JP4867668B2 - Isolated DC-DC converter - Google Patents

Description

  The present invention relates to an insulation type DC-DC converter, and more particularly, to an insulation type DC-DC converter using a transformer that doubles as a power transmission transformer and a signal transmission transformer.

  Patent Document 1 discloses a single transformer having a set of cores and serving as both a power transmission transformer and a signal transmission transformer, and an insulated DC-DC converter using the same.

  Here, the configuration of the transformer disclosed in Patent Document 1 will be described with reference to FIGS.

  1 and 2 are diagrams showing a configuration example of a transformer according to Patent Document 1. FIG. FIG. 2 is a diagram showing each layer pattern of the multilayer substrate, and FIG. 1 is a side view of the transformer at the X1-X1, X2-X2, X3-X3, and X4-X4 portions shown in FIG. As shown in FIGS. 1 and 2, the transformer includes a first printed coil board 11, a second printed coil board 12, a third printed coil board 13, a fourth printed coil board 14, and return lines of these coils. A multilayer substrate of 8 layers including the layers to be formed is provided.

  The eight-layer multilayer board has two outer holes through which two auxiliary legs 6a and 6c and one main leg 6b of an EE type or EI type three-leg core penetrate. 11a, 11c and one inner hole 11b are arranged and formed in a straight line. A closed magnetic circuit is formed by fitting the multilayer substrate between the pair of cores of the three legs.

  In the three-leg core, the cross-sectional area of the two sub-legs and the distance between the main leg and the sub-leg are equal, and the two magnetic paths formed by the main leg and each sub-leg are: Its magnetoresistance is equal. The first printed coil substrate 11 and the third printed coil substrate 13 are spirally wound around the inner hole 11b, that is, around the main leg portion to constitute a primary coil and a secondary coil of the power transmission transformer unit. is doing. On the second printed coil board 12 and the fourth printed coil board 14, a clockwise coil is wound around one outer hole 11a, that is, around the first auxiliary leg 6a, and around the other outer hole 11c. That is, the same number of counterclockwise coils are wound around the second auxiliary leg portion 6c, and these are connected in series to constitute a primary coil and a secondary coil of the signal transmission transformer.

  FIG. 3 shows a magnetic path of a transformer constituted by the EE type core. In the figure, loop-shaped arrows Ba and Bb are paths of magnetic flux by the power transmission transformer section, and Bc is a path of magnetic flux by the signal transmission transformer section. Thus, in the signal transmission transformer, the voltage induced in the coil wound around the first auxiliary leg 6a by the operation of the power transmission transformer is wound around the second auxiliary leg 6b. Since the absolute value is canceled out in the reverse direction induced in the coil, the voltage becomes zero volts. Since the magnetic flux generated in the first auxiliary leg and the magnetic flux generated in the second auxiliary leg due to the operation of the signal transmission transformer cancel each other out in the main leg, the operation of the signal transmission transformer is the power transmission transformer. Does not affect the department. According to this principle, the power transmission transformer unit and the signal transmission transformer unit operate independently of each other while sharing one core.

  The transformer having the structure as in Patent Document 1 can be used as a power transmission transformer T1 and a signal transmission transformer T2 of an insulated DC-DC converter as shown in FIG. 4, for example. In FIG. 4, a transformer T1 is a power transmission transformer, and a transformer T2 is a signal transmission transformer. The main switch element Q1 is connected in series to the winding A of the power transmission transformer T1, and this series circuit is connected between the input terminals + Vin and −Vin. A synchronous rectifier circuit including a rectifier switch element Q2, a commutation switch element Q3, a choke coil L1, and a capacitor C2 is connected to the winding C of the power transmission transformer T1. The synchronous rectifier drive circuit 23 controls on / off of the rectification switch element Q2 and the commutation switch element Q3. The winding B of the signal transmission transformer T2 is provided with a pulse signal generation circuit 21 that generates a pulse signal to be applied to the gate of the main switch element Q1 and the winding B of the signal transmission transformer T2. In addition, a capacitor C1 is connected in series to the winding B so that a differential signal of a pulse signal supplied to Q1 is supplied. Further, a diode D2 is connected in parallel to the winding B so that only the pulse signal at the rise timing of Q1 is generated in the winding D of the signal transmission transformer T2.

  A pulse signal regeneration circuit 22 is connected to the winding D of the signal transmission transformer T2. The pulse signal regeneration circuit 22 inputs an electromotive voltage of the winding D of the signal transmission transformer T2 and supplies a signal of the rising timing of the pulse signal generation circuit 21 to the synchronous rectifier drive circuit 23.

  FIG. 5 is a voltage waveform diagram of each part shown in FIG. (A) is the output signal of the pulse signal generation circuit 21, (b) is the winding voltage of the power transmission transformer T1, and (c) is the first auxiliary leg (6a shown in FIGS. 1 and 2) of the transformer. The voltage of the wound signal transmission winding, (d) is the voltage of the signal transmission winding wound on the second auxiliary leg portion (6c shown in FIGS. 1 and 2), and (e) is the signal. This is the voltage of the winding D of the transmission transformer T2.

The pulse signal regeneration circuit 22 shown in FIG. 4 generates a pulse signal similar to the pulse signal generated by the pulse signal generation circuit 21 in response to the pulse signal shown in FIG.
JP 2000-260639 A

  However, the waveform shown in FIG. 5E is an ideal case. Actually, there are variations in the cross-sectional areas and gap portions of the first and second auxiliary legs of the transformer. 5 is generated as shown in (f) or (g).

  When the magnetic flux Ba passing through the first auxiliary leg 6a is larger than the magnetic flux Bb passing through the second auxiliary leg 6c by the power transmission winding shown in FIG. 3, the signal wound around the first auxiliary leg 6a. Since the voltage of the transmission winding is relatively larger than the signal transmission winding voltage of the second auxiliary leg 6c, a voltage as shown in FIG. 5 (f) appears.

  On the contrary, when the magnetic flux Ba passing through the first auxiliary leg portion 6a is smaller than the magnetic flux Bb passing through the second auxiliary leg portion 6c by the power transmission winding shown in FIG. 3, the winding is wound around the first auxiliary leg portion 6b. Since the voltage of the signal transmission winding thus made becomes relatively larger than the signal transmission winding voltage of the second auxiliary leg 6c, a voltage as shown in FIG. 5G appears.

  In the case of FIG. 5F, the output signal voltage decreases, and noise N12 is generated in the same direction as the signal during a period when the pulse signal is not necessary. In the case of FIG. 5G, the output signal voltage is increased by V2 ′, and the period during which the pulse signal voltage is increased is extended by the noise N21.

  Note that the negative noise indicated by N11 and N22 is clamped by the diode D2 shown in FIG. 4 and does not increase in the negative direction.

  Particularly problematic here is the state shown in FIG. There is a possibility that noise N12 is generated during a period when the pulse signal is not required, and the control of the rectifying switch element Q2 and the commutation switch element Q3 by the synchronous rectifier driving circuit 23 malfunctions. In the state shown in FIG. 5G, if the increase V2 ′ of the pulse signal is too large, the pulse signal regeneration circuit 22 may malfunction.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an isolated DC-DC converter having high stability by solving the problem of noise generated on the secondary side of a signal transmission transformer.

The insulated DC-DC converter of the present invention is configured as follows.
(1) A power transmission primary winding and power including a core, a power transmission winding coupled to the core, and a signal transmission winding, wherein the power transmission winding is coupled to the main leg of the core. It consists of a secondary winding for transmission, and the signal transmission winding is coupled to at least two auxiliary legs of the core to cancel the electromotive force generated by receiving the magnetic flux generated by the power transmission winding. A transformer composed of a primary winding for signal transmission and a secondary winding for signal transmission, respectively connected as described above,
A main switch element (Q1) connected in series to the primary winding for power transmission;
A pulse signal generation circuit (21) for controlling the main switch element (Q1) with a pulse signal and applying a rising signal of the drive voltage of the main switch element to the primary winding for signal transmission (B);
A synchronous rectifier (Q2, Q3) connected to the secondary winding (C) for power transmission of the transformer and rectifying in synchronization with on / off of the main switch element (Q1);
A synchronous rectifier drive circuit (23) for driving the synchronous rectifier by an output signal of the signal transmission secondary winding;
The polarity of the voltage generated in the signal transmission primary winding (B) by the magnetic flux generated by the power transmission winding is determined by the pulse signal generation circuit (21) as the driving voltage of the main switch element (Q1). The at least two sub-legs (6a, 6a, 6a, 6b) to which the signal transmission winding is coupled so that the polarity of the output voltage to the signal transmission primary winding (B) is the same as 6c) different cross-sectional areas, or different winding times for the at least two auxiliary legs (6a, 6c) to which the signal transmission windings are coupled,
A power supply terminal (VDD) of the pulse signal generation circuit (21) for supplying a driving voltage to the main switch element (Q1) input to the signal transmission primary winding (B) and the signal transmission primary side A first clamping diode (D1) is connected between the winding (B) and the reverse bias direction.

  (2) A second clamping diode (D2) having both ends connected to both ends of the signal transmission primary winding (B) and a cathode connected to the output end of the pulse signal generation circuit is provided.

  (3) A capacitive load is provided between the primary winding (B) for signal transmission and the ground of the pulse signal generation circuit (21), and the ground of the pulse signal generation circuit (21) and the signal transmission are provided. Between the primary winding (B), a third clamping diode (D3) that conducts the falling signal of the drive voltage of the main switch element (Q1) is provided.

  (4) The main switch element (Q1) is a MOS-FET, the source of the MOS-FET is connected to the ground, and the gate is connected to the first clamping diode (D1) and the signal transmission primary side. The main switch element (Q1) is driven between the ground of the pulse signal generation circuit (21) and the primary winding for signal transmission (B). A third clamping diode (D3) that conducts a voltage falling signal is provided.

  (1) The polarity of the voltage generated in the signal transmission secondary winding (D) by the magnetic flux generated by the power transmission winding is determined by the pulse signal generation circuit (21) of the drive voltage of the main switch element (Q1). Since the polarity of the voltage output to the secondary winding (D) for signal transmission when a rising signal is applied is the same, the cross-sectional area of each of the first and second auxiliary legs of the transformer, the gap Even if there are variations in the portions, the state shown in FIG.

  Further, the power supply terminal and signal of the pulse signal generation circuit (21) which is a voltage source having the same potential as the transmission of the drive voltage rising signal to the main switch element (Q1) input to the signal transmission primary winding (B). When the first clamping diode (D1) is connected in the reverse bias direction between the primary winding for transmission (B) and the first clamping diode (D1), (g) in FIG. The rise of the voltage V2 'shown in Fig. 5 is limited to the forward voltage of the clamping diode and does not rise any further. Therefore, it is possible to prevent malfunction in any state shown in (f) and (g) of FIG.

  (2) By providing a second clamping diode (D2) having both ends connected to both ends of the primary winding for signal transmission and a cathode connected to the output end of the pulse signal generation circuit. The negative voltage of the primary winding for signal transmission is clamped by the forward voltage drop of the second clamping diode (D2), and a negative voltage is generated in the primary winding for signal transmission. Can be prevented.

  (3) Since the capacitive load (C1) is provided between the signal transmission primary winding (B) and the ground of the pulse signal generation circuit (21), the signal transmission secondary winding ( In D), a differential waveform voltage of the pulse signal generated by the pulse signal generation circuit 21 is generated. The third clamping diode (D3) is configured such that the drive voltage of the main switch element (Q1) falls between the ground of the pulse signal generation circuit (21) and the primary winding for signal transmission (B). Since the voltage is conducted, noise can be reduced even when the falling signal of the drive voltage of the main switch element (Q1) is transmitted.

  (4) The main switch element (Q1) is a MOSFET, the source of the MOSFET is connected to the ground, and the gate is connected to the connection between the first clamping diode (D1) and the signal transmission primary winding (B). By connecting, the parasitic capacitance between the gate and the source of the MOSFET can be used, and the capacitive load between the primary winding for signal transmission (B) and the ground of the pulse signal generation circuit (21) becomes unnecessary. .

<< First Embodiment >>
The configuration and operation of the isolated DC-DC converter according to the first embodiment will be described with reference to FIGS.
FIG. 6 is a circuit diagram of the isolated DC-DC converter according to the first embodiment. In FIG. 6, a transformer T1 is a power transmission transformer, and a transformer T2 is a signal transmission transformer. The main switch element Q1 is connected in series to the winding A of the power transmission transformer T1 (the primary winding for power transmission according to the present invention), and this series circuit is connected between the input terminals + Vin and -Vin. ing. A synchronous rectifier circuit composed of a rectifying switch element Q2, a commutation switch element Q3, a choke coil L1, and a capacitor C2 is connected to the winding C of the power transmission transformer T1 (secondary winding for power transmission according to the present invention). ing. Here, the rectifying switch element Q2 and the commutation switch element Q3 are synchronous rectifiers. The synchronous rectifier drive circuit 23 controls on / off of the rectification switch element Q2 and the commutation switch element Q3. A pulse signal applied to the gate of the main switch element Q1 and the winding B of the signal transmission transformer T2 is generated in the winding B of the signal transmission transformer T2 (primary winding for signal transmission according to the present invention). A pulse signal generation circuit 21 is provided. In addition, a capacitor C1 is connected in series to the winding B so that a differential signal of a pulse signal supplied to Q1 is supplied. Further, a second clamping diode D2 is connected in parallel to the winding B, and a pulse of the rising timing of Q1 is applied to the winding D of the signal transmission transformer T2 (the secondary winding for signal transmission according to the present invention). Only a signal is generated.

  A pulse signal regeneration circuit 22 is connected to the winding D of the signal transmission transformer T2. The pulse signal regeneration circuit 22 inputs an electromotive voltage of the winding D of the signal transmission transformer T2 and supplies a signal of the rising timing of the pulse signal generation circuit 21 to the synchronous rectifier drive circuit 23.

  Unlike the circuit of the conventional insulation type DC-DC converter shown in FIG. 4, a first clamping diode D <b> 1 is connected between the power supply terminal (VDD) of the pulse signal generation circuit 21 and the winding B. The voltage of the drive voltage to the gate of the main switch element Q1 and the voltage applied to the winding B are equal to the power supply voltage Vdd to the power supply terminal VDD of the pulse signal generation circuit 21.

  FIG. 7 is a diagram showing the configuration of the transformer used in the isolated DC-DC converter according to the first embodiment and the relationship with the main part of the circuit.

  In the example shown in FIG. 7A, the sectional area Sy of the second auxiliary leg portion 6c is larger than the sectional area Sx of the first auxiliary leg portion 6a of the transformer T. A power source E connected to the winding A of the main leg 6b is a power source connected to the input terminal + Vin · −vin shown in FIG.

  With this configuration, the polarity of the voltage generated in the winding B by the magnetic flux generated by the winding A is the voltage output to the winding B when the drive signal of the main switch element Q1 is applied by the pulse signal generation circuit 21. It becomes the same polarity.

  In the example shown in FIG. 7B, the number of winding turns Nx for the first auxiliary leg portion 6a is smaller than the number of winding turns Ny for the second auxiliary leg portion 6c. Also in this case, the polarity of the voltage generated in the winding B by the magnetic flux generated in the winding A is the voltage output to the winding B when the drive signal of the main switch element Q1 is applied by the pulse signal generation circuit 21. It becomes the same polarity.

  FIG. 8 is a voltage waveform diagram of each part of the circuit shown in FIGS. (A) is the output signal of the pulse signal generation circuit 21, (b) is the voltage across the winding A, (c) is the voltage across the winding B, and (d) is the voltage across the winding D.

  Thus, the noise component due to the magnetic flux generated by the winding A is superimposed on the voltage of the winding B. However, the voltage in the positive direction does not exceed the voltage because the diode D1 conducts when the potential of P1 in the circuit diagram exceeds Vdd + D1Vf (the forward drop voltage of the diode D1). That is, the potential of P1 is clamped to Vdd + D1Vf by the diode D1.

  On the other hand, in the minus direction, the potential at the point P1 does not fall below the forward voltage drop D2Vf of the diode D2. That is, it is clamped to D2Vf by the diode D2.

  Therefore, when such a voltage of the winding B is applied to the signal transmission transformer T2, a differential voltage signal of the winding B is generated in the winding D as shown in FIG. The noise voltage generated at this time does not exceed the voltage clamped by the diodes D1 and D2.

  The pulse signal regeneration circuit 22 shown in FIG. 6 normally reproduces the pulse signal generated by the pulse signal generation circuit 21, and the synchronous rectifier drive circuit 23 correctly drives the rectification switch element Q2 and the commutation switch element Q3. Can do.

<< Second Embodiment >>
An insulated DC-DC converter according to a second embodiment will be described with reference to FIGS.
FIG. 9 is a circuit diagram of an isolated DC-DC converter according to the second embodiment. In this example, the diode D2 of FIG. 6 shown as the first embodiment is removed, and a diode D3 is provided between the anode of the diode D1 (a connection point with the winding B) and the ground GND of the pulse signal generation circuit 21. ing.

  In the example shown in FIG. 6, the diode D2 is connected in parallel to the winding B, whereby the negative voltage of the pulse signal output from the pulse signal generation circuit 21 is applied to the diode D2 in the forward direction. In the second embodiment, a negative pulse signal is not generated at the output of the winding D. In the second embodiment, the fall timing of the output signal of the pulse signal generation circuit 21 (mainly The diode D2 is removed for use on the secondary side as well (turn-off timing of the switch element Q1).

  FIG. 10 is a diagram showing the configuration of the transformer used in the insulated DC-DC converter according to the second embodiment and the relationship with the main part of the circuit.

  In the example shown in FIG. 10A, the sectional area Sy of the second auxiliary leg portion 6c is larger than the sectional area Sx of the first auxiliary leg portion 6a of the transformer T. A power source E connected to the winding A of the main leg 6b is a power source connected to the input terminal + Vin · −vin shown in FIG.

  With this configuration, the polarity of the voltage generated in the winding B by the magnetic flux generated by the winding A is the voltage output to the winding B when the drive signal of the main switch element Q1 is applied by the pulse signal generation circuit 21. It becomes the same polarity.

  In the example shown in FIG. 10B, the number of winding turns Nx for the first auxiliary leg portion 6a is smaller than the number of winding turns Ny for the second auxiliary leg portion 6c. Also in this case, the polarity of the voltage generated in the winding B by the magnetic flux generated in the winding A is the voltage output to the winding B when the drive signal of the main switch element Q1 is applied by the pulse signal generation circuit 21. It becomes the same polarity.

  FIG. 11 is a voltage waveform diagram of each part of the circuit shown in FIGS. (A) is the output signal of the pulse signal generation circuit 21, (b) is the voltage across the winding A, (c) is the voltage across the winding B, and (d) is the voltage across the winding D.

  During the period when the output voltage of the pulse signal generation circuit 21 is positive, the noise component due to the magnetic flux generated by the winding A is superimposed on the voltage of the winding B as in the case of the first embodiment. However, the voltage in the positive direction does not exceed the voltage because the diode D1 conducts when the potential of P1 in the circuit diagram exceeds Vdd + D1Vf (the forward drop voltage of the diode D1). That is, the potential of P1 is clamped to Vdd + D1Vf by the diode D1.

  When the output voltage of the pulse signal generation circuit 21 is 0, the voltage across the winding B (P1 potential with respect to P0) is negative, but the output terminal OUT of the pulse signal generation circuit 21 becomes the ground potential, and the winding The applied voltage in the negative direction of B does not become larger on the negative side than the forward drop voltage D3Vf of the diode D3. That is, it is clamped by the diode D3.

  Therefore, the voltage of the winding D generates a differential voltage signal of the winding B as shown in FIG. However, the voltage level in a period other than the rise timing and fall timing of the output voltage generated by the pulse signal generation circuit 21 is the noise voltage level clamped by the diodes D1 and D3.

  As a result, the pulse signal regeneration circuit 22 reproduces the signal output from the pulse signal generation circuit 21 without malfunction, and the synchronous rectifier drive circuit 23 synchronizes with the ON / OFF of the main switch element Q1 and the rectification switch element Q2 and the switching circuit. The current switch element Q3 can be switched.

<< Third Embodiment >>
FIG. 12 is a circuit diagram of an isolated DC-DC converter according to the third embodiment.
The second embodiment is different from the circuit shown in FIG. 9 in that the capacitor C1 is not provided and the connection relationship between the diodes D1 and D3. That is, in the example shown in FIG. 12, the source of the main switch element Q1 is connected to the ground, and the gate is connected to the connection portion between the first clamping diode D1 and the winding B. Further, the third clamping diode D3 is provided between the connection portion between the diode D1 and the winding B and the ground GND as in the case of FIG.

  With this configuration, the parasitic capacitance between the gate and source of the main switch element Q1 acts just like the capacitor indicated by C1 in FIG. Therefore, the same effects as the circuit shown in the second embodiment can be achieved without using the capacitor C1 as an individual component.

It is a figure which shows the structure of the transformer shown by patent document 1. FIG. It is a figure which shows each layer pattern of the multilayer substrate of the transformer. It is a figure which shows the relationship of the magnetic flux by the coil | winding for electric power transmission of this transformer, and the coil | winding for signal transmission. It is a figure which shows the circuit example of the insulation type DC-DC converter using the transformer shown by patent document 1. FIG. It is a voltage waveform diagram of each part of the circuit. It is a circuit diagram of the insulation type DC-DC converter concerning a 1st embodiment. It is a figure which shows the relationship between the transformer and circuit main part which are used with the insulation type DC-DC converter. 6 is a voltage waveform diagram of each part. It is a circuit diagram of the insulation type DC-DC converter which concerns on 2nd Embodiment. It is a figure which shows the relationship between the transformer and circuit main part which are used with the insulation type DC-DC converter. 9 is a voltage waveform diagram of each part. It is a circuit diagram of the insulation type DC-DC converter which concerns on 3rd Embodiment.

Explanation of symbols

6a-first auxiliary leg 6b-main leg 6c-second auxiliary leg 21-pulse signal generation circuit 22,24-pulse signal regeneration circuit 23-synchronous rectifier drive circuit Q1-main switch element Q2-rectifier switch element Q3 -Commutation switch element L1-Choke coil T-Transformer T1-Power transmission transformer T2-Signal transmission transformer D1-First clamp diode D2-Second clamp diode D3-Third clamp diode

Claims (4)

A power transmission winding coupled to the core and a signal transmission winding, wherein the power transmission winding is coupled to the main leg of the core; Each of the windings for signal transmission is coupled to at least two sub-legs of the core to cancel the electromotive force generated by receiving the magnetic flux generated by the windings for power transmission. A transformer composed of a connected primary winding for signal transmission and a secondary winding for signal transmission;
A main switch element connected in series with the primary winding for power transmission;
A pulse signal generation circuit that controls the main switch element with a pulse signal and applies a rising signal of a drive voltage of the main switch element to the primary winding for signal transmission;
A synchronous rectifier connected to the secondary winding for power transmission of the transformer and rectifying in synchronization with on / off of the main switch element;
A synchronous rectifier driving circuit for driving the synchronous rectifier by an output signal of the signal transmission secondary winding;
The polarity of the voltage generated in the primary winding for signal transmission by the magnetic flux generated by the winding for power transmission is the signal transmission when the drive voltage of the main switch element is applied by the pulse signal generation circuit. The cross-sectional areas of the at least two sub-legs to which the signal transmission winding is coupled are made different from each other so that the polarity of the output voltage to the primary winding for use is different, or the signal transmission winding Varying the number of turns of the windings for the at least two secondary legs to be joined,
First in a reverse bias direction between a power supply terminal of the pulse signal generation circuit that supplies a driving voltage to the main switch element that is input to the primary winding for signal transmission and the primary winding for signal transmission. An insulated DC-DC converter characterized by connecting a clamping diode.   2. A second clamping diode having both ends connected to both ends of the signal transmission primary winding and a cathode connected to an output end of the pulse signal generation circuit is provided. Insulation type DC-DC converter.   A capacitive load is provided between the signal transmission primary winding and the ground of the pulse signal generation circuit, and the main transmission winding is connected between the pulse signal generation circuit ground and the signal transmission primary winding. 2. The insulated DC-DC converter according to claim 1, further comprising a third clamping diode for conducting a falling signal of a driving voltage of the switch element.   The main switch element is a MOS-FET, the source of the MOS-FET is connected to the ground, and the gate is connected to a connection portion between the first clamping diode and the signal transmission primary winding. A third clamping diode is provided between the ground of the pulse signal generating circuit and the primary winding for signal transmission to conduct the falling signal of the driving voltage of the main switch element. The insulated DC-DC converter according to claim 1.

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