JPH0574310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an improvement in the switching operation of a two-stone inverter circuit used in a switching power supply.

[Prior art] In a two-stone separately excited inverter circuit used in the DC→AC conversion section of a switching power supply, two
The transistors are designed to alternately turn on and off. FIG. 1 is a diagram showing the structural concept of a conventional device of this type. In the figure, Q ₁ , Q ₂
are transistors that are turned on and off alternately,
1 and 2 are drive circuits that drive each transistor, T is an output transformer driven by transistors Q ₁ and Q ₂ , L ₁ and L ₁ ' are primary windings of the transformer, and L ₂ and L ₂ ' is the secondary winding. input voltage
Vin is applied between the common connection point A of the transistors Q ₁ and Q ₂ and the common connection point B of the primary windings L ₁ and L ₁ '. The inverter output is taken out from the secondary side of the output transformer T. In this type of inverter circuit, it is absolutely necessary to avoid turning on the two transistors Q ₁ and Q ₂ at the same time, as this will lead to destruction of the device. For this reason, since there is always a time delay involved in the switching operation of the transistor, the time during which both transistors are turned off is set in consideration of this time. FIG. 2 is a timing chart showing the timing of the switching operation. In the figure, S ₁ is the base current of transistor Q ₁ , S ₂ is the base current of transistor Q ₂ ,
S ₃ indicates the collector current of transistor Q ₁ , and S ₄ indicates the collector current of transistor Q ₂ . Δt ₁ in the figure is the transistor (in this case
_Q1 ) indicates the time delay when turning from on to off.
As is clear from the figure, the time delay Δt ₁ is considerably larger than the time required for the transistor to turn on from off. This is mainly due to the storage time of the transistor. Therefore, there is a delay time (dead time) as shown in the figure between when Q ₂ turns off and when Q ₁ turns on.
It is necessary to provide Δt ₂ . Delay time Δt ₁
Of course, the type of transistor, drive conditions,
It changes depending on the amount of addition, temperature, etc., so sufficient care must be taken when designing.
The existence of the delay time Δt ₂ lowers the switching duty, making it impossible to increase the frequency. On the other hand, a self-excited inverter that utilizes the saturation phenomenon of a supersaturated reactor has the characteristic that one transistor is definitely turned off before the other transistor is turned on.
Ideally, a phenomenon in which both transistors are turned on at the same time (cross current) does not occur.

[Purpose of the Invention] The present invention has been made in view of the above-mentioned points. In a two-stone separately excited inverter used in a switching power supply, etc., two The present invention realizes an inverter circuit that avoids the phenomenon in which transistors are turned on at the same time, eliminates switching dead time, and can achieve high switching frequencies.

[Structure of the Invention] The present invention achieves the above object by adjusting the input voltage
A pair of transistors that alternately turn on and off V _io
a switching circuit 10 having Q ₁ and Q ₂ ; an output transformer T ₁ connected to the switching circuit;
A feedback circuit 20 that receives the output of the feedback winding _L3 wound around the output transistor, and a drive transformer _T2 that transmits the output of the feedback circuit to the drive section of the switching circuit via the drive winding _L4 . The inverter circuit has the following configuration.

That is, a circuit including a resistor R ₁ and a supersaturation reactor SC connected in series to both ends of the drive winding, and a bidirectional semiconductor switch D ₂ connected to both ends of the resistor.
and a transistor _Q3 that turns on and off the semiconductor switch according to an external control signal.

Then, an oscillation frequency (2f) on/off control signal is supplied from an external oscillator to the transistor _Q3 ,
When the semiconductor switch is turned on, the resistor is bypassed and the drive winding is short-circuited when the supersaturation reactor is saturated, so that the switching circuit switches at half (f) of the oscillator frequency. .

[Operation] By applying an on/off control signal sent from an external oscillator to the transistor _Q3 and the semiconductor switch _D2 , the on/off of the two transistors in the switching circuit is controlled. In this case, since the supersaturated reactor SC is interposed and the on/off inversion timing is obtained using the saturation of the supersaturated reactor, interlock between the transistors Q ₁ and Q ₂ can be achieved. Since the resistor _R1 is connected in series with the supersaturation reactor SC, a short circuit occurs in the drive winding in synchronization with the on/off of the semiconductor switch, thereby turning on/off the switching circuit.

[Embodiment] FIG. 3 is an electrical configuration diagram showing an embodiment of the present invention. In the figure, 10 is a switching circuit that switches on and off the input voltage Vin, Rs is a starting resistor that provides a starting current to the switching circuit, 20 is a feedback circuit, T ₁ is an output transformer, and T ₂ is a switching circuit that connects the output of the feedback circuit 20 to the switching circuit 10. This is a drive transformer that transmits information to the drive unit. The output transformer T ₁ is composed of a primary winding L ₁ , L ₁ ′, a secondary winding L ₂ , L ₂ ′, and a tertiary winding (feedback winding) L ₃ . The switching circuit 10 includes switching transistors Q ₁ , Q ₂ ,
It is composed of a diode D ₁ and a capacitor C. Diode D ₁ and capacitor C are connected when transistors Q ₁ and Q ₂ switch from on to off.
This is to provide a reverse bias between the base and emitter. The feedback circuit 20 is an output transformer.
It consists of a feedback winding L ₃ of T ₁ , a feedback resistor Rf, and a drive winding L ₄ . Feedback resistor Rf is output transformer T ₁
The value of the feedback current If fed back from the feedback winding L ₃ to the drive winding L ₄ is determined. Drive transformer T ₂ is 1
It is composed of a secondary winding (drive winding) L ₄ and secondary windings L ₅ and L ₅ '. SC is a supersaturated reactor with one end connected to the feedback circuit 20, and _R1 is a resistor connected in series with the supersaturated reactor, and the other end is connected to the feedback circuit 20. _D2 is a bidirectional semiconductor switch whose one end a is connected to the common connection point of the supersaturation reactor SC and the resistor _R1 , and the other end b is connected to the feedback circuit 20. For example, a diode switch is used as the semiconductor switch. both ends c of the other connection point of the semiconductor switch,
d is connected to the collector and emitter of transistor _Q3 , respectively. The transistor is turned on and off by an external pulse signal. The operation of the device configured as described above will be explained as follows.

In a steady state of operation, switching transistors Q ₁ and Q ₂ are alternately turned on and off. At this time, the feedback current If fed back from the feedback winding L ₃ appears as a base current in the secondary windings L ₅ and L ₅ ' according to the turns ratio of the winding of the drive transformer T ₂ , and flows through the switching transistor Q. ₁ and _Q2 . The base current _IB1 at this time is expressed by the following equation.

IB ₁ =If·N ₁₁ /N ₁₂ (1) Here, N ₁₁ is the number of turns of the drive winding L ₄ and N ₁₂ is the number of turns of the secondary winding L ₅ of the drive transformer T ₂ . The inductance of the supersaturated reactor SC sharply decreases when the time-integrated value of the voltage applied across it reaches its saturation magnetic flux. In principle, the circuit shown in the figure turns on and off the switching transistors Q ₁ and Q ₂ by utilizing the saturation phenomenon of the saturation sum reactor. The difference from conventional automatic systems is that the oscillation frequency is controlled by a switch circuit consisting of semiconductor switch D ₂ and transistor Q ₃ . That is, the oscillation frequency is controlled by the drive pulse applied to the base of transistor _Q3 .
The applied frequency is 2f when the oscillation frequency is f. As can be seen from the above description, the present invention eliminates the cross current by overcoming the drawback of the separately excited type, which causes cross current, with the advantage of the self excited type using a supersaturated reactor.

The specific operation of the present invention will be explained below with reference to the timing chart of FIG. In Figure 4, P ₁ is the waveform of the collector-emitter voltage Vce ₁ of the transistor Q ₁ , P ₂ is the waveform of the collector-emitter voltage Vce 2 of the transistor Q ₂ , and P ₃ is the waveform of the collector-emitter voltage Vce ₂ of the transistor Q _1. The waveform of current Ic ₁ is P ₄
is the voltage _V22 induced across the feedback winding _L3 , _P5
is the feedback current If, P ₆ is the 2 of the drive transformer T ₂
The voltage V ₁₂ induced across the next winding L ₅ , P ₇ the base current IB ₁ of the transistor Q ₁ , P ₈ the base-emitter voltage Vbe ₁ of the transistor Q ₁ , P ₉ the drive winding The voltage V ₁₁ applied to both ends of the line L ₄ is shown, P ₁₀ is the voltage Vsc applied to the supersaturation reactor SC, P ₁₁ is the current Isc flowing to the supersaturation reactor SC, and P ₁₂ is the external input frequency (2f). .

Since the operations of transistors Q ₁ and Q ₂ are symmetrical,
The following explanation focuses on transistor _Q1 . When a starting current is input via the starting resistor Rs, either transistor Q ₁ or Q ₂ is turned on. Now, Q ₁
When turned on, voltages V ₂₁ and V ₂₂ as shown by arrows in FIG. 3 appear in the output transformer T ₁ . (Figure). At this time, a feedback current If flows from winding _L3 to _L4 . The feedback current If is expressed by the following formula.

If=V ₂₂ −V ₁₁ /Rf (2) Here, the identification signal was used as it was as the value of the feedback resistor. Voltage across drive winding L ₄
V ₁₁ is given by the following equation.

V ₁₁ = V ₁₁ /N ₁₂ · V ₁₂ = V ₁₁ /N ₁₂ (Vf + Vbe ₁ ) (3) Here, Vf is the forward voltage drop of diode D ₁ . The base current IB ₁ of the transistor Q ₁ at this time is given by the following equation.

IB ₁ = If・V ₁₁ /N ₁₂ (4) Voltage V ₁₁ is applied to both ends of supersaturated reactor SC through resistor R ₁ , but since the impedance of reactor SC is sufficiently large compared to that of resistor R ₁ , reactor SC It can be assumed that almost a voltage of V ₁₁ is applied to . This voltage causes the magnetic flux of the reactor SC to increase over time. When this magnetic flux reaches the saturation magnetic flux of the reactor SC, the impedance of the reactor decreases rapidly and almost becomes a short circuit state. The period ts shown at _P10 in the figure is the time when the reactor SC is saturated. At this time, the reactor
Determined by SC material, shape, number of turns, etc.
Here, the settings are as follows.

1/4Ts<ts<1/2Ts (5) Here, Ts is the oscillation period of the interval.
Note that when the reactor SC is saturated, the current flowing through the resistor _R1 is set to be sufficiently smaller than the feedback current If.

When the reactor SC is saturated, an oscillation frequency 2f (f=1/Ts) is input from an external oscillator (not shown), and the transistor _Q3 is turned on (as shown). As a result, both ends of winding L ₄ are connected to semiconductor switches.
D ₂ , transistor Q ₃ and saturated reactor
It is short-circuited by SC, and most of the feedback current If flows toward reactor SC. Also, the voltage V ₁₁ decreases and therefore the voltage V ₁₂ also decreases. At this time, the base current of the transistor _Q1 flows in the opposite direction due to the potential across the capacitor C, drawing out the accumulated charge stored in the transistor _Q1 (as shown in the figure). When the accumulated charge of the transistor _Q1 is extracted and the transistor is completely turned off (as shown in the figure), the voltages at various parts of the output transistor _T1 become opposite to the direction shown in Figure 3, and the reactor SC becomes high impedance again. , while resetting the magnetic flux up to that point, it moves towards saturation in the opposite direction. At this time, due to the voltage V ₁₁ appearing in the opposite direction to that shown in Figure 3 and the feedback current If, the feedback signal is transmitted through the drive transformer T ₂ in the opposite direction, and the secondary winding L ₅ ' is connected to the transistor paired with Q ₁ .
Turn on _Q2 . The operation when the transistor Q ₁ is turned on from the state where the transistor Q ₂ is turned off is also the same, so a description thereof will be omitted. As explained above, in the case of the present invention, one switching transistor is always turned on after the other transistor is turned off, so interlock is automatically established and the above-mentioned cross current does not occur.

[Effects of the Invention] As described in detail above, according to the present invention, a resistor and a supersaturation reactor are connected in series to both ends of a drive winding, and a bidirectional semiconductor switch is further connected to both ends of the resistor. This switch is turned on and off by the output of a separately provided oscillator, and in a separately excited two-stone inverter, the cross current, which is one of the causes of destruction of the switching elements, is eliminated by one transistor, which is a characteristic of a self-commutated inverter. This can be avoided by using an interlock effect in which one transistor is turned off before the other transistor is turned on. Furthermore, the transistor drive circuit required for each transistor in the conventional system, but according to the present invention, one transformer and one transistor are required.
This can be realized with a single timing circuit. The former feature solves various problems that had to be taken into account in settings, such as timing fluctuations due to element variations, temperature, and load current, and improves duty by providing perfect square wave output. This enables high-frequency switching and allows for smaller parts, lower equipment costs, and improved response characteristics. The latter feature is expected to simplify the circuit and reduce the number of parts.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a conventional circuit, Fig. 2 is a timing chart during switching, Fig. 3 is an electrical configuration diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing a timing chart of each part. be. 1, 2...Drive circuit, 10...Switching circuit, 20...Feedback circuit, T, _T1 ...Output transformer, _T2 ...Drive transformer, _L1 , _L1 '...
Primary winding, _L2 , _L2 '...Secondary winding, _L3 ...Feedback winding, _L4 ...Drive winding, _L5 , _L5 '...Secondary winding,
Q ₁ , ~Q ₃ ... transistor, D ₁ ... Daoade,
D ₂ ...Semiconductor switch, C...Capacitor, Rs,
Rf, _R1 ...Resistance.

Claims (1)

[Claims] 1. Switching circuit 1 having a pair of transistors Q ₁ and Q ₂ that alternately turn on and off the input voltage V _io
0 and the output transformer connected to the switching circuit.
_T1 , a feedback circuit 20 that receives the output of the feedback winding _L3 wound around the output transformer, and a drive transformer that transmits the output of the feedback circuit to the drive section of the switching circuit via the drive winding _L4 . In an inverter circuit having T ₂ and a resistor R ₁ connected in series across the drive winding,
A bidirectional semiconductor switch _D2 connected to both ends of the resistor, and a transistor _Q3 that turns on and off the semiconductor switch according to _an external control signal are provided. An oscillation frequency (2f) is supplied as an on/off control signal from an external oscillator, and when the semiconductor switch is turned on, the resistor is bypassed, and when the supersaturation reactor is saturated, the drive winding is short-circuited, and the switching circuit is turned on. An inverter circuit characterized in that switching is performed at half (f) of the oscillator frequency.