JP2004159473A - Insulated voltage conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulated voltage conversion circuit wherein the duty ratio of pulse signals inputted to switching elements can be enhanced as much as possible and excessive load applied to a transformer and the switching elements can be suppressed. <P>SOLUTION: Output voltage Vout is compared with desired reference voltage Vr. If the output voltage Vout exceeds the reference voltage Vr, pulses equivalent to one cycle (period from the leading edge of a pulse of a pulse signal S1 to the leading edge of the next pulse (or period from the falling edge of a pulse of the pulse signal S1 to the falling edge of the next pulse)) of the drive pulse signal inputted to MOSFETs 51-1 to 51-4 are thinned out. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an insulation type voltage conversion circuit that converts a voltage value of input power into a predetermined voltage value using a bridge circuit including a plurality of switching elements and a transformer.
[0002]
[Prior art]
FIG. 5 is a diagram showing a conventional isolated voltage conversion circuit.
The insulated voltage conversion circuit 50 shown in FIG. 5 is for raising and lowering the voltage of the electric power, for example, in order to supply electric power from a main power supply of the electric vehicle to a sub power supply of each device in the electric vehicle. , MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors) 51-1 and 51-2, MOSFETs 51-3 and 51-4, and an H-bridge circuit 51 for converting input DC power into predetermined AC power; A main transformer 52 that converts a voltage value of the AC power output from the circuit 51 into a predetermined voltage value; a rectifying diode 53 that rectifies the AC power output from the main transformer 52 into a DC power; A smoothing coil 54 and a smoothing capacitor for smoothing the output DC power. A voltage detector 55 for detecting the voltage value Vout of the smoothed DC power, and a MOSFET 51-1 to 51-4 of the H-bridge circuit 51 based on the voltage value Vout detected by the voltage detector circuit 56. And a control circuit 57 for controlling the on / off operation of.
[0003]
The control circuit 57 varies the duty ratio of the pulse signal input to each MOSFET of the H-bridge circuit 51 so that the voltage value Vout of the DC power output from the insulation type voltage conversion circuit 50 becomes a desired voltage value. Let it. The voltage value of the voltage applied to the primary coil of the main transformer 52 is determined by controlling the ON period or the OFF period of each MOSFET. The voltage value of the output voltage of the insulation type voltage conversion circuit 50 is, as shown in the following equation (1), the voltage value applied to the primary coil of the main transformer 52 and the primary voltage of the main transformer 52. The ratio between the number of turns of the coil (n1) and the number of turns of the secondary coil (n2) (turn ratio: n1 / n2), and the duty of the pulse signal input to each of the MOSFETs 51-1 to 51-4 It is determined based on the ratio and the conversion efficiency when converting the voltage value of the input power to a desired voltage value.
(Output voltage) = {(Primary transformer voltage) / (Main transformer winding ratio)}
X (pulse signal duty ratio) x (conversion efficiency)-(1)
By the way, in such a conventional insulated voltage conversion circuit 50, there is a concern that the conversion efficiency is reduced due to the on-resistance loss and switching loss of each of the MOSFETs 51-1 to 51-4 constituting the H-bridge circuit 51. .
[0004]
In order to reduce the on-resistance loss of such a MOSFET, it is conceivable to employ a MOSFET with a low on-resistance.
Further, in order to reduce the switching loss of the MOSFET, there is a method of adding a resonance circuit including a coil and a capacitor to the H-bridge circuit 51 and driving the MOSFET by a soft switching method.
[0005]
However, there is a problem that using a MOSFET having a low on-resistance or adding components for performing soft switching increases costs.
Therefore, as another method of reducing the on-resistance loss and the switching loss of the MOSFET, a method of reducing the current value of the current flowing through each of the MOSFETs 51-1 to 51-4 is considered.
[0006]
Here, the following equation (2) is an equation showing the relationship between the current value of the current flowing through the MOSFET, the output current of the insulation type voltage conversion circuit 50, and the winding ratio of the main transformer 52.
(MOSFET current) = (output current) / (turn ratio of main transformer) − (2)
From the above equation (2), it can be seen that the winding ratio of the main transformer 52 should be increased in order to reduce the value of the current flowing through each of the MOSFETs 51-1 to 51-4.
[0007]
However, if only the winding ratio of the main transformer 52 is increased, a desired output voltage cannot be obtained from the above equation (1). Therefore, it is necessary to increase the duty ratio of each pulse signal input to each of the MOSFETs 51-1 to 51-4 while increasing the winding ratio of the main transformer 52.
[0008]
At this time, the control circuit 57 performs a dead time at a predetermined interval (for example, the MOSFETs 51-1 and 51-4) so that the upper and lower MOSFETs (for example, the MOSFETs 51-1 and 51-4) of the H-bridge circuit 51 do not turn on at the same time. It is necessary to generate a pulse signal to be input to each of the MOSFETs 51-1 to 51-4, taking into account the period during which both the -4 and -4 are on.
[0009]
However, when a dead time is provided for each pulse signal, the high-level period of each pulse signal is reduced by the dead time, and a problem arises that the duty ratio of each pulse signal cannot be made too high.
As described above, in the conventional insulation type voltage conversion circuit 50, the duty ratio cannot be made too high to secure the dead time. As a result, since the winding ratio of the main transformer 52 cannot be increased, there is a problem that the on-resistance loss and the switching loss of the MOSFET are not reduced, and the improvement of the conversion efficiency is hindered.
[0010]
By controlling the on / off operation of the switching element, a voltage conversion circuit that supplies a stable voltage of DC power can control the pulse of the control pulse signal that is input to the switching element to determine whether the output voltage is excessive or insufficient. There is a method in which the duty ratio of the pulse signal can be set to 50% of the maximum by thinning out or adding in accordance with the above. (See Patent Document 1)
[0011]
[Patent Document 1]
Japanese Patent Publication No. 6-103985 (Page 3 Figure 1)
[0012]
[Problems to be solved by the invention]
However, when the method described in Patent Document 1 is applied to an isolated voltage conversion circuit 50 using an H-bridge circuit 51 as shown in FIG. 5, pulses input to each of the MOSFETs 51-1 to 51-4 By thinning out or adding a signal pulse, for example, the MOSFET 51-1 and the MOSFET 51-2 may be continuously turned on. As described above, when the same switching element is continuously turned on, a voltage in the same direction is continuously applied to the primary coil and the like of the main transformer 52, so that the main transformer 52 may be saturated. Then, there is a problem that an excessive current flows through the MOSFETs 51-1 and 51-2 and is damaged.
[0013]
Further, even if the pulse signals input to the MOSFETs 51-1 to 51-4 can be controlled so that the main transformer 52 does not saturate, for example, since the duty ratio of each pulse signal is 50%, for example, There is a possibility that the MOSFET 51-1 and the MOSFET 51-4 are turned on at the same time and the arm is short-circuited. Thus, there is a problem that the MOSFETs 51-1 to 51-4 are damaged.
[0014]
Therefore, in the present invention, in consideration of the above problems, it is possible to increase the duty ratio of a pulse signal input to each switching element as much as possible and to suppress an excessive load on a transformer or a switching element. It is an object of the present invention to provide a type voltage conversion circuit.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs the following configuration.
That is, the insulation type voltage conversion circuit of the present invention is an insulation type voltage conversion circuit that generates an alternating magnetic flux in the core of the transformer by driving a pair of switching elements connected to the primary coil of the transformer. A detection circuit for detecting the voltage value of the pulse signal, and when the voltage value detected by the detection circuit exceeds a desired voltage value, a period from the rise of one pulse of the pulse signal to the rise of the next pulse, or the pulse signal And a drive stop circuit for stopping the drive of the switching element pair during a period from the fall of a certain pulse to the fall of the next pulse.
[0016]
As described above, by stopping the driving of the switching element pair for the above-described period according to the voltage value detected by the voltage detection circuit, the duty ratio of the pulse signal can be increased as much as possible. As a result, the winding ratio of the transformer can be increased, and the conversion efficiency can be increased.
[0017]
Further, since the duty ratio of the pulse signal can be increased as much as possible, the winding ratio of the transformer can be increased, and the current flowing through each switching element of the switching element pair can be reduced. This makes it possible to reduce the steady-state on-loss of each switching element, and further increase the conversion efficiency.
[0018]
By stopping the driving of the switching element pair for the above-described period, each switching element of the switching element pair is turned off for a predetermined period. As a result, the same switching element is not driven continuously, so that an excessive voltage is not applied to the primary coil of the transformer or the like, and it is possible to prevent the transformer from becoming saturated.
[0019]
Further, by stopping the driving of the switching element pair for the above period, the number of times of switching of each switching element is reduced, so that the switching loss of each switching element can be reduced. Thereby, the conversion efficiency can be further improved.
[0020]
Further, the drive stop circuit in the insulation type voltage conversion circuit is configured not to stop driving of the switching element pair when a duty ratio of the pulse signal is less than the predetermined duty ratio.
Further, when the drive stop circuit in the insulation type voltage conversion circuit starts the insulation type voltage conversion circuit, the duty ratio of the pulse signal is gradually increased, and the duty ratio of the pulse signal becomes the predetermined duty ratio. And a duty ratio control means for keeping the duty ratio of the pulse signal constant.
[0021]
As described above, by gradually increasing the duty ratio of the pulse signal until the duty ratio of the pulse signal becomes the predetermined duty ratio, it is possible to prevent a large current from suddenly flowing to each switching element. Can be prevented.
[0022]
Further, the drive stop circuit in the insulation type voltage conversion circuit, the predetermined duty ratio is set to a maximum so that high-level periods of respective pulse signals input to each switching element of the switching element pair do not overlap, When the voltage value converted by the transformer exceeds the desired voltage value, the driving of the switching element pair is stopped during a period in which each of the switching elements is continuously turned on one by one.
[0023]
Further, the pulse signal having the predetermined duty ratio in the insulation type voltage conversion circuit is composed of first and second pulse signals having different phases (for example, two pulse signals which are 180 degrees out of phase with each other). The first and second pulse signals are configured to be pulse signals having a high-level period excluding a period in which none of the switching elements are turned on from each high-level period of the pulse signal having a duty ratio of 50%. .
[0024]
As described above, by inputting a pulse signal whose duty ratio is increased as much as possible to each switching element and driving the bridge circuit, the winding ratio of the transformer can be increased, so that the conversion efficiency can be increased. .
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First embodiment>
FIG. 1 is a diagram showing an insulation type voltage conversion circuit 10 according to an embodiment of the present invention. The same components as those of the conventional insulation type voltage conversion circuit 50 shown in FIG. 5 are denoted by the same reference numerals.
[0026]
An insulation type voltage conversion circuit 10 shown in FIG. 1 includes MOSFETs 51-1 and 51-2 (a pair of switching elements) and MOSFETs 51-3 and 51-4 (a pair of switching elements), and converts input DC power to predetermined AC power. An H-bridge circuit 51 for converting the AC power output from the H-bridge circuit 51 into a predetermined voltage value; a main transformer 52 (transformer) for converting the AC power output from the H-bridge circuit 51 into a predetermined voltage value; Rectifying diode 53, a smoothing coil 54 and a smoothing capacitor 55 for smoothing the DC power output from the rectifying diode 53, and a voltage detecting circuit 56 for detecting a voltage value Vout of the smoothed DC power. Detection circuits) and the MOSFETs 51-1 to 51- based on the voltage value Vout detected by the voltage detection circuit 56. And a control circuit 11 (drive stop circuit) for controlling the on / off operation of the main transformer 52. The H-bridge circuit 51 connected to the primary side coil of the main transformer 52 is driven to drive the core of the main transformer 52. A predetermined alternating magnetic flux is generated.
[0027]
Next, the configuration of the control circuit 11 will be described.
FIG. 2 is a diagram illustrating a configuration of the control circuit 11.
As shown in FIG. 2, the control circuit 11 includes a soft start circuit 11-1 (duty ratio control circuit) that generates a pulse signal S1 serving as a reference of a pulse signal input to each of the MOSETs 51-1 to 51-4. A one-cycle count circuit 11-2 for counting one cycle (high-level period + low-level period) of the pulse signal S1 generated by the soft start circuit 11-1, and a voltage value of a DC voltage output from the voltage detection circuit 56 Comparison result between an F / B (FeedBack) circuit 11-3 for comparing Vout (hereinafter referred to as an output voltage) with a voltage value (hereinafter referred to as a reference voltage) Vr of a desired output voltage, and an F / B circuit 11-3 , A one-cycle output stop circuit 11-that stops one cycle of on / off operation of the MOSFETs 51-1 and 51-2 or the MOSFETs 51-3 and 51-4. And a pulse signal S5 having a duty ratio of 50% for generating the drive pulse signal A and a pulse signal S6 having a duty ratio of 50% for generating the drive pulse signal B based on the pulse signal S1. A / F (Flip Flop) circuit 11-5, an AND circuit 11-6 which performs an AND operation on the pulse signals S5 and S6, the pulse signal S4 and the pulse signal S1, and outputs the resultant pulse signals S7 and S8, The pulse signals S5 and S6 are provided with a dead time generation circuit 11-7 that generates a dead time so that the ON periods of the pulse signals S7 and S8 do not overlap.
[0028]
Next, the operation of the control circuit 11 will be described.
FIG. 3 is a diagram showing a timing chart of a pulse signal output from each circuit in the control circuit 11.
First, when the insulation type voltage conversion circuit 10 is started, the soft start circuit 11-1 gradually increases the duty ratio of the pulse signal S1 to 50% (soft start period), and thereafter maintains the duty ratio at 50%. . Then, the pulse signal S1 is input to the one-period counter circuit 11-2, the F / F circuit 11-5, and the AND circuit 11-6.
[0029]
The one-period counter circuit 11-2 starts counting at, for example, the rising (or falling) of the pulse signal S1, and when the counting for one cycle ends (ie, the second rising of the pulse signal S1 ( Alternatively, one reset pulse signal S2 is output at the timing of falling).
[0030]
The F / B circuit 11-3 compares the output voltage Vout with the reference voltage Vr, and outputs one trigger pulse signal S3 to the one-cycle output stop circuit 11-4 when the output voltage Vout exceeds the reference voltage Vr. .
The one-cycle output stop circuit 11-4 switches from the high level to the low level by the pulse signal S2 following the rising (or falling) of the pulse signal S3, and from the low level to the high level by the next pulse signal S2. The switching pulse signal S4 is output. The one-cycle output stop circuit 11-4 receives the pulse signal S3 based on the duty ratio signal (signal indicating whether the duty ratio is 50%) output from the soft start circuit 11-1. Switch on / off. That is, for example, during the soft start period (the duty ratio is less than 50%), the one-cycle output stop circuit 11-4 turns off the input of the pulse signal S3 and always outputs the high-level pulse signal S4.
[0031]
The F / F circuit 11-5 outputs a pulse signal S5 having the same phase as the pulse signal S1, and a pulse signal S6 having a phase 180 degrees different from the pulse signal S1.
The AND circuit 11-6 performs an AND operation on the pulse signals S5 and S6 output from the F / F circuit 11-5, the pulse signal S4, and the pulse signal S1 output from the soft start circuit 11-1. Generate the signals S7 and S8.
[0032]
Then, in each pulse of the pulse signals S7 and S8, the dead time creation circuit 11-7 generates pulse signals S9 and S10 (drive pulse signals A and B) obtained by removing a predetermined dead time period from a high level period. .
As described above, when the output voltage Vout exceeds the desired reference voltage Vr, the control circuit 11 thins out a certain pulse of the pulse signal S10 and also thins out a pulse of the pulse signal S9 generated next. Conversely, when thinning out a certain pulse of the pulse signal S9, the pulse of the next generated pulse signal S10 is also thinned out.
[0033]
In this way, the output voltage Vout is compared with the desired reference voltage Vr, and when the output voltage Vout exceeds the reference voltage Vr, one cycle (pulse) of the drive pulse signal input to each of the MOSFETs 51-1 to 51-4. Pulses in a period from the rise of a certain pulse of the signal S1 to the rise of the next pulse (or the period from the fall of one pulse of the pulse signal S1 to the fall of the next pulse) are thinned out, that is, the output voltage Vout is reduced. When the reference voltage Vr is exceeded, the MOSFETs 51-1 and 51-4 and the MOSFETs 51-2 and 51-3 are stopped for the same period until the output voltage Vout becomes equal to or lower than the reference voltage Vr. The duty ratio of B can be increased as much as possible. As a result, the winding ratio of the main transformer 52 can be increased (see equation (1)), and the conversion efficiency can be increased.
[0034]
Further, since the duty ratio of the drive pulse signals A and B can be increased as much as possible, the winding ratio of the main transformer 52 can be increased (see the above equation (1)), and the current flowing through each MOSFET can be reduced. Yes (see equation (2) above). This makes it possible to reduce the steady-state on-loss of each MOSFET, and further increase the conversion efficiency.
[0035]
Further, since the same MOSFET is not driven continuously by thinning out the pulses of one cycle of the drive pulse signals A and B, it is possible to prevent the main transformer 32 from being saturated. .
Also, by thinning out one cycle of the drive pulse signal input to each MOSFET, the number of switching times of each MOSFET is reduced, so that the switching loss of each MOSFET can be reduced. Thereby, the conversion efficiency can be further improved.
[0036]
Further, by gradually increasing the duty ratio of the pulse signal S1 until the duty ratio becomes 50%, it is possible to prevent the primary coil of the transformer from becoming saturated.
<Other embodiments>
The present invention is not limited to the above embodiment, and various configurations can be adopted within the scope described in each claim. For example, the following configuration changes are possible.
[0037]
(1) In the insulation type voltage conversion circuit 10 of the above embodiment, the H-bridge circuit 51 is employed, but as shown in FIG. 4, a switching element pair 40 composed of two transistors (bipolar transistors or MOSFETs) is employed. May be.
The switching element pair 40 illustrated in FIG. 4 includes transistors 40-1 and 40-2. For example, the drive pulse signal A output from the dead time generation circuit 11-7 is input to the transistor 40-1. When the drive pulse signal B is input to 40-2, the transistors 40-1 and 40-2 are alternately driven to apply a predetermined voltage to the primary coil of the main transformer 52 (core of the main transformer 52). To generate a predetermined alternating magnetic flux).
[0038]
(2) In the insulation type voltage conversion circuit 10 of the above-described embodiment, the H-bridge circuit 51 is configured by a MOSFET. However, the H-bridge circuit 51 is configured by a switching element such as a bipolar transistor or an IGBT (Insulated Gate Bipolar Transistor). You may.
[0039]
(3) The one-cycle output stop circuit 11-4 of the control circuit 11 switches on / off the input of the pulse signal S3 based on the duty ratio signal output from the soft start circuit 11-1. However, the duty ratio signal may not be output from the soft start circuit 11-1 to the one-cycle output stop circuit 11-4. That is, when the output voltage Vout exceeds the reference voltage Vr even during the soft start period, the control circuit 11 may be configured to control the drive stop of the switching element.
[0040]
(4) The pulse signal S1 output from the soft start circuit 11-1 is used for determining the duty ratio at the time of soft start, and the operation clock of the F / F circuit 11-5 and the one-period counter circuit 11-2. However, a configuration may be adopted in which a clock generation circuit that generates an operation clock for the F / F circuit 11-5 and the one-period counter circuit 11-2 is provided, and the pulse signal S1 is not shared as described above. At this time, the pulse signal of the pulse signal S1 during the 50% duty cycle period is always at the high level.
[0041]
【The invention's effect】
As described above, according to the insulated voltage conversion circuit of the present invention, the duty ratio of the pulse signal input to each switching element of the bridge circuit can be increased as much as possible, so that the winding ratio of the transformer can be increased, and the conversion efficiency can be improved. Can be raised.
[0042]
Further, since the duty ratio of the pulse signal input to each switching element of the bridge circuit can be increased as much as possible, the winding ratio of the transformer can be increased, and the current flowing through each switching element can be reduced. This makes it possible to reduce the steady-state on-loss of each switching element, and further increase the conversion efficiency.
[0043]
In addition, a pulse from a rising edge of a certain pulse of the pulse signal input to each switching element of the bridge circuit to a rising edge of the next pulse, or a pulse from a falling edge of a certain pulse of the pulse signal to a falling edge of the next pulse. , The same switching element is not driven continuously, so that it is possible to prevent the transformer from becoming saturated.
[0044]
Further, a period from the rising of a certain pulse of the pulse signal input to each switching element of the bridge circuit to the rising of the next pulse, or the period from the falling of a certain pulse of the pulse signal to the falling of the next pulse. By thinning out the pulses, the number of times of switching of each switching element is reduced, and the switching loss of each switching element can be reduced. Thereby, the conversion efficiency can be further improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an insulation type voltage conversion circuit according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of a control circuit according to the embodiment of the present invention.
FIG. 3 is a diagram showing a timing chart of a pulse signal output from each circuit in the control circuit according to the embodiment of the present invention.
FIG. 4 is a diagram showing an insulation type voltage conversion circuit according to another embodiment of the present invention.
FIG. 5 is a diagram showing a conventional insulation type voltage conversion circuit.
[Explanation of symbols]
10 Insulated voltage conversion circuit 11 Control circuit (drive stop circuit)
11-1 Soft start circuit (duty ratio control circuit)
11-2 One-cycle count circuit 11-3 F / B circuit 11-4 One-cycle output stop circuit 11-5 F / F circuit 11-6 AND circuit 11-7 Dead time creation circuit 12 Push-pull circuit 40 Switching element pair 40 -1, 40-2 Transistor 50 Insulated voltage conversion circuit 51 H-bridge circuit 51-1 to 51-4 MOSFET
52 Main Transformer (Transformer)
56 Voltage detection circuit (detection circuit)
57 control circuit

Claims (5)

An insulation type voltage conversion circuit that generates an alternating magnetic flux in a core of the transformer by driving a pair of switching elements connected to a primary coil of the transformer,
A detection circuit for detecting a voltage value converted by the transformer;
When the voltage value detected by the detection circuit exceeds a desired voltage value, a period from the rise of a certain pulse of the pulse signal to the rise of the next pulse, or the time from the fall of a certain pulse of the pulse signal to the next pulse In the period until the fall of, a drive stop circuit for stopping the drive of the switching element pair,
An insulated voltage conversion circuit comprising: The isolated voltage conversion circuit according to claim 1,
The insulated voltage conversion circuit, wherein the drive stop circuit does not stop driving of the switching element pair when a duty ratio of the pulse signal is less than the predetermined duty ratio. The isolated voltage conversion circuit according to claim 1,
The drive stop circuit gradually increases the duty ratio of the pulse signal when the insulation type voltage conversion circuit is started, and when the duty ratio of the pulse signal reaches the predetermined duty ratio, the duty ratio of the pulse signal is kept constant. An insulated voltage conversion circuit, comprising: a duty ratio control unit that maintains the duty ratio. The isolated voltage conversion circuit according to claim 1,
The drive stop circuit sets the predetermined duty ratio to a maximum so that high-level periods of respective pulse signals input to the switching elements of the switching element pair do not overlap, and the voltage value converted by the transformer is When the desired voltage value is exceeded,
An insulated voltage conversion circuit, wherein the driving of the switching element pair is stopped during a period in which each of the switching elements is continuously turned on once. The isolated voltage conversion circuit according to claim 1,
The pulse signal having the predetermined duty ratio is composed of first and second pulse signals having different phases.
The first and second pulse signals are pulse signals having a high-level period excluding a period during which none of the switching elements of the switching element pair are turned on from each high-level period of the pulse signal having a duty ratio of 50%. An isolated voltage conversion circuit characterized by the above-mentioned.

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