JP3010609B2 - Step-up / step-down chopper type DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-operation type step-up / step-down chopper type DC-DC which operates a step-down switching element and a step-up switching element separately during step-down and step-up.
The present invention relates to a DC-DC converter in which a loss occurring in a series diode during a step-down operation is reduced.

[0002]

2. Description of the Related Art FIG. 4 is a simplified connection diagram showing a conventional DC / DC converter circuit of a single operation type step-up / step-down chopper system.
Step-down switching element 1, reactor 2
DC power supply 8 connected to one end of external load 11 via series diode 3 and connected to the other end of the external load.
A reflux diode 4, a step-up switching element 5, and a smoothing capacitor 6 are connected between the cathode side of the power supply and the output terminals of the step-down switching element 1, the reactor 2, and the series diode 3, respectively. DC-
A DC converter circuit is configured.

[0003] Further, the DC-
The step-down operation and the step-up operation of the DC converter circuit are performed, for example.
For example, a step-down switch composed of bipolar transistors
ON / OFF control of the switching element 1 and the boost switching element 5
Depending on the drive signal 1d or 5d generated by the control unit 10.
This is performed by various controls. That is, step-down operation
In the case of, the boost switching element 5 is driven by the drive signal 5d.
In the off state, the step-down switching element 1 is driven by the drive signal 1d.
On / off control at a desired timing. At this time,
During the ON period of the step-down switching element 1, the DC power supply 8
Current I on load 11 _LAt the same time that
Energy is stored in the reactor 2 and the step-down switch
Energy stored in reactor 2 during off period of switching element 1
Discharges through the load 11 and the reflux diode 4.
Now, let the current flowing through reactor 2 be I_L,Entering reactor
Output voltage is V_i,V_OOccupies the on / off period T, the period T
The on-time and the off-time, T_On,T_OffToss
Then, the input / output voltage ratio V_O/ V_iIs a step-down switching element
ON ratio D of 1_on= T_on/ T. At this time
Duty ratio D_onTakes a value of 1 or less, so that the output voltage V_OEnters
Force voltage V_iThe step-down operation becomes smaller.

On the other hand, the step-up operation is performed by the step-down switching element 1.
Is maintained at an on-time ratio of 1 by the drive signal 1d, and the boosting switching element 5 is controlled to be turned on and off at a desired timing by the drive signal 5d. At this time, boost energy in the reactor 2 by the current I _L from the ON period in the DC power supply 8 of the switching element 5 - are accumulated, discharge energy of the off period in the reactor 2 of the step-up switching element 5 - newly supplied from and the DC power source The supplied current is supplied to the load 11 via the series diode 3. At this time, the input / output voltage ratio V
_O / V _i is off when the ratio D _off the step-up switching element 5
= T _Off / T in inverse proportion to it, since the off-time ratio D _off takes a value of 1 or less, the step-up operation of the output voltage V _O is higher than the input voltage V _i.

[0005]

THE INVENTION to be solved INVENTION aforementioned so constructed conventional independent operation type buck chopper of the DC-DC converter - in capacitor circuit, the smoothing capacitor 6 is charged to the voltage V _O at the time of boosting operation A series diode 3 is provided to prevent the charge from being discharged through the boosting switching element 5 during the ON period. However, the series diode - de 3 despite not required at the time of step-down operation, current I _L series diode - to be supplied to the load 11 through the de 3, series diode - power loss due to the internal resistance of the de As a result, the conversion efficiency of the converter circuit is reduced, and the forward voltage drop that varies with the current value adversely affects the voltage stability of the load 11.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a single-operation buck-boost chopper type DC-DC converter having a small output loss and a stable output voltage during a step-down operation.

[0007]

According to the present invention, a step-down switching element, a reactor, and a series diode connected in series to one end of a DC power supply are provided. A freewheeling diode, a boosting switching element, and a smoothing capacitor connected between the other end of the step-down switching element, the step-down switching element, the reactor, and the output terminal of each of the series diodes.
A step-down control or a step-up control of the output voltage with respect to the DC power supply voltage by separately controlling the step-down switching element and the step-up switching element based on a command signal of a control unit, wherein the output voltage is connected in parallel to the series diode. And a means for reducing the loss of the series diode that bypasses the current flowing through the series diode to the parallel transistor during the step-down operation.

The loss reducing means includes a bypass transistor in which a collector and an emitter are connected in parallel to a series diode, and a drive signal for a step-down switching element. And a switching control unit for issuing an ON command to the base of the transistor. Furthermore, the switching control unit
A level shift circuit for detecting a drive pulse signal of the step-down switching element and converting an average value thereof to a voltage proportional thereto, and a differential for generating a signal during a period when the output voltage of the level shift circuit does not exceed a predetermined threshold value It is assumed that the amplifier circuit includes an amplifier circuit and an output circuit that adjusts the level of the output signal of the differential amplifier circuit and outputs the signal as an ON signal of a bypass transistor.

[0009]

In the structure of the present invention, a means for reducing the loss of the series diode which includes a bypass transistor connected in parallel to the series diode and bypasses the current flowing through the series diode to the bypass transistor during the step-down operation is provided. By using the characteristics of a transistor, the forward voltage drop (saturation voltage) between the collector and the emitter in the saturation region is as low as several times lower than the forward voltage drop of the diode. The function of reducing both the power loss and the voltage loss during the step-down operation of the series diode to a fraction of the conventional value can be obtained.

The loss reducing means includes a bypass transistor in which a collector and an emitter are connected in parallel to a series diode, and a bypass transistor in a step-down operation in which a drive signal of a step-down switching element is detected and its ON ratio becomes 1 or less. A switching control unit for issuing an ON command to the base, for example, a level shift circuit for detecting a drive pulse signal of a step-down switching element and converting an average value thereof to a voltage proportional thereto, and an output voltage of the level shift circuit If the differential amplifier circuit generates a signal during a period during which the voltage does not exceed a predetermined threshold value, and an output circuit that adjusts the level of the output signal of the differential amplifier circuit and outputs the signal as an on signal of a bypass transistor, At the time of boosting operation in which the on-time ratio of the element becomes 1, the bypass transistor is turned off and the serial It was operating normally, the on-time ratio 1
At the time of the step-down operation described below, the function of reducing the loss is obtained by turning on the bypass transistor to pass the current flowing through the series diode to the bypass transistor side.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a simplified connection diagram showing a step-up / step-down chopper type DC-DC converter according to an embodiment of the present invention.
The same components as in the prior art are denoted by the same reference numerals, and redundant description will be omitted. In the figure, a loss reducing means 20 of a series diode 3 detects a bypass transistor 21 having a collector and an emitter connected in parallel to the series diode 3, and a drive signal 1d of the step-down switching element 1 generated by the control unit 10. And a switching control unit 22 for issuing an ON command 21d toward the base of the bypass transistor 21 during the step-down operation in which the ON ratio becomes 1 or less.

[0012] Figure 2 is a block diagram showing an example of a switching control unit in the first embodiment, FIG. 3 is a characteristic diagram showing the operation of the switching control unit in the first embodiment, the voltage V _d, the period T, the on-time T
_A drive signal 1d composed of a pulse voltage having _{on and} off times T _off
Is added to the level shift circuit 24. When the on-time ratio T _on / T of the drive signal 1d is 0%, the voltage is 0 V, and when it is 100%, for example, 5 V.
V is converted to a comparison voltage Vc,
is compared with the reference voltage Vs by the differential amplifier circuit 25, and when the comparison voltage Vc is lower than the reference voltage Vs, it is determined that the DC-DC converter circuit is performing the step-down operation, and the output signal is output via the output circuit 26. The ON command 21d to the bypass transistor 2
1 is output.

The loss reducing means 20 configured as described above
During the step-up operation of the step-up / step-down chopper type DC-DC converter having the above, the step-down switching element 1 is turned on (on-time ratio 100%), and the step-up switching element 5 is turned on / off by a drive signal 5d having a desired on-time ratio. Thus, the output voltage V ₀ that increases in inverse proportion to the off-time ratio of the boost switching element 5 is supplied to the load 11. At this time, since the comparison voltage of the switching control unit 22 indicates 5 V corresponding to the on-time ratio of the step-down switching element 1 of 100%, the reference voltage is set to about 4.5 V, for example, corresponding to the on-time ratio of 90%. In this case, the switching control unit 22 does not output the ON command 21d and the bypass transistor 21 keeps the OFF state.
The discharge to the step-up switching element 5 side is prevented by the node 3, and the buck-boost chopper type DC is used as in the prior art.
-The boost operation of the DC converter is performed.

On the other hand, during step-down operation, step-up switching
The element 5 is held in the off state, and the step-down switch is activated by the drive signal 1d.
On / off control of the switching element 1 at a desired on-duty ratio
By this, the on-time ratio of the step-down switching element 1 is
Output voltage V that drops in proportion ₀Is supplied to the load 11.
At this time, the on-time ratio of the step-down switching element 1 is 90%.
If it is less than or equal to, the comparison voltage V_cIs
Reference voltage V_sLower, the differential amplifier 25 outputs the signal
And the bypass transistor 21 receiving the ON command 21d
Turns on and the current I flowing through the series diode 3_LThe vipa
Since it bypasses to the transistor side,
-Power or voltage loss caused by
Can be reduced.

[0015]

According to the present invention, as described above, a series diode
A bypass transistor is connected in parallel with the bypass diode, and a step-down / step-up chopper type DC-DC converter includes a series diode loss reducing means for bypassing a current flowing through the series diode to the bypass transistor side during a step-down operation. Configured. As a result, compared to the forward voltage drop of the diode,
Utilizing the characteristics of a transistor in which the forward voltage drop (saturation voltage) between the collector and the emitter in the saturation region is as low as several tenths, both the power loss and the voltage loss during the step-down operation, which have been a problem in the past, can be reduced by the conventional method. A step-down / step-up chopper type DC having a power conversion efficiency and a small output voltage fluctuation
-A DC converter can be provided.

Further, the loss reducing means may include a switching control unit for detecting a drive signal of the step-down switching element and issuing an on-command to the base of the bypass transistor during the step-down operation in which the on-time ratio becomes 1 or less. With this configuration, the current flowing through the series diode can be bypassed to the bypass transistor during the step-down operation without affecting the function of the series diode during the step-up operation, thereby providing an advantage that the loss can be reduced.

[Brief description of the drawings]

FIG. 1 shows a buck-boost chopper system D according to an embodiment of the present invention.
Connection diagram showing simplified C-DC converter

FIG. 2 is a block diagram illustrating an example of a switching control unit according to the embodiment;

FIG. 3 is a characteristic diagram illustrating an operation of a switching control unit in the embodiment.

FIG. 4 shows a conventional single-operation type buck-boost chopper type DC-
Connection diagram showing a simplified DC converter circuit

[Explanation of symbols]

REFERENCE SIGNS LIST 1 step-down switching element 1 d drive signal 2 reactor 3 series diode 4 reflux diode 5 step-up switching element 5 d drive signal 6 smoothing capacitor 8 DC power supply 10 control unit 11 load 20 loss reduction means 21 bypass transistor 21 d on command 22 switching control part 24 level shift circuit 25 a differential amplifier circuit 26 output circuit V _c comparison voltage V _s reference voltage

Claims (3)

(57) [Claims] 1. A step-down switching element, a reactor, and a series diode connected in series to one end of a DC power supply, and each of a step-down switching element, a reactor, and a series diode connected to the other end of the DC power supply. A return diode, a boost switching element, and a smoothing capacitor connected between the output terminal and the output terminal. The step-down switching element and the boost switching element are separately controlled in a time ratio based on a command signal from a control unit. A step-down control or a step-up control of the output voltage with respect to the DC power supply voltage includes a bypass transistor connected in parallel to the series diode, and a current flowing through the series diode during the step-down operation is bypassed to the parallel transistor side. Lifting and lowering means comprising means for reducing loss of a series diode Chopper type DC-DC converter -
Ta. And a bypass transistor having a collector and an emitter connected in parallel to a series diode and a drive signal for a step-down switching element. 2. A step-up / step-down chopper type DC-DC converter according to claim 1, further comprising a switching control section for issuing an ON command to the base of the transistor. 3. A level shift circuit for detecting a drive pulse signal of a step-down switching element and converting an average value of the drive pulse signal into a voltage proportional to the drive pulse signal. 3. A lift circuit according to claim 2, further comprising a differential amplifier circuit for generating a signal during a period not exceeding the threshold value, and an output circuit for adjusting a level of an output signal of the differential amplifier circuit and outputting the signal as an ON signal of a bypass transistor. Pressure chopper type DC-DC converter.