JP3475630B2 - Transistor inverter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited control type inverter in which a load circuit controls a switching transistor using a series current feedback transformer. 2. Description of the Related Art FIG. 2 shows a conventional transistor inverter.
This will be described below. The device shown in FIG. 2 includes a switching transistor 2, a vibration inductor 3 to which a DC power supply 1 voltage is intermittently applied via the switching transistor 2,
Vibration capacitor 4 connected in parallel with one of switching transistor 2 and vibration inductor 3
And a flywheel diode 5 anti-parallel to the switching transistor 2. The load circuit 90 is connected to both ends of the vibration inductor 3. The primary coil 61 of the saturable current feedback transformer 6 is inserted in series with the load circuit 90. A base circuit including a base-emitter junction of the switching transistor 2, a secondary coil 62 of the current feedback transformer 6, and a base capacitor 71 is provided. A charge discharging circuit (73, 74) for slowly discharging the forward polarity charge of the base capacitor 71 accumulated when a base current flows through the base circuit. 91 is a discharge lamp, 9
Reference numeral 2 denotes a ballast inductor in series with the discharge lamp 91, and 93 denotes a preheating capacitor in parallel with the discharge lamp 91. The whole of these constitutes a load circuit 90 receiving an inverter output.
72 is a base resistor, and 75 is a reverse charge preventing diode. The reverse charge blocking diode 75 allows the base capacitor 71 to store charge in the forward direction and prevents charge storage in the reverse direction. Reference numeral 73 denotes an auxiliary diode, and reference numeral 74 denotes an auxiliary resistor. Both of them constitute a charge discharging circuit (73/74). First, illustration of a starting resistor for turning on the switching transistor 2 and the like is omitted. Although the inverter operation of the device shown in FIG. 2 is well known, its description is omitted, but an upward current flows through the oscillating inductor 3 during the operation. This upward current charges the oscillation capacitor 4 to the polarity shown. When the voltage of the vibration capacitor 4 rises to a level that matches the voltage of the DC power supply 1, the upward current thereafter flows through the DC power supply 1 and the flywheel diode 5 to form a power supply return current. This is an operation of extracting excess power from the DC power supply 1 during the ON period of the switching transistor 2 and converting the excess power to the DC power supply 1 later, and has a characteristic of reactive power. [0003] Since the reactive power due to the power supply feedback current causes circuit loss, it is better to reduce the reactive power. Ideally, when the voltage of the vibration capacitor 4 matches the voltage of the DC power supply 1, the electromagnetic energy of the vibration inductor 3 becomes zero without excess or deficiency, but this is difficult. If the electromagnetic energy is excessive, reactive power is generated by the power supply return current. If the electromagnetic energy is insufficient,
The voltage of the vibration capacitor 4 is insufficient. In the latter case, when the switching transistor 2 is turned on next time, the shortage of the charge of the oscillation capacitor 4 is instantaneously charged via the switching transistor 2, resulting in an excessive switching loss of the switching transistor 2. . An object of the present invention is to reduce the power supply return current and reduce the circuit loss. According to the present invention, a primary coil of a saturable current feedback transformer is arranged at a position in series with a load circuit and also in series with a flywheel diode. The connection polarity between the secondary coil and the flywheel diode is determined such that the forward polarity charge of the base capacitor increases when a power supply return current flows through the primary coil via the flywheel diode. An embodiment of the present invention will be described with reference to FIG. Here, the symbol of FIG. 2 is diverted as it is, and redundant description is omitted as appropriate. The difference between FIG. 1 and FIG. 2 on the circuit is that the arrangement of the flywheel diode 5 is changed. Others match. In the device shown in FIG. 1, the primary coil 61 of the saturable current feedback transformer 6 is arranged at a position in series with the load circuit 90 and also in series with the flywheel diode 5. Also,
The connection polarity between the primary coil 61 and the flywheel diode 5 is set such that the forward polarity charge of the base capacitor 71 increases when a power supply return current flows through the primary coil 61 via the flywheel diode 5. Determine. The power supply return current flowing through the flywheel diode 5 is 1
Via the next coil 61. The point through the primary coil 61 is different from the device of FIG. As shown in FIG. 1, when the power supply feedback current passes through the primary coil 61, the ON period of the switching transistor 2 decreases. Hereinafter, the reason will be described. The power supply return current of the flywheel diode 5 flows through 5-61-3-1-5. The current feedback transformer 6 converts the current proportional to the power supply feedback current of the primary coil 61 to 2
The next coil 62 is formed. The current of the secondary coil 62 is 62−
The base current flows through the base circuit of 72-base-emitter junction-71-62. The base current enables the switching transistor 2 to be turned on, but does not actually turn on while the power supply feedback current is flowing. The base current accumulates a forward polarity (polarity shown) charge in the base capacitor 71. During the period, the power supply feedback current is interrupted, and the switching transistor 2 is turned on. The operating condition during the subsequent on-period is almost the same as that in the general case. The current in the load circuit 90 is converted by the current feedback transformer 6, and a base current is formed on the secondary coil 62 side. 2
Are kept in the ON state. During this ON period, the voltage of the base capacitor 71 increases, the voltage of the current feedback transformer 6 increases, and the magnetic flux of the current feedback transformer 6 also increases.
Eventually, the current feedback transformer 6 is magnetically saturated, and the ON period ends. The length of the on-period until then becomes shorter due to the influence of the power supply feedback current. When the power supply feedback current is generated in the immediately preceding OFF period, and there is the process for charging the base capacitor 71 to the forward polarity (the polarity shown), the current feedback transformer 6 at the next turn-on time is affected by the process. And the magnetic flux level in the subsequent ON period is accelerated. For this reason, the ON period is shortened. When the ON period becomes short, the electromagnetic energy stored in the oscillation inductor 3 during the ON period decreases, and the next power supply feedback current is suppressed. On the other hand, when the power supply return current is zero or small, the above-described electromagnetic energy reducing action caused by the power supply return current does not function.
For this reason, the electromagnetic energy becomes insufficient, and the vibration capacitor 4
There is no concern that the voltage is insufficient and an excessive charging current flows when the switching transistor 2 is turned on. In general, the power supply return current does not become zero, but has a characteristic of approaching zero. When the power supply feedback current becomes zero, the above-mentioned reactive power decreases, the collector current of the switching transistor 2 decreases accordingly, the on-voltage loss of the switching transistor 2 and the circuit loss therefor are reduced, and the inverter efficiency is reduced. Contribute to the improvement of According to the present invention, the primary coil is arranged at a position in series with the load circuit and also in series with the flywheel diode, and the connection polarity of the primary coil and the flywheel diode is changed to the flywheel. 1 through the diode for
The forward polarity charge of the base capacitor is increased when the power supply return current flows through the next coil. According to this, the power supply return current can be reduced, and the circuit loss can be reduced. Further, since no harmful action exceeding the limit of setting the power supply return current to zero is not brought about and no new parts are required, the present invention can be easily implemented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a transistor inverter according to the present invention. FIG. 2 is a circuit diagram of a conventional transistor inverter. [Description of References] 1: DC power supply, 2: Switching transistor, 3:
Vibration inductor, 4: Vibration capacitor, 5: Flywheel diode, 6: Current feedback transformer, 61:
Primary coil, 62: secondary coil, 71: base capacitor, 73: auxiliary diode, 74: auxiliary resistance, 90:
Load circuit

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Claims (1)

(57) Claims: 1. A switching transistor (2), and a vibration inductor (3) to which a DC power supply (1) voltage is intermittently applied via the switching transistor (2). ), An oscillation capacitor (4) connected in parallel with one of the switching transistor (2) and the oscillation inductor (3), and a flywheel diode anti-parallel to the switching transistor (2). (5), a load circuit (90) is connected to both ends of the oscillation inductor (3), and a primary coil (6) of a saturable current feedback transformer (6) is connected in series with the load circuit (90).
1) and the switching transistor (2)
Base-emitter junction and current feedback transformer (6)
And a base circuit including a secondary coil (62) and a base capacitor (71), and slowly discharges the forward-polarity charge of the base capacitor (71) accumulated when a base current flows through the base circuit. In the transistor inverter provided with a charge discharging circuit (73, 74), the primary coil (61) is arranged at a position in series with the load circuit (90) and also in series with the diode for flywheel (5). The connection polarity between the primary coil (61) and the flywheel diode (5) is changed when a power supply return current flows through the primary coil (61) via the flywheel diode (5). 2. The transistor inverter according to claim 1, wherein the forward polarity charge of the base capacitor is increased.