JP2615965B2 - Switching device and inverter - Google Patents

Description

The present invention relates to a switching device and an inverter used for a discharge lamp lighting device, for example.

(Conventional technology) As a conventional switching device of this type, for example, a configuration described in Japanese Patent Application Laid-Open No. 60-236498 is known.

This is a cascode connection of a bipolar transistor and a field effect transistor as a switching element,
A current transformer is provided for driving these switching elements,
The current transformer drives the bipolar transistor and the field-effect transistor to turn on and off at the same time to perform oscillation control.

(Problems to be Solved by the Invention) However, when the bipolar transistor is turned off, an excessive extraction current flows through the collector and the base,
Large switching loss results.

The present invention has been made in view of the above problems, and has as its object to provide a switching device and an inverter that can reduce switching loss.

[Configuration of the invention]

(Means for Solving the Problems) According to the invention of claim 1, in a switching device in which a bipolar transistor and a field-effect transistor are cascode-connected, the bipolar transistor is turned off earlier than the field-effect transistor is turned off.

An inverter according to a second aspect includes the switching device according to the first aspect.

(Operation) The switching device according to claim 1 turns off the bipolar transistor before turning off the field-effect transistor when turning off the bipolar transistor and the field-effect transistor.

According to a second aspect of the invention, an inverter converts direct current into alternating current using the switching device according to the first aspect.

(Embodiment) Hereinafter, a discharge lamp lighting circuit based on a single inverter using the switching device of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a commercial AC power supply. A rectifier circuit 2 is connected to the commercial AC power supply 1, and a smoothing capacitor 3 is connected between DC output terminals of the rectifier circuit 2. Further, a bias resistor 4 is connected to a DC output terminal of the rectifier circuit 2.
And a capacitor 5 are connected in series, and a zener diode 6 is connected to the capacitor 5 in parallel. The connection point of the bias resistor 4, the capacitor 5 and the Zener diode 6 is connected to the cathode of a resistor 7 and a diode 8 connected in parallel, and connected to the primary winding of the current transformer 10 via the diode 9. The collector and the emitter of the transistor 11 are connected to both ends of the primary winding, respectively, and the collector is connected to the negative output terminal of the rectifier circuit 2 via the resistor 12.

A DC power supply 13 is connected to the rectifier circuit 2 with a common ground. Between the positive and negative electrodes of the DC power supply 13, for example, a timer IC manufactured by Texas Instruments, a model TA75
The power supply terminals of the first and second oscillation control units 14 and 15 using the 55 are connected, and the first oscillation control unit 14 has a voltage / frequency (VF) conversion function, The oscillation control unit 15 outputs the signal with a certain time delay from the first oscillation control unit 14. Further, the first oscillation control unit 14 is connected to the second oscillation control unit 15 and the base of the transistor 11.

Then, a discharge lamp lighting circuit 16 using a single-type inverter is connected to these power supply and control circuits. The discharge lamp lighting circuit 16 includes a coil 17 having an iron core between the DC output terminals of the rectifier circuit 2, a secondary winding of the current transformer 10, a diode 18 for preventing backflow, an emitter / collector of a bibola transistor 19, and a MOS type. The drain-source of the field effect transistor 20 is connected, that is, the bipolar transistor 19 and the field effect transistor 20 are cascode-connected. The base of the bipolar transistor 19 is connected to a connection point of the resistor 7, the diode 8 and the diode 9, and the gate of the field-effect transistor 20 is connected to the second oscillation control unit 15. Also, coil 17
One end of a capacitor 21 is connected to a connection portion of the DC output terminal on the positive side of the rectifier circuit 2, and the other end of the capacitor 21 is connected to an intermediate portion of the coil 17. Both ends of the coil 17 are connected to respective filaments of a discharge lamp 23 such as a fluorescent lamp through a reactor 22 containing an iron core,
Further, a capacitor 24 is connected between both filaments of the discharge lamp 23.

Further, a feedback diode 25 and a resistor 26 connected in series are connected between the connection point of the secondary winding and the diode 18 of the current transformer 10 and the negative DC output terminal of the rectifier circuit 2. The connection point between the diode 25 and the resistor 26 is the first oscillation control unit.
Connected to 14.

 Next, the operation of the above embodiment will be described.

First, when the bipolar transistor 19 and the field effect transistor 20 are turned on, first, the first oscillation control unit 14 is caused to output a high level, the base current of the transistor 11 is stopped, and the transistor 11 is turned off. By causing the second oscillation control unit 15 to output a high level with a delay and applying a voltage to the gate of the field effect transistor 20, the bipolar transistor 19 and the field effect transistor 20 are turned on. The bipolar transistor 19 is biased via the bias resistor 4. However, since the base current is insufficient and the collector current does not flow when the field effect transistor 20 is off, the bipolar transistor 19 remains on until the field effect transistor 20 turns on. Transistor 19
Does not turn on. When the bipolar transistor 19 and the field effect transistor 20 are turned on, the coil 17 and the capacitor 21, the current transformer 10, the diode 18, the bipolar transistor 19 and the field effect transistor 20
The current flows through the path. At this time, the current induced in the primary winding of the current transformer 10 flows as the base current of the bipolar transistor 19, and an appropriate base current corresponding to the collector current of the bipolar transistor 19 is supplied.

Next, when turning off the bipolar transistor 19 and the field effect transistor 20, first, the first oscillation control unit
The base current is supplied to the transistor 11 by setting the output of 14 to a low level, the transistor 11 is turned on, and the base current of the bipolar transistor 19 is bypassed to turn off the bipolar transistor 19. Next, when the output of the second oscillation control unit 15 becomes low level, the field effect transistor 20 is turned off. When the bipolar transistor 19 and the field effect transistor 20 are turned off, the capacitor 24 and the reactor 22 resonate.

As described above, the bipolar transistor 19 and the field-effect transistor 20 are repeatedly turned on and off to oscillate, form an AC waveform, and turn on the discharge lamp 23.

Also, a current flowing through the feedback diode is detected as a voltage value by the resistor 26, and according to the detected voltage value,
The output frequency of the first oscillation control unit 14 is controlled to keep the output of the inverter constant.

According to the above embodiment, as shown in FIG. 2, the present invention (a) is different from the conventional example (b) in that even when the same voltage (V _CE ) is applied between the collector and the emitter, the collector current (I
_C) and the base current (pull-out current of I _B) (alpha)
Since (β) can be suppressed, switching loss can be reduced. Further, by using the high-breakdown-voltage bipolar transistor 19 and the low-breakdown-voltage field-effect transistor 20, the loss due to the switching element can be reduced as compared with the case where one high-breakdown-voltage MOS field-effect transistor is used.

Further, in the above-described embodiment, the DC power supply 13 is used as the power supply with the oscillation control units 14 and 15 and the like, but the input voltage of the inverter can be applied instead of the DC power supply 13.

Next, another embodiment will be described with reference to FIG. In addition,
Parts corresponding to those in the embodiment shown in FIG.

In this circuit, an AC input terminal of a rectifier circuit 2 is connected between both ends of an AC power supply 1, an electrolytic capacitor 3 for smoothing is connected to a DC output terminal, and a negative electrode of the rectifier circuit 2 and the electrolytic capacitor 3 is connected. DC power supply 1 with common side and negative potential
A first oscillation control unit 14 and a second oscillation control unit 15 are connected to the DC power supplies 13 and 13, respectively.

The first oscillation control unit 14 has a variable resistor 31, a resistor 32, and a capacitor 33 connected in series between both ends of the DC power supply 13, a resistor 34, a resistor 35, and a resistor 36 connected in series. The positive output terminal of the power supply 13 is connected to an input terminal of the flip-flop circuit 37 having an inversion circuit. The output terminal of an operational amplifier 38 is connected to the reset terminal of the flip-flop circuit 37. One input terminal of the operational amplifier 38 is connected to the connection point between the resistor 32 and the capacitor 33, and the other input terminal having an inverting circuit is connected to the input terminal. Resistance 34 and resistance
Connected to the connection point with 35, and also a flip-flop circuit
The set terminal of 37 is connected to the output terminal of an operational amplifier 39, and one input terminal of the operational amplifier 39 is connected to a resistor 35 and a resistor 35.
The inverting output terminal of the flip-flop 37 is connected to an input terminal of the operational amplifier 40 having an inverting circuit. Also, the connection point of the resistor 32 and the DC power
The collector and the emitter of the transistor 41 are connected between the negative electrode of the transistor 13 and the negative electrode of the transistor 13. Note that these resistors 34, 35,
The resistor 36, the flip-flop 37, the operational amplifier 38, the operational amplifier 39, and the operational amplifier 40 are formed by, for example, a timer IC 42 and a model TA7555 manufactured by Texas Instruments. Further, a capacitor 43 is connected to the timer IC 42, an output terminal of the operational amplifier 40 is connected to a transistor 45 having a resistor 44 connected between the base and the collector, and a collector of the transistor 45 is connected to a negative electrode of the DC power supply 13. ing. Further, the positive electrode of the DC power supply 13 is connected via a resistor 46 to the collector of a transistor 48 having a base resistor 47 between the base and the collector.

The second oscillation control unit 15 includes a resistor 51, a resistor 52, and a resistor 53 connected in series between both ends of the DC power supply 13,
A resistor 54 and a resistor 55 connected in series are connected in parallel. The base of the transistor 56 is connected to the connection point of the resistor 52 and the resistor 53, and the collector of the transistor 56 is connected to the positive electrode of the DC power supply 13 through the collector and emitter of the transistor 57 whose base and collector are short-circuited. Is connected to the negative electrode of the DC power supply 13 via the resistor 58. The base of a transistor 59 is connected to the connection point of the resistor 54 and the resistor 55.
The collector of 59 is the positive pole of the DC power supply 13 and the emitter is a resistor.
58 and the connection point of the emitter of the transistor. In addition, transistor 57
The base of the transistor 60 is connected, the emitter of the transistor 60 is connected to the positive electrode of the DC power supply 13, the collector is connected to the negative electrode of the DC power supply 13 via a diode 61 and a capacitor 62 connected in series, and the diode 61 is connected in series. Are connected to a resistor 63 and a variable resistor 64 connected to the resistor. The connection point of the variable resistor 64 and the diode 61 is connected to the emitter of a transistor 67 via two diodes 65 and 66. The base of the transistor 67 is connected to the positive electrode of the DC power Is connected to the base of a transistor 70 via a resistor 69, and the collector of the transistor 70 is connected to the base of a transistor 67 via a resistor 71. Furthermore, a resistor 72 and a resistor
73 and resistor 74 are connected in series, and resistor 72 and resistor 73
One input terminal having an inverting circuit of the operational amplifier 75 is connected to a connection point of the operational amplifier 75, and the other input terminal of the operational amplifier 75 is connected to a connection point of the diode 61 and the capacitor 62,
An operational amplifier 76 is connected to the connection point of the resistor 73 and the resistor 74.
Is connected to the connection point of the diode 61 and the capacitor 62. The other input terminal having the inverting circuit of the operational amplifier 76 is connected to the connection point of the diode 61 and the capacitor 62. The output terminal of the operational amplifier 75 is connected to the reset terminal of the flip-flop circuit 77, and the output terminal of the operational amplifier 76 is connected to the flip-flop circuit.
This flip-flop circuit is connected to the 77 set terminal.
The inverting output terminal of 77 is connected to the input terminal of the operational amplifier 78 having an inverting circuit, and is also connected to the negative electrode of the DC power supply 13. The collector and the emitter of the transistor 79 are connected between them. Also,
The other input terminal of the operational amplifier 76 is connected to the other input terminal of the operational amplifier 75. Note that the resistors 72, 73,
The resistor 74, the operational amplifier 75, the operational amplifier 76, the flip-flop circuit 77, the operational amplifier 78, and the transistor 79 are formed of, for example, a timer IC 80 manufactured by Texas Instruments and a model TA7555.

Furthermore, a capacitor is connected between the DC output terminals of the rectifier circuit 2.
21, the diode 18, the collector / emitter of the bipolar transistor 19, and the drain / source of the field effect transistor 20 are connected, that is, the bipolar transistor 19 and the field effect transistor 20 are cascoded. A diode 9 connected to the emitter of the transistor 48 is connected to the base of the transistor 19, and a resistor 7 connected in series to the negative electrode of the rectifier circuit 2.
The resistor 7 has a diode 8 in parallel, and the zener diode 6 has a capacitor 5 in parallel. In addition, the field effect transistor 20
Is connected to the output terminal of an operational amplifier 78 via a resistor 81. In addition, capacitor 21 and diode
The connection point 18 is connected to the negative DC output terminal of the rectifier circuit 2 via a diode 25 and a resistance 26 connected in series, and the connection point of the diode 25 and the resistance 26 is connected to the emitter of a transistor 70. ing.

Further, one end of a coil 17 is connected to a DC output terminal of the rectifier circuit 2, and a filament of a discharge lamp 23 is connected to one end of the coil 17 and the other end via the reactor 22, respectively. Is connected to a connection point of the capacitor 21 and the diode 18 to the intermediate tap of the coil 17.

Next, the operation of the embodiment shown in FIG. 3 will be described.

When turning on the bipolar transistor 19 and the field effect transistor 20, the operational amplifier of the timer IC 42
A high level output is applied to the transistor 40, the transistor 45 is turned off without applying a base current to the transistor 45, a base current is supplied to the transistor 48 via the bias resistor 47, and the transistor 48 is kept on, and the first oscillation is performed. The control section 14 outputs a high level, supplies a base current to the transistor 19, delays a certain time, outputs the high level to the operational amplifier 78 of the timer IC 80, outputs the high level to the second oscillation control section 15, and outputs the gate of the field effect transistor 20. , The bipolar transistor 19 and the field effect transistor 20 are turned on. In addition, a bipolar transistor
In the transistor 19, the collector current does not flow when the field effect transistor 20 is turned off. Therefore, the bipolar transistor 19 does not turn on until the field effect transistor 20 turns on. Thus, when the bipolar transistor 19 and the field effect transistor 20 are turned on, a current flows from the rectifier circuit 2 through the path of the coil 17 and the capacitor 21, the diode 18, the bipolar transistor 19 and the field effect transistor 20.

Next, when turning off the bipolar transistor 19 and the field-effect transistor 20, first, the low-level output is given to the operational amplifier 40 of the timer IC 42, the base current is given to the transistor 45, and the transistor 45 is turned on.
The transistor 48 is turned off by bypassing the base current of the transistor 48, the output of the first oscillation control unit 14 is set to a low level, and the base current of the bipolar transistor 19 is turned off, thereby turning off the bipolar transistor 19. Next, by setting the output of the operational amplifier 78 of the timer IC 80 to low level and the output of the second oscillation control unit 15 to low level, the gate voltage of the field effect transistor 20 is lost and the field effect transistor 20 is turned off.

As described above, the bipolar transistor 19 and the field-effect transistor 20 are repeatedly turned on and off to oscillate, form an AC waveform, and turn on the discharge lamp 23.

According to the above embodiment, since no current transformer for driving the bipolar transistor 19 and the field effect transistor 20 is provided, the size of the entire device can be reduced,
It can be formed at low cost, and can achieve higher frequencies.

Next, the circuit shown in FIG. 4 is a simplified circuit of the circuit shown in FIG. 3, and considers switching loss.

This circuit includes the transistor 48 of the first oscillation control unit 14.
Is replaced with a mechanical switch 82, and the second oscillation control unit 15
The bipolar transistor 19 has 2SC2535-0, and the field-effect transistor 20 has 2SK673.
Is used.

Then, the switch 82 is turned on / off to control the current supplied to the base of the bipolar transistor 19, as shown in FIG. Therefore, a bipolar transistor
The timing at which the 19 base current is cut off can be set arbitrarily. Note that τ represents the difference between the timing of shutting off the base current of the bipolar transistor 19 and the timing of shutting off the collector current (timing at which the gate voltage of the field effect transistor 20 becomes 0).

First, the switching loss and the temperature rise of the bipolar transistor 19 when the timing of shutting off the base current of the bipolar transistor 19 and the timing of shutting off the collector current are equal to τ = 0 will be considered.

FIG. 6 shows the temperature rise of three bipolar transistors having different common emitter DC amplification factors _hFE when the base current is changed. In this case, if the base current is small, insufficient driving occurs, the collector-emitter voltage V _CE increases, the loss increases, and the temperature of the bipolar transistor increases.
In particular, as the common emitter current transfer ratio h _FE is smaller, shows a marked tendency. Conversely, when the base current is increased, the switching loss due to insufficient driving is reduced, but as shown in FIG. 7 (b), the tail current It at the time of turning off the collector current Ic is reduced to the level shown in FIG. 7 (a). Tail current is larger than when the base current is small.
The loss due to It causes a temperature rise of the bipolar transistor.

Therefore, from the above results, the base current is set to 0.21 to 0.
If it is set in the range of 24 Ao-p, the temperature rise of the bipolar transistor can be suppressed to 14 ° C. or less even when the variation of the common emitter DC current amplification factor h _FE (h _FE = 15 to 30) is taken into consideration.

Then the timing of the interruption of the base current I _B of the bipolar transistor, consider the case that earlier timing of interruption of the collector current Ic.

8 to 11 show different base currents I _B
Under the conditions of, and the difference τ in timing of the blocking of the base current I _B and the collector current Ic of different bipolar transistors grounded emitter DC current amplification factor h _FE, it is a graph showing the relationship between the temperature rise. FIG. 8 shows the base current I _B
= 0.16Ao-p, Fig. 9 is the base current I _B = 0.21Ao-p, the
10 FIG base current I _B = 0.24Ao-p, Fig. 11 is the base current
The case for I _B = 0.30Ao-p. In FIG. 8, with the common emitter DC current gain h _FE = 30, the temperature rise can be suppressed, but the common emitter DC current gain h _FE = 15.
In this case, the temperature rise value rapidly increases as the timing difference τ increases due to insufficient driving. Conversely, as shown in FIG. 11, by increasing the base current I _B, in loss due to tail current It of the collector current Ic, the temperature rise value becomes larger. However, if earlier than the timing for interrupting the collector current Ic when to cut off the base current I _B, because the excess charge accumulated in the base of the bipolar transistor 19 is reduced, reducing the tail temperature It collector current Ic Temperature rise due to loss.

For example, as shown in FIG. 10, the base current I _B = 0.24
In the case of Ao-p, if the timing difference τ is set to 2 to 4 μs, the temperature rise of the bipolar transistor 19 can be reduced to 12 ° C. or less which does not adversely affect the operation in any case.

If the bipolar transistor 20 is turned off earlier than the field effect transistor 20 is turned off at the above-mentioned timing difference τ, the temperature of the bipolar transistor 19 due to the loss of the bipolar transistor 19 is reduced regardless of the variation in the common emitter DC amplification factor _hFE of the bipolar transistor 19. The increase can be suppressed as much as possible.

Further, in each of the above embodiments, an example in which the present invention is applied to a single-type inverter has been described. However, the present invention is not limited to the single-type inverter, but may be applied to any one in which a bipolar transistor and a field-effect transistor are cascode-connected.

〔The invention's effect〕

According to the present invention, by turning off the bipolar transistor earlier than turning off the field effect transistor, the extraction current of the bipolar transistor can be reduced, so that the switching loss can be reduced and the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG.
Fig. 2 (b) of the present invention is a waveform diagram of a conventional example, Fig. 3 is a circuit diagram showing another embodiment, Fig. 4 is a simplified circuit diagram of the same circuit, and Fig. 5 is a diagram of Fig. 4. FIG. 6 is a graph showing the base current and temperature rise of the bipolar transistor, FIG. 7 is a graph of the base current when the bipolar transistor is turned off, and FIGS. 8 to 11 are the timing differences. It is a graph of a temperature rise. 19: Bipolar transistor, 20: Field effect transistor.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H03K 17/16 9184-5K H03K 17/16 F H05B 41/24 H05B 41/24 H

Claims (2)

(57) [Claims] 1. A switching device in which a bipolar transistor and a field effect transistor are cascode-connected, wherein the bipolar transistor is turned off earlier than the field effect transistor is turned off. 2. An inverter using the switching device according to claim 1.