JP4321408B2 - DC-DC converter for control power supply of power switching device - Google Patents

Description

  The present invention relates to a DC-DC converter that can suppress an increase in output ripple at low temperatures. The DC-DC converter of the present invention is suitably used as a control power source for a power switching device.

  In a vehicle-mounted power supply system, a two-battery vehicle power supply device that forms a vehicle-mounted power supply system with two batteries having different voltages is known or put into practical use in hybrid vehicles and idle stop vehicles. This two-battery type vehicle power supply device includes a high voltage battery charged by a generator, a low voltage battery fed from a high voltage battery or a generator through a step-down DC-DC converter, and a low voltage electric load connected thereto. Have. In this two-battery type vehicle power supply device, a semiconductor power switching element built in the step-down DC-DC converter is used to converge the output voltage of the step-down DC-DC converter (terminal voltage of the low-voltage battery) to a predetermined target value. Is normally controlled by PWM switching, and a control circuit for PWM switching control of the semiconductor power switching element is attached.

As this type of two-battery type vehicle power supply device that performs step-down power transmission using a DC-DC converter, for example, Patent Document 1 below is known.
JP 2003-033015 A

  In the two-battery type vehicle power supply device described above, the power supply to the control circuit is supplied from a high-voltage battery on the input side of the step-down DC-DC converter or a low-voltage battery on the output side of the step-down DC-DC converter. Preferably, it is powered from a low voltage battery. These batteries have a voltage that fluctuates due to variations in temperature, capacity, current consumption of an electric load connected to the battery, and the like.

  However, since fluctuations in the power supply voltage of the control circuit cause changes in its control function, the voltage of these batteries is preferably determined by a DC-DC converter (hereinafter also referred to as a control power supply DC-DC converter). Usually, the voltage is made constant by the voltage power supply circuit and then applied to the control circuit as the power supply voltage.

  Note that the DC-DC converter is used as the constant voltage power supply circuit because the DC-DC converter converts the input DC power into AC power of a constant frequency and rectifies it, so that the input / output insulation can be separated and controlled. This is because the output voltage of the circuit can be easily generated based on a desired voltage level.

  This control power supply DC-DC converter, like a normal DC-DC converter, has an inverter that converts an input DC voltage into an AC voltage by switching of a built-in switching element, and a rectifier circuit that rectifies the output voltage of the inverter. And a smoothing circuit for smoothing the output voltage of the rectifier circuit. As is well known, the rectifier circuit includes a choke coil and a smoothing capacitor. By adopting a large-capacitance capacitor such as an electrolytic capacitor as the smoothing capacitor, the output ripple of the DC-DC converter for control power supply is reduced.

  The ripple reduction effect of the smoothing circuit using a large-capacitance capacitor such as the above-described electrolytic capacitor is a satisfactory level in the normal use temperature range, but is significantly reduced at cold and low temperatures. FIG. 8 shows the temperature characteristics of the ripple voltage superimposed on the DC voltage output from the smoothing circuit when an electrolytic capacitor usually used as a smoothing capacitor is used. In FIG. 8, the solid line indicates the ripple voltage at room temperature and high temperature, and the broken line indicates the ripple voltage at extremely low temperature (for example, −30 ° C.).

  This decrease in the ripple ripple reduction effect of the smoothing circuit is due to the fact that the electrolytic capacitor used as the smoothing capacitor is accompanied by ion movement in the gel or liquid, so that the AC impedance and its DC resistance in the switching frequency band of the DC-DC converter for control power supply This is due to a significant increase at low temperatures. FIG. 9 shows the temperature change characteristic of the DC conductance of the electrolytic capacitor.

  For this reason, in a DC-DC converter for a control power supply of a vehicle that is greatly affected by the outside air temperature, there is a possibility that the power supply voltage applied to the control circuit fluctuates during cold start and the characteristics of the control circuit fluctuate. In order to avoid this, in order to improve the conductance characteristics at low temperature, the physique of the smoothing circuit has to be increased, resulting in an increase in the physique of the product.

  Further, in the above-described control power DC-DC converter, when an abnormal surge voltage (hereinafter also referred to as reverse input surge voltage) is applied from the outside to the output terminal of the control power DC-DC converter, this surge voltage In order to avoid reverse current flowing into the DC-DC converter for the control power supply and destroying the diode of the rectifier circuit, a surge absorbing snubber circuit is added, or radio noise increases with an increase in the breakdown voltage of the diode of the rectifier circuit There was a problem.

  The present invention has been made in view of the above problems, and an object thereof is to provide a DC-DC converter that has excellent output ripple reduction performance and excellent external surge voltage blocking characteristics and is suitable as a control power supply. It is said.

The DC-DC converter of the present invention includes an inverter that converts an input DC voltage into an AC voltage by switching of a built-in switching element (T1), a rectifier circuit (D1, D2) that rectifies the output voltage of the inverter, and a choke A power switching device comprising a smoothing circuit having a coil (54) and a smoothing capacitor (55) to smooth the output voltage of the rectifier circuit (D1, D2), and a controller (52) for intermittently controlling the switching element. In a DC-DC converter that operates as a control power source, a rectifying element (D3) connected to a connection point between the choke coil and the smoothing capacitor , a hold capacitor (57), and the rectifying element are arranged in parallel. A peak hold circuit ( 58) that is applied with the terminal voltage of the smoothing capacitor. 56) and outputs the voltage of the hold capacitor (57) to the outside (R) and the controller (52). The controller (52) outputs the output voltage output from the hold capacitor (57) and The output voltage is maintained at the target voltage by PWM control of the switching element (T1) based on a deviation from the target voltage, and the short-circuit switch (58) is turned on at a low temperature . .

  That is, according to the DC-DC converter of the present invention, the large ripple power output from the rectifier circuit of the DC-DC converter is first reduced by the LC type smoothing circuit, and is relatively small attenuated by the smoothing circuit. The remaining ripple power is further attenuated by the peak hold circuit. Thereby, a DC-DC converter with a small output ripple is realizable.

  In the present invention as well, it is preferable to employ a large-capacity capacitor such as an electrolytic capacitor as the smoothing capacitor of the smoothing circuit as in the past. In this case, although the AC impedance and resistance value of the smoothing capacitor increase at low temperatures and the ripple attenuation characteristic decreases, the ripple voltage output from the smoothing circuit can be further reduced by the peak hold circuit in the next stage.

  Further, according to the DC-DC converter of the present invention, even when a reverse input surge voltage is applied to the output terminal of the control power supply DC-DC converter from the outside, the surge voltage is generated in the control power supply DC-DC converter. It is possible to produce an effect that it is possible to prevent reverse current flow and destroy the diode of the rectifier circuit. More specifically, the withstand voltage of the DC-DC converter with respect to the reverse input surge voltage is the sum of the reverse withstand voltage of the rectifier element of the peak hold circuit and the reverse withstand voltage of the rectifier element of the rectifier circuit, and greatly increases. Therefore, it is possible to improve surge resistance characteristics of the DC-DC converter.

  In a preferred aspect, the hold capacitor is constituted by a capacitor having a smaller impedance increasing characteristic at a low temperature than the smoothing capacitor. Examples of such a capacitor include a ceramic capacitor and a film capacitor that have remarkably low impedance increase characteristics at a low temperature as compared with an electrolytic capacitor.

  In this way, even if the AC impedance or resistance value of the smoothing capacitor of the smoothing circuit increases at low temperatures and its ripple attenuation characteristics decrease, the hold capacitor of the next-stage peak hold circuit has good ripple attenuation even at low temperatures. Due to the characteristics, an increase in output ripple at a low temperature of the DC-DC converter can be suppressed. In addition, ceramic capacitors and film capacitors with significantly low impedance increase characteristics at low temperatures have a higher manufacturing cost per capacitance than electrolytic capacitors, but this hold capacitor is attenuated by the first-stage smoothing circuit and has a small ripple power. Therefore, the capacitance can be made relatively small compared to the smoothing capacitor of the smoothing circuit, and the increase in cost can be suppressed.

  In a preferred aspect, the rectifying element comprises a plurality of semiconductor diodes connected in series with each other.

  In this way, even if the ripple voltage output from the rectifier circuit is large at low temperatures, it can be satisfactorily attenuated, and the withstand voltage of the DC-DC converter against the reverse input surge voltage can be further improved.

  Preferred embodiments of the power switching device of the present invention will be described below with reference to the drawings. However, the present invention is not limited to this embodiment, and it goes without saying that some or all of the constituent elements of the present invention may be replaced with other known techniques or techniques having equivalent functions. is there.

Example 1
A two-battery vehicle power supply device to which the DC-DC converter of the present invention is applied will be described with reference to the circuit diagram shown in FIG.

  The two-battery vehicle power supply device is for voltage-converting and supplying power from the main battery 1 for storing the running energy of the hybrid vehicle to the auxiliary battery 2 for supplying power to the auxiliary device and the electronic control device. 3 is a DC-DC converter for battery charging which constitutes a power circuit unit referred to in the present invention, and 4 is a DC-DC converter control circuit for controlling the switching operation of the DC-DC converter 3 for battery charging. This DC-DC converter The control circuit 4 constitutes a control section referred to in the present invention and an auxiliary power supply 5 serving as a constant voltage power circuit section referred to in the present invention.

  The battery-charging DC-DC converter 3 employs a well-known circuit configuration including an input smoothing capacitor 31, a full-bridge inverter circuit 32, a step-down transformer 33, a synchronous rectifier circuit 34, a choke coil 35, and an output smoothing capacitor 36. Other known DC-DC converter circuit configurations may be employed. The choke coil 35 and the output smoothing capacitor 36 constitute a known output smoothing circuit.

  The DC-DC converter control circuit 4 reads the current detection value detected by the current sensor 6 that detects the output current of the battery charging DC-DC converter 3 and the output voltage of the battery charging DC-DC converter 3. A controller 41 that outputs a control signal for setting the deviation between the output voltage and a predetermined target voltage value to 0, and a gate voltage for PWM control are formed by the control signal input from the controller 41, and these gate voltages are converted into an inverter circuit 32. And a drive circuit 42 for outputting to each MOS transistor of the synchronous rectifier circuit 34. The controller 41 also has a function of stopping the switching operation of the battery charging DC-DC converter 3 and protecting it when the read current detection value deviates from a predetermined range.

  By switching and driving each MOS transistor of the inverter circuit 32 by the gate voltage input from the drive circuit 42, the average output voltage of the inverter circuit 32 is equal to the output voltage of the battery charging DC-DC converter 3 and a predetermined target voltage value. PWM control is performed so that the deviation from is zero. Further, a pair of transistors constituting the synchronous rectifier circuit 34 are also controlled in synchronization with each MOS transistor of the inverter circuit 32 to synchronously rectify the secondary voltage of the step-down transformer 33. The output voltage of the synchronous rectifier circuit 34 is an output smoothing circuit. After being smoothed by the above, the auxiliary battery 2 constituting the in-vehicle battery referred to in the present invention is charged.

  The circuit configuration of the battery charging DC-DC converter 3, the controller 41, and the drive circuit 42 includes various variations in addition to the circuit configuration of FIG. 1 described above, but these are already known and are the gist of the present invention. Since it is not, description is abbreviate | omitted.

  The auxiliary power supply 5 is a constant voltage power supply circuit, converts the input power supplied from the auxiliary battery 2 to a constant voltage, and supplies the power to the controller 41 and the drive circuit 42 that constitute the control unit in the present invention. The circuit configuration of the auxiliary power supply 5 that characterizes this embodiment will be described below with reference to FIG.

  The auxiliary power supply 5 includes a control power output DC-DC converter 51 that is a forward DC-DC converter that converts the input power fed from the auxiliary battery 2 to a constant voltage, and an output of the control power output DC-DC converter 51. It comprises an auxiliary power supply controller 52 that performs feedback PWM control of the voltage.

  The control power output DC-DC converter 51 includes an input smoothing capacitor 53, a transistor T1, a transformer T, diodes D1 and D2, a choke coil 54, an output smoothing capacitor 55, a peak hold circuit 56, and a resistor R. The choke coil 54 and the output smoothing capacitor 55 constitute an output smoothing circuit.

  The alternating current formed by PWM switching control of the transistor T1 is boosted by the transformer T, half-wave rectified by the diode D1, smoothed by the output smoothing circuit, and output to the peak hold circuit 56. During the half-wave period in which the diode D1 is turned off, current is supplied from the diode D2 to the peak hold circuit 56 through the choke coil 54 by the magnetic energy accumulated in the choke coil 54.

  The circuit configuration and operation of the control power output DC-DC converter 51 excluding the peak hold circuit 56 are well known, and further description thereof is omitted. However, the control power output DC-DC converter 51 may be configured by adding a peak hold circuit to various final stages other than the circuit configuration of FIG. Since the transformer T electrically insulates the input and output, the output voltage of the control power output DC-DC converter 51 can be used with a desired potential as a reference.

  The peak hold circuit 56 includes a diode D3 and a hold capacitor 57. The connection point between the choke coil 54 and the output smoothing capacitor 55 is connected to the anode electrode of the diode D3, and the cathode electrode of the diode D3 constitutes the output terminal on the high potential side of the DC-DC converter 51 for control power output. The output smoothing capacitor 55 and the resistor R are connected to a pair of output terminals of the control power output DC-DC converter 51.

  During the period when the output voltage of the output smoothing circuit is rising, the total of the output current to the control power output DC-DC converter 51 and the charging current of the hold capacitor 57 flows through the diode D3, and the diode forward direction corresponding to the sum A voltage drop occurs, the hold capacitor 57 is charged, and the terminal voltage rises. However, this diode forward voltage drop is substantially constant as is well known.

  When the output voltage VA1 of the output smoothing circuit starts to drop and becomes smaller than the sum of the output voltage of the control power output DC-DC converter 51, that is, the terminal voltage VB1 of the output smoothing capacitor 55 and the forward voltage drop VF of the diode D3, The diode D3 is cut off, the hold capacitor 57 is discharged, and the decrease in the output voltage of the control power output DC-DC converter 51 is suppressed.

  The auxiliary power supply controller 52 is an error amplifier that amplifies the deviation between the output voltage of the control power output DC-DC converter 51 and its target voltage and outputs an analog DC voltage, and an analog DC voltage output from the error amplifier. It has a PWM comparator that outputs a PWM voltage (PWM control signal) having a corresponding duty ratio and a carrier frequency of a predetermined period, and a drive circuit that amplifies the output voltage of this PWM comparator. The auxiliary power supply controller 52 outputs the PWM control signal input from the PWM comparator to the transistor T1 through the drive circuit, and performs PWM control on the transistor T1. As a result, a known PWM feedback control is performed in which the output voltage of the control power output DC-DC converter 51 is maintained at the target voltage. The voltage waveform of each part is shown in FIG.

  According to this embodiment, even when the ripple of the output voltage output from the output smoothing circuit is large, the output ripple of the DC-DC converter 51 for control power output can be greatly reduced by the ripple reduction drop of the peak hold circuit 56. Can do.

  Further, the peak hold circuit 56 does not require a large and heavy choke coil, and when the MOS of the inverter circuit 32 connected to the load, for example, the drive circuit 42 is accidentally damaged, that is, on the input side of the drive circuit 42, that is, Even when a high voltage is applied to the output terminal of the control power output DC-DC converter 51, the voltage withstand voltage performance of the output terminal of the auxiliary power source 5 has a function of blocking it in cooperation with the diode D 1. By improving the above, it is possible to prevent secondary destruction of the product, and it is possible to safely transmit an abnormal signal to an external computer or the like (not shown).

(Example 2)
A two-battery vehicle power supply device to which the DC-DC converter of the present invention is applied will be described with reference to a circuit diagram shown in FIG.

In this embodiment, a diode D4 is connected in series with the diode D3 of the peak hold circuit 56 shown in FIG. 2, and the output ripple of the DC-DC converter 51 for controlling power output is further reduced as shown in FIG. In addition, the withstand voltage characteristic of the output end of the control power output DC-DC converter 51 can be further improved.

(Example 3)
A two-battery vehicle power supply device to which the DC-DC converter of the present invention is applied will be described with reference to a circuit diagram shown in FIG.

  In this embodiment, the diode D4 of the peak hold circuit 56 shown in FIG. 3 is rearranged to the low level side, and the same effect as that of the second embodiment can be obtained.

(Example 4)
A two-battery vehicle power supply device to which the DC-DC converter of the present invention is applied will be described with reference to a circuit diagram shown in FIG.

  In this embodiment, a MOS transistor 58 is additionally provided which forms a short-circuit switch in parallel with the diode D3 of the peak hold circuit 56 shown in FIG.

  The MOS transistor 58 forming the short-circuit switch is turned on at a non-low temperature when the ripple voltage of the voltage VA1 at the connection point between the choke coil 54 and the output smoothing capacitor 55 is small. Therefore, in this case, the output smoothing capacitor 55 and the hold capacitor 57 can be regarded as a parallel capacitor. Thereby, the loss and heat generation of the diode D3 of the peak hold circuit 56 can be reduced when the temperature is not low, and the ripple increase at the low temperature can be reduced while improving the efficiency of the auxiliary power supply 5.

  In FIG. 7, the MOS is arranged on the high potential side, but may be arranged on the low potential side.

(Modification)
In each of the above embodiments, an electrolytic capacitor is used as the output smoothing capacitor 55, and a ceramic capacitor or a film capacitor is used as the hold capacitor 57. However, it is obvious that other types of capacitors may be combined.

It is a circuit diagram which shows the power supply apparatus for 2 battery type vehicles which employ | adopted this invention. FIG. 2 is a circuit diagram illustrating in detail Embodiment 1 of the auxiliary power source illustrated in FIG. 1. It is a timing chart which shows each part voltage waveform of FIG. FIG. 5 is a circuit diagram illustrating in detail Embodiment 2 of the auxiliary power source illustrated in FIG. 1. It is a timing chart which shows each part voltage waveform of FIG. FIG. 6 is a circuit diagram illustrating in detail Embodiment 3 of the auxiliary power source illustrated in FIG. 1. FIG. 6 is a circuit diagram illustrating in detail Embodiment 4 of the auxiliary power source illustrated in FIG. 1. It is a timing chart which shows the relationship between the output ripple of the conventional auxiliary power supply, and temperature. It is a characteristic view which shows the temperature change characteristic of the direct-current conductance of an electrolytic capacitor.

Explanation of symbols

D1 to D4 Diode R Resistance T Transformer T1 Transistor 1 Main battery 2 Auxiliary battery 3 DC-DC converter 4 Converter control circuit 5 Auxiliary power supply 6 Current sensor 31 Input smoothing capacitor 32 Inverter circuit 33 Step-down transformer 34 Synchronous rectifier circuit 35 Choke coil 36 Output smoothing capacitor 41 Controller 42 Drive circuit 51 DC-DC converter for control power output 52 Auxiliary power supply controller 53 Input smoothing capacitor 54 Choke coil 55 Output smoothing capacitor 56 Peak hold circuit 57 Hold capacitor or smoothing capacitor 58 Transistor 59 Choke coil

Claims (3)

An inverter that converts an input DC voltage into an AC voltage by switching of a built-in switching element (T1), a rectifier circuit (D1, D2) that rectifies the output voltage of the inverter, a choke coil (54), and a smoothing capacitor (55 And a smoothing circuit that smoothes the output voltage of the rectifier circuit (D1, D2) and a controller (52) that intermittently controls the switching element, and operates as a control power source of a power switching device. In the converter
A rectifier (D3) connected to a connection point between the choke coil and the smoothing capacitor ; a hold capacitor (57); and a short-circuit switch (58) arranged in parallel with the rectifier. A peak hold circuit (56) to which a terminal voltage of the smoothing capacitor is applied;
The voltage of the hold capacitor (57) is output to the outside (R) and the controller (52),
The controller (52) maintains the output voltage at the target voltage by PWM controlling the switching element (T1) based on a deviation between the output voltage output from the hold capacitor (57) and the target voltage. The DC-DC converter is characterized in that the short-circuit switch (58) is turned on when the temperature is not low . The DC-DC converter according to claim 1, wherein
The DC-DC converter according to claim 1, wherein the hold capacitor is a capacitor having a smaller impedance increase characteristic at a low temperature than the smoothing capacitor. The DC-DC converter according to claim 1 or 2,
The DC-DC converter according to claim 1, wherein the rectifier element comprises a plurality of rectifiers connected in series with each other.

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