JPH0715213Y2 - Switching transistor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a circuit for separately driving a switching transistor, and more specifically, a rectangular wave output from a feedback winding provided in a main transformer and a control circuit. The present invention relates to a drive circuit that switches a transistor with a combined signal of a positive and negative timing pulse signal.

[Prior Art] In a separately excited switching power supply, a switching transistor that turns on / off a current flowing through a primary winding of a main transformer is controlled by an external drive circuit. All necessary energy is supplied from an external circuit.

The conventional technique will be briefly described with reference to FIG. The primary side main circuit of the power supply includes a primary winding of the main transformer T ₁ and a switching transistor Q ₁ connected in series with the primary winding, and the secondary side main circuit includes a secondary side winding and a rectifying / smoothing circuit 10 connected thereto. Composed of. AC input is auxiliary transformer T ₃ and rectifier diode D ₁
In addition, it is converted into direct current by the auxiliary power supply 12 composed of the smoothing capacitor C ₁ and supplied to various control drive circuits. Most of that power is used to drive the switching transistor Q ₁ via the pulse transformer T ₄ by switching the control transistor Q ₄ .

For the collector current I _c flowing through the switching transistor Q ₁ , it is necessary to flow the base current I _B of 1 / h _fe , but all the energy of this base current is transferred from the AC input to the auxiliary transformer T ₃ and the pulse transformer T. Supplied on route through ₄ . The switching transistor is turned on and off by the on / off operation of the control transistor Q _4.
Of the on-off operation Q ₁ is controlled.

[Problems to be solved by the invention] However, in the conventional technology, originally, all the energy required for the primary side of the switching power supply is converted to the secondary side by the auxiliary transformer T ₃ and returned to the primary side by the pulse transformer T ₄ . Therefore, the components that make up them require high power. The power generated by the auxiliary power supply 12 is also used for constant voltage control of the switching power supply, etc., but in the prior art, the ratio of supplying the base current of the switching transistor Q ₁ is extremely large.

For this reason, the conventional technique has a drawback in that the components in the drive control circuit are inevitably large in size, not only requiring a wide mounting space but also being expensive.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology and to reduce the energy supplied from the outside because the switching transistor is separately excited and controlled. Therefore, the components used can be downsized and the mounting space can be reduced. It is to provide a drive circuit of a switching transistor that can realize reduction and cost reduction.

[Means for Solving Problems] The present invention relates to a drive circuit for a switching transistor in a switching power supply, a control circuit for generating a positive / negative pulse signal that defines timing for causing switching,
A circuit for supplying power for keeping the conduction state of the switching transistor is separately provided and combined in parallel, and the switching transistor is driven by the combined signal thereof. The power supply circuit is a circuit including a feedback winding provided in the main transformer of the switching power supply, and is configured to use the rectangular wave output induced in the feedback winding. Further, the control circuit includes a pulse transformer and is configured to generate a positive and negative timing pulse signal from a secondary winding of the pulse transformer via a capacitor that blocks a DC component.

[Operation] The switching transistor is turned on / off by a positive / negative timing pulse signal generated from the control circuit. When the control terminal of the switching transistor is forward biased by the pulse signal from the control circuit, the switching transistor is turned on and a current flows through the primary winding of the main transformer. As a result, a voltage is induced in the feedback winding and applied to the control terminal of the switching transistor, so that the transistor continues to maintain the conducting state.

Next, when a reverse pulse is supplied from the control circuit and the control terminal of the switching transistor is reverse biased, the transistor is turned off and the current flowing in the primary winding of the main transformer is cut off, and the current to the feedback winding is cut off. No induced voltage is generated, and the transistor remains off.

In this way, the signal supplied from the control circuit is a pulse signal, no direct current flows, and the energy required for the switching transistor to keep conducting is directly supplied from the main transformer, so that the control circuit and the drive circuit The current capacity of the auxiliary power supply etc. can be extremely small.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of a monolithic switching power supply incorporating a switching transistor drive circuit according to the present invention, and FIG. 2 is a base current waveform diagram in the drive circuit. is there. The main circuit of the switching power supply is the fourth
It may be similar to the conventional one as shown. The primary side of the main transformer T ₁ includes a series circuit of a primary winding N ₁₁ and a switching transistor Q _1, and the secondary side includes a secondary winding N ₁₂ and a rectifying / smoothing circuit 10 connected thereto.

The first difference of the present invention from the prior art is that the main transformer is used in spite of the separately excited switching power supply.
The point is that another feedback winding N ₁₃ is provided at T ₁ , and its output is connected to the base of the switching transistor Q ₁ via the diode D ₂ and the resistor R ₁ . Here, the feedback winding N ₁₃ , the diode D _2, and the resistors R ₁ and R _{2 form the} power supply circuit 14.

The second difference of the present invention from the prior art is that a control circuit 16 for supplying positive and negative timing pulse signals to the base of the switching transistor Q ₁ is connected in parallel with the power supply circuit 14. The control circuit 16 is mainly composed of a pulse transformer T ₂ connected to the auxiliary power supply 12 and two control transistors Q ₂ and Q ₃ . The winding N ₂₁ of the pulse transformer T ₂ is connected to the control transistor Q ₂ and
₂₂ is connected to the control transistor Q ₃ . Pulse transformer
The secondary winding N ₂₃ of T ₂ is connected between the base and emitter of the switching transistor Q ₁ via a capacitor C ₂ that blocks a DC component. In FIG. ₁ , black circles attached to the windings of the main transformer T ₁ and the pulse transformer T ₂ represent the polarities of the respective transformer windings.

The operation of the thus configured switching power supply is as follows. First, the main circuit of the switching power supply main body excluding the control circuit 16 has almost the same circuit configuration as that of a known converter based on blocking oscillation. In principle, if the starting resistance is added by replacing the diode D ₂ with a capacitor, self-excitation will occur. Oscillate. That is, the base of the switching transistor Q ₁ −
If the emitter is forward-biased, the collector current thereof causes an induced voltage in each winding of the transformer, and the induced voltage of the base winding is positively fed back to the base of the transistor. As a result, a regeneration action occurs and the transistor continues to be turned on (however, I _c ≦ h _FE · I _B is satisfied). When the collector current further increases, the base current becomes insufficient, and a reverse reproducing action occurs, turning off the transistor. The operating frequency of this on / off is basically determined by the circuit constants of the converter including the inductance of the transformer and its stray capacitance and winding resistance, and also varies depending on the input and output conditions.

The control circuit 16 of the present invention fulfills the function of determining the positive and negative timing pulse signals from the outside, not the timing of switching the converter on and off by the circuit constants of the converter. Control transistor Q ₂ , Q ₃
The base of is connected to a control pulse generator (not shown) for constant voltage operation, and is controlled to alternately turn on and off by an output generated there.
Now, if the control transistor Q ₂ is turned on, a current will flow in the N ₂₁ winding of the pulse transformer T ₂ and this will lead to winding N 2.
_The base current I _B2 flows due to the voltage induced in ₂₃ . This base current I _B2 is a narrow positive pulse 34 as shown in FIG. 2 because the DC component is blocked by the capacitor C ₂ . Since it is a positive pulse, the base-emitter of the switching transistor Q ₁ is forward-biased and turned on, and the collector current I _c flows through the primary winding N ₁₁ of the main transformer T ₁ .
This collector current I _c induces a voltage in the feedback winding N ₁₃ , which passes through the diode D ₂ and the resistor R ₁ to generate the base current I _B1.
Flows. Then, the base current I _B1 causes a collector current I _c (= h _EF · I _B1 ) to flow. This is a reproducing action similar to the blocking oscillation described above. Due to this reproducing action, the switching transistor Q ₁ continues to be turned on while the switching transistor Q ₁ satisfies I _c ≦ h _FE · I _B1 . That is, the power for keeping the switching transistor Q ₁ in the ON state is continuously supplied from the feedback winding N ₁₃ .

Next, while the switching transistor Q ₁ continues to be turned on, when the control transistor Q ₃ is turned on, a current flows through the winding N ₂₂ of the pulse transformer T ₂ , which causes a voltage in the winding N ₂₃ . This voltage has a polarity opposite to that when the control transistor Q ₂ is turned on. Therefore, the base current I _B2 becomes the narrow negative pulse 36. This negative pulse reverse biases the base-emitter of the switching transistor Q ₁ in spite of the presence of the base current I _B1 , that is, the negative pulse 36 also draws the base current I _B1 at the same time, and the switching transistor Q ₁ is shorted by the base current. Turn off. Therefore, the collector current I _c becomes zero and no voltage is induced in the feedback winding N _13, and the switching transistor Q ₁ continues to maintain the off state.

In this way, the control transistors Q ₂ and Q ₃ are turned on alternately.
Corresponding to repeated off-states, the base of switching transistor Q ₁ has a base current generated by control circuit 16.
The I _B2 and a power supply circuit 14 the base current I _B1 and the synthesized current I _B is supplied on and off states of the words the present invention produced by the timing of switching the blocking oscillator on and off, the converter circuit constants It is not determined by, but by a positive or negative timing pulse signal from the outside. As can be seen from the operation waveform diagram of FIG. 2, most of the energy required to drive the switching transistor Q ₁ is supplied from the power supply circuit 14 including the feedback winding N ₁₃ , and the signal generated by the control circuit 16 is Since it is a pulse signal with a narrow width and no DC component flows, only a very small amount of energy needs to be handled. Since most of the energy does not pass through the auxiliary transformer T ₃ and the pulse transformer T ₂ , the circuits can be remarkably downsized and the power loss can be kept low.

The case of the one-stone switching power supply has been described above as an example, but the present invention can be similarly applied to other switching power supplies, such as a half-bridge type power supply. Third example applied to half-bridge type power supply
Shown in the figure. Since the basic circuit configuration and its operation are the same as those shown in FIG. 1, detailed description will be omitted. Here, reference numeral T ₅ is a main transformer, N ₅₁ is its primary winding, N ₅₂ is a secondary winding, N ₅₃ and N ₅₄ are feedback windings, Q ₅ and Q ₆ are switching transistors, and T ₆ and Each T ₇ is a pulse transformer. Reference numeral 24 indicates a power supply circuit, and reference numeral 26 indicates a control circuit.

[Advantages of the Invention] Since the present invention is configured such that the power supply circuit including the feedback winding provided in the main transformer and the control circuit for generating the positive and negative timing pulse signals are combined in parallel and connected to the control terminal of the switching transistor. , The relatively large energy required to keep the switching transistor in the ON state is supplied directly from the main transformer,
Since the control circuit does not need to supply direct current and only needs to apply positive and negative timing pulses at the rising and falling edges, the control circuit and the auxiliary power supply have an excellent effect that the required power is significantly reduced.

As a result, the size can be reduced, the mounting space can be reduced, and inexpensive parts can be used.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a monolithic switching power supply incorporating a drive circuit according to the present invention, FIG. 2 is an operation waveform diagram of the drive circuit, and FIG. 3 is a circuit showing another embodiment of the present invention. FIG. 4 and FIG. 4 are circuit diagrams showing an example of a conventional technique. 10 …… Rectifying and smoothing circuit, 12 …… Auxiliary power supply, 14,24 …… Power supply circuit, 16,26 …… Control circuit, T ₁ …… Main transformer, Q
₁ …… Switching transistor, T ₂ …… Pulse transformer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-56528 (JP, A) Actual development S53-164753 (JP, U) JP-B 58-43935 (JP, B2)

Claims (1)

[Scope of utility model registration request] 1. A circuit for separately driving a switching transistor for turning on / off a current flowing through a primary side winding of a main transformer of a switching power supply, including a feedback winding provided in the main transformer to generate a rectangular wave output. Generating a positive timing pulse signal through a power supply circuit and a capacitor for blocking a direct current component from a secondary winding of the transformer by applying an auxiliary power supply voltage to the pulse transformer through the first control transistor; A control circuit for applying an auxiliary power supply voltage to the pulse transformer via the second control transistor and generating a negative timing pulse signal via a capacitor for blocking a direct current component from the secondary winding of the transformer;
A switching transistor drive circuit, wherein the output of the power supply circuit and positive and negative timing pulse signals of the control circuit are applied in parallel to the control terminal of the switching transistor.