and a resistor 15 connected between the base of the transistor 14 and the tap of the choke coil 3.
, a transformer 16 , and a diode 17 . The anode side of the diode 17 is connected to the bases of switching transistors 5a and 5b via base resistors 10a and 10b, respectively.

The transistor 14 in FIG.
It turns on and off depending on the voltage polarity. The charge in the capacitor 13 charged with the smoothing current is discharged through the primary coil 16a of the transformer 16 when the transistor 14 is turned on. At this time, electromagnetic energy is stored in the transformer 16. The accumulated electromagnetic energy of the transformer 16 is transferred to its primary coil 16a and secondary coil 1.
6b, forming a current in a closed circuit including the diode 17. This is the switching transistor 5a,
5b becomes the base current.

The waveforms in FIG. 5 are for the circuit in FIG. Of these, a is the voltage of the chiyoke coil 3, and when it becomes a negative half wave, the transistor 1
4 is turned on. b is the primary coil 1 of the transformer 16
This is the collector current of the transistor 14 that flows through the transistor 6a, and electromagnetic energy is stored in the transformer 16 by this energization. c is a current flowing through the secondary coil 16b of the transformer 16, and by this energization, the electromagnetic energy of the transformer 16 is released as a base current. The slight negative wave of c is transistor 1
When the diode 4 is turned on, opposite voltages are induced in the primary coil 16a and the secondary coil 16b, and disappear when the diode 17 returns to non-conduction. This also acts to hasten the turn-off of the switching transistor, such as 5a, which should be turned off. d is the collector current of one switching transistor 5a. A base current is intermittently supplied to each switching transistor 5a, 5b, but a continuous current flows through the entire switching transistor 5a, 5b to the choke coil 3 due to the delay in carrier disappearance of the transistor.

As described above, the present invention provides a DC-DC converter for alternating the smoothing current flowing through the smoothing coil, and supplies the output current of the DC-DC converter to each switching transistor as a base current. .

According to this, even if a pulsed current is generated when the switching transistor is turned off, the base current does not increase rapidly, so that the switching speed of the switching transistor can be increased and switching loss can be reduced.

Furthermore, since the smoothed current is transformed, it is possible to supply a base current according to the weight and weight of the load, and the power loss is lower than when the base current is directly derived from the DC power supply voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional transistor inverter, FIG. 2 is a waveform diagram thereof, FIG. 3 is a circuit diagram showing a transistor inverter according to the present invention, and FIG.
The figure is a circuit diagram showing a specific example thereof, and FIG. 5 is a waveform diagram of the circuit of FIG. 4. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Rectifier, 3... Chiyoke coil, 4... Resonance capacitor, 5a... Switching transistor, 5b... Switching transistor, 6... Starting auxiliary resistor, 7...
Oscillation transformer, 7a...Input winding, 7b...Input winding, 7c...Base winding, 7d...Output winding,
10a...Base resistance, 10b...Base resistance,
11...Load, 12...DC-DC converter, 1
3...Capacitor, 14...Transistor, 15
...Resistor, 16...Transformer, 16a...Primary coil, 16b...Secondary coil, 17...Diode.

Claims (1)

[Claims] 1. An AC power supply, a rectifier that rectifies the AC power supply voltage, an oscillation transformer having a pair of input windings, a resonance capacitor that resonates with the oscillation transformer, and a rectifier that smooths the output current of the rectifier. a pair of push-pull connected switching transistors that alternately supply the smoothed current to each input winding of the oscillation transformer; In the transistor inverter, the transistor inverter includes a DC-DC converter that transforms the smoothed current flowing through the chiyoke coil into a DC current according to the magnitude of the smoothed current, and a DC-DC converter that converts the DC current output from the DC-DC converter into the DC current that is output from the DC-DC converter. A transistor inverter comprising a pair of base resistors for supplying a base current to a switching transistor.