JPH0435987B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching control circuit used for DC-AC conversion or DC-DC conversion.

Conventionally, some conversion circuits of this type generate turn-on and turn-off pulse signals using pulse width modulation signals, and use these signals to control switching of the main switching circuit. Control elements used in such switching control circuits include transistors, field effect transistors, etc., but in the case where a transistor is used as a control element, two examples of conventional control circuits for the main switching circuit are described in Part 1. This will be explained with reference to FIG.

In the conventional example shown in FIG. 1, reference numeral 1 denotes a pulse control circuit which includes a pulse generation circuit, a pulse width modulation circuit, etc., although not shown. 2 is a turn-on drive circuit comprising a turn-on coupling circuit 2a formed by a capacitor C and a resistor R, and a turn-on drive element Q ₁ (NPN transistor in the figure). Reference numeral 3 denotes a turn-off drive circuit, which includes a turn-off coupling circuit 3a consisting of a capacitor C and a diode D, and a turn-off drive element Q ₂ (PNP transistor in the figure).

In the above, the turn-on drive circuit 2 and the turn-off drive circuit 3 control the forward current (base current IB 1 ) and the reverse current (base current IB ₁ ) of the gate of the switch element Q ₃ (the base of the transistor in the figure), respectively, according to the input signal from the pulse control circuit 1. Directional current (base current
The circuit is connected to flow IB ₂ ). 4 is a switch element Q ₃ consisting of the above-mentioned transistor, etc.
5 is an error for comparing the output voltage V of this switching control circuit with a reference voltage E, amplifying the error in the output voltage V, and inputting it to the pulse control circuit 1. It's an amplifier. T is an output transformer whose primary side is connected in series to the main switching circuit 4, and whose secondary side is connected to the output end 8 via a rectifier circuit 6 and a smoothing circuit 7.
It is connected to the.

Next, the operation of such a conventional circuit will be explained.

In the pulse control circuit 1, the modulated pulse (control pulse) whose pulse width is modulated by the output of the error amplifier 5 becomes a rectangular wave pulse signal as shown in FIG. 1A.

This signal is transmitted to the turn-on drive element _Q1 via the turn-on coupling circuit 2a of the turn-on drive circuit 2.
As a result, the turn-on driving element _Q1 is turned on and the storage time (storage time) tst as shown in Fig. 1a (b) ends (falling edge).
As long as the turn-off drive element _Q2 is not turned on, this current becomes the base current _IB1 in the direction of turning on the switch element _Q3 , and flows in the direction of the arrow in Figure 1. . On the other hand, the turn-on coupling circuit 3a operates only at the end of the turn-on pulse (a), and sends the necessary short pulse (FIG. 1a, c) to the base of the switch element _Q3 as the emitter output current of the turn-off drive element _Q2 . The base current _IB2 shown by the arrow turns off the switch element _Q3 of the main switching circuit 4, and flows in the opposite direction to the base current _IB1 .

In this way, the switch element Q ₃ has a base current IB ₁ ,
Since IB ₂ suddenly flows in opposite directions like an arrow, it rapidly changes from turn-on to turn-off.

However, at the end of the turn-on pulse in FIG. 1a, the turn-on driving element _Q1 is still turned on because it is within the storage time _tstg1 , and when the turn-off driving element _Q2 is turned on, the turn-on driving element _Q1 is turned off. As the short-circuit current flows through element Q ₂ , the base currents IB ₁ and IB ₂ of switch element Q ₃ cancel each other out, and in reality, the base current IB ₂ of switch element Q ₃ has a distorted waveform as shown in the solid line in the figure (e). This prevents sharp nonconduction. In addition, due to the above short circuit current, the turn-on driving element Q ₁ and the turn-off driving element
A large amount of heat is generated in Q ₂ , which not only causes drive loss but also causes damage to the switch element Q _3.
The collector current of is also as shown in the same figure. Another conventional example is a circuit as shown in FIG. In FIG. 2, the same parts as in FIG. 1 are denoted by the same reference numerals, and their explanation will be omitted. The output of the pulse control circuit 1 is input to a coupling circuit 10 via a drive circuit 9 consisting of a transistor _Q4 connected in series with a pulse transformer PT. It is added to a turn-on coupling circuit 10a consisting of a capacitor C and a resistor R, and a turn-off coupling circuit 10b having a diode D connected in parallel with it _. Added. In this way, the switch element _Q3 is made conductive or non-conductive through the turn-on coupling circuit 10a during turn-on and through the turn-off coupling circuit 10b during turn-off.

In the figure, RT is a reset circuit for the pulse transformer PT.

Next, to explain the operation of this conventional circuit, in FIG. 2, when the output signal of the pulse control circuit 1 is applied to the base of the transistor Q ₄ of the drive circuit 9, the transistor Q ₄ becomes conductive, and the pulse transformer PT is turned on. The primary side is excited, and this excitation energy is applied from the secondary side of the pulse transformer PT to the base of the switch element _Q3 of the main switching circuit 4 via the turn-on coupling circuit 10a, and the turn-on base current IB of the switch element _Q3 is ₁ flows as shown by the arrow in the figure, and when the transistor _Q4 is made non-conductive, the accumulated energy of the pulse transformer PT generates a back electromotive force, which makes the turn-off coupling circuit 10b conductive, causing the base of the switch element _Q3 to turn off. Turn on base current IB ₂ like an arrow
This produces a non-conducting effect that causes IB ₁ to flow in the opposite direction. In this case, rapid turn-off requires a large turn-off base current IB ₂ and a sufficient duration;
It is necessary to store a large amount of stored energy in the pulse transformer PT within the conduction time of _Q4 . This requires the existence of a leakage flux between the primary and secondary sides of the pulse transformer PT, and this leakage flux equivalently becomes an inductance in series with the primary side. However, this makes the rise of the turn-on base current _IB1 worse.

Therefore, in this conventional circuit as well, if one of the rise and fall characteristics of the turn-on base current is improved, the other deteriorates, and it is difficult to obtain good characteristics for both.

The present invention was made in view of the above-mentioned problems, and by improving the method of driving the switch element of the main switching circuit, the turn-on base current and turn-off base current of the switch element flow simultaneously. It is an object of the present invention to provide a switching control circuit that can significantly reduce transient loss of switching elements by eliminating current and short-circuit current caused by driving elements and improving driving efficiency, while realizing sharp rises and falls. This is the purpose.

Several embodiments of this invention have been described above in Figures 3 to 8.
This will be explained with figures. In addition, Fig. 1, Fig. 1a, Fig. 2
Circuits or elements that are the same or have the same functions as those of the above-mentioned conventional example shown in the figures are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 3 shows a first embodiment of the present invention, and the circuit configuration is characterized by a turn-off base current IB ₂ of the switch element Q ₃ compared to the conventional example shown in FIG. 1.
A turn-off delay circuit 11 is inserted at the front stage of the input side of the turn-off coupling circuit 3a of the drive circuit 3, that is, the turn-off drive circuit 3.

In such a circuit configuration, the drive of the turn-on base current _IB1 of the main switching circuit 4 is basically the same as the conventional example shown in FIG.
Its operation also has the same waveform as in Fig. 1a A and B, that is, the modulated pulse voltage waveform A in Fig. 3A, and the output current of the turn-on drive element _Q1 of the turn-on drive circuit 2 are exactly the same as in Fig. 1A A and B. switch element
There is no change in the conductivity of _Q3 . However, since the turn-off delay circuit 11 is inserted in the drive circuit for the turn-off base current IB ₂ , that is, in the preceding stage of the turn-off drive circuit 3, the switching element _Q3 is rendered non-conductive. The first stage of non-conduction is performed by the fall of the base voltage of the turn-on driving element _Q1 . That is _, the base current of the turn-on driving element Q ₁ is reversed by the fall of the modulated pulse voltage waveform shown in FIG. Shown in the output current waveform. After the accumulation time tstg ₁ of the turn-on drive element Q ₁ has elapsed, the emitter current of the turn-on drive element Q ₁ stops, the turn-on base current IB ₁ to the switch element Q ₃ is cut off, and the switch element Q ₃
A first stage of deconduction is performed.

The turn-off delay circuit 11 inserted in the drive side circuit of the turn-off base current IB ₂ creates a delay time t _f based on the fall of the modulated pulse voltage waveform A, as shown in FIG. The turn-off base current IB ₂ is driven by the fall of the output voltage waveform of the turn-off delay circuit 11 shown in FIG. 3A and C.

By appropriately setting the delay time t _f , it is possible to drive _{the chain-on base current IB 2 to the switch element Q 3 while} avoiding the storage time tstg ₁ of the turn-on driving element Q 1 . Undesirable currents in the conventional circuit example shown can be avoided.

Therefore, driving loss can be reduced and damage to the driving element can be prevented.

In this way, since no undesirable current is generated, the third
The emitter current waveform of the turn-off drive element _Q2 shown in FIG. 2A and the waveform of the turn-off base current _IB2 of the switch element _Q3 shown in FIG.

The timing at which the second stage of turning off the switch element _Q3 by the turn-off base current _IB2 drive circuit is started has another meaning.

In other words, immediately after the turn-on base current IB ₁ to the switch element Q ₃ becomes non-conductive, the switch element
Q ₃ storage time tstg ₃ initial switch element
There are enough minority carriers near the base in Q ₃ that a fairly large amount of charge must be pumped from its base by the turn-on base current IB ₂ in order to turn the switch element Q ₃ from a conducting state to a non-conducting state.

In addition, the turn-on base current IB ₁ for switch element Q _{3 is}
The conduction state is good, and the turn-on base current _IB1 is almost the same as when it flows in. Turn-off base current
Starting IB ₂ drive immediately after storage tstg ₁ has elapsed is not effective since the drive loss is large.

If the difference time (t _f −tstg) between the delay time t _f and the total storage time tstg (tstg = tstg ₁ + tstg ₃ ) of each element becomes too long (see Fig. 3a), the switching element Q ₃ Continuity deteriorates, the VCE saturation voltage of switch element _Q3 begins to rise, and collector loss of switch element _Q3 increases.

Therefore, by setting the delay time t _f to an appropriate value, the best drive that minimizes the overall switching loss can be obtained. The collector current waveform of switch element _Q3 in this state is as shown in FIG. 3a.

Next, a second embodiment will be explained with reference to FIG. 4. In this embodiment _, separate drive circuits _12a ,
13a to form a turn-on operation circuit 12 and a turn-off drive circuit 13, and these drive circuits 12
a and 13a each consist of a pulse transformer PT reset circuit RT and a turn-on drive element _Q1 or a turn-off drive element _Q2 , and have almost the same configuration as the drive circuit 9 in FIG.
A turn-off delay circuit 11 is inserted before the circuit 3a.

The operation of such a circuit configuration is achieved by separating the drive pulse transformers for driving the turn-on base current IB ₁ and the turn-off base current _{IB 2 .}
It is no longer necessary to store energy in the pulse transformer PT of 2a, and the conflict between the turn-on base current IB ₁ drive characteristic and the turn-off base current IB ₂ drive characteristic, which was a conventional drawback, can be resolved.

In the third embodiment shown in FIG. 5, in contrast to the circuit configuration of the first embodiment (FIG. 3), a turn-on delay circuit 14 is also provided at the front stage of the turn-on drive circuit 2 for driving the turn-on base current IB ₁ . This is to deal with the drawbacks that occur in the case of high-speed switching operations in the first and second embodiments.

That is, in terms of normal pulse response characteristics, the switch element Q ₃ is the slowest, and the turn-on drive element Q ₁ ,
Since the turn-off drive element _Q2 is also slower than the response of the delay circuit, it is sufficient to insert the delay circuit only for the turn-off base current _IB2 as shown in the first and second embodiments.

However, when the switching frequency becomes high and each drive element Q ₁ , Q ₂ and switch element Q ₃ are used with good response, each of the above-mentioned elements Q ₁ , Q ₂ , Q ₃ depends on the selection of the delay circuit. A case may occur in which the response of the delay circuit becomes faster than the minimum delay time of the delay circuit. In other words, when the switching frequency is increased, the pulse width must be narrowed, and accordingly, the operating time of the turn-off delay circuit must also be shortened. At this time, since there is a limit to how much the turn-off delay circuit alone can shorten the delay time, the required time (t _f −t _stg ) in Figure 3a, B, and C is shorter than the minimum delay time of the delay circuit. If this happens, problems will arise, and the first and second embodiments cannot satisfy the requirements.

Therefore, in such a case, by inserting a turn-on delay circuit for the turn-on base current IB ₁ and delaying the IB ₁ current, the 5th a.
The above objective can be achieved by making it possible to change the _{t o} time and t _f time shown in Figs.

The timing during this period is shown in Figure 5a, A, B, C,
It is shown by the chart of 2. In the same figure, the time difference t _f −(tn + tstg) between the fall of the output voltage waveform C of the turn-on drive circuit 12 and the fall of the output voltage waveform E of the turn-off drive circuit 13 is freely set until it reaches zero as shown in the figure F. You can achieve your goals.

In this case, the collector current waveform of switch element _Q3 is as shown in FIG.

The circuit shown in FIG _. 6 as the fourth embodiment replaces the turn-off drive element Q1 and turn-on drive element _Q2 in the first, second, and third embodiments, which had opposite polarities to an element Q with the same polarity. ₅ , _Q6 , and the polarity inversion circuit 15 is used to make this replacement possible.
is inserted before the turn-off base current _IB2 drive circuit. In this case, the polarity reversing circuit 15 can be omitted by using Q _2,2 (not shown) as a turn-off driving element with forward and reverse polarity as the turn-off driving element Q ₂ to form _a two-terminal type.

In addition, in this embodiment, the power supply from the control input voltage power source to the turn-on driving element _Q1 is cut off,
An example is shown in which the collector of the turn-on drive element _Q1 is connected to the intermediate tap Ta of the primary coil of the output transformer T. By this connection change, the collector resistance of the turn-on drive element _Q5 can be removed as shown. As a result, there is an advantage that driving loss can be reduced. Also turn-on drive element
Since the collector current of Q ₅ also becomes the primary current of the output transformer T, it not only reduces drive loss but also reduces the load on switch element Q ₃ , which has the advantage of reducing the loss of switch element Q ₃ . be.

As the fifth embodiment, the circuit shown in FIG.
In the embodiment (FIG. 4), a turn-on delay circuit 16 is also inserted for the turn-on base current _IB1 .

As a sixth implementation, the circuit shown in _FIG .
This is an example in which a direct coupling type is combined as the turn-off drive circuit 17 for the turn-off base current _IB2 .

As described above, the present invention is configured to delay the transmission of the turn-off pulse signal output from the turn-off drive circuit for a desired time from the end point of the turn-on pulse output from the turn-on drive circuit, thereby reducing the turn-on base current. It is possible to eliminate simultaneous positive and negative base currents due to storage and short-circuit currents due to the drive element between the turn-off base current and the turn-off base current, thus preventing loss of drive power caused by this, and furthermore, when switching the output current of the switch element. By realizing sharp rise and fall, the transient loss of the switch element can be significantly reduced, and therefore high efficiency DC to AC or DC
~DC conversion circuit is obtained.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram of one example of a conventional switching control circuit, Fig. 1a is a waveform diagram of the main part in Fig. 1, Fig. 2 is an electric circuit diagram of another conventional example, and Fig. 3 is an electric circuit diagram of an example of a conventional switching control circuit.
8 to 8 are related to the present invention, and FIG. 3 is a circuit diagram of the first embodiment, FIG. 3a is a waveform diagram of the main part in FIG. 3, and FIG. 4 is a circuit diagram of the second embodiment. , FIG. 5 is a circuit diagram of the third embodiment, FIG. 5a is a waveform diagram of the main part in FIG. 5, FIG. 6 is a circuit diagram of the fourth embodiment, and FIG. 7 is a circuit diagram of the fifth embodiment. Circuit diagram: FIG. 8 is a circuit diagram of the sixth embodiment. 1... Pulse control circuit, 2, 12... Turn-on drive circuit, 3, 13... Turn-off drive circuit,
4... Main switching circuit, 11, 14, 16...
...Delay circuit.

Claims (1)

[Claims] 1. A pulse control circuit that outputs a pulse width modulation signal, a main switching circuit that switches the main power supply current, and a turn-on drive that turns on and off switch elements of the main switching circuit according to the pulse width modulation signal. The switching control circuit includes a turn-off drive circuit and a turn-off drive circuit, and the turn-off drive circuit is configured to output a turn-off pulse after a desired time delay from the end of the turn-on pulse output from the turn-on drive circuit. Features a switching control circuit. 2. The switching control circuit according to claim 1, wherein a delay circuit is added at a stage before each of the turn-on drive circuit and the turn-off drive circuit. 3. The switching control circuit according to claim 1, characterized in that a delay circuit is added only at a stage before the turn-off drive circuit.