JPH0327765A - Switching regulator - Google Patents

Abstract

PURPOSE:To elevate efficiency by constituting a rectifying element on the secondary side of a transformer out of a FET, etc., and turning on or turning off this synchronously with a switching element. CONSTITUTION:A switching regulator is constituted of a transformer 3 for voltage conversion, a switching element 4, a chock coil 7, a rectifying element 13, etc., and also this is equipped with a driving circuit 10, a pulse width modulating circuit 11, and an oscillating circuit 12 for the switching element 4. And a FET is used for this rectifying element 13, and the second driving circuit 14, which turns on or turns off this synchronously with the switching element 4, and an insulating buffer circuit 15 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching regulator using a voltage conversion transformer, and particularly to a regulator with an improved rectifier circuit.

[Conventional technology]

An example of a switching regulator using a conventional voltage conversion transformer is explained using Figure 2. In this figure, la and lb are input terminals, 2a and 2b are output terminals, and the input voltage is converted into voltage by a voltage conversion transformer 3 and output.

A switching element 4 constituted by an FET is connected to the primary winding N of the transformer 3. Further, the secondary winding N2 of the transformer 3 includes a rectifying element 5 that performs a rectifying operation when the switching element 4 is ON, a rectifying element 6 that performs a rectifying operation when the switching element 4 is OFF, and a rectifying element 5 that operates. When the rectifying element 6 is in operation, the choke coil 7 and the capacitors 8a and 8a supply power to the outside through the output terminals 2a and 2a, and the switching element 4 is connected to the transformer 3 when it is OFF. A rectifying element 9 is connected to fix the output voltage to a constant output voltage, and to suppress the voltage applied when the switching element 4 and the rectifying element 5 are turned off to below the rated value.

Further, a drive circuit 10 for driving the switching element 4 is connected to the switching element 4, and the output voltage is detected and the variation thereof is converted into a change in pulse width, and the drive circuit is operated, thereby controlling the switching element 4. A pulse width conversion circuit l1 that operates to change the ON/OFF ratio and keep the output voltage constant is connected to an oscillation circuit 12 that determines the repetition frequency of the pulse width modulation circuit.

In this switching regulator, when the switching element 4 is turned on by a signal from the drive circuit 10, the rectifying element 5 is turned on depending on the polarity of each winding N1, Nt of the voltage conversion transformer 3, and energy is stored in the choke coil. At the same time, power is supplied to the outside via the output terminals 2a and 2b.

Furthermore, when the switching element 4 is turned off, the rectifying element 5 is turned off, and the rectifying element 6 is turned on, so that the energy stored in the choke coil 7 is supplied to the outside via the output terminals 2a, 2a.

At this time, the voltage is detected by the pulse width modulation circuit l1, converted into a change in pulse width, and kept constant by changing the ON/OFF ratio of the switching element 4 via the drive circuit 10.

[Problem to be solved by the invention]

In the switching regulator described above, when the switching element 4 changes from ON to OFF, the rectifying element 5 changes from ON to OFF, and the rectifying element 6 changes from OFF to ON.

However, normally. Since diodes are used for the rectifying elements 5 and 6, there is a reverse recovery time even though the rectifying element 5 is in a reverse bias state when it is OFF, and during this period, the rectifying element 5 is in a conductive state and the voltage conversion transformer is The N2 winding No. 3 is short-circuited by the rectifying elements 5 and 6.

As a result, transient losses in the voltage conversion transformer 3, switching element 4, and rectifying elements 5 and 6 increase.

In particular, as the repetition frequency of the switching element 4 is increased, such transient loss increases, and there is a problem that excessive stress is applied to the voltage conversion transformer 3, the switching element 4, and the rectifying elements 5 and 6.

An object of the present invention is to provide a switching regulator that prevents iPJ loss and excessive stress.

[Means to solve the problem]

The switching regulator of the present invention includes a rectifying element such as an FET as a rectifying element inserted on the secondary side of a voltage converting transformer, and a switching regulator in which this rectifying element is inserted on the primary side of the voltage converting transformer. ON, OFF in sync with
It is configured to be capable of F drive.

[Operation] In this configuration, the rectifying element on the secondary side is turned ON and OFF in synchronization with the switching element on the primary side, thereby preventing transient loss of the rectifying element.

〔Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, the same parts as in the conventional circuit of FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, instead of the rectifying element 5 in the configuration of FIG. 2, an ON/OFF type rectifying element 13 made of an N-channel field effect transistor (FET) is connected to the winding N2 of the voltage conversion transformer 3. , this is connected to the second drive circuit 14
It is configured to be driven by. Also, this second
The drive circuit l4 is connected to the pulse width modulation circuit 11 via an insulated buffer circuit l5, and this pulse width modulation circuit l
The device is configured to be driven by one electrically isolated output signal.

According to this configuration, the switching element 4 is operated by the drive circuit 10 operated by the output signal of the pulse width modulation circuit 1.
turns ON, the windings N1 and Nz of the voltage conversion transformer 3
Due to the polarity of , a voltage is generated in the direction of the ↑ mark in the winding Nt. At this time, the rectifying element 13 is turned on in synchronization with the switching element 3 by the second drive circuit 14 operated by the output signal of the pulse width modulation circuit l1 via the insulated buffer circuit 15. Therefore, the voltage generated in the winding N2 is supplied to the outside via the second switching element 13 and the choke coil 7 from the output terminals 2a and 2b.

Next, the switching element 4 and the rectifying element l3 are rapidly turned off in synchronization by the drive circuit 10 and the second drive circuit 14 operated by the output signal of the pulse width modulation circuit 1l. No voltage is supplied to the outside. When the rectifying element 13 is turned off in this way, the energy stored in the choke coil 7 is supplied to the outside from the output terminals 2a and 2b via the rectifying element 6, and the voltage is converted by the rectifying element l3 and the rectifying element 6. There is almost no short-circuit period in the N2 winding of transformer 3. Therefore, the transient losses of the voltage conversion transformer 3, the switching element 4, and the rectifying elements 6 and 13 can be almost ignored, and higher efficiency of the circuit can be expected.

Furthermore, even if the repetition frequency of the switching element 4 is set to a high value, the increase in loss due to the high frequency is considerably smaller than when using a diode, since a FET with a switching speed faster than a diode is used as the rectifier element l3. can be expected. Furthermore, the saturation voltage between the drain and the source in the ON state of the FET changes linearly as the current increases or decreases, so it can be considered as a resistance component. When the forward voltage drop of the diode is VF and the resistance when the FET is ON is R DS (ON, and the flowing current is l0, vF can be considered to be an almost constant value, so the following formula, Vy > I@ If the FET is used within the range of current ■ that satisfies ×Ros(oN>), it becomes possible to design the FET with less loss caused by the above-mentioned I0 than with a diode.

Note that the present invention can obtain similar effects even when a bibolar transistor is used as the switching element.
Also, the polarity of the power supply voltage. Regarding the polarity of the output voltage, etc.
This can be changed by appropriately changing the insertion position of the rectifying element.

Further, the FET as a rectifying element may be a P-channel FET.

〔Effect of the invention〕

As explained above, in the present invention, the rectifying element inserted on the secondary side of the voltage conversion transformer is configured with a rectifying element such as a FET, and this can be turned on and off in synchronization with a switching element. This prevents transient loss in the rectifying element, prevents excessive stress on the transformer, and provides a highly efficient and compact switching regulator.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a switching regulator according to the present invention, and FIG. 2 is a circuit diagram of an example of a conventional switching regulator. la, lb...input terminal, 2a, 2b...output terminal, 3...voltage conversion transformer, 4...switching element, 5, 6...rectifying element, 7...choke coil, 8a, 8b... Capacitor, 9... Rectifying element, 1
0...Drive circuit, 11...Pulse width modulation circuit, l2
...Oscillation circuit, 13... Rectifier element (FET), 14
. . . second drive circuit, l5 . . . insulation buffer circuit. Figure 2 4 3 5 7

Claims (1)

[Claims] 1. A switching element is inserted into the primary side of a voltage conversion transformer, a rectifying element is inserted into the secondary side, and the voltage output from the secondary side is detected to control the drive pulse width of the switching element. In the switching regulator configured as shown in FIG.
A switching regulator characterized in that it is configured to be capable of F drive.