JPS645987Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to improvement of switching characteristics of a switching regulator.

(Prior Art) There are two types of DC power supply circuits: non-switching type and switching type. As the non-switching DC power supply, for example, a series control power supply is used. A series control type power supply connects a variable voltage element such as a transistor between an unregulated DC voltage and a regulated output, and controls the output with the variable voltage element so that the output is always at a constant voltage. however,
In such a series control type power supply, the voltage variable element consumes power determined by the product of the voltage applied to the voltage variable element and the load current, so heat generation increases and efficiency deteriorates. Therefore, in recent years, switching power supplies, ie, switching regulators, have come to be used instead of non-switching power supplies. In particular, since power supplies for digital circuits require large capacity, switching regulators are mostly used.

FIG. 1 is a block diagram showing an example of a conventional switching regulator. In the figure,
Q ₁ and Q ₂ are Darlington-connected transistors. The base of the first transistor _Q1 is connected to the emitter of the second transistor _Q2 , and the first and second transistors _Q1 , _Q2
The collectors of each are connected in common, forming a Darlington connection. R ₁ is a bias resistor connected between the base and emitter of the first transistor (main transistor) Q ₁ , and R ₂ is a bias resistor connected between the base and emitter of the second transistor Q ₂ across R ₁ . It is resistance. Reference numeral 1 designates a switching circuit that is composed of transistors Q ₁ and Q ₂ and resistors R ₁ and R ₂ and turns on and off a DC voltage V, and 2 a drive circuit that drives the switching circuit 1 . The drive circuit 2 drives the switching circuit 1 via a resistor _R3 . Since the switching circuit 1 is composed of transistors Q ₁ and Q ₂ connected in Darlington, the current amplification factor of the transistor is equivalently
Hfe can be increased, and large current switching can be performed with a small current drive signal from the drive circuit 2. Furthermore, the transistor
Q ₁ and Q ₂ do not have to be of PNP type as shown in the figure, but may be of NPN type. T is a high frequency transformer driven by the switching circuit 1. When the high frequency transformer T is turned on and off by the switching circuit 1, it transmits energy to the secondary side. The AC voltage transmitted to the secondary side is rectified and converted into DC voltage. The magnitude of this DC voltage is constantly monitored, and the driving circuit 2 drives the switching circuit 1 so that the magnitude is always constant.

By the way, when an emitter grounded circuit is used as the switching circuit 1, as shown in the figure,
The following problems arise. In other words, the main transistor _Q1 needs to switch at high speed,
Since there is a charge accumulation time, the switching speed when turning from on to off is generally slow. In order to increase this switching speed, it is necessary to make the base potential higher than the emitter potential (the opposite is true for NPN transistors) to remove the charge that has been charged from the base. operation is impossible. In addition, since transistors Q ₁ and Q ₂ are Darlington-connected (in particular, the higher the voltage resistance of the transistor, the smaller the current amplification factor Hfe is, Darlington connection is necessary), the base-emitter voltage V _BE of transistor Q ₁ is The voltage corresponding to the voltage drop drops, and power determined by the product of this voltage drop and the flowing current is consumed, causing the main transistor _Q1 to generate heat and reduce its efficiency.

(Objective of the Invention) The present invention has been made in consideration of the above points, and its objective is to realize a switching regulator that can increase the switching speed of the main transistor and correct the voltage drop of the main transistor to increase efficiency.

(Structure of the invention) The present invention that achieves the above object includes a switching circuit composed of Darlington-connected transistors that turn on and off a DC voltage, a drive circuit that drives the switching circuit, and a switch that is driven by the switching circuit. A switching regulator comprising a high frequency transformer, characterized in that a weak positive feedback winding is connected between the Darlington connected first transistor and second transistor. .

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. Components that are the same as those in FIG. 1 are designated by the same numbers. In the figure, 1' is a switching circuit;
T' is a high frequency transformer composed of primary windings L ₁ and L ₂ and secondary winding L ₃ . Among the primary windings, the _L2 winding is connected between the base of the first transistor _Q1 and the emitter of the second transistor _Q2 . In the figure, the black circles attached to the primary windings L ₁ and L ₂ indicate the polarity of the windings. As is clear from the figure,
The _L2 winding is wound with opposite polarity to the _L1 winding. Therefore, positive feedback is applied from the base of the main transistor _Q1 to the emitter of the transistor _Q2 . In this invention, the number of turns of the _L2 winding (positive feedback winding) is reduced to apply weak positive feedback, and the turns ratio is taken into consideration so that the positive feedback winding _L2 alone will never run free. There is a need. The operation of the circuit configured as described above will be explained as follows.

In the circuit shown in the figure, switching circuit 1'
is switched by a drive signal from the drive circuit 2, and switches the DC voltage V. Due to this intermittent DC voltage V, a charging/discharging current flows through the high frequency transistor T', transmitting energy to the secondary side. The high frequency alternating current transmitted to the secondary side is rectified,
After being smoothed, it is supplied as a DC voltage to external electrical circuits, etc. In this case, in the switching operation of the main transistor _Q1 , the base potential becomes higher than the emitter potential due to the voltage induced in the positive feedback winding _L2 . As a result, transistor Q ₁
The charge stored in Q1 is quickly discharged from its base, reducing the switching speed when the transistor _Q1 turns from on to off.

FIG. 3 is a diagram showing the overall configuration of the switching regulator shown in FIG. 2. 3 is a rectifier circuit that converts AC voltage to DC voltage V, D is a rectifier diode that rectifies the high frequency AC generated in the secondary winding L ₃ of high frequency transformer T', C ₁ is a smoothing electrolytic capacitor, C ₂ is also a smoothing capacitor.
The direct current smoothed by capacitors C ₁ and C ₂ is taken out as an output voltage for the power supply. Since the rectifier diode D smoothes high frequencies, it must be capable of high-speed switching operation compared to the rectifier diode used in the rectifier circuit 3.
Furthermore, since the smoothing capacitor _C2 removes high frequency noise, it must be a capacitor with good high frequency characteristics (for example, a ceramic capacitor).
The secondary side DC output is input to the voltage detection and switching drive circuit 2'.

In the circuit configured in this way, the voltage detection and switching drive circuit 2' constantly monitors the secondary side DC output, and drives the switching circuit 1' so that the secondary side DC output always takes a constant value. do. As a result, the secondary side DC output is always kept constant regardless of the magnitude of the load current taken out to the outside. As a method of such voltage control, for example, a pulse width modulation (PWM) method is used. The PWM method changes the pulse duty ratio depending on the magnitude of the load current.
When the load current is small, the duty ratio is made small, and when the load current is large, the duty ratio is made large to maintain the output voltage constant. like this
PWM control is performed by voltage detection and switching drive circuit 2'.

The switching operation of the switching circuit 1' using Darlington transistors Q ₁ and Q ₂ is as follows.
Since the explanation is the same as that for the figure, the explanation will be omitted. In other words, due to the positive feedback action of the positive feedback winding _L2 wound on the primary side of the transformer, the main transistor
_Q1 's on-to-off time is significantly reduced,
High-speed switching operation becomes possible.

FIG. 4 is a diagram showing a comparison between a conventional switching regulator and a switching regulator according to the present invention. A shows the case of the conventional example, and b shows the case of the present invention. A is the second transistor
B indicates the base potential E ₃ of Q ₂ , B indicates the base potential E ₂ of the first transistor (main transistor) Q ₁ , and C indicates the collector potential E ₁ of the first transistor Q ₁ . As is clear from the figure B, in the present invention, the base potential E ₂ of the first transistor Q ₁
The upper and lower limits of e ₁ and
The amplitude increases by e ₂ . These amplitude differences produce the following effects.

First, if the upper limit of the base potential E ₂ of the main transistor Q ₁ is large in amplitude by e ₁ , then the transistor Q ₁
This has the effect of drawing out charge from the base of Q1, thereby reducing the operating speed required to turn off the main transistor _Q1 . As a result, efficiency increases because power loss during turn-off is reduced. Next, if the lower limit of the base potential E ₂ of the main transistor Q ₁ has a larger amplitude by e ₂ , then the transistor
Q ₁ can be turned on completely. As shown in Figure C, in the case of the conventional example, the main transistor
Since Q ₁ is not completely turned off, a difference of e ₃ occurs between the power supply voltage V and the collector potential as shown in the figure. Power determined by the product of this difference e ₃ and the flowing current is consumed and heat is generated, causing a decrease in efficiency.

The positive feedback winding L ₂ used in the present invention has a relatively small current and a voltage that is similar to that of the main transistor Q ₁
It is designed to be large enough to compensate for the voltage drop in the base-emitter voltage _VBE . In many cases, this winding has a small number of turns and can be manufactured very easily.

In the above explanation, a flyback type switching regulator was used as an example.
The present invention is not limited to this, and can be applied not only to other forward type switching regulators but also to all switching circuits that drive high frequency transformers. Further, the transistor used for the Darlington connection is not limited to the PNP type, and may be an NPN type.

(Effects of the invention) As explained in detail above, according to the invention,
By connecting a weak positive feedback winding between the first and second transistors that make up the Darlington connection, the switching speed of the transistors can be increased and the voltage drop of the switching transistor can be compensated for. A switching regulator that can increase efficiency can be realized.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a conventional device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a diagram showing the overall structure of the switching regulator shown in Fig. 2. , FIG. 4 is a diagram showing a comparison between the conventional device and the device of the present invention. 1, 1'... Switching circuit, 2... Drive circuit, 2'... Voltage detection and switching drive circuit,
3... Rectifier circuit, Q ₁ , Q ₂ ... Transistor, T,
T′...High frequency transformer, R ₁ ~ R ₃ ... Resistor, L ₁ ~
L ₃ ... winding, D ... diode, C ₁ , C ₂ ... capacitor.

Claims (1)

[Scope of utility model registration request] a switching circuit composed of Darlington-connected transistors that turns on and off a DC voltage; a drive circuit that drives the switching circuit;
In a switching regulator constituted by a high frequency transformer driven by the switching circuit, a weak positive feedback winding is connected between the Darlington connected first transistor and second transistor. Features a switching regulator.