JPH028548B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching type power supply device such as a DC/CD converter.

Switching type power supplies generally employ a method in which pulse width control (PWM) is used to control the current in the primary winding of a power transformer using a transistor switch. Figure 1 shows the basic block configuration of a conventional device. It is a diagram.

In the figure, a DC power supply 2 and a switching transistor 3 are connected to the primary winding side of a power transformer 1.
are connected in series with the collector circuit, and a rectifying and smoothing circuit 4 is connected to the secondary winding side thereof. The output voltage of the rectifying and smoothing circuit 4 is detected by a voltage dividing resistor 5 and transmitted to a pulse width control (PWM) circuit 6, which generates a pulse signal with a pulse width corresponding to the detected voltage. This pulse signal is supplied to the drive circuit 7, and the drive circuit 7 drives the base current of the transistor 3 with this pulse signal, thereby controlling the switching of the primary winding current of the power transformer 1. In addition, a pulse width control circuit 6, a drive circuit 7
An operating power supply voltage Vc is supplied from an auxiliary power supply 8 to the auxiliary power supply 8.

FIG. 2 is a more detailed circuit diagram of the power transformer 1, transistor 3, and drive circuit 7 portions shown in FIG. In the drive circuit 7, a pulse signal from the pulse width control circuit 6 is input to the base of the transistor 10. The collector current of this transistor 10 is supplied from the auxiliary power supply 8 via the primary winding of an insulating transformer 11. As described above, the secondary winding of the transformer 11 is connected to the base of the transistor 3 via the resistor 12, and the collector of the transistor 3 is connected to the primary winding of the power transformer 1. Note that the resistor 13 is a bias resistor.

In such a conventional device, when the power supply output is large or the input voltage is low, the primary winding current of the power transformer 1, and therefore the collector current Ic of the transistor 3, increases, and the A large base current must be supplied. That is, in this conventional device, since the output voltage Vc of the auxiliary power supply 8 is constant, the base current Ib of the transistor 3 is driven by a constant current and becomes constant, and has no relation to the collector current Ic.
Normally, the base current Ib is the value obtained by dividing the maximum value of the collector current Ic by the current amplification factor h _fe with some margin, so if h _fe =10, then Ib = Ic/7 to Ic/5. This base current Ib has a value that cannot be ignored compared to the collector current Ic. Since this base current Ib is supplied from the auxiliary power supply 8 through the transformer 11, the output of the auxiliary power supply 8 is also required to have a size that cannot be ignored from the perspective of the entire power supply device. In addition, the base-emitter voltage Vbe of transistor 3 and the auxiliary power output voltage
The resistor 12 is required to absorb variations in Vc, but since a large base current Ib flows through this resistor 12, the power loss here cannot be ignored. Furthermore, since the drive circuit 7 is designed to match the maximum output of the power supply device, unnecessary power loss occurs when the output is small. If the power handled by the drive circuit 7 increases, current loss increases, the voltage and current of the components increases, the shape of the components increases, and the device becomes larger.

Furthermore, since the base current Ib of the transistor 3 is constant, when the collector current Ic is small, that is, when the output is small, the transistor 3 becomes overdriven, and the storage time of the transistor 3 increases due to the surplus carrier. There is a drawback that the switching frequency cannot be increased and the power transformer 1 cannot be made smaller.

FIG. 3 shows a conventional CT drive circuit which is sometimes used to solve the drawbacks of the conventional device.

In the figure, two transistors 16 and 17 are connected to the primary winding 151 of a current transformer ₁₅ , and these transistors 16 and 17 are driven by two-phase pulses, respectively. In addition, the secondary side of the current transformer 15 has two secondary windings 15.
_{The secondary winding 15 2 is} connected to the base of the transistor ₃ . This transistor 3
The collector of the transformer 1 is connected to the transformer 1 through the secondary winding 15 ₃ .
connected to the primary winding of the

In this CT drive circuit, when the primary winding ₁₅₁ of the current transformer 15 is driven with a sawtooth waveform current as shown in FIG. The current fed back through the transformer 15, Ib=Ic・n ₃ /n ₂ , where n ₂ is the number of turns in the secondary winding 15 ₂ n ₃ is the number of turns in the secondary winding 15 ₃ . It flows in a square wave shape as shown in b. In other words, part of the collector current Ic is fed back to the base current Ib, and the drive circuit 7
can reduce power consumption. Also, the base current
Since Ib is a current proportional to collector current Ic,
By appropriately selecting the turns ratio n ₃ /n ₂ , the storage time of transistor 1 can be reduced and the switching frequency can be increased.

Although such a drive circuit is advantageous in terms of power, since two-phase pulses are required to drive the drive circuit, the circuit configuration is complicated and it is difficult to increase the switching frequency.
Another drawback is that it is difficult to use control ICs for switching power supplies, which have recently become popular.

The present invention has been made to solve the drawbacks of the conventional device described above, and its purpose is to always optimize the base current of the switching transistor for driving the power transformer. The storage time is reduced, the switching frequency is increased to a high frequency, the power transformer is made smaller, and the power loss of the drive circuit that supplies the base current to the switching transistor is reduced to improve efficiency.
Accordingly, it is an object of the present invention to provide a small, highly efficient, and high frequency switching type power supply device that is capable of downsizing an auxiliary power source.

The present invention is characterized by a current transformer in which the current flowing through the primary winding of the power transformer flows to the primary side, and a secondary current of this current transformer is transferred to a secondary current for driving the primary winding of the power transformer. a second switching element connected to the control input of the first switching element, and configured to apply a variable pulse width pulse signal for output voltage control to the control input of the second switching element; be.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be explained based on the drawings.

FIG. 5 is a circuit diagram of a device according to an embodiment of the present invention, and this circuit is applied to portions corresponding to the power transformer 1, switching transistor 3, and drive circuit 7 in FIG.

In the figure, a variable pulse width pulse signal from the pulse width control circuit 6 is input to the base of a transistor 20, and the collector of this transistor 20 is connected to the output voltage Vc of the auxiliary power supply 8 via the primary winding of an insulating transformer 21. Connect to. Isolation transformer 21
The secondary winding of is connected at one end to the base of transistor 23 via resistor 22 and at the other end directly to the base of transistor 3. Further, the collector of the transistor 3 is connected to the primary winding of the power transformer 1 via the primary winding of the current transformer 24. On the secondary side of the current transformer 24, the current flowing through the secondary winding is connected to a backflow prevention diode 2.
5. Connect to the base of the transistor 3 via the collector and emitter of the transistor 23. Note that the resistors 26 and 27 are bias resistors. Further, the resistor 28 connected between the collectors of the transistors 3 and 23 is a starting resistor,
Current flows only the first time transistor 3 becomes conductive.

Next, the operation of this embodiment device will be explained.

Similar to the conventional CT system, this device converts the collector current Ic of transistor 3 into current transformer 2.
4 to the base current Ib,
This differs from the conventional method in that the base current Ib of the transistor 3 is controlled on and off by the transistor 23.

That is, the pulse signal from the pulse width control circuit 6 is transmitted through the transistor 20 and the current transformer 21.
It is input to the base of transistor 23 via.
As a result, when transistor 23 becomes conductive, a base current flows from the positive power supply V ₊ to the base of transistor 3 via power transformer 1, current transformer 24, resistor 28, and transistor 23, transistor 3 becomes conductive, and collector current Ic increases. current·
It flows into the primary winding of the transformer 24. Then, an induced current flows in the secondary winding, and this current flows into the base of the transistor 3 via the diode 25 and between the emitter and collector of the transistor 23.
Therefore, part of the collector current Ic becomes the base current
He will be returned to Ib.

When the drive circuit is configured in this way, the base current Ib' of the transistor 23 is sufficiently small compared to the drive circuit shown in FIG.
output can be reduced. In addition, the transistor 20
Since the circuit configuration at the earlier stage is the same as that of the conventional device shown in FIG. 2, it is easy to use a control IC. Furthermore, since an appropriate base current Ib can always be supplied to the transistor 3 according to its collector current Ic, surplus carriers are sufficiently reduced and its storage time is shortened.
The switching frequency can be increased by considering the operating speed.

Figures 6 and 7 are circuit diagrams showing an application example of the power supply device of the present invention, and this application example circuit has an additional circuit for removing surplus carriers in order to further improve the storage time of transistor 3. .

In the circuit of FIG. 6, the transformer 21 in FIG. 5 is replaced with a transformer 21' having two secondary windings, and one of the secondary windings is connected between the base and emitter of the transistor 3. The surplus carrier of the transistor 3 is removed by the reverse polarity when it is off, and the voltage from this winding is used to start the transistor 3 when it is on, and the starting resistor 28 is omitted.

In the circuit of FIG. 7, the base of the transistor 31 is connected to the secondary winding of the transformer 21 in the circuit of FIG.
The emitter and collector of transistor 1 are connected between the base and emitter of transistor 3.
Excess carrier is removed from the base of.

As explained above, according to the present invention, it is possible to maintain the base current of the switching transistor for driving the power transformer at an optimal value according to its collector current, and thereby the switching transistor
It is possible to reduce the storage time of the transistor, increase the switching frequency, and downsize the power transformer. Also, switching
By controlling the on/off of the transistor using a separate transistor, power loss in the drive circuit can be reduced, efficiency can be improved, and the components used can be made smaller. Along with this, it is also possible to reduce the output of the auxiliary power source and thereby downsize the device. Furthermore, since the device of the present invention does not use two-phase pulses unlike the conventional CT system, the circuit configuration is simple and the use of a control IC is easy. In this manner, the present invention realizes a small, highly efficient switching type power supply device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the basic parts of a conventional switching type power supply device. FIG. 2 is a circuit diagram of the main parts in FIG. 1. FIG. 3 is a circuit diagram of a drive circuit of a conventional CT type power supply device. FIG. 4 is a waveform diagram of the primary winding n ₁ current and base current Ib in FIG. 3. FIG. 5 is a circuit diagram of a device according to an embodiment of the present invention. FIG. 6 and FIG. 7 are circuit diagrams showing an example of application of the device of the present invention. DESCRIPTION OF SYMBOLS 1... Power transformer, 2... DC power supply, 3... Transistor, 4... Rectifying and smoothing circuit, 6... Pulse width control circuit, 7... Drive circuit, 23... Transistor, 2
4...Current transformer.

Claims (1)

[Claims] 1 A power transformer 1 is provided, a DC power source and a first switching element 3 are connected in series on the primary winding side of the power transformer, and a rectifying and smoothing device is connected on the secondary winding side of the power transformer. In a switching type power supply device, the circuit is connected, a pulse signal with a variable pulse width corresponding to the output voltage of the rectifying and smoothing circuit is generated, and opening/closing control of the first switching element is performed in accordance with this pulse signal. , a current transformer 24 whose primary winding is connected in series to the primary winding of the power transformer 1; a second switching element 23 whose output is connected to the control input of the first switching element 3; A circuit that supplies the pulse signal with the variable pulse width to the control input of the second switching element; and a diode 25 that supplies the operating DC current of the second switching element from the secondary winding of the current transformer. A switching type power supply device characterized by: 2 the first switching element and the second switching element;
2. The switching type power supply device according to claim 1, wherein each of the switching elements is a transistor, and the control input thereof is a base input. 3. The switching type power supply device according to claim 1, further comprising means for applying to the control electrode a voltage having a polarity that discharges the accumulated charge in the control electrode when the first switching element is in an open state.