JP2006081238A - Power circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power circuit which can make a series regulator perform normal operation. <P>SOLUTION: A power circuit 100 has a DC-DC converter 102 which converts the output voltage of a battery 200, a series regulator 104 which converts the output voltage of the DC-DC converter 102 and supplies it to a device 300, a bypass circuit 108 whose input end is connected between the battery 200 and the input end of the DC-DC converter 102 and whose output end is connected between the output side of the DC-DC converter and the input side of the series regulator 104, and a voltage detecting/detour control part 106 which detects the output voltage of the battery 200 andperforms the control of supplying the output voltage of the battery 200 directly to the series regulator 104, bypassing the DC-DC converter 102, by making a bypass circuit 108 conductive in case that this output voltage drops to a specified value or under, and also makes the bypass circuit 108 nonconductive after passage of a specified time since conduction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power supply circuit that is used in in-vehicle electrical equipment and the like and controls the output voltage of a power supply to supply the device.

  In recent years, with the advancement of functions of devices used in in-vehicle electrical equipment such as navigation devices and audio devices, when the output voltage of a power supply is supplied to the device, it is highly efficient in addition to high efficiency. That is also required. In response to such a demand, a power supply circuit in which a DC-DC converter and a series regulator are connected in series has been proposed.

  FIG. 4 is a block diagram of a conventional power supply circuit. The power supply circuit 500 shown in the figure has a DC-DC converter 502 and a series regulator 504, and outputs the output voltage of the battery 600 (here, 6 to 16 V in a normal state) to the operating voltage of the device 700 in the in-vehicle electrical equipment (here Then, it is lowered to 3.3V ± 2%).

  The DC-DC converter 502 drops the output voltage of the battery 600 to a predetermined voltage (here, 4.5 V ± 5%) and supplies it to the series regulator 504. The series regulator 504 further drops the output voltage of the DC-DC converter 502 to a voltage at which the device 700 can operate and supplies the voltage to the device 700.

  In the power supply circuit 500, the voltage can be controlled while maintaining the power of the battery 600 by the DC-DC converter 502, and the accuracy of the voltage can be improved by the series regulator 504.

  By the way, in the device 700 in the in-vehicle electrical equipment, there is a device in which a process called a shutdown process is performed in preparation for a decrease in the output voltage of the battery 600 when the engine is stopped. As the fall processing, for example, in a radio broadcast receiver, there is a process of holding information indicating a channel selection state before stopping the engine in a memory or the like, and when the engine is started after that process, It becomes possible to take over the state of channel selection before the engine stops.

  However, when the engine is started, the output voltage of the battery 600 may temporarily decrease. In the conventional power supply circuit 500 shown in FIG. 4, the voltage at which the device 700 can operate is 3.3V ± 2%, and in order to maintain this voltage, the output voltage of the battery 600 is 6V or more. Is required. However, when the engine is started, the output voltage of the battery 600 can easily be 6 V or less. As described above, when the output voltage of the battery 600 temporarily decreases, the shutdown process is not performed, and the state before the engine is stopped after the engine is started cannot be taken over.

For such a problem, a measure for bypassing the DC-DC converter 502 and connecting the series regulator 504 directly to the battery 600 can be considered. As a result of such measures, when the output voltage of the battery 600 decreases, a voltage drop in the DC-DC converter 502 does not occur, so that a voltage capable of operating the device 700 can be supplied to the device 700. Become. Patent Document 1 also proposes a measure for bypassing the switching regulator and connecting the series regulator directly to the power supply from the same viewpoint.
JP-A-5-236650

  However, if the series regulator 504 is directly connected to the battery 600, the voltage supplied to the series regulator 504 becomes higher than normal, and the amount of heat generation increases, which may cause malfunction. For such an increase in the amount of heat generation, a measure to attach a huge heat sink to the series regulator 504 can be considered, but it is not realistic in terms of space and cost.

  An object of the present invention is to solve the above-described problems and to provide a power supply circuit capable of causing a series regulator to perform a normal operation.

  A power supply circuit according to the present invention controls an output voltage of a power supply and supplies the device to a device, the DC-DC converter converting the output voltage of the power supply into a voltage having a first predetermined value, and the DC- A series regulator that converts the output voltage of the DC converter into a second predetermined value and supplies the device to the device, voltage detection means for detecting the output voltage of the power supply, and the power supply and the input side of the DC-DC converter A detour having an input end connected between the output side of the DC-DC converter and an input side of the series regulator, and an output of the power source detected by the voltage detecting means When the voltage drops below a third predetermined value, the bypass circuit is turned on, the DC-DC converter is bypassed, and the output voltage of the power source is directly transferred to the series regulator. Performs control to supply, and a bypass control means for non-conductive the detour from the conductive after a predetermined time has elapsed.

  With this configuration, when the output voltage of the power supply is normal, the series regulator is supplied with a voltage from the DC-DC converter. On the other hand, when the output voltage of the power supply decreases, the DC- A voltage is supplied directly from the power supply bypassing the DC converter. For this reason, even if the output voltage of a power supply falls, a series regulator can supply the voltage which can operate the said device with respect to a device. In addition, when a predetermined time has passed since the detour is turned on, the detour is turned off again and the voltage supplied to the series regulator is reduced, thereby suppressing the increase in junction temperature as much as possible. Thus, the series regulator can be operated normally.

  Further, in the power supply circuit according to the present invention, the time during which the bypass is conducted is set so that the series regulator does not exceed the limit value of the junction temperature.

  With this configuration, it is possible to prevent the junction temperature of the series regulator from reaching the limit value and to cause the series regulator to perform normal operation.

  In addition, the power supply circuit according to the present invention provides for a reduction in the voltage supplied to the device when the output voltage of the power supply detected by the voltage detection means falls below the third predetermined value. A process instruction means for instructing the process.

  With this configuration, it is possible to cause the device to perform a predetermined process such as a falling process in preparation for a decrease in the voltage supplied to the device.

  In the power supply circuit according to the present invention, the bypass circuit includes a switch that performs switching operation between an on state and an off state, and the bypass control unit is configured such that the output voltage of the power source detected by the voltage detection unit is When the voltage falls below the third predetermined value, the switch is turned on.

  With such a configuration, when the output voltage of the power supply is equal to or lower than the third predetermined value, the switch is turned on so that the bypass circuit is conducted and the output voltage of the power supply is directly supplied to the series regulator. Become.

  According to the present invention, when the output voltage of the power supply is equal to or lower than the third predetermined value, the bypass circuit for bypassing the DC-DC converter is conducted and the output voltage of the power supply is directly supplied to the series regulator. After that, after the predetermined time elapses, the detour is turned off again, so that the amount of heat generated in the series regulator is prevented from increasing, and the series regulator can be operated normally.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

  FIG. 1 is a block diagram of a power supply circuit according to an embodiment of the present invention. The power supply circuit 100 shown in the figure controls the output voltage of the battery 200 and supplies it to a device 300 used for in-vehicle electrical equipment such as a navigation device and an audio device. The power supply circuit 100 includes a DC-DC converter 102, a series regulator 104, a voltage detection / bypass control unit 106, a bypass circuit 108, a bypass switch 110, and a diode 112. Among these, a timer 107 is configured in the voltage detection / bypass control unit 106. The power supply circuit 100 drops the output voltage of the battery 200 to a voltage at which the device 300 can operate.

  In the power supply circuit 100, the DC-DC converter 102, the diode 112, and the series regulator 104 are connected in series between the battery 200 and the device 300. The diode 112 is connected with the DC-DC converter 102 side as an anode and the series regulator 104 side as a cathode. Further, the bypass circuit 108 directly connects the battery 200 and the series regulator without passing through the DC-DC converter 102 and the diode 112. The bypass switch 110 makes the bypass circuit 108 conductive in the on state and non-conductive in the off state.

  The DC-DC converter 102 drops the output voltage of the battery 200 to a predetermined voltage without losing power, and supplies it to the series regulator 104 via the diode 112. The series regulator 104 further reduces the output voltage of the DC-DC converter 102 to a voltage at which the device 300 can operate, and supplies the voltage to the device 300. The power loss due to the voltage drop in the series regulator 104 becomes heat and is released from the series regulator 104.

  The voltage detection / bypass control unit 106 detects the output voltage of the battery 200. The voltage detection / bypass control unit 106 supplies the output voltage of the battery 200 to the series regulator 104 via the DC-DC converter 102 according to the value of the output voltage, and the DC-DC converter 102. One of the controls to be supplied directly to the series regulator 104 without going through is performed. Further, the voltage detection / bypass control unit 106 controls the operation of the device 300 according to the value of the output voltage of the battery 200.

  The detailed operation of the voltage detection / bypass control unit 106 and the operation of each unit of the power supply circuit 100 and the device 300 accompanying this operation will be described below.

  FIG. 2 is a flowchart showing a detailed operation of the voltage detection / bypass control unit 106. Initially, the output voltage of the battery 200 is normal, and the output voltage is dropped to a voltage capable of operating the device 300 via the DC-DC converter 102, the diode 112, and the series regulator 104, and then the device 300. To be supplied. The device 300 operates with this supplied voltage.

  Here, the voltage at which the device 300 can operate is 3.3V ± 2%. In order to maintain this voltage, it is assumed that the output voltage of the battery 600 is 6 to 16V in a normal state. Furthermore, the DC-DC converter 102 reduces the output voltage 6 to 16 V when the battery is normal to 4.5 V ± 5%, and the series regulator 104 outputs the output voltage 4.5 V ± 5% of the DC-DC converter 102. Can be lowered to a voltage 3.3V ± 2% at which the device 300 can operate. It is assumed that the minimum input / output potential difference in series regulator 104 is 0.4V.

  In this state, the voltage detection / bypass control unit 106 determines whether or not the output voltage of the battery 200 is equal to or lower than a predetermined threshold (S101). The threshold is an output voltage (here, 8V) of the battery 200 that allows the device 300 to operate even when a voltage drop occurs in the DC-DC converter 102 and the series regulator 104.

  When the output voltage of the battery 200 is equal to or lower than the threshold, the voltage detection / bypass control unit 106 activates the built-in timer 107 (S102). Further, the voltage detection / bypass control unit 106 turns on the bypass switch 110 (S103).

  When the bypass switch 110 is turned on, the bypass circuit 108 becomes conductive. For this reason, the output voltage of the battery 200 is directly supplied to the series regulator 104 without passing through the DC-DC converter 102 and the diode 112. At this time, since the diode 112 is connected with the DC-DC converter 102 side as an anode and the series regulator 104 side as a cathode, current is prevented from flowing from the detour 108 to the output terminal of the DC-DC converter 102. Is done.

  As described above, when the output voltage of the battery 200 decreases, the output voltage is directly supplied to the series regulator 104 without passing through the DC-DC converter 102 and the diode 112. For this reason, even if the voltage drop of the minimum input / output potential difference occurs in the series regulator 104, the series regulator 104 operates with respect to the device 300 as in the case where the output voltage of the battery 200 is normal. A possible voltage can be supplied.

  Specifically, the minimum input / output potential difference in the series regulator 104 is 0.4 V, and the voltage at which the device 300 can operate is 3.3 V. Therefore, the output voltage of the battery 200 is 3.7 V or more including these. If so, the device 300 is operable. That is, even if the output voltage of the battery 200 cannot be maintained at 6 to 16 V in a normal state and becomes 6 V or less, the device 300 can operate if the voltage is 3.7 V or more. The minimum output voltage of the battery 200 required for the device 300 to be operable can be reduced from 6V to 3.7V.

  Next, the voltage detection / bypass control unit 106 transmits a signal to the device 300 to instruct the shutdown process (S104). Upon receiving this signal, the device 300 performs a fall process. In the fall processing, for example, securing of necessary information or the like (storing in a memory) is performed so as not to hinder the operation after the recovery even if the voltage is interrupted.

  Further, the voltage detection / bypass control unit 106 determines whether or not the timer 107 has expired (S105). The time from when the timer 107 is started until the time is up (time up time) is set in consideration of the following points.

  That is, the series regulator 104 is designed so that the junction temperature does not exceed a predetermined value even when the output voltage of the battery 200 is normal and the voltage is continuously supplied from the DC-DC converter 102. However, the voltage directly supplied from the battery 200 to the series regulator 104 when the output voltage of the battery 200 decreases is supplied from the DC-DC converter 102 to the series regulator 104 when the output voltage of the battery 200 is normal. May be greater than the applied voltage. For this reason, when the battery 200 continuously supplies voltage directly to the series regulator 104, the series regulator 104 increases power loss due to a large voltage drop, and accordingly increases the heat generation amount. There is a possibility that the temperature will reach its limit and be destroyed. For this reason, it is necessary to set the time-up time so as not to exceed the limit value of the junction temperature in the series regulator 104. In addition, the time-up time needs to be set to be longer than the time when the device 300 can end the shutdown process.

  For example, let us consider a case where the output voltage of the battery 200 is 8 V, the time required for the device 300 shutdown process is 10 ms, and the current consumption in the device 300 shutdown process is 1 A. When the output voltage of the battery 200 is directly supplied to the series regulator 104, the voltage drop (input / output potential difference) in the series regulator 104 is 8V-3.234V (= 3.3V-2%) = 4.776V. The power loss accompanying the voltage drop in the series regulator 104 is 4.766 V × 1 A≈4.8 W. Furthermore, using the graph of thermal resistance over time in FIG. 3, when the power loss due to the voltage drop in the series regulator 104 continues for 10 ms, which is the time required for the device 300 to fall, the series regulator 104 The thermal resistance is about 2 ° C./W. Therefore, when the output voltage of the battery 200 is directly supplied to the series regulator 104 for 10 ms, the temperature rise of the series regulator 104 is 4.8 W × 2 ° C./W=9.6° C. That is, when the time-up time is 10 ms and the bypass switch 110 is turned on in S103, the junction temperature of the series regulator 104 is set to a temperature lower than the limit value by 9.6 ° C. Breakage of the series regulator 104 is prevented.

  When the timer 107 expires, the voltage detection / bypass control unit 106 returns the bypass switch 110 to the off state in order to prevent the series regulator 104 from being destroyed due to the temperature rise (S106). When the bypass switch 110 is turned off, the bypass circuit 108 becomes non-conductive again. For this reason, the output voltage of the battery 200 is supplied again to the device 300 via the DC-DC converter 102, the diode 112, and the series regulator 104. At this time, if the output voltage of the battery 200 is restored, the voltage at the normal time is supplied to the series regulator 104, and if it is not restored, a voltage lower than that at the normal time is supplied. In any case, the voltage supplied to the series regulator 104 is a voltage within a range where the junction temperature of the series regulator 104 does not further increase, in other words, a range where the series regulator 104 can continuously operate.

  Thereafter, the voltage detection / bypass control unit 106 transmits a signal for instructing standby processing to the device 300 (S107). Upon receiving this signal, the device 300 performs standby processing. Here, the standby process means an operation in the low current mode by the device 300. In the operation in the low current mode, since the current consumption of the device 300 is about 0 to several mA, the series regulator 104 is gradually cooled. For example, if the time from when the bypass switch 110 is turned on to when it is returned to the off state is 10 ms, the device 300 is operated in the low current mode for 10 ms or more (for example, several hundred ms), so that the series regulator 104 The junction temperature decreases to a temperature just before the bypass switch 110 is turned on in S103.

  If the junction temperature of the series regulator 104 decreases to a temperature just before the bypass switch 110 is turned on in S103 by the operation in the low current mode in the device 300, the output voltage of the battery 200 is again increased by the operation after S101. The series regulator 104 can be directly supplied without using the DC-DC converter 102 and the diode 112.

  Instead of causing the device 300 to perform standby processing, the supply of voltage from the battery 200 to the DC-DC converter 102 or the series regulator 104 may be cut off. Also in this case, the series regulator 104 is gradually cooled because it does not perform any voltage conversion operation. If the junction temperature of the series regulator 104 decreases to the temperature just before the bypass switch 110 is turned on in S103, the output voltage of the battery 200 is again changed to DC-DC by the operation after S101. The series regulator 104 can be directly supplied without going through the converter 102 and the diode 112.

  As described above, in the power supply circuit 100 of this embodiment, when the output voltage of the battery 200 is normal, the series regulator 104 is supplied with a voltage lower than the output voltage of the battery 200 by the DC-DC converter 102. On the other hand, when the output voltage of the battery 200 decreases, the bypass circuit 108 bypasses the DC-DC converter 102 and the voltage is directly supplied from the battery 200. For this reason, the series regulator 104 can operate the device 300 with respect to the device 300 by compensating for the decrease by bypassing the DC-DC converter 102 even when the output voltage of the battery 200 decreases. A voltage can be supplied.

  Further, when the detour circuit 108 is turned on, a voltage larger than that when the output voltage of the battery 200 is normal is supplied to the series regulator 104, and the junction temperature may increase. Since the detour circuit 108 becomes non-conductive again before the voltage reaches the threshold voltage and the voltage supplied to the series regulator 104 is reduced, the junction temperature is prevented from rising, so that the series regulator 104 can operate normally. It becomes possible.

  In the above-described embodiment, when the output voltage of the battery 200 is equal to or lower than the threshold value, the voltage detection / detour control unit 106 turns on the switch 110 and instructs the device 300 to perform a shutdown process. However, the threshold value of the output voltage of the battery 200 that triggers the switch 110 to turn on is different from the threshold value of the output voltage of the battery 200 that triggers the device 300 to instruct the shutdown process. Also good. That is, for example, when the output voltage of the battery 200 becomes equal to or lower than the first threshold, the voltage detection / bypass control unit 106 turns on the switch 110, and further the output voltage of the battery 200 is lower than the first threshold. When the value is smaller than the small second threshold value, the device 300 may be instructed to perform a falling process. Conversely, when the output voltage of the battery 200 is equal to or smaller than the first threshold value, the device The switch 110 may be turned on when an instructing process is instructed to 300 and the output voltage of the battery 200 falls below a second threshold value that is smaller than the first threshold value.

  As described above, the power supply circuit according to the present invention has an effect of allowing the series regulator to perform a normal operation, and is useful as a power supply circuit.

It is a block diagram of the power supply circuit concerning embodiment of this invention. It is a flowchart which shows the detailed operation | movement of a voltage detection and detour control part. It is a figure which shows an example of the time passage of the thermal resistance in a series regulator. It is a figure which shows an example of the conventional power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Power supply circuit 102 DC-DC converter 104 Series regulator 106 Voltage detection / detour control part 107 Timer 108 Detour circuit 110 Bypass switch 112 Diode 200 Battery 300 Device

Claims (4)

A power supply circuit that controls the output voltage of a power supply and supplies it to a device,
A DC-DC converter that converts the output voltage of the power source into a voltage of a first predetermined value;
A series regulator for converting the output voltage of the DC-DC converter into a second predetermined value and supplying the converted voltage to the device;
Voltage detection means for detecting an output voltage of the power supply;
A detour in which an input end is connected between the power source and the input side of the DC-DC converter, and an output end is connected between the output side of the DC-DC converter and the input side of the series regulator When,
When the output voltage of the power source detected by the voltage detection means falls below a third predetermined value, the bypass circuit is turned on, the DC-DC converter is bypassed, and the output voltage of the power source is changed to the series regulator. A power supply circuit comprising: a detour control unit that performs control to directly supply the detour to a non-conduction state after a predetermined time has elapsed from the conduction. 2. The power supply circuit according to claim 1, wherein a time during which the bypass circuit is conductive is set so that the series regulator does not exceed a limit value of a junction temperature. When the output voltage of the power source detected by the voltage detection unit drops below the third predetermined value, the device has a process instruction unit for instructing the device to perform a preparation for a drop in the supplied voltage. The power supply circuit according to claim 1, wherein: The detour has a switch for switching between an on state and an off state, and the detour control unit is configured such that the output voltage of the power source detected by the voltage detection unit falls below the third predetermined value. 4. The power supply circuit according to claim 1, wherein the switch is turned on.

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