Abstract:
There is a need for improving switching regulator characteristics and providing a stable power supply controller. The power supply controller uses a battery and either or both functions of stepping up and stepping down a battery voltage. The power supply controller includes a means that prevents a ripple voltage from occurring by stopping the up conversion function for a switching operation in connection with a battery during a predetermined period without changing conditions for a conventional switching device or smoothing circuit and fast stabilizes a primary voltage using only the down conversion function.

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese patent application serial No. 2007-320828 filed on Dec. 12, 2007, the content of which is hereby incorporated by reference into this application 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power supply controller used for a device control circuit of electric equipment in a mechanical apparatus such as a car. 
     2. Description of the Related Art 
     A power supply controller supplies a drive voltage to a control circuit for electric devices mounted on a mechanical apparatus such as a car by generating a specific operating voltage such as 5 V or 3.3 V from a battery voltage. However, there is an increasing request from customers for ensuring operations against a battery voltage drop when an engine starts. To satisfy this demand, there is a need for a power supply controller featuring both an up conversion function and a down conversion function. 
       FIG. 18  shows a conventional example of the power supply controller. In  FIG. 18 , a battery  1  is connected to a smoothing circuit  4 . A pulse width modulation (PWM) control section  9  includes a down conversion control circuit  9   a  and an up conversion control circuit  9   b . The down conversion control circuit  9   a  drives a switching device for down conversion  3 . The up conversion control circuit  9   b  drives a switching device for up conversion  5 . The battery generates a primary voltage  6  using the switching device for down conversion  3  and the switching device for up conversion  5 . The smoothing circuit  4  includes diodes  4   a  and  4   c , an inductor  4   b , and a capacitor  4   d.    
     In order to decrease an effect of battery voltage variation, the PWM control section  9  allows a reference voltage generation circuit  10  to generate a reference voltage  10   a  from the battery voltage  1   a  or the primary voltage  6  whichever is higher. The battery voltage  1   a  passes through a voltage divider  18  and is supplied to a voltage comparator for battery voltage monitoring  14 . The voltage comparator for battery voltage monitoring  14  compares the battery voltage  1   a  with an up conversion switching voltage  16   a  and a down conversion switching voltage  16   b  ( 16   a &lt; 16   b ) predetermined in an up/down conversion switching voltage setting circuit  16  for determination. The voltage comparator for battery voltage monitoring  14  outputs battery voltage monitoring information  14   a  after the determination. An up/down conversion switching circuit  15  processes the battery voltage monitoring information  14   a  and notifies up/down conversion switching information  15   a  to the down conversion control circuit  9   a  and the up conversion control circuit  9   b  in the PWM control section  9 . 
     The primary voltage  6  passes through the voltage divider  8  and is supplied to the voltage comparator for primary voltage monitoring  7 . The voltage comparator for primary voltage monitoring  7  compares the primary voltage  6  with the reference voltage to detect a level of the primary voltage  6 . An output  7   a  is fed back to the PWM control section  9  for generating the primary voltage that is modified by controlling the switching device for down conversion  3  or the switching device for up conversion  5 . 
       FIG. 19  shows operational waveforms of the signals in  FIG. 18  when the power is turned on. Normally, the battery voltage  1   a  increases when the battery  1  is connected to the power supply controller at timing  300 . The reference voltage  10   a  generated from the battery voltage  1   a  also increases as indicated by reference numeral  304 . When the reference voltage  10   a  reaches a predetermined value, the up/down conversion switching information  15   a  outputs  0  (down conversion control notification). The down conversion control circuit  9   a  starts stepping down the primary voltage  6 . 
     The voltage comparator for battery voltage monitoring  14  monitors a voltage based on the battery voltage  1   a  and the reference voltage  10   a  and may incorrectly determine detection of the up conversion switching voltage  16   a  while the battery voltage  1   a  or the reference voltage  10   a  is in a increasing process as indicated by reference numeral  301 . At this time, the up/down conversion switching information  15   a  outputs  1  (up conversion control notification). The up conversion control circuit  9   b  of the PWM control section  9  operates and supplies a large current to the battery smoothing circuit  4  to increase the primary voltage  6 . 
     A large current may occur while the battery voltage  1   a  is in a increasing process and the reference voltage generation circuit  10  is in a generating process of the reference voltage  10   a . In such case, the voltage decreases due to the impedance of a battery connection cable, causing a local decrease in the reference voltage  10   a  as indicated by reference numeral  305 . The decrease of the battery voltage  1   a  causes the voltage comparator for battery voltage monitoring  14  to incorrectly determine detection of the down conversion switching voltage  16   b . The up/down conversion switching information  15   a  outputs  0  (down conversion control notification) to stop the up conversion control circuit  9   b  of the PWM control section  9  and operate the down conversion control circuit  9   a . The down conversion control decreases the current to the battery  1 , stops decreasing the voltage due to the cable, and increases the battery voltage  1   a.    
     The voltage comparator for battery voltage monitoring  14  may become incapable of correctly monitoring the battery-voltage  1   a  while the battery voltage  1   a  is in a increasing process as indicated by reference numeral  302  and the reference voltage generation circuit  10  is in a generating process of the reference voltage  10   a  as indicated by reference numeral  304 . As a result, the up conversion control circuit  9   b  and the down conversion control circuit  9   a  repeatedly switch between down and up conversion operations based on the incorrect determination to increase and decrease a current from the battery  1  and ripple the battery voltage  1   a . The up/down conversion switching information  15   a  causes an unstable up/down conversion switching state as indicated by reference numeral  307  while the battery voltage  1   a  is in the increasing process as indicated by reference numeral  302 . The switching device for up conversion  5  erratically operates to abnormally increase the primary voltage  6  as indicated by reference numeral  308 . 
       FIG. 20  shows operational waveforms corresponding to the following. The battery voltage  1   a  steps down to the up conversion switching voltage  16   a  specified by the up/down conversion switching voltage setting circuit  16 . The PWM control section changes from the down conversion operation to the up conversion operation to recover the battery voltage la to the down conversion switching voltage  16   b  or higher. 
     At timing  401 , the battery voltage  1   a  is lower than the up conversion switching voltage  16   a . The voltage comparator for battery voltage monitoring  14  causes output of the up/down conversion switching information  15   a  set to  1  (up conversion control notification). The up conversion control circuit  9   b  operates to generate the primary voltage  6 . The up conversion control circuit  9   b  in the PWM control section  9  controls the switching device for up conversion  5  to stepwise increase a current from the battery  1 . The battery voltage  1   a  ripples due to an impedance of a connected harness. 
     During the ripple under the up conversion control, the battery voltage  1   a  recovers and reaches the down conversion switching voltage  16   b  at a time point  403 . The up/down conversion switching information  15   a  of the up/down conversion switching circuit  15  outputs  0  (down conversion control notification). However, the battery voltage  1   a  still ripples under control of the up conversion control circuit  9   b  and becomes lower than the up conversion switching voltage  16   a  again. The up/down conversion switching information  15   a  outputs  1  (up conversion control notification). 
     A specified hysteresis voltage width is provided between the up conversion switching voltage  16   a  and the down conversion switching voltage  16   b . However, the rippling battery voltage  1   a  makes an up/down conversion switching operation unstable near the down conversion switching voltage  16   b  or the up conversion switching voltage  16   a  as indicated by timing  403 . The up conversion control circuit  9   b  in the PWM control section  9  does not generate a normal control pulse. The erratically generated up/down conversion switching information  15   a  passes control to the switching device for up conversion  5 . The primary voltage  6  abnormally rises as indicated by reference numeral  405 . 
       FIG. 21  shows operational waveforms when the battery is removed from the power supply controller. The battery voltage  1   a  decreases when the battery  1  is removed at timing  501 . The battery voltage  1   a  is lower than the up conversion switching voltage  16   a  at timing  502 . The voltage comparator for battery voltage monitoring  14  causes output of the up/down conversion switching information  15   a  set to be  1  (up conversion control notification). The up conversion control circuit  9   b  operates to generate the primary voltage  6 . 
     When the battery voltage  1   a  further decreases to point  503 , the decrease exceeds a limit that can be controlled by the up conversion control circuit  9   b  in the PWM control section  9 . Accordingly, the primary voltage  6  decreases. The reference voltage  10   a  also decreases. The voltage comparator for battery voltage monitoring  14  or the voltage comparator for primary voltage monitoring  7  cannot correctly monitor voltage. Since the battery voltage  1   a  ripples due to the up conversion control, the reference voltage  10   a  becomes unstable as indicated by reference numeral  504 . Consequently, the up/down conversion switching information  15   a  also becomes unstable as indicated by reference numeral  505 . Control is passed to the switching device for up conversion  5  at an incorrect timing. The primary voltage  6  abnormally rises as indicated by reference numeral  506 . 
     As a conventional solution, Patent Document 1 discloses a method of stabilizing linear voltage characteristics by supplying a linear regulator circuit and a switching regulator circuit with a stable reference voltage generated from another system. 
     Patent Document: JP-A No. 168043/1994 
     Recently, there is an increasing demand for ensuring operations at a low battery voltage. A power supply controller is requested to ensure operations of circuits using a battery even when a battery voltage drops due to a cranking noise generated during starter activation. Specifically, operations are requested to be ensured even when the battery voltage becomes lower than a primary voltage generated by a switching regulator. According to a conventional technology, voltage monitoring circuits cannot monitor the battery voltage while the battery voltage is increasing. An incorrect up/down conversion switching operation is repeated to abnormally increase the primary voltage  6 . 
     SUMMARY OF THE INVENTION 
     To solve the above-mentioned problem, it is an object of the present invention to generate a primary voltage by operating a switching regulator only under down conversion control by using a means for disabling up conversion control until a battery voltage increases to stable a reference voltage. It is another object of the present invention to compare a secondary voltage generated from a primary voltage with a reference voltage, prevent incorrect up/down conversion switching control from occurring, and prevent a primary voltage from abnormally rising by using a means for forcibly masking an up conversion control operation until the secondary voltage reaches a regulation value. 
     It is still another object of the present invention to prevent incorrect up/down conversion switching control due to a battery voltage ripple occurring during engine startup and prevent a primary voltage from abnormally rising by providing a given hysteresis width for a changeover voltage around a voltage at which the battery voltage recovers and down conversion control is enabled. 
     It is yet another object of the present invention to prevent incorrect up/down conversion switching control from occurring and prevent a primary voltage from abnormally rising by using a means for forcibly disabling an up conversion control operation when the battery voltage decreases to or lower than a voltage capable of stepping up. 
     According to the present invention, a means for disabling up conversion control is used to forcibly stop an up conversion control operation until a battery voltage increases and a reference voltage is stabled. A switching regulator is operated only under down conversion control. The down conversion control is provided until a primary voltage is generated and a secondary voltage reaches a regulation value, preventing incorrect up/down conversion switching control from occurring and preventing the primary voltage from abnormally rising. It is possible to prevent an overcurrent from occurring and stably provide the primary voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing a first embodiment of the invention; 
         FIG. 2  is a circuit diagram showing a second embodiment of the invention; 
         FIG. 3  is a circuit diagram showing a third embodiment of the invention; 
         FIG. 4  is an operational waveform diagram according to the first embodiment of the invention; 
         FIG. 5  is an operational waveform diagram according to the first embodiment of the invention; 
         FIG. 6  is a circuit diagram showing a fourth embodiment of the invention; 
         FIG. 7  is an operational waveform diagram according to the fourth embodiment of the invention; 
         FIG. 8  is an operational waveform diagram according to the fourth embodiment of the invention; 
         FIG. 9  is a circuit diagram showing a fifth embodiment of the invention; 
         FIG. 10  is a circuit diagram showing a sixth embodiment of the invention; 
         FIG. 11  is an operational waveform diagram according to the sixth embodiment of the invention; 
         FIG. 12  is a circuit diagram showing a seventh embodiment of the invention; 
         FIG. 13  is a circuit diagram showing an eighth embodiment of the invention; 
         FIG. 14  is an operational waveform diagram according to the sixth embodiment of the invention; 
         FIG. 15  is a circuit diagram showing a ninth embodiment of the invention; 
         FIG. 16  is an operational waveform diagram according to the ninth embodiment of the invention; 
         FIG. 17  is a block diagram showing a tenth embodiment of the invention; 
         FIG. 18  is a circuit diagram showing a prior art; 
         FIG. 19  is an operational waveform diagram according to the prior art when a battery voltage increases; 
         FIG. 20  is an operational waveform diagram according to the prior art when a decreased battery voltage recovers; and 
         FIG. 21  is an operational waveform diagram according to the prior art when a battery voltage decreases. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described in further detail with reference to the accompanying drawings. The invention is not limited to the embodiments. 
     First Embodiment 
       FIG. 1  shows a first embodiment of the invention. A battery voltage  1   a  is connected to a smoothing circuit  4  via a switching device for down conversion  3 . The switching device for down conversion  3 , a switching device for up conversion  5 , and a PWM control section  9  are used for up conversion control and down conversion control to generate a primary voltage. The smoothing circuit  4  includes diodes  4   a  and  4   c , an inductor  4   b , and a capacitor  4   d  using the same devices as used for the prior art. 
     The PWM control section  9  allows a reference voltage generation circuit  10  to generate a reference voltage  10   a  from the battery voltage  1   a  or the primary voltage whichever is higher. A battery voltage detection means includes a voltage comparator for battery voltage monitoring  14  and an up/down conversion switching voltage setting circuit  16 . The battery voltage  1   a  is supplied to the voltage comparator for battery voltage monitoring  14  via a voltage divider  18  for determining an up conversion switching voltage  16   a  and a down conversion switching voltage  16   b  specified by the up/down conversion switching voltage setting circuit  16 . A hysteresis is provided between the up conversion switching voltage  16   a  and the down conversion switching voltage  16   b  for stabilizing a detection circuit. The up/down conversion switching voltage setting circuit  16  can assign any values to the voltages  16   a  and  16   b . The voltage comparator for battery voltage monitoring  14  outputs battery voltage monitoring information  14   a  as a determination result. The battery voltage monitoring information  14   a  passes through a mask means  20   a . An up/down conversion switching circuit  15  notifies the battery voltage monitoring information  14   a  to a down conversion control circuit  9   a  and an up conversion control circuit  9   b  in the PWM control section  9 . 
     The primary voltage  6  passes through a voltage divider  8  and is supplied to a voltage comparator for primary voltage monitoring  7  that detects a level. The voltage comparator for primary voltage monitoring  7  feeds primary voltage monitoring information  7   a  back to the PWM control section  9 . The PWM control section  9  controls a switching regulator including the switching device for down conversion  3  or the switching device for up conversion  5  to generate a primary voltage. 
     The primary voltage  6  is generated from the switching regulator for providing a voltage to each device control circuit. A secondary voltage generation circuit  11  is used to generate a secondary voltage  11   a  from the primary voltage  6 . The generated secondary voltage  11   a  passes through the voltage divider  19  and is supplied to a voltage comparator for secondary voltage monitoring  12 . The voltage comparator for secondary voltage monitoring  12  compares the secondary voltage  11   a  with the reference voltage  10   a  to determine whether or not the secondary voltage  11   a  is greater than or equal to a regulation value. The voltage comparator for secondary voltage monitoring  12  outputs secondary voltage monitoring information  12   a . The secondary voltage monitoring information  12   a  is connected to the mask means  20   a . The mask means  20   a  forcibly masks the up/down conversion switching operation of the up/down conversion switching circuit  15  while the secondary voltage does not reach the regulation value. The mask forcibly stops control to be passed to the switching device for up conversion  5  and prevents the primary voltage  6  from abnormally rising. 
     The battery voltage detection means can include a proper circuit means. Using a secondary voltage monitoring signal  12   a , the battery voltage detection means directly controls and stops the voltage comparator for battery voltage monitoring  14  until the secondary voltage reaches the regulation value. This operation similarly stops control to be passed to the switching device for up conversion  5  and prevents the primary voltage  6  from abnormally rising. 
     Second Embodiment 
       FIG. 2  shows a second embodiment of the invention. In  FIG. 2 , a mask means  20   b  precedes the up conversion control circuit  9   b  of the PWM control section  9 . The mask means  20   b  forcibly masks an up conversion operation of the up conversion control circuit  9   b  until the secondary voltage monitoring signal  12   a  detects that the secondary voltage  11   a  reaches a regulation value. 
     Third Embodiment 
       FIG. 3  shows a third embodiment of the invention. In  FIG. 3 , a mask means  20   c  is provided between the up conversion control circuit  9   b  and the switching device for up conversion  5 . Similarly to the second embodiment, the mask means  20   c  forcibly masks an up conversion operation of the switching device for up conversion  5  until the secondary voltage monitoring signal  12   a  detects that the secondary voltage  11   a  reaches a regulation value. 
     The embodiments describe only examples of the mask means and do not limit positions for installing the mask means. 
       FIG. 4  is an operational waveform diagram for voltages showing operations of a power control circuit according to the first embodiment. The operations of the first embodiment will be described with reference to  FIG. 4 . The battery  1  is connected to the power control circuit at timing  100 . The battery voltage  1   a  increases to start increasing the reference voltage  10   a  that is generated from the battery voltage  1   a . At this time, the secondary voltage  11   a  is equal to the reference voltage  10   a  and does not reach a regulation value  104 . The PWM control section  9  uses the mask means  20   a  based on the secondary voltage monitoring information  12   a  to control the up/down conversion switching information  15   a  to be output as  0  (down conversion control notification) for generating the primary voltage  6 . 
     The secondary voltage generation circuit  11  generates the secondary voltage  11   a  from the primary voltage  6  generated by the down conversion control circuit  9   a . The voltage comparator for secondary voltage monitoring  12  transmits the secondary voltage monitoring information  12   a  output as  0  until the secondary voltage  11   a  reaches a value  104  specified by the reference voltage  10   a . The voltage comparator for secondary voltage monitoring  12  transmits the secondary voltage monitoring information  12   a  output as  1  when the secondary voltage  11   a  exceeds the value  104  specified by the reference voltage  10   a . The secondary voltage monitoring information  12   a  is used for controlling the up/down conversion switching information  15   a.    
     These means increase both the battery voltage  1   a  and the reference voltage  10   a  until the battery voltage  1   a  reaches a voltage  103 . After reaching a voltage  101 , the battery voltage  1   a  exceeds the up conversion switching voltage  16   a  specified by the up/down conversion switching voltage setting circuit  16 . When reaching a voltage  102 , the battery voltage  1   a  exceeds the down conversion switching voltage  16   b . At this time, a forcible down conversion control means is used to prevent an incorrect up/down conversion switching operation from occurring while the battery voltage  1   a  is increasing, thus preventing the primary voltage  6  from abnormally rising. 
       FIG. 5  is an operational waveform diagram for voltages showing operations when up conversion control is applied to the battery voltage. The following describes operations when the secondary voltage decreases. In  FIG. 5 , the secondary voltage  11   a  temporarily drops for some reasons as indicated by reference numeral  105  and becomes lower than a regulation voltage  104 . At this time, the secondary voltage monitoring information  12   a  is output as  0 . As indicated by reference numeral  106  in  FIG. 5 , the mask means  20   a  does not perform an up conversion function masking process to keep the up/down conversion switching information  15   a  output as  1  (up conversion control notification). The primary voltage  6  is subject to no effect and can be supplied stably. 
     Fourth Embodiment 
       FIG. 6  shows a fourth embodiment of the invention. In  FIG. 6 , a Power On Reset signal pulse generation circuit  13  initializes the devices providing the secondary voltage  11   a  by outputting a Power On Reset signal  13   a  to the devices based on the secondary voltage monitoring information  12   a . The fourth embodiment uses the Power On Reset signal  13   a  so that the mask means disables up conversion control over the switching device for up conversion  5  while the battery voltage  1   a  is increasing. 
     The voltage comparator for battery voltage monitoring  14  monitors the battery voltage. It may be preferable to stop the voltage comparator for battery voltage monitoring  14  until the Power On Reset signal  13   a  is released. This stops control passed to the switching device for up conversion  5  and prevents the primary voltage  6  from abnormally rising. 
       FIG. 7  is an operational waveform diagram showing operations according to a fourth embodiment. Operations of the fourth embodiment will be described with reference to  FIG. 7 . With reference to  FIG. 4 , there have been described in detail the operations in which the battery voltage  1   a  reaches the voltage  103  and the secondary voltage  11   a  reaches the regulation value  104 . Only differences will be described below. When the secondary voltage  11   a  is greater than or equal to the regulation value  104 , the secondary voltage monitoring information  12   a  is output as  1 . When a given interval  107  elapses after the secondary voltage monitoring information  12   a  is output as  1 , the Power On Reset signal pulse generation circuit  13  transmits  1  as output  13   a  to the devices. 
     It is possible to prevent the primary voltage  6  from rising abnormally by keeping the up/down conversion switching information  15   a  being output as  0  (down conversion control notification) until the Power On Reset signal  13   a  is output as  1 . The fourth embodiment controls the up conversion control operation by combining the conventionally used Power On Reset signal with no additional cost. 
       FIG. 8  is an operational waveform diagram showing operations when the battery voltage is under the up conversion control according to the fourth embodiment in  FIG. 7 . The following describes operations when the secondary voltage temporarily drops and a Power On Reset signal is generated. The secondary voltage  11   a  temporarily drops for some_reasons as indicated by reference numeral  105  and becomes lower than the regulation voltage  104 . At this time, the secondary voltage monitoring information  12   a  is output as  0  and the Power On Reset signal  13   a  is output as  0  for a given period  107 . As indicated by reference numeral  106  in  FIG. 8 , the mask means  20   a  does not perform an up conversion function masking process to keep the up/down conversion switching information  15   a  output as  1  (up conversion control notification). The primary voltage  6  is subject to no effect and can be supplied stably. 
     Fifth Embodiment 
       FIG. 9  shows a fifth embodiment of the invention. The embodiment concerns a case where the battery voltage  1   a  recovers to the down conversion switching voltage  16   b  or higher after the battery voltage  1   a  decreases to the up conversion switching voltage  16   a  and changes to the up conversion control from the down conversion control as described in the preceding embodiments. When the battery voltage  1   a  reaches the up conversion switching voltage  16   a  or lower, the voltage comparator for battery voltage monitoring  14  outputs the up/down conversion switching information  15   a  set to  1  (up conversion control notification). The up conversion control circuit  9   b  operates to generate the primary voltage  6 . However, the up conversion control circuit  9   b  in the PWM control section  9  controls the switching device for up conversion  5  and increases a current from the battery  1 . The battery voltage  1   a  ripples due to an impedance of the connected harness. 
     A hysteresis voltage width is provided between the up conversion switching voltage  16   a  and the down conversion switching voltage  16   b  so as to prevent the voltage comparator for battery voltage monitoring  14  from erratically functioning due to the rippling battery voltage  1   a . The battery voltage  1   a  may cause a ripple voltage greater than or equal to a voltage difference specified by the up/down conversion switching voltage setting circuit  16  under an operating environment such as an impedance of the harness to be used or a consumption current for the primary voltage. As a result, the voltage comparator for battery voltage monitoring  14  may malfunction. The embodiment uses a hysteresis changeover signal  21  so that the hysteresis voltage width in the up/down conversion switching voltage setting circuit  16  is variable. The hysteresis changeover signal  21  prevents an effect of the ripple voltage from the battery voltage  1   a  near the down conversion switching voltage  16   b  or the up conversion switching voltage  16   a . The hysteresis changeover signal  21  also prevents an unstable up/down conversion switching operation and can stably generate the primary voltage  6 . 
     Sixth Embodiment 
       FIG. 10  shows a sixth embodiment of the invention. The embodiment concerns a case where the battery voltage  1   a  decreases to the up conversion switching voltage  16   a , changes to the up conversion control from the down conversion control, and then recovers to the down conversion switching voltage  16   b  or higher. In  FIG. 10 , a ripple voltage detection circuit  23  is used to monitor a ripple width of the battery voltage  1   a . This is because the battery voltage  1   a  ripples variously depending on operational conditions under the up conversion control. 
     The ripple voltage detection circuit  23  uses the up/down conversion switching information  15   a  to detect a ripple voltage width during the up conversion control and notifies detected ripple voltage detection information  23   a  to the up/down conversion switching voltage setting circuit  16 . Using the ripple voltage detection information  23   a , the up/down conversion switching voltage setting circuit  16  changes a voltage difference between the down conversion switching voltage  16   b  and the up conversion switching voltage  16   a  specified as initial values to a hysteresis width compliant with the operational environment. The construction can prevent the battery voltage monitoring information  14   a  from erratically varying due to the rippling battery voltage  1   a , prevent an unstable up/down conversion switching operation, and stably generate the primary voltage  6 . 
       FIG. 11  is an operational waveform diagram showing operations of the sixth embodiment. The sixth embodiment will be described with reference to  FIG. 11 . When the battery voltage  1   a  becomes smaller than or equal to the up conversion switching voltage  16   a  as indicated by reference numeral  111 , the battery voltage  1   a  ripples while the up conversion control circuit  9   b  in the PWM control section  9  controls the switching device for up conversion  5 . The ripple voltage detection circuit  23  detects a voltage difference and outputs a ripple voltage width as ripple voltage detection information  23   a.    
     The up/down conversion switching voltage setting circuit  16  compares the ripple voltage detection information  23   a  with a hysteresis voltage as an initial value  113  settled based on the ripple voltage detection information  23   a . As indicated by reference numeral  114 , the up/down conversion switching voltage setting circuit  16  detects ripple voltage values exceeding the predetermined initial value  113  and varies the threshold from the initial value for the down conversion switching voltage  16   b . Further, the up/down conversion switching voltage setting circuit  16  can use a function that adds a value  115  for preventing an error and changes the down conversion switching voltage  16   b  to a hysteresis width compliant with the operational environment as indicated by reference numeral  116 . The construction can prevent the battery voltage monitoring information  14   a  from erratically varying due to the rippling battery voltage  1   a , prevent an unstable up/down conversion switching operation, and stably generate the primary voltage  6 . 
     Seventh Embodiment 
       FIG. 12  shows a seventh embodiment of the invention. The embodiment concerns a case where the battery voltage  1   a  decreases to the up conversion switching voltage  16   a , changes to the up conversion control from the down conversion control, and then recovers to the down conversion switching voltage  16   b  or higher. When the battery voltage  1   a  causes a ripple greater than or equal to the hysteresis width specified by the up/down conversion switching voltage setting circuit  16 , the voltage comparator for battery voltage monitoring  14  erratically detects a voltage change. The up/down conversion switching circuit  15  erratically passes changeover control to the PWM control section  9 . 
     To solve the problem, a guard time circuit  22  is used to provide guard time for keeping the battery voltage monitoring information  14   a  output for a given period of time. The voltage comparator for battery voltage monitoring  14  detects and outputs the battery voltage monitoring information  14   a . The construction can prevent an unstable up/down conversion switching operation and stably generate the primary voltage  6 . 
     Further, the guard time circuit  22  can be provided with a guard time changeover function using a guard time changeover signal  24  supplied from the outside so as to be able to change the guard time in accordance with the operational environment. It is possible to prevent an unstable up/down conversion switching operation and stably generate the primary voltage  6 . 
     Eighth Embodiment 
       FIG. 13  concerns the guard time described with reference to  FIG. 12  and shows an eighth embodiment of the invention having a construction of calculating the guard time from the PWM control information. Since the battery voltage  1   a  ripples during the up conversion control, the guard time circuit  22  detects control duty time from control signals using the up/down conversion switching information  15   a , a down conversion control signal  3   a , and an up conversion control signal  5   a . The guard time circuit  22  generates guard time from the detected time and provides the guard time for the battery voltage monitoring information  14   a  detected by the voltage comparator for battery voltage monitoring  14 . The construction can prevent an unstable up/down conversion switching operation and stably generate the primary voltage  6 . 
       FIG. 14  is an operational waveform diagram showing operations of the eighth embodiment. The eighth embodiment will be described with reference to  FIG. 14 . While the battery voltage  1   a  ripples, the guard time circuit  22  detects guard times T 1  through T 5  from the down conversion control signal  3   a  and the up conversion control signal  5   a  under the up conversion control in process. The guard time circuit  22  calculates an average time value for five cycles of the detected time and settles five cycles of the average value as a guard time  122 . 
     The voltage comparator for battery voltage monitoring  14  erratically detects a voltage when the battery voltage  1   a  causes a ripple greater than or equal to the hysteresis width near the up conversion switching voltage  16   a  or the down conversion switching voltage  16   b . At a time point  120  in  FIG. 14 , the embodiment provides guard time  122  for the battery voltage monitoring information  14   a  detected by the voltage comparator for battery voltage monitoring  14 . It is possible to prevent an unstable up/down conversion switching operation and stably generate the primary voltage  6 . The embodiment has described the guard time setting as an example only and does not limit a specific means. The embodiment automatically extracts the guard time from the PWM control information and generates the guard time. 
     Ninth Embodiment 
       FIG. 15  shows a ninth embodiment of the invention when the battery is removed. As described in the preceding embodiments, a decrease in the battery voltage  1   a  also decreases the primary voltage  6  or the reference voltage  10   a . The voltage comparator for primary voltage monitoring  7  or the voltage comparator for battery voltage monitoring  14  cannot correctly monitor voltage levels. This makes it impossible to normally control the down conversion control circuit  9   a  or the up conversion control circuit  9   b  in the PWM control section  9 , thus abnormally increasing the primary voltage. To solve the problem, a voltage comparator for low voltage monitoring  17  monitors a low voltage in the battery voltage  1   a . Before a low voltage causes abnormal control, low voltage monitoring information  17   a  allows the mask means  20   a  to stop controlling the switching device for up conversion  5  and prevent the primary voltage from abnormally rising. The mask means may be arranged as described in the second or third embodiment. 
     When detecting a low voltage in the battery, the embodiment stops the voltage comparator for battery voltage monitoring  14  for monitoring the battery voltage. As mentioned above, this stops controlling the switching device for up conversion  5  and prevents the primary voltage  6  from abnormally rising. It is known that a large current is needed to step up the battery voltage when decreased. Decreasing the battery voltage requires a large current for generating the primary voltage and destroys a switching regulator device as a result. The embodiment can prevent the device from being destroyed. 
       FIG. 16  is an operational waveform diagram showing operations of the ninth embodiment. The following describes operations when the battery voltage decreases. The battery voltage  1   a  decreases because the battery  1  is removed at timing  201 . The battery voltage  1   a  is smaller than or equal to the up conversion switching voltage  16   a  at a time point  202 . The up/down conversion switching information  15   a  is output as  1  (up conversion control notification) for up conversion control. When the battery voltage  1   a  decreases to a specified voltage  17  or lower as indicated by reference numeral  203 , the low voltage monitoring information  17   a  is output as  0  (low voltage detection notification). This keeps the up/down conversion switching information  15   a  being output as  0  (down conversion control notification) to stop controlling the switching device for up conversion  5  and prevent the primary voltage from abnormally rising. 
     Tenth Embodiment 
       FIG. 17  is a tenth embodiment of mounting the power supply controller according to the invention on a mechanical apparatus such as a car.  FIG. 17  shows a car  30  mounted with a power supply control circuit (PSC) as the power supply controller according to the invention. The car  30  includes constituent devices such as an engine  35 , a steering unit  36 , a lighting system  37 , and a brake system  38 . The car  30  further includes an engine control means  31 , a steering control means  32 , a lighting control means  33 , and a brake system control means  34  for controlling the devices. The device control means are stably supplied with operating voltages from the power supply controller according to the invention.