CN1135682C

CN1135682C - Synchronous flyback converter

Info

Publication number: CN1135682C
Application number: CNB99814777XA
Authority: CN
Inventors: B��յ�˹�Ƹ�; B·赫登斯科格; C·斯韦德舍
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1998-12-21
Filing date: 1999-12-16
Publication date: 2004-01-21
Anticipated expiration: 2019-12-16
Also published as: KR20010093856A; JP2002534049A; HK1043447A1; SE517220C2; EP1145415A1; CA2356187A1; SE9804454D0; WO2000038305A9; TW456096B; HK1043447B; AU3092000A; WO2000038305A1; CN1331863A; SE9804454L

Abstract

In a continuous mode flyback converter having a synchronous switch (Q2), the drive pulse to the switch (Q2) on the secondary side is generated by an inverting buffer circuit being fed from the output voltage terminal. By using such an arrangement, several advantages are obtained. Hence, the pulse generating circuit arrangement generates a drive signal to the synchronous switch which is independent of the input voltage and the drive losses can thereby be minimized.

Description

Synchronous flyback converter

The present invention relates to a kind of DC-DC translation circuit, relate in particular to a kind of synchronous flyback converter circuit of operation in a continuous manner.

In the DC-DC of different types of electric equipment power supply, utilize power rectifier so that export correct rectifier output voltage.In order to obtain rectifier output voltage, generally use diode at secondary side.

A kind of mode that obtains suitable rectification circuit is to use the flyback layout.In the flyback layout, between charge period, primary side is stored magnetic energy in magnetizable magnetic core or its analog.Then be called as retrace interval during, described energy feed-in secondary side.Compare with other rectification circuit, the major advantage with power rectifier circuit of flyback layout is simple in structure, and this makes low cost of manufacture.

In addition, flyback converter can be divided into two classes: promptly

The continuation mode flyback converter, and

Interrupted mode flyback converter.

In the continuation mode flyback converter, magnetic energy can be less than 0, makes energy flow into or flow out from transformer fe continuously in the heart, and in interrupted mode, has energy and neither flow into the time interval of yet not flowing out transformer core.

Conventional flyback converter comprises at primary side and the main winding and the switch of transformer comprises transformer auxiliary winding and the output capacitor that links to each other with diode at secondary side that load can be connected to the output capacitor two ends.

This converter has big voltage drop on diode.Thereby under the low situation of the output voltage on the output capacitor, the voltage drop on the diode just becomes a significant part of total voltage, thereby for this low voltage application, this power converter has low efficient.

In order to address this problem, can use FET transistor (field-effect transistor) at secondary side with low voltage drop.This structure will reduce the loss on the secondary side.The FET transistor for example can be directly with link to each other with the auxiliary winding of the auxiliary winding series connection of transformer.Converter according to this principle design has for example been described in the open 9801595-1 of Swedish patent application.

Yet in the Drive Structure of the auxiliary winding of this use, the size of the control signal of the FET on secondary side depends on input voltage, promptly puts on the voltage on the primary side.This causes excessive driving loss, because the amplitude of drive signal must be according to minimum input voltage design in this case.Under the situation of the big input voltage range of needs, this more becomes problem.In addition, described in WO98/04028 and WO95/02918 according to other DC-DC converter of prior art.

In addition, in United States Patent (USP) 5719755, also disclosed a kind of DC-DC converter.

The objective of the invention is to overcome the problems referred to above, and a kind of flyback converter of continuation mode is provided, it has simple structure, but has the efficient higher than the converter of prior art, and is particularly useful for the situation of big input voltage range.

This purpose of the present invention and other purpose are by using the power converter that limits in the claim to realize.

Thereby buffer circuits is anti-phase to be produced driving pulse by making, and it is supplied with by output voltage.By using this pulse-generating circuit, make the drive signal of synchro switch be independent of input voltage, reduce to minimum thereby make to drive to lose.

With reference to the accompanying drawings with nonrestrictive way of example explanation the present invention, wherein:

Fig. 1 is the circuit diagram of the DC-DC converter of continuation mode;

Fig. 2 a-2c is a timing diagram.

A kind of DC-DC converter has been shown among Fig. 1.Shown converter comprises main winding 101 and switch 103 at primary side.Main winding is by direct voltage source 105 power supplies.Described switch can be n channel-type MOSFET Q1, as shown in the figure.First end of the drain electrode of transistor Q1 and main winding 101 links to each other, and the low pressure input of source electrode and voltage source 105 links to each other.The control device (not shown) control that described switch is linked to each other by the grid with transistor Q1, described control device are set to make transistor Q1 in the conducting of the moment of needs or end.Described control device for example can be gathered the control data from the output of the secondary side of converter.

Direct voltage source 105 can link to each other with the alternating-current voltage source (not shown) by rectification circuit.Primary side is presented energy by transformer M2 to secondary side.Secondary side comprises auxiliary winding 109, and it has the winding opposite with the winding direction of primary side.The emitter 115 of first end 111 of winding 109 and first end 113 of resistance R 1, PNP transistor Q3 and first end 117 of output capacitance C0 link to each other.Second end 119 of resistance R 1 and first end 121 of resistance R 2 link to each other, and second end 125 of its second end 123 and winding 109 links to each other.

Second end 119 of the base stage 127 of transistor Q3 and resistance R 1 links to each other with node 129 between first end 121 of resistance R 2.The collector electrode 131 of transistor Q3 links to each other with the collector electrode 133 of NPN transistor Q4.

In a preferred embodiment, the base stage 135 of transistor Q4 links to each other by second end 125 of resistance R 3 and capacitor C 1 that is connected in series and winding 109.Second end 139 of the emitter 137 of transistor Q4 and capacitor C 0 links to each other, and links to each other with the source electrode 141 of FET transistor Q2.Node 145 between the grid 143 of transistor Q2 and the collector terminal of transistor Q3, Q4 links to each other.Second end 125 of the drain electrode of transistor Q2 and winding 109 links to each other.Load ZL is connected between the terminal of output capacitance C0.

When operation, in the conduction period of Q1, that is, when control device made the mosfet transistor conducting, energy was stored in the iron core of transformer M2.Because the direction of winding, at the drain electrode end of transistor Q2 a positive voltage will appear.Meanwhile, transistor Q4 conducting, so transistor Q2 will end.

When control device ended transistor Q2, the energy of storing in the iron core owing to transformer M2 made the pole reversal of the winding of transformer M2.Opposite polarity makes at negative voltage of drain electrode appearance of transistor Q2.By the driving of the voltage that provided by resistance R 1, R2, opposite polarity will make transistor Q3 conducting on secondary side.When transistor Q3 began conducting, the gate terminal 143 of transistor Q2 uprised, thereby transistor Q2 begins conducting.Capacitor C 1 and resistance R 3 are provided like this, make that the time by with conducting of transistor Q3 is low.

In Fig. 2 a-2c, show the timing of circuit shown in Figure 1.In Fig. 2 c, show the voltage that on the grid of transistor Q1, occurs.

In Fig. 2 b, show the voltage that occurs between the terminal of the auxiliary winding that when corresponding, is engraved in transformer M2.In Fig. 2 c, show in the corresponding moment and appear at the grid of transistor Q2 and the voltage between the source terminal.

Thereby, by a kind of device is provided, wherein the transistorized driving pulse of the FET on the secondary side is produced by the anti-phase buffer circuit by the output voltage terminal power supply, can obtain some advantages.Like this, this pulse-generating circuit device produces the drive signal of the synchro switch that is independent of input voltage, and can reduce to drive loss.

In addition, need be at the auxiliary winding of secondary side, as Swedish patent application 9801595-1, this may be an advantage in some applications.

The invention is not restricted to described embodiment, within the scope of the appended claims, can make various changes and remodeling in conjunction with Fig. 1,2a-2c.

Claims

1. the flyback converter of a continuation mode, it has primary side and secondary side, wherein secondary side comprises a mosfet transistor (Q2) and response transform device output voltage and the control structure of operating, be positioned to control mosfet transistor (Q2), it is characterized in that, described control structure comprises a PNP transistor (Q3), its emitter links to each other with first output (117) of converter, also comprise a NPN transistor (Q4), its emitter links to each other with second output (139) of converter and links to each other with the source electrode of mosfet transistor (Q2), the collector electrode of this NPN transistor links to each other with the transistorized collector electrode of described PNP, tie point between two collector terminals (145) links to each other with the grid (143) of mosfet transistor (Q2), the base terminal (127) of PNP transistor (Q3) and two resistance (R1 that are arranged to voltage divider, R2) tie point between links to each other, these two resistance (R1, R2) be connected between the drain electrode of first output (117) of converter and mosfet transistor (Q2), the base terminal (135) of NPN transistor (Q4) links to each other with the drain electrode of mosfet transistor (Q2).

2. the flyback converter of continuation mode as claimed in claim 1 is characterized in that, the base terminal (135) of described NPN transistor (Q4) is connected in the drain electrode of mosfet transistor (Q2) through a resistance (R3) of connecting with an electric capacity (C1).