JPS61210877A - Drive circuit of inverter - Google Patents

Abstract

PURPOSE:To prevent a surge voltage from being applied to a drive switch element by flowing a phase advancing current by a capacitive load, and absorbing the surge voltage by a surge absorber through a diode when a circulating diode is conducted. CONSTITUTION:Surge voltages are generated in the secondary windings L11, L21 through the secondary windings L12, L22 and feedback windings L13, L23 of current transformers T1, T2 when a discharge lamp is started and fired or when the phase of the current flowed to the lamp is advanced. The surge voltage is applied through a closed circuit of diodes D3, D4 to a surge absorber 9, a current is flowed through the diodes D3, D4, a surge absorber 9, a capacitor C8 and a resistor R5, and clamped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a drive circuit for an inverter device that converts direct current voltage into high frequency voltage.

[Background Art] Conventionally, there is an inverter device of this type for discharge lamps as shown in FIG. 9, in which a series circuit of capacitors C1 and C2 is connected to both ends of a DC power source E, and switching transistors Q, . Connect the series circuit of Q2 and connect the connection point of the capacitor CIVC2 and the switching transistor Q
2. Connection of C2, a series circuit of capacitor C2, Chirok coil Ll, and discharge lamp α is inserted between α and
A capacitor C4 is connected in parallel to the discharge lamp t. Here, capacitors C1, C4, and Chirok coil L,
is a current limiting element, and in addition to the above circuit, the circuit shown in the Bis diagram may be used to limit the current flowing through the discharge lamp. α constitutes a vibration circuit. Freewheeling diodes DISD2 are connected to both ends of the switching transistors Q, C2, respectively, and a drive circuit 1 is connected to the bases of the switching transistors Q, C2. The general operation of this inverter device is as follows. Here, the DC power source E is created, for example, by rectifying and smoothing a commercial power source, and the DC power source E1 of the drive circuit 1 is generally created in the same manner. Therefore, if DC power E is applied to the inverter device, DC power E1 is also applied to drive circuit 1 at the same time, and drive circuit 1 alternately drives switching transistors Q1 and C2. Then, assuming that the switching transistor Q1 is driven, the switching transistor Q1, the current limiting element, the discharge lamp t, and the capacitor C
When a current flows through the capacitor CI, the discharge lamp t, the current limiting element, and the switching transistor Q2, a current in the opposite direction to the above current flows through the capacitor CI, the discharge lamp t, the current limiting element, and the switching transistor Q2, causing a high-frequency current to flow through the discharge lamp α. , which starts and maintains the lighting of the discharge lamp α. Here, the freewheeling diodes D1 and D2 discharge the electric charge stored in the capacitors C, , C, and turn on during the dead-off time period, which is provided so that both the switching transistors Q2 and C2 are not turned on. This is to prevent a pause section from occurring in the current i. The drive circuit 1 that drives the switching transistors Q1 and C2 described above has the circuit configuration shown in FIG.
Lip 70 tube 3, AND circuit 6.7, buffer r 4.5
, current transformer T, ST, and driving transistor Q
It consists of Q, Ql, etc. The drive circuit 1 operates roughly as follows.

When the DC power source E1 is supplied, the timer circuit 2 performs an unstable multi-pipe rake operation and produces a rectangular wave output from the output terminal (2). Here, the on/off cycle of the rectangular wave output is determined by a time constant determined by the capacitor C5 and the resistors R, , R2. Output terminal of this time circuit 2 ■ Output is 7 rip 7
It is used as a clock pulse of 0/3. here,
Timer circuit 2 is ICM7555 manufactured by Intern.
can be used. This clock pulse is input to the input terminal (2) of the 7-rip 70 tube 3, and the 7-rip 70 tube 3 outputs a rectangular wave whose high level and low level are inverted from each other from the Q output terminal (2) and the q output terminal (3). here 7
As the lip 70 tube 3, for example, a dual D7 lip prop MC14013B made by Motorola can be used.

Furthermore, in the AND circuit 6.7, the Q and Q outputs are sent to the buffer 74.
．． 5 is ANDed with the clock pulse through 5. This AND circuit 6.7 is a Motorola 1110/' I A Q quad 2-implant circuit.
Q I pat ts L h L J-1chi”P
The output of circuit 6.7 is applied to the bases of driving transistors Q, , Q, via base resistors R3 and R1. Here, capacitors C8 and C7 are connected in parallel to the base resistors R,,R, of the driving transistors Q,,Q,.
is a speeding up capacitor, and a timer circuit 2.7, a lip 70 tube 3, an AND circuit 6.7, etc. constitute a control circuit 81.82.

When a pulse voltage is applied to the driving transistors Q, Q, in this way, the driving transistors Q1, Q, alternately turn on and off, supplying current to the primary winding LII% L21 of the current transformer T, %T2. Here, capacitors CI, C inserted in series with current transformers T1, T2
, are capacitors that function to cause a rush current to flow in order to rapidly store energy in the primary windings 1 and L21 when the driving transistors Q1 and C4 are turned on, and the resistor R1
, R6 are resistors for discharging the capacitors C@, C1.

And the current transformer T, %T2 has the primary winding Lll, L
In addition to SI, there are feedback windings AIL, C, L23 and secondary winding, □
, L22 is wound M-f poor n- one earth smell T,, -T,
- or 1 know-how transistor Q1, Q! and feedback windings L13, L2 . is connected between the base and emitter of the switching transistors QI and Qz, and both IT wires, □, L22, L1, and L23 are the primary windings L l l
, L21 and the winding direction is different. Therefore, when the driving transistors Q1 and Q4 are off, the feedback windings L13 and L are generated by the back electromotive force generated at the primary winding joint L2+.
A voltage is induced in zs, and this induced voltage causes the transistor Q to
, , Q2 are driven. Here, the switching of the switching transistors Q, , Q will be explained in detail with reference to FIGS. 11 and 12 as follows.

Since the operation is similar to the circuit described above, the explanation will be omitted, and only the switching of the switching transistors Q, , Q, will be explained here. First, in the control circuit 81, $1
As shown in Figure 2(b), when a voltage is applied to the base of the driving transistor Q, the driving transistor Q is turned on and direct current is generated! In the IE, an inrush current flows mainly through the capacitor C1, the primary winding 1 of the current transformer T, and the driving transistor Q as shown in Fig. 12(e), and as shown in Fig. 12(h). capacitor C8 is rapidly charged,
Thereafter, a constant collector current flows through the driving transistor Q3 via the resistor R3. At this time, the current transformer T
The iron core of , is excited in one direction, and the voltage across the negative winding L 1 H is maintained at a constant voltage as shown in FIG. 4(d).

Then, the time 1 shown in FIG. 12(h). When the driving transistor Q is turned off, the switching transistor Q is turned off in the feedback winding L13 of the current transformer T due to the back electromotive force caused by the energy stored in the negative windings L and H.
, an induced voltage is generated in the opposite direction, and a base current flows as shown in FIG. Then, the collector current of the switching transistor Q flows slightly, so that the collector current also flows in the first and secondary windings L+2, and positive feedback is applied to the feedback winding L1 to turn on the switching transistor Q, and the switching Transistor Q.

suddenly transitions to the on state. The time required for the switching transistor Q1 to turn on completely is the delay time td. At the same time as the driving transistor Q is turned off, the electric charge charged in the capacitor C6 is transferred to the resistor R.
The battery is gradually discharged at 6, and the state becomes as shown at time t to t in FIG. 12(h). This time 1. If the driving transistor Q is turned on again at , the current transformer T
A current flows through the primary 8#EL+1 of the switch 1, and this current generates an induced voltage in the feedback winding L l 2 in the direction of turning off the switching transistor Q, thereby reducing the base current of the switching transistor Q1. Then, the collector current of the switching transistor Q also decreases, and the feedback winding L1 . The positive feedback voltage to Q also decreases, causing the switching transistor Q to turn off. Thereafter, the above-mentioned operation is repeated, and the operation of the switching transistor Q is the operation of the switching transistor Q. On the other hand, the switching transistor Q, @ performs the on/off operation opposite to that of the switching transistor Q, and the driving transistor Q1 is arranged so that the on period of the switching transistor Q2 does not overlap with the on period of the switching transistor Q. , Q, as shown in FIGS. 12(a) and 12(b), a control circuit 81.
A voltage is applied at 82. Here, Fig. 12 (,
) indicates the voltage applied to the base of the driving transistor Q4, and the period during which both driving transistors Q and Q are turned on simultaneously is the dead-off time ts. As described above, by alternately turning on and off the switching transistors Q1 and Q2, a DC voltage is converted to an AC voltage and the discharge lamp is lit. Here, the current i flowing through the discharge lamp has two modes. As shown in FIG. 113(a), there are cases in which the phase of the current i is leading with respect to the voltage across the discharge lamp α, and cases in which the phase is lagging as shown in FIG. 14(, ). In the case of phase advance, current flows through the freewheeling diodes D1 and D2 during the dead-off time ts when both the switching transistors Q1 and Q2 are off.
The freewheeling diodes D1 and D2 are in the on state, but when the switching transistors Q, , Q are turned on at this time, when the switching transistor Q2 is turned on, a signal is transmitted to the switching transistor Q2 via the freewheeling diode D1 (see FIG. 13). A short-circuit current flows as shown in c), and when the switching transistor Q1 is turned on, a short-circuit current flows through the freewheeling diode D2 to the switching transistor Q1 as shown in FIG. 13(b). This short circuit current is caused by switching transistors Q, , Q2
As well as the secondary winding LI2 of current transformer T3, T2
, L22, and further flows through the secondary windings L12 and L22, a large current also flows through the feedback windings L+2 and Li2. Therefore, as shown in Fig. 15(b), a surge voltage is generated in the primary windings L + + and L21, and a surge current also flows in the drive transistors Q1 and Q, damaging the drive transistors Q3 and Q4. It had the disadvantage of

This state does not occur in the case of a slow phase because the on states of the freewheeling diodes D, %D2 and the switching transistors Q, , Q, do not overlap, as shown in Fig. 14(b) and (c). , if the discharge lamp t is operated in a slow phase, there is a drawback that it becomes difficult to start the discharge lamp t.
Constants must be selected so that the oscillating circuit consisting of 1 and capacitors C and -C becomes capacitive.For this reason, the drive transistor Q3 is operated in phase-advance mode at the time of starting lighting, and the driving transistor Q3 is activated during normal lighting. , Q, is normally operated in a slow phase mode to prevent deterioration of the signals. However, since the phase advances at the time of starting, there is a drawback that the risk of deterioration or damage to the drive transistors Q3, Q remains unresolved.

[Object of the Invention] The present invention has been made in view of the above points, and its object is to prevent surge voltage from being applied to the drive transistor even when the phase of the current flowing through the discharge lamp is advanced. An object of the present invention is to provide a drive circuit for an inverter device that does not require any voltage applied.

■Disclosure of the Invention] (Embodiment 1) Fig. 1 shows an embodiment of the present invention, in which the surge voltage generated in the primary windings ML L1%Lit of current transformers T1 and T2 is transferred to the respective current transformers ThT2. Primary winding L
+ +, L This is suppressed by a surge absorption circuit 9 connected in parallel with each switching transistor Q, , Q when viewed from 21. In this embodiment, the primary winding AIL of current transformer TI, T2, .・From the connection point between L2I and driving transistors Q,,Q4)'D,,
The circuit 9 is connected to the circuit D4, and the other end is connected to the positive side of the DC current IIE. Here, driving transistors Q5 and Q4 are used as driving switching elements, but it goes without saying that thyristors may also be used.

The operation of the above circuit configuration is as follows. Here, since the circuit operation other than the circuit operation of the surge absorption circuit 9 is the same as that of the conventional example, the explanation will be omitted, and only the operation of the surge absorption circuit 9 will be explained. When the discharge lamp α is started and lit, and the phase of the current i flowing through the discharge lamp α is advanced, the secondary winding # of the current transformers T, T2 is processed as explained in the conventional example. L l
A surge voltage is generated in the primary windings LII and L21 via Lzt and the feedback windings L13 and Li2. Finally, this surge voltage is transmitted to the circuit 9 using diodes D, , D, which are connected in parallel to the resistor R shown in Figure 8 (a) or the resistor R and capacitor C shown in Figure 8 (b). Alternatively, a diode D is connected in series to a parallel circuit of a resistor R and a capacitor C as shown in FIG. 3(c).

Then, the negative winding L10 of the current transformer T1,T,
L! The surge voltage generated on + is connected to diodes D- and D
4. The surge voltage is clamped by being circulated through the closed circuit of the surge absorption circuit 9, the capacitor C1, and the resistor R3, and prevents the surge voltage from being applied to the driving transistors Q, Q4.

(Embodiment 2) FIG. 2 is a diagram showing another embodiment of the present invention, in which a diode is D1,
A surge absorption circuit 9 is connected to the power supply D through D, and the other end is connected to the negative side of the DC power supply E.

In the first embodiment, the primary winding 4 of current transformers T1 and T2
The surge voltage generated at L 21 was clamped by the surge absorption circuit 9, but in this embodiment, the surge absorption circuit 9 was used to prevent a voltage exceeding the absolute maximum rated voltage from being applied between the emitters. This is for bypassing the current, and the other aspects are substantially the same as in the first embodiment, so a description thereof will be omitted.

(Embodiment 3) FIG. 3 is a diagram showing still another embodiment of the present invention.
21 and the holding circuit 10, but in this embodiment, only the voltage across the current transformers T and T2 is clamped, and the capacitor C8
The parallel circuit of the resistor R9 and the resistor R9 is shared by the current transformers T3 and T2. The operation of this embodiment is also substantially the same as that of the first embodiment, so the explanation will be omitted.

(Embodiment 4) FIG. 4 is a diagram showing still another embodiment of the present invention. This bypasses the current so that a voltage higher than the absolute maximum rated voltage is not applied.

(Embodiment 5) FIG. 5 is a diagram showing still another embodiment of the present invention, in which a parallel circuit of a capacitor C1 and a resistor R6 is connected to a current transformer T.
+, Tz, and the above-mentioned parallel circuit having the same circuit configuration is also used as the surge absorption circuit 9.

(Embodiment 6) FIG. 6 shows the circuit of Embodiment 1, with transistors Q,...
A surge absorption circuit 9 is connected directly between the collector and emitter of Q.
is connected.

(Embodiment 7) In Fig. 7, the above parallel circuit is shared by current transformers T1 and T2, and a surge absorption circuit 9 is connected between the collectors and emitters of drive transistors Q, Q, as in Embodiment 6. It is.

[Effects of the Invention] As described above, the present invention includes two switching transistors connected in series to both ends of a DC power source and turned on and off alternately so as to flow an AC current to a load, and two switching transistors connected to both ends of each switching transistor. A oscillation circuit that is inserted between a connection point of the switching transistor and a DC power source, an LC circuit, and a load, and exhibits a capacitive mode, including a freewheeling diode that prevents the current flowing through the load from having a rest period. and a current transformer provided corresponding to the switching transistor, with a feedback winding connected between the base and emitter of the switching transistor, and a secondary winding inserted in series with the switching transistor, and a primary winding of each current transformer. A driving switching element that is inserted in series and drives a corresponding switching transistor via a current transformer, a control circuit that performs switching control of the driving switching element, and a respective Since it is equipped with a surge absorption circuit connected in parallel with the switching transistor, a leading phase current flows due to the capacitive load, and when the freewheeling diode is conductive, the switching transistor is turned on and a short-circuit current flows to the switching transistor. Even if a surge voltage occurs in the primary winding of the current transformer, the surge absorption circuit can prevent voltage exceeding the absolute maximum rated voltage from being applied to the drive switching element, thereby preventing damage to the drive switching element. be effective.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing the main part of an embodiment of the present invention, #
FIG. 12 is a circuit configuration diagram showing the main part of another embodiment of the present invention,
3 to 7 are circuit configuration diagrams showing main parts of still other embodiments of the present invention, FIG. 8 is a circuit diagram showing the same surge absorption circuit, and FIG. 9 is a circuit diagram showing a conventional example. , Figure 10 is a circuit diagram showing the main parts of the same as above, Figure 11 is a circuit diagram showing other main parts of the same as above, Figures 12 to 15 are operation explanatory diagrams of the same as above, and Figure 16 is the same as above. FIG. 7 is a circuit diagram showing another current-limiting element. 1 is a drive circuit, 9 is a surge absorption circuit, C6 is a capacitor, 81.82 is a control circuit, Q, ~Q are transistors, T1, T2 are current transformers, Lll ~ L13, L21
~L23 is a winding, ESE+ is a DC power supply, and D and ~D4 are diodes.

Claims (3)

[Claims] (1) Two switching transistors that are connected in series to both ends of a DC power supply and turn on and off alternately so that alternating current flows to the load, and two switching transistors that are connected to both ends of each switching transistor so that there are no rest periods in the current flowing to the load. A freewheeling diode is inserted between the connection point of the switching transistor and the DC power supply, and the LC
An oscillating circuit consisting of a circuit and a load and exhibiting a capacitive mode, and a feedback winding provided corresponding to the switching transistor and connected between the base and emitter of the switching transistor, and a secondary winding connected in series with the switching transistor. an inserted current transformer, a driving switching element that is inserted in series with the primary winding of each current transformer and drives a corresponding switching transistor via the current transformer, and a control circuit that performs switching control of the driving switching element; A drive circuit for an inverter device comprising a surge absorption circuit connected in parallel with each switching transistor when viewed from the primary winding of each of the current transformers. (2) The drive circuit for an inverter device according to claim 1, wherein the switching transistor is controlled to switch at a switching frequency that is lower than the natural vibration frequency of the vibration circuit. (3) The drive circuit for an inverter device according to claim 1, wherein the load is a discharge lamp.