JP2013038693A - Pulse generation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse generation circuit that implements desired control by a controlled object while adopting a configuration for generating an irregular pulse signal.SOLUTION: If a predetermined time passes, a count value of a counter CO1 of a counting circuit 7 reaches a predetermined value. The counter CO1 of the counting circuit 7 then outputs a pulse to cause a threshold voltage switching circuit 8 to forcibly change a threshold to be compared in a comparison circuit 5 by means of a control switch SW2. When magnetic energy in an inductor L1 is later transferred to a load side to drop a voltage at a node N4, a pulse detection circuit 6 detects the voltage drop timing to output a pulse. An output voltage of a signal generation circuit 3 is then initialized.

Description

  The present invention relates to a pulse generation circuit that generates a pulse to be supplied to a control target whose generation timing of a control signal supplied to the control target is indefinite and whose signal width is variable.

  For example, a switching drive type DC / DC converter generally generates a pulse signal using a time-varying signal such as a triangular wave or a sawtooth wave and a threshold signal, and supplies output power by driving the switching element with the pulse signal. (For example, refer to Patent Documents 1 to 3). As a driving method of the switching element for stably maintaining the output voltage, a PWM (Pulse Width Modulation) method, a PFM (Pulse frequency modulation) method, a PSM (Pulse Skip Modulation) method, and the like are known.

  In general, the PWM method is a method in which the on-timing of the switching element is always constant, and the on-time of the switching element is controlled in accordance with the converter output voltage. On the other hand, the PFM method has the generation timing of the drive signal applied to the switching element. The pure PFM system that is continuously controlled according to the converter output voltage, and the generation timing of the drive signal applied to the switching element is constant, and the drive signal is applied to the switching element according to the converter output voltage or skipped without being applied. There is known a pseudo PFM method (the above-mentioned PSM method) that operates in the following manner.

  In the DC / DC converter described in Patent Document 1, the triangular wave generating circuit charges and discharges the capacitor to generate a triangular wave, and the comparator compares the output voltage of the error amplifier with the triangular wave of the triangular wave generating circuit. A level signal is output. In this case, for example, the duty ratio limiting voltage is compared with the output of the error amplifier, and the duty ratio is determined by the duty ratio limiting voltage when the output of the error amplifier exceeds the duty ratio limiting voltage. Thus, the pulse generation circuit can generate a pulse signal by limiting the maximum value of the duty ratio.

  Further, in the power supply control circuit described in Patent Document 2, when driving the pulse width modulation unit of the switching regulator, a triangular pulse is used to generate a control pulse having a pulse width that changes according to the output voltage, and a limited pulse width output is generated. , So that you get in sync with the sync input. Further, the DC-DC converter described in Patent Document 3 employs a chopper type boost type converter based on PSM control.

  For example, in the PWM system and the PSM system DC / DC converter, since the generation period of the pulse signal given to the switching element is constant, as shown in FIG. By masking the second half of the original signal, the on-time of the switching element can be limited.

  However, in the PFM method or the PWFM method in which the PFM method and the PWM method are mixed, the specification for generating a pulse signal at a constant cycle is not used. Therefore, as shown in FIG. 8B and FIG. Even if a certain off time is secured and masked in the latter half of the period, an output of an on time deficit (FIG. 8B) and an ON control failure (FIG. 8C) is obtained. Therefore, a device for eliminating the on-time deficit and the on-control failure is desired. In addition, it may be necessary to maintain the desired control even when the control target generates an abnormal state such as an element characteristic change corresponding to a load fluctuation, temperature change, durability deterioration, or the like due to some factor.

JP 11-214971 A Japanese Patent Laid-Open No. 2-223381 JP 2004-297925 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pulse generation circuit capable of maintaining desired control by a control target while adopting a configuration for generating a pulse signal at an indefinite period. There is.

  According to the first aspect of the present invention, the signal generating means generates a signal that changes with time. The fluctuation threshold generating means raises the fluctuation threshold when the output voltage to be controlled decreases, and lowers the fluctuation threshold when the output voltage to be controlled rises. The comparison means changes to a predetermined release threshold lower than the fluctuation threshold when the signal generated by the signal generation means becomes higher than the fluctuation threshold, and generates a fluctuation threshold at the fluctuation threshold when the signal generated by the signal generation means becomes lower than the release threshold. It has a hysteresis characteristic that changes the threshold value of the means, and outputs a logic signal that compares the threshold value of the fluctuation threshold value generating means and the generated signal of the signal generating means to the control target. The detection means detects the start of the control cycle of the controlled object, but the initialization means initializes the signal generated by the signal generation means when the detection means detects the start timing of the control cycle.

  The counting means counts time from the start timing of the control cycle detected by the detecting means or the initialization timing initialized by the initializing means. When the predetermined time is counted by the counting means, When the generated signal of the signal generating means is lower than the fluctuation threshold, the levels of the generated signal of the signal generating means and the fluctuation threshold are reversed.

  Since the invention described in claim 1 has such a function, it is assumed that when the predetermined time has elapsed, the level of the generated signal of the signal generating means and the fluctuation threshold of the fluctuation threshold generating means In addition, the signal generated by the signal generating means can be made higher than the fluctuation threshold of the fluctuation threshold generating means. The comparison means considers that the signal generated by the signal generation means is higher than the fluctuation threshold, sets the threshold to be compared as a predetermined release threshold, and allows the control object to forcibly continue the desired control according to the output of the comparison means . Therefore, the desired control by the controlled object can be maintained even when the configuration for generating the pulse signal at an indefinite period is adopted.

  According to a second aspect of the invention, in place of the counting means according to the first aspect, an overcurrent detection means for detecting an overcurrent to be controlled is provided. When the overcurrent is detected by the overcurrent detection means, the inversion means reverses the level of the generated signal of the signal generation means and the fluctuation threshold when the signal generated by the signal generation means is lower than the fluctuation threshold. Since the invention described in claim 2 has such a function, when the overcurrent flows through the controlled object, the level relationship between the generated signal of the signal generating means and the fluctuation threshold of the fluctuation threshold generating means is Even so, the signal generated by the signal generating means can be made higher than the fluctuation threshold of the fluctuation threshold generating means. The comparison means considers that the signal generated by the signal generation means has become higher than the fluctuation threshold, and sets the threshold to be compared as a predetermined release threshold, and the control object can forcibly continue the desired control according to the output of the comparison means. . Therefore, the desired control by the controlled object can be maintained even when the configuration for generating the pulse signal at an indefinite period is adopted.

  According to the invention described in claim 3, in place of the counting means described in claim 1, overheat detecting means for detecting the overheat state of the controlled object is provided. When the overheat state is detected by the overheat detecting means, the reversing means reverses the level of the generated signal of the signal generating means and the fluctuation threshold when the signal generated by the signal generating means is lower than the fluctuation threshold. Since the invention according to claim 3 has such a function, when the overheated state of the control object is detected, what level relationship between the generated signal of the signal generating means and the fluctuation threshold of the fluctuation threshold generating means Even if it is, the signal generated by the signal generating means can be made higher than the fluctuation threshold of the fluctuation threshold generating means. The comparison means considers that the signal generated by the signal generation means has become higher than the fluctuation threshold, and sets the threshold to be compared as a predetermined release threshold, and the control object can forcibly continue the desired control according to the output of the comparison means. . Therefore, the desired control by the controlled object can be maintained even when the configuration for generating the pulse signal at an indefinite period is adopted.

  According to the invention of claim 4, the inverting means is a inverting threshold that is lower than the variability threshold and equal to or higher than the release threshold, and is set to a predetermined inverting threshold lower than the signal generated by the signal generating means. Therefore, the signal generated by the signal generating means can be made higher than the inversion threshold. According to the fifth aspect of the present invention, since the inverting means sets the generated signal of the signal generating means to be higher than the fluctuation threshold, it is possible to make the generated signal of the signal generating means higher than the fluctuation threshold.

The electrical block diagram of the control system which shows 1st Embodiment of this invention. Timing chart in normal state ((a) is standard load, (b) is light load, (c) is heavy load) Timing chart when an abnormal condition occurs (part 1) Timing chart when an abnormal condition occurs (part 2) FIG. 1 equivalent view showing a second embodiment of the present invention FIG. 1 equivalent view showing a third embodiment of the present invention FIG. 1 equivalent view showing a fourth embodiment of the present invention Illustration of prior art

(First embodiment)
Hereinafter, a first embodiment of a pulse generation circuit for supplying a pulse signal to be applied to a switching element constituting a step-up chopper type DC / DC converter (control target) will be described with reference to FIGS.

  FIG. 1 shows the electrical configuration of the control system. As shown in FIG. 1, a DC / DC converter (corresponding to a control target) 1 serving as a switching power supply circuit is configured. The DC / DC converter 1 is, for example, a non-insulated step-up chopper type DC / DC converter, which includes a switching element M1 and outputs an input voltage in response to a pulse drive signal applied to a control terminal of the switching element M1. Convert to voltage (<> input voltage) and output.

  In the DC / DC converter 1, the anode and the cathode of the inductor L1 and the diode D1 are connected in series from the first input node N1 on the input side to the output side. For example, the switching element M1 composed of an N-channel MOS transistor is provided. The inductor L1 is connected between the common connection node N4 of the diode D1 and the second input node N2, and the capacitor C1 is connected between the cathode of the diode D1 and the second input node N2. .

  The output voltage (output voltage to be controlled) of the DC / DC converter 1 is given to the pulse generation circuit 2, and the pulse generation circuit 2 has a switching timing of the switching element M1 (start timing of the control cycle of the control target). The pulse drive signal (pulse period, pulse width) applied to the switching element M1 of the DC / DC converter 1 is changed in accordance with the output voltage (change) of the DC / DC converter 1. In the present embodiment, a so-called PWFM (Pulse Wide Frequency Modulation) driving method that changes both the pulse width and the pulse period of the pulse driving signal is employed.

  Hereinafter, a configuration example of the pulse generation circuit 2 will be described. The pulse generation circuit 2 includes a signal generation circuit (signal generation means) 3, a threshold voltage generation circuit (variation threshold generation means) 4, a comparison circuit (comparison means) 5, a pulse detection circuit (detection means) 6, and a counting circuit (counting means). 7) A threshold voltage switching circuit (inversion means) 8 and drive circuits 9 and 10 are connected in the illustrated manner.

  The signal generating circuit 3 is configured by connecting a control switch (initializing means) M2 in parallel to a capacitor C2 of the CR series circuits R2 and C2, for example, and the CR series circuits R2 and C2 while the control switch M2 is OFF. The charging voltage at the common connection point N3 is output.

  The threshold voltage generation circuit 4 is configured by connecting, for example, an operational amplifier OP1 and resistors R3 to R6, and is configured to change an output threshold voltage (corresponding to a variation threshold) according to the output voltage of the DC / DC converter 1. ing. When the illustrated circuit configuration is applied, the threshold voltage generation circuit 4 increases the output threshold voltage when the output voltage of the DC / DC converter 1 decreases, and decreases the output threshold voltage when the output voltage of the DC / DC converter 1 increases. .

  A comparison circuit 5 is connected to an output of the threshold voltage generation circuit 4 through a threshold voltage switching circuit 8. The comparison circuit 5 mainly compares the threshold voltage of the threshold voltage generation circuit 4 with the output voltage of the signal generation circuit 3. It is configured as a circuit.

  The comparison circuit 5 is configured by using the comparator OP2 and the control switch SW1, and switches the control switch SW1 in accordance with the logic signal (comparison result) output from the comparison circuit 5, whereby the output voltage of the threshold voltage switching circuit 8 is changed. It is switched between a comparison target and a predetermined release threshold voltage (release threshold) as a comparison target.

  The pulse detection circuit 6 is configured by connecting a differential circuit combining a capacitor C3 and resistors R7 and R8, and an inverting gate (pulse output circuit) G1 in the illustrated form, and a common connection node between the inductor L1 and the anode of the diode D1 The N4 signal (voltage) is input, the voltage change of the common connection node N4 is detected by the differentiation circuit, and the detection result is output as a pulse (initialization pulse). The detection signal of the pulse detection circuit 6 is given to the control terminal of the control switch M2 through the drive circuit 9.

  The counting circuit 7 includes a counter CO1 that inputs a detection signal of the pulse detection circuit 6 to a reset terminal. The counter CO1 counts the clock pulse in response to inputting a clock signal having a predetermined clock cycle. Then, a comparison result obtained by comparing the count result with a predetermined value is output to the threshold voltage switching circuit 8.

  The threshold voltage switching circuit 8 includes a control switch SW2, switches the state of the control switch SW2 according to the output of the counting circuit 7 (comparison result by the counter CO1), and the threshold voltage (variation threshold) output from the threshold voltage generation circuit 4 Alternatively, a predetermined inversion threshold voltage (corresponding to the inversion threshold) is output to the comparison circuit 5.

  The drive circuit 9 drives the control switch M2 according to the initialization pulse output from the pulse detection circuit 6, and when the pulse detection circuit 6 outputs the initialization pulse, the control switch M2 is temporarily turned on. When the control switch M2 is temporarily turned on, the charge charged in the capacitor C2 is discharged. The drive circuit 10 generates a PWFM drive signal according to the output logic signal of the comparison circuit 5, and drives the switching element M1 with the PWFM drive signal.

  The operation of the above configuration will be described with reference to FIGS. FIG. 2A to FIG. 2C show timing charts for basic operations at normal times. FIG. 2A shows a case of driving a standard load, FIG. 2B shows a case of driving a light load, and FIG. 2C shows a case of driving a heavy load. Indicates the operating state.

  The signal generating circuit 3 outputs a charging voltage corresponding to the time constants of the capacitor C2 and the resistor R2. Therefore, the signal generation circuit 3 outputs a rising voltage that gradually increases from the initial state (minimum voltage output state: timing (A)). On the other hand, the threshold voltage generation circuit 4 outputs a voltage corresponding to the output voltage of the DC / DC converter 1, but outputs a lower voltage in the case of a light load than in the case of a standard load (FIG. 2 ( b)), in the case of a heavy load, a voltage higher than that of the standard load is output (see FIG. 2C).

  The comparison circuit 5 compares the output voltage of the threshold voltage generation circuit 4 with the output voltage of the signal generation circuit 3, and when the output voltage of the threshold voltage generation circuit 4 is higher than the output voltage of the signal generation circuit 3, a high signal (logic Signal: “H”) to the drive circuit 10. Then, since the drive circuit 10 outputs an on drive signal to the control terminal of the switching element M1, the switching element M1 is turned on (timing (A) in FIG. 2), and the input voltage is applied to the inductor L1. Magnetic energy is stored in the inductor L1.

  After that, when the signal voltage of the signal generation circuit 3 rises and exceeds the output voltage of the threshold voltage generation circuit 4, the comparison circuit 5 outputs a low signal (logic signal: “L”) that is the inverted output to the drive circuit 10. To do. Since the drive circuit 10 outputs an off drive signal to the control terminal of the switching element M1, the switching element M1 is turned off (timing (B) in FIG. 2), and the voltage of the inductor L1 and the voltage of the node N4 rise rapidly. .

  On the other hand, since the output of the comparison circuit 5 is given to the control terminal of the control switch SW1, when the comparison circuit 5 outputs a low signal “L”, the control switch SW1 is switched and the comparison target voltage of the comparator OP2 is released. The threshold voltage (corresponding to the release threshold: <variation threshold) is switched.

  During this time, a voltage is supplied to the load of the DC / DC converter 1, but the pulse detection circuit 6 is connected to the common connection node N4 of the inductor L1 and the anode of the diode D1, and the voltage change of the common connection node N4 is detected. To detect. For this reason, when the magnetic energy accumulated in the inductor L1 is transmitted to the load side and the voltage of the common connection node N4 decreases, the pulse detection circuit 6 detects this voltage decrease timing (energy release timing: ≈control cycle start timing). ) Is detected by the differentiating circuit, and then an initialization pulse is output by the inverting gate G1.

  Therefore, when the pulse detection circuit 6 detects the voltage drop timing, it outputs an initialization pulse to the drive circuit 9 (see (5) in FIG. 2), but when the drive circuit 9 accepts the initialization pulse, the signal generation circuit 3 An ON control signal (initialization signal) is output to the control switch M2. Then, when the control switch M2 is turned on, the charge stored in the capacitor C2 is discharged, and the output voltage of the signal generation circuit 3 rapidly decreases and returns to the initial state (minimum voltage output state). The reason why the pulse detecting circuit 6 controls the switching element M1 after detecting the voltage drop timing is to reduce the switching loss and realize soft switching.

  During this time, the counter CO1 of the counting circuit 7 continues to count every time a clock signal CLK (independent period) having a predetermined period is input from the initial state, but the pulse detection circuit 6 does not reach the predetermined value and is initially When the initialization pulse is output, this initialization pulse is given as a reset signal for the counter CO1, so the count value is cleared (initialized), and the counting according to the clock signal CLK is repeated again from the initial state (initialization timing).

  In this way, in the DC / DC converter 1, the switching element M1 is driven according to the output logic signal of the comparison circuit 5 of the pulse generation circuit 2, and the accumulation and transmission of the magnetic energy of the inductor L1 are repeated. The input voltage is converted to the output voltage.

  Depending on factors such as an increase in load, temperature change, and durability deterioration, abnormal conditions such as changes in element characteristics, fluctuations in each node voltage, current, and non-output may occur. In this abnormal state, if the energization time of the switching element M1 becomes long, there is a risk of rapid progress such as element degradation. Therefore, in this embodiment, a function for limiting the on-energization time is provided in preparation for this abnormal state. Hereinafter, this description will be described with reference to FIGS.

  FIG. 3 shows an example when an abnormality occurs in the signal generation circuit 3. For some reason, when the resistance R2 of the signal generation circuit 3 increases, the time constant increases, and the rising gradient of the output voltage of the signal generation circuit 3 decreases compared to the normal operation (corresponding to FIG. 2). At this time, as shown in FIG. 3, even when the ON upper limit time of the switching element M1 has elapsed, the output voltage of the signal generation circuit 3 cannot exceed the output voltage (variation threshold) of the threshold voltage generation circuit 4. Therefore, it is necessary to protect the switching element M1.

  Therefore, as shown in FIG. 3, when a predetermined time (maximum ON time of the switching element M1) elapses and the count value of the counter CO1 constituting the counting circuit 7 reaches a predetermined value, the counting circuit 7 Output a pulse (timing (D) in FIG. 3), the threshold voltage switching circuit 8 forcibly changes the threshold value to be compared by the comparison circuit 5 using the control switch SW2 (FIG. 3 (1)). (See “Inversion threshold voltage”).

  The inversion threshold voltage switched by the threshold voltage switching circuit 8 is preferably set to a value closer to a predetermined release threshold voltage (release threshold) than the variation threshold voltage. This inversion threshold voltage (inversion threshold) is set to a threshold that is assumed in advance for the output voltage of the signal generation circuit 3 at the timing when the desired maximum on-time of the switching element M1 elapses in consideration of the deterioration state and margin of each element. Then, it may be a value close to the aforementioned release threshold voltage, and may be equal to the release threshold voltage.

  Then, the output voltage of the threshold voltage switching circuit 8 is lower than the output voltage of the signal generation circuit 3 (timing (D) in FIG. 3), and the comparison circuit 5 outputs an off control signal, thereby driving the drive circuit 10. Outputs an off drive signal to the switching element M1. As a result, the switching element M1 is turned off, magnetic energy is accumulated in the inductor L1, and the voltage of the inductor L1 rises. Thereafter, when the magnetic energy stored in the inductor L1 is transmitted to the load side and time elapses, the voltage at the node N4 decreases. At this time, the pulse detection circuit 6 detects this voltage drop timing (energy release timing: control cycle start timing), and the pulse detection circuit 6 outputs a pulse (timing (E) in FIG. 3). Then, as described above, the output voltage of the signal generation circuit 3 is initialized, and the same operation as the normal operation is repeated.

  FIG. 4 shows an example when an abnormality occurs in the threshold voltage generation circuit 4. Consider a case in which element degradation of the threshold voltage generation circuit 4 occurs due to some influence and the output voltage of the threshold voltage generation circuit 4 becomes higher than usual. At this time, similarly to FIG. 3 described above, even if the ON upper limit time of the switching element M1 has elapsed as shown in FIG. 4, the output voltage of the signal generation circuit 3 is the output voltage (variation threshold) of the threshold voltage generation circuit 4. There is a concern that it cannot be exceeded.

  Therefore, as shown in FIG. 4, when a predetermined time (maximum ON time of the switching element M1) elapses and the count value of the counter CO1 constituting the counting circuit 7 reaches a predetermined value, the counting circuit 7 4 outputs a pulse (timing (F) in FIG. 4), the threshold voltage switching circuit 8 forcibly changes the threshold value to be compared by the comparison circuit 5 using the control switch SW2 (FIG. 4 (1)). (See “Inversion threshold voltage”).

  Thereafter, when the magnetic energy stored in the inductor L1 is transmitted to the load side and time elapses, the voltage at the node N4 decreases. At this time, the pulse detection circuit 6 outputs a pulse (timing (G) in FIG. 4) by detecting this voltage drop timing (energy release timing: start timing of the control cycle). Then, as described above, the output voltage of the signal generation circuit 3 is initialized, and the same operation as the normal operation is repeated.

  According to the present embodiment, an abnormal state such as a change in element characteristics occurs in response to a load change, temperature change, durability deterioration, or the like due to some factor, and the output voltage of the signal generation circuit 3 is the output of the threshold voltage generation circuit 4. Even if the voltage cannot be exceeded, the threshold value to be compared by the comparison circuit 5 is set as an inversion threshold voltage (inversion threshold value) when a predetermined time has elapsed.

  Therefore, the switching element M1 can be turned off when the comparison circuit 5 outputs the off control signal and the drive circuit 10 outputs the off drive signal to the switching element M1. When the magnetic energy accumulated in the inductor L1 is transmitted to the load side of the DC / DC converter 1, the pulse detection circuit 6 detects the voltage drop timing (control cycle start timing) of the common connection node N4 of the inductor L1 and the diode D1. After this timing, the output of the signal generation circuit 3 can be returned to the initial state. Thereby, the ON time of the switching element M1 can be limited while maintaining the desired control by the DC / DC converter 1. Thereafter, if the abnormal operation state shown in FIGS. 3 and 4 returns to the normal operation state shown in FIG. 2, this normal operation can be repeated.

  Moreover, since the ON upper limit time can be determined in one cycle even if the controlled object is an indefinite cycle, the pulse width (the ON time of the switching element M1) can be quickly limited, and a time of a plurality of cycles is not required.

(Second Embodiment)
FIG. 5 shows a second embodiment of the present invention, which is different from the previous embodiment in that when a predetermined time elapses, the signal generated by the signal generating means is a predetermined value higher than the fluctuation threshold of the fluctuation threshold generating means. It is in the place set to. Parts having the same functions and similar functions as those of the above-described embodiment are denoted by the same reference numerals or similar numerals, and the description thereof will be omitted.

  The signal generation circuit 3 is connected to a comparison circuit (comparison means) 5a in place of the comparison circuit 5 described above. The comparison circuit 5a includes a control switch SW3 and a comparator OP3, and a signal generated by the signal generation circuit 3 is input to an inverting input terminal of the comparator OP3 through a threshold voltage switching circuit 8a instead of the threshold voltage switching circuit 8 described above. Yes.

  The threshold voltage switching circuit 8a is configured to include a control switch SW4, and normally outputs the output voltage of the signal generation circuit 3, but when the counter CO1 of the counting circuit 7 reaches a predetermined value, the control switch SW4 is switched. A predetermined voltage (predetermined value) that is higher than the upper limit value of the generated signal of the generating circuit 3 and higher than the upper limit value of the fluctuation threshold value output by the threshold voltage generating circuit 4 is output.

  That is, when a predetermined time elapses after the pulse detection circuit 6 generates a pulse and the counter CO1 resets the count, the output voltage (generated signal) of the signal generation circuit 3 is output from the threshold voltage generation circuit 4. It is switched to an inversion threshold voltage (predetermined value: inversion threshold) set higher than the upper limit value and input to the inverting input terminal of the comparator OP3 of the comparison circuit 5a.

  Therefore, when the predetermined time elapses, the threshold voltage switching circuit 8a outputs the inversion threshold voltage, so that it can be forcibly made higher than the output voltage of the threshold voltage generation circuit 4. Thereby, the output voltage of the threshold voltage switching circuit 8a can be made higher than the output voltage of the threshold voltage generating circuit 4. Then, the output of the comparator OP3 can be forcibly set to the low signal “L”, the drive signal applied to the switching element M1 through the drive circuit 10 can be an off drive signal, and the switching element M1 can be forcibly turned off.

  Therefore, the on-time of the switching element M1 can be limited while maintaining desired control for the DC / DC converter 1. Thereafter, if the normal operation state is restored, this normal operation can be repeated. Thereby, substantially the same operation effect as the above-mentioned embodiment is obtained.

(Third embodiment)
FIG. 6 shows a third embodiment of the present invention. The difference from the previous embodiment is that the overcurrent detection means detects the overcurrent of the switching element, and when the overcurrent is detected, the signal generation means. When the generation signal is lower than the fluctuation threshold, the level of the generation signal of the signal generation means and the fluctuation threshold is reversed. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described below.

FIG. 6 shows a circuit configuration of the present embodiment, and shows a circuit configuration in which overcurrent detection means is added instead of the counting circuit of the configuration of FIG.
As shown in FIG. 6, an overcurrent detection circuit (overcurrent detection means) 11 is configured instead of the counting circuit 7. The overcurrent detection circuit 11 is mainly configured by a comparator OP4 having a threshold value given as a comparison target. The overcurrent detection circuit 11 detects an energization current of the current detection resistor R9 of the switching element M1, and whether or not the current exceeds a predetermined threshold value. When the value is exceeded, a switching control signal for switching to the inversion threshold voltage is input to the control terminal of the control switch SW2 of the threshold voltage switching circuit 8.

  When a switching control signal is input to the control terminal of the control switch SW2, the threshold voltage switching circuit 8 outputs an inversion threshold voltage (inversion threshold) and forcibly inputs it as a comparison target of the comparison circuit 5. Then, as in the first embodiment, the output voltage (generated signal) of the signal generation circuit 3 exceeds the inversion threshold voltage of the threshold voltage switching circuit 8, and the comparison circuit 5 outputs a low signal to the drive circuit 10. As a result, the drive circuit 10 outputs an off drive signal to the control terminal of the switching element M1, thereby forcibly turning off the switching element M1. Thereby, the ON time of the switching element M1 can be limited according to the overcurrent detection result of the switching element M1. The same effects as those in the previous embodiment can be obtained.

(Fourth embodiment)
FIG. 7 shows a fourth embodiment of the present invention. The difference from the previous embodiment is that the overheat detecting means detects overheating of the switching element, and when the overheat is detected, the signal generated by the signal generating means is shown. Is lower than the fluctuation threshold, the level of the signal generated by the signal generating means and the fluctuation threshold is reversed. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described below.

FIG. 7 shows a circuit configuration of the present embodiment, and shows a circuit configuration in which an overheat detecting means is added instead of the counting circuit of the circuit shown in FIG.
As shown in FIG. 7, an overheat detection circuit (overheat detection means) 12 is configured in place of the counting circuit 7 of the first embodiment. The overheat detection circuit 12 mainly includes a comparator OP5 to which a threshold voltage is given as a comparison target, and is connected to a detection circuit 12a including a current source I1 and a diode D2.

  The diode D2 is disposed close to (in the specific example, adjacent to the switching element M1) the DC / DC converter 1 that is a temperature measurement target. The forward voltage of the diode D2 generally decreases as the temperature rises, and the slope is generally set to -2 [mV / ° C].

  Therefore, when the temperature of the DC / DC converter 1 is a standard temperature environment, when a constant current is supplied from the current source I1 to the diode D2, the forward voltage of the diode D2 becomes constant. When the temperature of the DC / DC converter 1 increases from the standard temperature and the ambient temperature of the diode D2 increases, the temperature of the diode D2 also increases and the forward voltage decreases. The comparator OP5 detects a state in which the forward voltage of the diode D2 decreases, and when it falls below the threshold voltage, inputs a switching control signal to the control terminal of the control switch SW2 of the threshold voltage switching circuit 8.

  When a switching control signal is input to the control terminal of the control switch SW2, the threshold voltage switching circuit 8 outputs an inversion threshold voltage and forcibly inputs it as a comparison target of the comparison circuit 5. Then, as in the first embodiment, the output voltage (generated signal) of the signal generation circuit 3 exceeds the inversion threshold voltage of the threshold voltage switching circuit 8, and the comparison circuit 5 outputs a low signal to the drive circuit 10. Thus, the drive circuit 10 outputs an off drive signal, and the switching element M1 can be forcibly turned off. Thereby, the ON time of the switching element M1 can be limited according to the overheat detection result of the switching element M1. Thereby, the ON time of the switching element M1 can be limited. The same effects as those in the previous embodiment can be obtained.

(Other embodiments)
The present invention is not limited to the above embodiment, and for example, the following modifications or expansions are possible.
In the second embodiment, when the counter value of the counting circuit 7 reaches a predetermined value (that is, when a predetermined time has elapsed), the output voltage of the signal generating circuit 3 (the signal generated by the signal generating means) is used as the threshold voltage generating circuit 4. In the embodiment, the predetermined voltage (predetermined value) is set to be higher than the output voltage (variation threshold) of the first embodiment. The predetermined voltage (predetermined value) is set in the third embodiment (overcurrent detecting means), the fourth embodiment. The present invention can also be applied to the embodiment (overheat detection means).

  That is, when the circuit configuration using the overcurrent detection unit of the third embodiment is applied, when the overcurrent detection circuit 11 (overcurrent detection unit) detects the overcurrent of the control target (for example, the switching element M1), As shown in the second embodiment, the output voltage of the signal generation circuit 3 may be set to a predetermined voltage (predetermined value) higher than the output voltage (variation threshold) of the threshold voltage generation circuit 4.

  In addition, when the circuit configuration using the overheat detection unit of the fourth embodiment is applied, the second embodiment is performed when the overheat detection circuit 12 (overheat detection unit) detects overheating of the control target (for example, the switching element M1). As shown in FIG. 6, the output voltage of the signal generation circuit 3 may be set to a predetermined voltage (predetermined value) higher than the output voltage (variation threshold) of the threshold voltage generation circuit 4.

  In the first and second embodiments, the counter circuit 1 is initialized by inputting a reset signal to the counter CO1 at the initialization timing of the pulse detection circuit 6, and the counting circuit 7 is initialized and starts counting. However, the control switch M2 ( The counting circuit 7 may be initialized to start counting by causing the counter CO1 to input the timing at which the ON timing of the initialization means) is detected to the counter CO1.

  Although the embodiment applied to the non-insulated step-up chopper DC / DC converter 1 as a controlled object is shown, the circuit form of the controlled object is not limited to the form shown in the above-described embodiment. As long as the start of the control cycle of the control target can be detected, the control target of any circuit form may be applied.

  In the drawings, 1 is a DC / DC converter (control target), 2 is a pulse generation circuit, 3 is a signal generation circuit (signal generation means), 4 is a threshold voltage generation circuit (variation threshold generation means), and 5 and 5a are comparison circuits. (Comparison means), 6 is a pulse detection circuit (detection means), 7 is a counting circuit (counting means), 8 and 8a are threshold voltage switching circuits (inversion means), 9, 10 are drive circuits, and 11 is an overcurrent detection circuit. (Overcurrent detection means), 12 is an overheat detection circuit (overheat detection means), L1 is an inductor, M1 is a switching element, M2 is a control switch (initialization means), D1 is a diode, C1 is a capacitor, and CO1 is a counter. Show.

Claims (5)

Signal generating means for generating a signal that changes over time;
A fluctuation threshold generating means for raising the fluctuation threshold when the output voltage of the controlled object decreases, and lowering the fluctuation threshold when the output voltage of the controlled object rises;
When the signal generated by the signal generating means becomes higher than the fluctuation threshold, the fluctuation threshold is changed to a predetermined release threshold lower than the fluctuation threshold, and when the signal generated by the signal generating means becomes lower than the release threshold, the fluctuation threshold is changed to the fluctuation threshold. Comparing means having a hysteresis characteristic for changing the threshold value of the threshold value generating means, and outputting a logic signal obtained by comparing the threshold value of the fluctuation threshold value generating means and the generated signal of the signal generating means to the control target;
Detecting means for detecting a start of a control cycle of the control object;
Initializing means for initializing the generated signal of the signal generating means when the detecting means detects the start timing of the control cycle;
Counting means for counting time from the start timing of the control cycle detected by the detection means, or the initialization timing initialized by the initialization means,
When the predetermined time is counted by the counting means, when the generated signal of the signal generating means is lower than the fluctuation threshold, the inverting means for reversing the level of the generated signal of the signal generating means and the fluctuation threshold And a pulse generation circuit. Signal generating means for generating a signal that changes over time;
A fluctuation threshold generating means for raising the fluctuation threshold when the output voltage of the controlled object decreases, and lowering the fluctuation threshold when the output voltage of the controlled object rises;
When the signal generated by the signal generating means becomes higher than the fluctuation threshold, the fluctuation threshold is changed to a predetermined release threshold lower than the fluctuation threshold, and when the signal generated by the signal generating means becomes lower than the release threshold, the fluctuation threshold is changed to the fluctuation threshold. Comparing means having a hysteresis characteristic for changing the threshold value of the threshold value generating means, and outputting a logic signal obtained by comparing the threshold value of the fluctuation threshold value generating means and the generated signal of the signal generating means to the control target;
Detecting means for detecting a start of a control cycle of the control object;
Initializing means for initializing the generated signal of the signal generating means when the detecting means detects the start timing of the control cycle;
Overcurrent detection means for detecting the overcurrent of the control object;
When an overcurrent is detected by the overcurrent detection means, when the signal generated by the signal generation means is lower than the fluctuation threshold, an inversion means for reversing the level of the signal generated by the signal generation means and the fluctuation threshold is provided. A pulse generation circuit comprising: Signal generating means for generating a signal that changes over time;
A fluctuation threshold generating means for raising the fluctuation threshold when the output voltage of the controlled object decreases, and lowering the fluctuation threshold when the output voltage of the controlled object rises;
When the signal generated by the signal generating means becomes higher than the fluctuation threshold, the fluctuation threshold is changed to a predetermined release threshold lower than the fluctuation threshold. When the signal generated by the signal generating means becomes lower than the release threshold, the fluctuation threshold is changed to Comparing means that has a hysteresis characteristic for changing the threshold value of the threshold value generating means and outputs a logic signal that compares the threshold value of the fluctuation threshold value generating means and the generated signal of the signal generating means to the control object;
Detecting means for detecting a start of a control cycle of the control object;
Initializing means for initializing the generated signal of the signal generating means when the detecting means detects the start timing of the control cycle;
An overheat detecting means for detecting an overheat state of the control object;
When the overheat state is detected by the overheat detecting means, the reversing means reverses the level of the generated signal of the signal generating means and the fluctuation threshold when the signal generated by the signal generating means is lower than the fluctuation threshold. A pulse generation circuit characterized by that. The inversion means is
4. The variation threshold is an inversion threshold that is lower than the variation threshold and equal to or greater than the release threshold, and is a predetermined inversion threshold that is lower than a signal generated by the signal generation unit. The pulse generation circuit according to any one of the above.   4. The pulse generation circuit according to claim 1, wherein the inversion means sets the signal generated by the signal generation means to a predetermined value higher than the fluctuation threshold.

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