JP3132614B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a storage battery or a dry battery as a power supply, and supplies the battery power supply voltage to a load in a non-control mode in which the boosting switching element stops operating when the battery power supply voltage is higher than a reference level. The present invention also relates to a DC-DC converter that supplies a DC voltage boosted to a reference voltage in a boost control mode in which a switching element operates when a battery power supply voltage falls below a reference level to a load.

[0002]

2. Description of the Related Art FIG. 5 is a simplified connection diagram showing a conventional DC-DC converter. A reactor 2 and a series diode 3 are provided on the anode side of a battery power supply 8 having a power supply-side smoothing capacitor 9. One end of an external load 10 is connected to the other end of the external load, and the step-up switching element 1 is connected between the cathode side of the battery power supply 8 connected to the other end of the external load and the output terminals of the reactor 2 and the series diode 3. , And a smoothing capacitor 4, and a battery power supply voltage Vin is input to a control circuit 5 connected to the base of the boosting switching element 1 composed of, for example, a bipolar transistor. -DC switching between boost mode and boost mode
-A DC converter circuit is formed.

FIG. 6 is a characteristic diagram showing the operation of a conventional DC-DC converter. In the region where the battery power supply 8 is in a good charge state and its output voltage Vin exceeds the reference level Vs, this voltage is shown. The control circuit 5 which has detected the operation stops operation,
Since the boost switching element 1 keeps the off state, the output current IL of the battery power supply 8 is supplied to the external load via the reactor 2 and the series diode 3 and the DC
-The output voltage Vout of the DC converter becomes approximately equal to Vin, and the operation in the non-control mode in which the battery power supply voltage Vin is directly supplied to the external load 10 is performed.

When the battery power is consumed by the supply of power to the load 10 and the battery power voltage Vin gradually decreases to the reference level Vs, the control circuit 5 detecting this detects and starts the duty ratio control operation. The on / off control of the boost switching element 1 is performed 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 switching element 1 of the ON period in the battery power supply 8 - are accumulated, discharge energy of the off period in the reactor 2 of the step-up switching element 1 - newly supplied from and the DC power source The supplied current is supplied to the load 10 via the series diode 3. At this time, the input / output voltage ratio Vout / Vin is inversely proportional to the _off -time ratio D _off = T _Off / T of the step-up switching element 1. However, since the off-time ratio D _off takes a value of 1 or less, the output voltage Vout becomes The operation becomes a boosting operation higher than the input voltage Vin, and the operation is performed in the boosting mode in which the output voltage Vout is maintained at the reference level Vs which is the voltage set in the control circuit 5.

[0005] The DC-DC converter configured as described above.
If the reference level Vs is set near the lower limit of the voltage required by the load 10, the battery usage period that cannot be used when the voltage drops to the reference level due to the consumption in the uncontrolled mode operation is set. Thus, the time corresponding to the operation period in the boost mode can be extended. Therefore, when the battery power source 8 is a dry battery, there is an advantage that the stored energy remaining during the operation in the boost mode can be effectively used. When the battery power source 8 is a storage battery, when the switching time from the non-control mode to the boost mode is notified, the charging of the alternative battery is started at this time, and the battery is charged during the operation in the boost mode. Is completed, there is an advantage that load operation failure due to battery exhaustion can be avoided.

[0006]

In the conventional DC-DC converter configured as described above, the charge of the smoothing capacitor 4 charged during the boosting operation causes the boosting switching element 1 during the ON period to be charged. A series diode 3 is provided to prevent discharge through the circuit. However, the series diode - to be supplied to the load 11 through the de 3, series diode - - de 3 uncontrolled mode - in spite it is not required during operation in de, current I _L series diode de The conversion efficiency of the converter circuit is reduced due to the power loss due to the internal resistance of the load 10, and the forward voltage drop that varies with the current value adversely affects the voltage stability of the load 10.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-efficiency DC-DC converter with less power loss and voltage drop occurring in a series diode portion during uncontrolled operation.

[0008]

According to the present invention, there is provided a reactor connected in series between one end of a battery power supply and an output terminal, and a series diode connected to the reactor. A boost switching element and a control circuit connected between the diode connection point and the other end of the battery power supply, and a smoothing capacitor connected in parallel to the output terminal, wherein the control circuit monitors the battery power supply voltage During the period in which the battery power supply voltage maintains a voltage exceeding the reference level, the boosting switching element is kept in the off state to command the operation in the non-control mode, and when the battery power supply voltage falls below the reference level, the boosting is performed. In the DC-DC converter for instructing a boost mode operation in which a switching element is duty-controlled to maintain an output voltage at a reference level, Diode loss reducing means comprising a bypass switching element connected in parallel with a diode and a switching circuit for issuing an ON command to the bypass switching element during the operation period of the non-control mode, wherein the switching circuit changes the battery power supply voltage. Is monitored by the reverse conduction voltage of the Zener diode, and an ON command is issued to the bypass switching element while the battery power supply voltage keeps a voltage exceeding the reference level.

The switching circuit monitors a change in the battery power supply voltage in response to an output off command from the control circuit.
It is assumed that an ON command is issued to the bypass switching element during the period in which the% OFF command signal is output.

[0010]

In the present invention, a diode loss reducing means comprising a bypass switching element connected in parallel to a series diode of a DC-DC converter circuit, and a switching circuit for issuing an ON command to the bypass switching element during a non-control mode operation period. The switching circuit monitors the change in the battery power supply voltage by the reverse conduction voltage of the Zener diode, and issues an ON command to the bypass switching element during a period in which the battery power supply voltage maintains a voltage exceeding the reference level. By setting the reverse conduction voltage of the Zener diode to a voltage value corresponding to the reference level, the switching circuit detects that the battery power supply voltage is equal to or higher than the reference level. During the operation period of the non-control mode. Most of the current flowing in the column diode is connected to a bypass switching element connected in parallel with the bypass diode (a bypass switching element comprising a MOSFET, a bipolar transistor, etc., whose forward voltage drop is a few times lower than the forward voltage drop of the diode). ) Side, and the function of reducing the power loss and the voltage drop in the non-control mode to a fraction of that of the conventional series diode is obtained.

[0011]

In addition, if the changeover circuit is configured to monitor the change in the battery power supply voltage by the output off command signal of the control circuit and issue an on command to the bypass switching element during the period when the 100% off command signal is output. , 100%
During operation in the non-control mode in which the boost switching element stops its operation in response to the OFF command signal, the bypass switching element is turned on, and most of the current flowing through the series diode is sent to the bypass switching element connected in parallel to the diode. And the function of reducing power loss and voltage drop in the uncontrolled mode to a fraction of that of a conventional series diode is obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 shows a DC-DC converter according to an embodiment of the present invention.
FIG. 2 is a connection diagram showing an example of a main part of FIG. 1, and the same components as those in the prior art are denoted by the same reference numerals to omit redundant description. In the figure, the loss reducing means 11 of the series diode 3 includes a bypass switching element 12 composed of a MOSFET in the figure in which a drain and a source are connected in parallel to the series diode 3, and a Zener diode for detecting a change in the battery power supply voltage Vin. The ON command 11 is supplied to the bypass switching element during the operation of the non-control mode in which the battery power supply voltage is maintained at a voltage exceeding the reference level Vs by monitoring the reverse conduction voltage of the mode 14.
and a switching circuit 13 for generating d.

In the DC-DC converter having the loss reducing means 11 constructed as described above, the resistors R1, R2
By setting the reverse conduction voltage of the Zener diode 14 receiving the battery power supply voltage Vin divided by the above to a voltage value corresponding to the reference level Vs, the battery power supply voltage becomes equal to the reference level Vs.
In the region exceeding s, the Zener diode 14 reversely conducts and a base voltage is applied to the transistor switch 15, whereby the transistor switch 15 conducts and the MOSF
Since the gate voltage of the bypass switching element 12 made of ET (p-channel) becomes zero and becomes conductive, most of the current flowing through the series diode 3 during the operation in the non-control mode is reduced. DC-DC converter which can reduce the power loss and the voltage loss in the uncontrolled mode to about several fractions of that of the conventional series diode. −
The effect of improving the power conversion efficiency of the power supply is obtained.

FIG. 3 shows a DC according to a different embodiment of the present invention.
FIG. 4 is a simplified connection diagram of the DC converter, and FIG.
FIG. 3 is a block diagram showing an example of a main part of the first embodiment, in which a loss reducing means 21 of a series diode 3 is connected to a bypass switching element 22 composed of a MOSFET in a figure in which a drain and a source are connected in parallel to the series diode 3. , Battery power supply voltage V
The change in is monitored by the output off command signal 5d of the control circuit 5, and the switching circuit 23 that issues the on command 21d to the bypass switching element during the period in which the 100% off command signal is output is configured as described above. This is different from the embodiment.

The switching circuit 23 has a voltage V as shown in FIG.
_A drive signal 5d consisting of a pulse voltage having _d, cycle T, on time T _{on, and} off time T _{off is} applied to the level shift circuit 24. When the off-time ratio T off / T of the drive signal 5 d is 100%, 5 V, 0% When the comparison voltage Vc becomes 0V, for example,
The comparison voltage Vc is compared with a reference voltage Vs (for example, 4.9 V) by the differential amplifier circuit 25. When the comparison voltage Vc exceeds the reference voltage Vs, the DC-DC converter circuit is not controlled. A non-control mode in which the on-state command 21d is output to the base of the bypass transistor 21 by judging that the step-up switching element is in the mode, and the boosting switching element stops its operation by a 100% off command signal. During the operation, the bypass switching element is turned on, so that most of the current flowing through the series diode 3 can flow to the bypass switching element 22 connected in parallel to the series diode 3, and in the non-control mode. The effect of increasing the efficiency of the DC-DC converter, which can reduce the power loss and the voltage loss to a fraction of that of the conventional series diode, is obtained.

The bypass switching elements 12, 2
2 is not limited to MOSFETs,
A switching element having a low forward voltage drop, such as a transistor or an IGBT, may be used.

[0018]

According to the first aspect of the present invention, there is provided a bypass switching element connected in parallel to a series diode of a DC-DC converter operated in a non-control mode and a step-up mode; A switching circuit for issuing an ON command to the bypass switching element, the switching circuit monitoring a change in the battery power supply voltage by a reverse conduction voltage of the zener diode, and detecting a voltage at which the battery power supply voltage exceeds a reference level. Since the ON command is issued to the bypass switching element during the holding period, the reverse conduction voltage of the Zener diode is set to a voltage value corresponding to the reference level, so that the switching circuit sets the battery power supply voltage to the reference value. Detects that the level is higher than the level and performs bypass switching during the non-control mode A large amount of current flowing in the series diode during the non-control mode period can flow to the bypass switching element connected in parallel with this, and power loss during the non-control mode period And a DC-DC converter in which the voltage drop is reduced to a fraction of that of the conventional series diode. Further, in the invention according to claim 2, the switching circuit monitors a change in the battery power supply voltage according to an output off command of the control circuit, and turns on the bypass switching element during a period in which a 100% off command signal is output. Since the command is issued, during the non-control mode in which the boost switching element stops its operation by the 100% off command signal, most of the current flowing through the series diode due to the on state of the bypass switching element is reduced to this. Provided is a DC-DC converter capable of flowing to a bypass switching element connected in parallel and reducing power loss and voltage drop during a non-control mode period to a fraction of that of a conventional series diode. be able to.

[Brief description of the drawings]

FIG. 1 is a simplified connection diagram showing a DC-DC converter according to an embodiment of the present invention.

FIG. 2 is a connection diagram showing an example of a main part of FIG. 1;

FIG. 3 is a connection diagram showing a DC-DC converter according to a different embodiment of the present invention.

FIG. 4 is a block diagram showing an example of a main part of FIG. 3;

FIG. 5 is a simplified connection diagram showing a conventional DC-DC converter.

FIG. 6 is a characteristic diagram showing the operation of a conventional DC-DC converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Step-up switching element 2 Reactor 3 Series diode 4 Smoothing capacitor 5 Control circuit 5 d Drive signal 8 Battery power supply 10 Load 11 Loss reduction means 12 Bypass switching element 13 Switching circuit 14 Zener diode 15 Transistor switch 21 Loss reduction means 22 Bypass switching Element 23 Switching circuit 24 Level shift circuit 25 Differential amplifier circuit Vin Battery power supply voltage Vout Output voltage Vs Reference voltage

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 3/155 H02J 1/00 304

Claims (2)

(57) [Claims] 1. A reactor and a series diode connected to each other between one end of a battery power supply and an output terminal, and a booster connected between a connection point between the reactor and the series diode and the other end of the battery power supply. A switching element and a control circuit thereof, and a smoothing capacitor connected in parallel to the output terminal, wherein the control circuit monitors a battery power supply voltage, and the battery power supply voltage keeps a voltage exceeding a reference level. In the boost mode, the boost switching element is kept in the off state to command the operation in the non-control mode, and when the battery power supply voltage falls below the reference level, the boost switching element controls the duty ratio to hold the output voltage at the reference level. In a DC-DC converter for instructing operation, a bypass switching element connected in parallel to the series diode; A switching circuit for issuing an ON command to the bypass switching element during an operation period of the control mode, wherein the switching circuit monitors a change in the battery power supply voltage by a reverse conduction voltage of a zener diode, and A DC-DC converter characterized by issuing an ON command to said bypass switching element during a period in which a power supply voltage exceeds a reference level. 2. The switching circuit monitors a change in the battery power supply voltage in accordance with an output off command from the control circuit, and the switching circuit monitors the change in the battery power supply voltage by 100%
The DC-DC converter according to claim 1, wherein an on command is issued to the bypass switching element during a period in which an off command signal is output.