JPH0246117Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor drive circuit that uses a drive transformer to operate in a switching mode.

This type of transistor drive circuit is widely used, for example, in switching power supplies, etc., but conventionally, as shown in FIG. 1, a transistor circuit using a pre-driver transistor _Q1 ,
It had a circuit configuration in which a transistor circuit consisting of the main transistor _Q2 was connected to a drive transformer _T1 . In this circuit, when transistor _Q1 is turned on by a pulse input to its base, an electromotive force is induced in winding _N12 based on the magnetomotive force due to the on-current flowing through winding _N11 , and electromotive force E ₂ is the base of transistor Q ₂ .
The emitter is forward biased and transistor _Q2 is turned on.

When transistor Q ₁ is then turned off, the excitation energy stored when it was on causes winding N ₁₂
A flyback voltage E ₂ ' in the opposite direction to the electromotive force E ₂ is induced. This flyback voltage
E ₂ ' is the base of transistor Q ₂ . Since the emitters are biased in the opposite direction, transistor _Q2 is turned off. In this way, the switching action of transistor Q ₁ causes transistor Q ₂ coupled via transformer T ₁ to switch,
This turns on and off the DC input _V2 . Note that +V ₁ is the DC power supply voltage of transistor Q ₁ , and R ₁ is a resistor for limiting the base current of transistor Q ₂ .

By the way, when operating a transistor in the switching mode as described above, it is possible to reduce loss, make the transistor smaller and lower in price, and
In order to improve efficiency and reliability, it is necessary to shorten the turn-on and turn-off times of transistors to speed up switching. However, conventional transistor drive circuits use a transformer _T1 to connect two transistor circuits for reasons such as insulation.
A fatal drawback was that the leakage inductance in the windings N ₁₁ and N ₁₂ of the transformer T ₁ acted to slow down the switching of the transistor.
That is, a transformer generally has an equivalent circuit in which a leakage inductance L ₁₁ of a primary winding N ₁₁ and a leakage inductance L ₁₂ of a secondary winding N ₁₂ are connected in a T-shape, as shown in the equivalent circuit of FIG.
Because of this leakage inductance L ₁₁ , L ₁₂ ,
Even if a pulse with a good rise as shown in Figure 3a is supplied to the base of transistor _Q1 , the electromotive force _E2 generated in the winding _N12 of transformer _T1 will be as shown in Figure 3b. The rise is slow. Therefore, the rise of the base current of transistor _Q2 is also as shown in Fig. 3c.
As shown in Figure 2, the collector is the switching output of transistor _Q2 . Emitter voltage VCE
The rise characteristic of the current becomes sluggish as shown in Fig. 3(d). For this reason, conventional transistor drive circuits have had limitations in reducing loss, making transistors smaller, lowering prices, and improving efficiency and reliability.

In particular, using this transistor drive circuit, the collector of transistor Q ₂ is connected to winding N ₂₁ of transformer T ₂ and winding N ₂₂ is connected as shown in FIG.
When a switching power supply is configured by connecting a rectifying and smoothing circuit consisting of diodes D ₁ , D ₂ , chiyoke coil L ₁ , capacitor C _{1 ,} etc., due to the recovery time of flywheel diodes D ₁ , D ₂ , When transistor Q ₂ turns on, diode D ₂ becomes shorted,
A large inrush current flows through transistor _Q2 . Most of the loss in transistor Q ₂ is due to this turn-on loss, and transistor Q ₂
It increases as the turn-on speed becomes slower. For this reason, the switching power supply shown in Figure 4 has the disadvantage that the loss of transistor Q ₂ is large, that a large-capacity and expensive transistor Q ₂ must be used, and that efficiency and reliability are low. .

The present invention eliminates this conventional drawback and improves the transistor turn. on. The purpose of the present invention is to provide a transistor drive circuit with increased speed, reduced loss, smaller transistor size and lower cost, and improved efficiency and reliability.

To achieve this object, the present invention provides a circuit in which, among two transistor circuits connected by a transformer, the switching operation of one transistor circuit causes the other transistor circuit to switch. The turn of the one transistor circuit is charged by flyback energy generated in the circuit when the one transistor circuit is turned off. During off-operation, a charging/discharging circuit is connected that adds the charging voltage to the DC power supply voltage applied to the one transistor circuit or a voltage proportional thereto, and the other transistor circuit is turned on by the added voltage signal. It is characterized by being turned on.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be specifically described below with reference to the accompanying drawings, which are examples. FIG. 5 is a circuit diagram of a transistor drive circuit according to the present invention. In the figures, the same reference numerals as in FIG. 1 indicate functionally identical components. In this embodiment, a diode D ₃ is connected in series with the primary winding of the drive transformer T ₁ , and this primary winding N ₁₁
A charging/discharging circuit is constructed by dividing into windings N ₁₃ and N ₁₄ and connecting a capacitor C ₂ between the connection point of both windings N ₁₃ and N ₁₄ and the anode of diode D ₃ . be. As another example of the charging/discharging circuit,
The diode D ₃ is inserted and connected between the DC power supply voltage V ₁ and the winding N ₁₁ , the winding N ₁₁ and the transistor
Q ₁ , connect the anode of the diode D ₃ to one end of the winding N ₁₃ , and connect the cathode to the collector of the transistor Q ₁ , and connect the anode of the diode D ₃ to one end of the winding N 13.
A circuit configuration in which a capacitor C ₂ is connected between the cathode of and the connection point of the windings N ₁₃ and N ₁₄ can also be considered.

Next, the circuit operation will be explained. First, the capacitor
The operation at startup when the charge on C ₂ is zero will be explained. When a high level "1" input pulse is supplied to the base of the transistor Q ₁ while the DC power supply voltage V ₁ is being supplied, the transistor Q ₁ is turned on. When the transistor Q ₁ is turned on, an exciting current flows through the diode D ₃ to the winding N ₁₁ , and a voltage according to the turns ratio _{N 12 /} N ₁₁ = α ₂ is induced in the winding N 12 of the transformer T ₁ . Transistor Q ₂ is driven by this induced voltage and turned on. in this case,
The capacitor C ₂ is connected to the winding with the terminal on the DC power supply voltage V ₁ side being (+) and the terminal on the winding N ₁₄ side being (-).
It is charged to a voltage approximately equal to the voltage across _N14 .

Next, when the input pulse supplied to the transistor Q ₁ becomes a low level "0", the transistor Q ₁
is the turn. Turn off. This is followed by a transistor
Q ₂ also turns. Turn off. Turns of transistors Q ₁ and Q ₂ . Due to the OFF operation, the excitation energy during the ON state is transferred to the transformer T ₁ as flyback energy.
is stored in the winding. In this case, if we focus on the flyback voltage of the winding _N11 , the polarity of the flyback voltage is opposite to that during the on operation, so the potential is highest on the collector side of the transistor _Q1 .
Then winding N ₁₃ and winding N ₁₄ with connected capacitor C ₂
The connection point with is high, and the end of winding N ₁₄ , connected with diode D ₃ , is the lowest. Therefore, the terminal of capacitor C ₂ at the connection point between windings N ₁₃ and N ₁₄ is connected to (+), and the terminal at the connection point to diode D ₃ is connected to (−).
and is charged through diode _D3 with a voltage approximately equal to the flyback voltage developed across winding _N14 . Therefore, when the capacitor _C2 is off, it is charged with the opposite polarity to when it is on.

After capacitor C ₂ is charged by flyback energy as described above, transistor Q ₁ is turned on by the high level "1" pulse input of FIG. 6a. Turn on. Here, the charging voltage charged in the capacitor C ₂ when it is off is, as described above, the terminal on the connection point side of the winding N ₁₃ and the winding N ₁₄ (+), and the terminal on the connection point side with the diode D ₃ . The polarity is set to (-), and the DC power supply voltage V ₁
It has the same polarity as Moreover, turn. At the initial stage of ON, the charging voltage stored in capacitor _C2 due to flyback energy is transferred to diode _D3.
Since the diode D3 is applied in the opposite direction to the diode D3, the diode _D3 is non-conducting. For this reason, turn. When turned on, the winding N ₁₃ of the transformer T ₁ is connected to the DC supply voltage V ₁
The electromotive force E ₂₁ generated in the winding N ₁₂ is driven by the voltage obtained by adding the charging voltage of the capacitor C ₂ to
As shown by A in Figure 6b, the level increases,
The base current of transistor _Q2 is as shown in FIG. 6c. It peaks at the beginning of on, and the transistor _Q2 turns rapidly as shown in Figure 6d. It will be turned on.

In addition, in the case of the embodiment shown in Fig. 5, the DC power supply voltage
From V ₁ through the capacitor C ₂ , the winding of the transformer T ₁
N ₁₃ is driven, the secondary winding of the transformer T ₁ N ₁₂
An electromotive force E ₂₁ proportional to the turns ratio N ₁₂ /N ₁₃ = α ₁ between the winding N ₁₃ and the winding N ₁₂ is generated, and this electromotive force E ₂₁ causes a base current to flow to the transistor Q ₂ , and the transistor Q ₂ is the turn. Turn on. Winding with winding N ₁₃
The turns ratio α ₁ with N ₁₂ is the total winding N ₁₁ on the primary side and the winding
The turns ratio with N ₁₂ is larger than N ₁₂ /N ₁₁ = α ₂ , and the winding
The electromotive force E ₂₁ generated in N ₁₂ increases. For this reason,
turn. When on, the induced voltage due to the addition of the charging voltage of capacitor C ₂ to DC power supply voltage V ₁
Due to the increasing effect of E ₁₂ and the increasing effect of induced voltage E ₁₂ due to the increase in the turns ratio α ₁ , the electromotive force E ₂₁ generated in the winding N ₁₂ further increases, and as a result, the transistor Q ₂ turns rapidly. It will turn on.

After this, when capacitor C ₂ is charged in the opposite direction to when it is off, diode D ₃ becomes conductive and transformer T ₁
It is driven through the total winding N ₁₁ (= N ₁₃ + N ₁₄ ) on the primary side, and an electromotive force proportional to the turns ratio α ₂ is generated in the secondary winding N ₁₂ , and this electromotive force drives the transistor. Q ₂ turns. Continues on operation.

Then when transistor _Q1 turns off,
The charge stored in the capacitor _C2 is discharged through the diode _D3 and the winding _N14 , and the flyback energy generated in the windings _N11 and _N12 of the transformer _T1 causes the capacitor _C2 to turn. Charges in the opposite direction to when it is on. At the same time, transistor _Q2 turns off rapidly. By repeating the above operation, transistor Q ₂ becomes a transistor.
Continues the switching operation in synchronization with the switching operation of _Q1 .

As mentioned above, in this invention, the capacitor
C ₂ , transformer T ₁ charging/discharging circuit with diode D ₃
The flyback energy generated in the circuit when transistor Q ₁ turns off is used to charge capacitor C ₂ .
Q ₁ 's turn. During ON operation, the charging voltage of the capacitor C ₂ is added to the DC power supply voltage V ₁ , and the transistor Q ₂ is turned on by the added voltage signal. Since I turned it on, I turned on the power transistor _Q2 . By increasing the on-speed, reducing loss, and reducing the size and cost of transistor _Q2 ,
Efficiency and reliability can be improved. Incidentally, in the conventional circuit, the loss of the power transistor _Q2 was about 8W, but with the present invention, this was able to be reduced to about 5W.

The method of configuring the charging/discharging circuit using the diode D ₃ and the capacitor C ₂ is not limited to the one shown in FIG. 5, and various modifications can be considered. Figures 7 and 8
The figure shows an example. First, Figure 7 shows the transformer
The secondary winding N ₁₂ of T ₁ is divided into windings N ₁₅ and N ₁₆ ,
A capacitor C ₂ and a diode are connected to this winding N ₁₅ and N ₁₆ .
It has a circuit configuration in which a charging/discharging circuit consisting of _D3 is connected. One end of the capacitor C ₂ may be connected to the connection point between the resistor R ₁ and the base of the transistor Q ₂ so that the base limiting resistor R ₁ is included in the charging/discharging circuit. For this example, transistor Q ₁
During the off-operation of the transistor _Q1 , the flyback energy produced in the winding _N16 of the transformer T1 charges the capacitor _C2 and the turn of the transistor _Q1 . During on-operation, the charging voltage of capacitor C ₂ is connected to the winding
It is added to the induced voltage generated in _N12 (a voltage proportional to the DC power supply voltage _V1 ), and transistor _Q2 is turned on by this added voltage. It's supposed to be turned on. When the transistor Q ₁ is turned off, the terminal side of the capacitor C ₂ connected to the winding N ₁₆ is (-), and the terminal side connected to the cathode of the diode D ₃ is (+).
It is charged so that This charging voltage causes transistor _Q1 to turn. When turned on, the induced voltage generated in the winding _N12 and the polarity are in the same direction.

In addition, Fig. 8 shows the switching power supply, etc.
When transistor Q ₁ is turned off, the main transformer T ₂
The flyback energy generated in the winding N ₂₃ is used to charge the capacitor C ₂ and the transistor
Q ₁ turns. When turned on, this charging voltage is added to the DC power supply voltage _V1 , and the winding _N11 of the transformer _T1 is driven by this added voltage.
_D4 is a diode for flyback energy charging.

Note that the windings N ₁₃ , N ₁₄ , N ₁₅ , and N ₁₆ may be constructed by individual windings, or the windings N ₁₁ and N ₁₂ may be constructed by providing an intermediate tap. Furthermore, the transistors Q ₁ and Q ₂ can be freely configured with PNP type transistors. Furthermore, the base limiting resistor
R ₁ may be provided on the primary winding N ₁₁ side.

As described above, the present invention provides a circuit in which, among two transistor circuits connected by a transformer, the switching operation of one transistor circuit causes the other transistor circuit to switch. , is charged by flyback energy generated in the circuit when the one transistor circuit is turned off, and is charged by the turn of the one transistor circuit. At the time of ON operation, a charging/discharging circuit that adds the charging voltage to the DC power supply voltage applied to the one transistor circuit or a voltage proportional thereto is connected, and the other transistor circuit is turned on by the added voltage signal. Since it is characterized by turning on, the turn of the transistor. It is possible to provide a transistor drive circuit in which on-speed is increased, loss is reduced, transistors are made smaller and cheaper, and efficiency and reliability are improved.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional transistor drive circuit, Figure 2 is an equivalent circuit diagram of a transformer, Figure 3 is a waveform diagram at each point of the transistor drive circuit in Figure 1, and Figure 4 is a diagram of the transistor drive circuit in Figure 1. Circuit diagram of a switching power supply using a transistor drive circuit, No. 5
The figure is a circuit diagram of a transistor drive circuit according to the present invention, and FIG. 6 is a waveform diagram at each point,
FIGS. 7 and 8 similarly show circuit diagrams in other embodiments. Q ₁ , Q ₂ ...transistor, T ₁ ...transformer,
N ₁₁ , N ₁₂ , N ₁₃ , N ₁₄ , N ₁₅ , N ₁₆ ...Winding, D ₃ ...
...diode, C ₂ ...capacitor.

Claims (1)

[Claims for Utility Model Registration] (1) In a circuit in which the switching operation of one transistor circuit switches the other transistor circuit among two transistor circuits connected by a transformer, the winding of the transformer is charged by flyback energy generated in the circuit when the one transistor circuit turns off, and is charged by the turn of the one transistor circuit. At the time of ON operation, a charging/discharging circuit that adds the charging voltage to the DC power supply voltage applied to the one transistor circuit or a voltage proportional thereto is connected, and the other transistor circuit is turned on by the added voltage signal. A transistor drive circuit characterized by being turned on. (2) The transistor drive circuit according to claim 1, wherein the charging/discharging circuit is connected to a primary winding of the transformer. (3) The transistor drive circuit according to claim 1, wherein the charging/discharging circuit is connected to a secondary winding of the transformer. (4) The transistor drive circuit according to claim 2 of the utility model registration claim, characterized in that the primary winding of the transformer is divided into two parts, and a capacitor constituting the charging/discharging circuit is connected to the connection point thereof. . (5) Utility model registration claim 3, characterized in that the secondary winding of the transformer is divided into two, and the charging/discharging circuit is configured as a circuit loop including one of the two divided windings. Transistor drive circuit described in section.