JP2018074787A - Inductive load drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inductive load drive circuit which enables the achievement of high response to the reduction in current when an inductive load is stopped without generating heat.SOLUTION: An inductive load drive circuit 1 comprises: a switching power supply circuit 10; an energy recovery circuit 30 which recovers energy while generating a counter electromotive force of an inductive load 11 when a current of the inductive load decreases; and a control circuit 20. The energy recovery circuit includes: a recovery transformer 31 having, on the same iron core, a couple of primary coils LP1 and LP2 connected in series with the inductive load so that they are opposite to each other in polarity, and a recovery secondary coil RSL connected to the primary LP of a switching transformer 16; and a recovery control element 32 which controls a current passing through the primary coil by pulse signals by a second pulse signal generator circuit 33. When the inductive load current decreases, the control circuit adjusts the pulse width of pulse signals of the second pulse signal generator circuit to the recovery control element to control the recovery control element so as to stay off for a fixed length of time, thereby transmitting an energy to the secondary coil.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a circuit for driving an inductive load such as a solenoid or a motor, and more particularly, to an inductive load driving circuit that controls current by combining an energy recovery circuit with a circuit configuration of a switching power supply by a PWM control system. is there.

  Inductive loads such as motors and solenoids that have coil components and convert electrical energy into mechanical motion via electromagnetic force are used as actuators in various devices. Inductive load drive control systems are broadly divided into pulse width modulation, so-called PWM (pulse width modulation) control and proportional control. In the former, the duty ratio of the pulse width, that is, the on / off ratio is changed according to the magnitude of the input signal when the load is turned on / off, and the latter is applied to both ends of the control element connected in series with the load. Control is performed by varying the voltage and causing loss.

  As a PWM system, for example, a circuit configuration of a switching power supply as shown in Patent Document 1 is used, and current control is performed by a drive circuit that stably supplies a commercial high AC voltage as a low DC voltage to an inductive load. is there.

  Specifically, as shown in FIG. 5A, the alternating current from the power supply 112 is first rectified by the bridge diode 113 and the direct current smoothed by the smoothing capacitor 114 is converted into the direct current based on the command signal 121. Switching is performed by switching the switching element 115 made of a semiconductor element such as an FET (Field Effect Transistor) into a pulse wave alternating current by switching and then sending it to the switching transformer 116 to step down the alternating voltage to a predetermined alternating voltage. This is an inductive load driving circuit 100 using a power supply circuit.

  When current control is performed in the inductive load driving circuit 100, when the input side DC is converted into AC on the primary side of the switching transformer 116, a predetermined pulse wave width (switching ON / OFF cycle) is determined based on the command signal 121 in the control circuit. For example, a pulse signal is generated from a pulse signal generator 124 such as a PWM controller (PWM-IC). Since the pulse wave width can be adjusted and switched by feedback control based on the command signal and the detection result by the current sensor 125 on the output side, the output current can be kept constant even when the power source and the load fluctuate, and the stabilized DC Is obtained.

  In this method, the energy on the primary side is electromagnetically induced by the switching transformer 116 from the primary side coil Lp to the secondary side coil Ls by switching the switching element 115 on / off to generate high-frequency alternating current. Although it is transmitted, the transformer itself can be made small by using high-frequency alternating current, and it is highly efficient because it generates little heat. The alternating current transmitted in this way is rectified by the rectifier diode 117 on the secondary side and flows to the inductive load 111. However, the induced current rectified by the diode has an intermittent waveform. The voltage across the load will vary greatly. Therefore, in order to smooth this, a smoothing capacitor 118 is disposed on the secondary side, and the smoothed direct current is output to the inductive load 111.

  The smoothing capacitor 118 on the secondary side has a faster circuit response as the capacitance is smaller. On the other hand, since the capacitor cannot be completely smoothed and the ripple voltage increases, the stability of current control is deteriorated. Therefore, it is possible to increase the response by making the PWM cycle faster and absorbing the ripple current even if the capacitor capacity is small, but the response when the inductive load current is off is structural as follows: It will be slow.

  That is, in order to turn off the inductive load current, it is necessary to stop the induction to the transformer secondary side by setting the switching element 115 on the primary side of the switching transformer to be constant OFF and to discharge the smoothing capacitor 118 completely. However, when the capacity of the smoothing capacitor is sufficiently smaller than the counter electromotive force generated by the load, when the smoothing capacitor is discharged, the commutation current 101 of the inductive load reverses the smoothing capacitor 118 as shown in FIG. At the same time as charging in the direction, a commutation current also flows through the rectifier diode in the transformer secondary coil Ls. At this time, the induced current 102 also flows to the primary side coil Lp via the internal diode of the FET, although the time is negligible compared to the commutation time of the inductive load. Further, since the impedance of the transformer secondary side coil is also low, most of the commutation current when the inductive load is off flows through the rectifier diode. As a result, the response is equivalent to a drive circuit having a diode commutation circuit, and a response time is required.

  As described above, the inductive load drive circuit using the circuit configuration of the PWM type switching power supply is excellent in efficiency, but has a problem in responsiveness and cannot control the rate of decrease of the inductive load current. On the other hand, the proportional control method has a problem that heat is generated because it is controlled by variably adjusting the voltage at both ends of the control element to cause loss.

JP 2012-217238 A Japanese Patent Application Laid-Open No. 07-59397

  On the other hand, in the case of a normal solenoid or the like with a small output of power of 100 W or less, the energy stored in the load is consumed due to heat generation, but the energy consumed is only a few watts, so the cost effectiveness of collecting power is low. Because it is not suitable, energy recovery is not performed. The same applies to the motor drive device. In a low output system, regenerative energy is consumed by heat generation. Since there is no need for energy recovery in the current situation where there is no high power solenoid, a drive circuit having a mechanism for this purpose has not been substantially constructed.

  However, in the case of a load that requires a power supply of DC 48V or higher, which is generally used for driving voltage, the load power becomes large, and when the current of the inductive load is reduced, a surge voltage is generated, and the energy is generated by heat generation. There is waste to consume. Furthermore, any driving method requires an AC-DC power supply or a DC-DC (step-up) power supply, which increases the circuit scale.

  For example, as in Patent Document 2, some inductive load driving devices include means for recovering commutation energy so that a good fall of the load current can be secured when the inductive load is stopped. In Patent Document 2, a secondary winding of a transformer is disposed in a return path for returning a load current when an inductive load is not driven, and a switch means for short-circuiting the secondary winding or the primary winding is provided. The switch means is turned off when the load is stopped. As a result, a high voltage is generated in the direction in which the load current converges on the secondary winding, the load current is lowered, a current is generated on the primary side of the transformer, and the energy accumulated in the inductive load is regenerated to the power source. Yes.

  However, even if a current is passed through the transformer secondary side when the inductive load is turned off, the voltage changes only once, so that the energy cannot be effectively returned to the primary side. Even if the switch means connected in parallel to the secondary winding is turned on / off, the current circuit of the transformer winding is not cut off, so the coil current of the secondary transformer cannot be cut off instantaneously and induction Since the energy consumption of the load is insufficient, the responsiveness of the inductive load is insufficient.

  In view of the above problems, the object of the present invention is to realize high responsiveness to a decrease in current when an inductive load is stopped without generating heat even when the inductive load is large, and is more responsive and more efficient than before. It is an object of the present invention to provide an inductive load driving circuit capable of performing an accurate current control.

In order to achieve the above object, an inductive load driving circuit according to claim 1 includes a rectifying bridge diode that rectifies alternating current from a power source, a primary-side smoothing capacitor that smoothes rectified direct current, and the primary The direct current smoothed by the side smoothing capacitor is converted to a pulse wave alternating current by switching the switching element on / off in a cycle based on the pulse signal from the pulse signal generator to a predetermined alternating voltage. And a switching transformer that transmits to the secondary side, a secondary side diode that rectifies the alternating current transmitted to the secondary side, and a secondary side smoothing capacitor that further smoothes and outputs the rectified direct current A pulse signal generated by the pulse signal generator based on the power circuit, the command signal, and the detection result on the output side of the switching power circuit. In inductive load drive circuit to adjust the pulse width and a control circuit for controlling the on / off switching of the switching element,
An energy recovery circuit for recovering while generating a counter electromotive force of the inductive load when the current of the inductive load is reduced;
The energy recovery circuit includes two primary coils having different resistance values connected in series with the inductive load in opposite polarities and one secondary coil connected to the primary side of the switching transformer. A second pulse based on a recovery command signal from the control circuit, which is arranged in series with a recovery transformer having the same iron core and a small resistance primary side coil having a relatively small resistance value among the two primary side coils. A recovery control element that operates in response to a pulse signal from the signal generator and controls a current flowing through the small-resistance primary coil;
The control circuit adjusts the pulse width of the pulse signal by the second pulse signal generator with respect to the recovery control element when the current of the inductive load is reduced, and controls the recovery control element to be off for a certain period of time. While generating the back electromotive force of the inductive load, the current is passed through the large resistance primary side coil having a relatively large resistance value of the recovery transformer to change the core magnetic flux and transmit the energy to the corresponding secondary side coil. Is.

An inductive load driving circuit according to a second aspect of the present invention is the inductive load driving circuit according to the first aspect,
A current flowing through the large resistance primary side coil is arranged in series with the large resistance primary side coil of the recovery transformer, and the voltage when the recovery control element of the small resistance primary side coil is turned off is made constant. A second recovery control element for limiting is further provided.

  According to the inductive load driving circuit of the present invention, the switching power supply circuit configuration further includes an energy recovery circuit using a recovery transformer in which an inductive load and a primary side coil are connected in series, so that the inductive load is insulated from the power source side. When the current is reduced, it can be recovered satisfactorily while generating the counter electromotive force of the inductive load, so that a high response can be achieved efficiently when the inductive load current is stopped without heat loss. In particular, the primary side of the recovery transformer of the energy recovery circuit is composed of two coils with a large resistance and a small resistance with opposite polarities, so there is no induction in the steady state and there is a delay in the current rise rate when the load current increases. At the same time, the current of the small resistance primary side coil is controlled via a recovery control element controlled by PWM drive, so that the load current decrease rate at the time of inductive load stop can be controlled at high speed. There is an effect that current control of the inductive load can be performed efficiently and with high response.

It is a schematic block diagram of the inductive load drive circuit by one Example of this invention. It is a graph (horizontal axis: time [msec], vertical axis: current [A]) showing the solenoid falling characteristics with and without the energy recovery circuit. FIG. 3 is a graph showing power recovery characteristics during energy recovery in FIG. 2 (horizontal axis: time [msec], vertical axis: recovered power [W] and solenoid current [A]). It is a partial circuit diagram which shows what improved the energy recovery circuit of FIG. It is a schematic block diagram which shows the example of the conventional inductive load drive circuit which has a switching power supply circuit, (a) is a current control circuit diagram, (b) is a partial circuit diagram which shows the operation | movement at the time of inductive load current OFF.

  An inductive load driving circuit according to the present invention includes a rectifier bridge diode that rectifies an alternating current from a power source, a primary side smoothing capacitor that smoothes the rectified direct current, and a pulse signal that generates a direct current smoothed by the primary side smoothing capacitor. A switching transformer for transforming a pulse wave converted to alternating current by on / off switching of the switching element in a cycle based on a pulse signal from the device into a predetermined alternating voltage and transmitting the same to the secondary side; A switching power supply circuit comprising a secondary side diode for rectifying the alternating current transmitted to the secondary side, and a secondary side smoothing capacitor for further smoothing and outputting the rectified direct current, a command signal, and an output of the switching power supply circuit A pulse width of the pulse signal by the pulse signal generator based on the detection result on the side, A control circuit for controlling the on / off switching elements, and in which further comprising an energy recovery circuit for recovering while generating counter electromotive force of the inductive load during a current decrease in the inductive load.

  With the above configuration, the present invention enables the energy recovery circuit to successfully recover the back electromotive force of the inductive load without heat generation due to consumption when the current of the inductive load is reduced. High responsiveness is realized.

  That is, the energy recovery circuit of the present invention includes two primary coils connected in series with an inductive load and having opposite resistances and different resistance values, and one secondary connected to the primary side of the switching transformer. A recovery transformer having a coil in the same iron core, and a first resistor based on a recovery command signal from the control circuit, arranged in series with a relatively small resistance primary side coil of the two primary side coils. A recovery control element that operates in response to a pulse signal generated by the pulse signal generator 2 and controls a current flowing through the small resistance primary coil, and the control circuit is configured to reduce the current of the inductive load when the recovery control element is reduced. By adjusting the pulse width of the pulse signal by the second pulse signal generator with respect to the recovery control element, the recovery control element is controlled to be off for a certain period of time. In which by changing the core flux to transfer energy to a corresponding secondary coil by passing a current through the large resistance primary coil greater the recovery transformer relatively resistance while generating power.

  In the energy recovery circuit described above, the small resistance primary side coil may be reduced in winding resistance to such an extent that resistance loss can be ignored. When the current to the inductive load is constant, the current flows almost to the small resistance primary coil from the balance of the coil resistance value to excite the transformer core. However, the current increase rate is larger than the inductance of the small resistance primary coil. If it is large, the current flows through the large resistance primary coil wound in the opposite direction, so that no current is induced and delay in current response is prevented.

  When increasing the rate of decrease of the inductive load current, turning off the recovery control element for a certain period of time causes all current to flow to the large resistance primary side coil. Since voltage is generated and the excitation of the transformer / core is changed, the induced current flows through the secondary coil of the recovery transformer, and energy is recovered. At this time, the reduction rate of the inductive load current can be controlled at a high speed by varying the duty ratio of the recovery control element that is PWM-controlled by the control circuit.

  The present invention further includes a second recovery control element arranged in series with the large resistance primary side coil of the recovery transformer, wherein the recovery control element of the small resistance primary side coil is turned off. The current flowing through the large resistance primary coil can be limited so as to keep the voltage constant. As a result, even if the current decreases and the voltage across the large resistance primary side coil decreases, the amount of transmission to the secondary side coil is suppressed, and the inductive load current decreases due to the loss of the second recovery control element. Speed can be increased.

  FIG. 1 shows a schematic configuration diagram of an inductive load driving circuit according to an embodiment of the present invention. The inductive load driving circuit 1 of the present embodiment includes a switching power supply circuit 10 as a basic configuration. That is, the bridge diode 13 that rectifies the alternating current from the power supply 12, the primary side smoothing capacitor 14 that smoothes the rectified direct current, and the direct current smoothed by the primary side smoothing capacitor 14 is converted into a pulse signal by the control circuit 20. A switching element (FET) 15 that performs on / off switching in a cycle based on the pulse signal generated by the generator 24 to convert the pulse wave to alternating current, and the pulse wave alternating current from the primary coil LP to the secondary coil LS. A switching transformer 16 that transforms and transmits the voltage to a predetermined voltage, a secondary rectifier diode 17 that rectifies the alternating current transmitted to the secondary side, and an inductive load (solenoid) that further smoothes the rectified direct current 11 is provided with a secondary side smoothing capacitor 18 to be sent to 11.

  A current sensor 25 is disposed on the output side of the switching power supply circuit 10, and the control circuit 20 performs current feedback control based on the command signal 21 and the detection result of the current sensor 25.

  In the present embodiment, the switching power supply circuit 10 having the above configuration is further provided with an energy recovery circuit 30 that recovers the back electromotive force when the solenoid current decreases. The energy recovery circuit 30 includes a recovery transformer 31 whose primary side is connected in series to the solenoid 11, and energy is transmitted to the secondary side by PWM control of the primary side coil.

  Specifically, the recovery transformer 31 is connected to the solenoid 11 in series and opposite in polarity to the large resistance primary coil LP1 having a relatively large resistance value and a small resistance primary side having a relatively small resistance value. Two primary coils with the coil LP2 and one recovery secondary coil RLS connected to the primary side of the switching transformer 16 are provided in the same iron core. And it arrange | positions in series with the small resistance primary side coil LP2 of two primary side coils, operates according to the pulse signal by the 2nd pulse signal generator 33 based on the collection | recovery command signal from the control circuit 20, and is small. A recovery control element 32 that controls the current flowing through the resistance primary coil LP2 is provided.

  In this energy recovery circuit 30, since the large resistance primary side coil LP1 and the small resistance primary side coil LP2 have opposite polarities, the large resistance primary side coil LP1 and the small resistance primary side coil LP2 are excited when the current increases. The non-induction is prevented, and a delay in the rise speed of the solenoid current is prevented.

  In this embodiment, when the current of the solenoid 11 decreases, the control circuit 20 changes the pulse width of the pulse signal from the second pulse signal generator 33 for the recovery control element 32 to turn off the recovery control element 32 for a certain period of time. By controlling, the core magnetic flux is changed by causing a current to flow through the large resistance primary side coil LP1 while generating a back electromotive force of the solenoid 11, and energy is transmitted to the secondary coil RLS for recovery.

  Along with this, since all the current tends to flow to the large resistance primary coil LP1, a high voltage is generated at both ends of the large resistance primary coil LP1, and the excitation of the transformer core is changed. An induced current flows through the RLS to recover energy. At this time, the decreasing speed of the solenoid current can be controlled at high speed by changing the duty ratio of the recovery control element 32 that is PWM-driven.

  Here, the result of having confirmed the effect by the energy recovery circuit 30 by the comparison test with the inductive load drive circuit which does not have the energy recovery circuit 30 is shown. In this comparative test, the inductive load driving circuit 100 having the conventional switching power supply circuit configuration shown in FIG. 5A is contrasted, and the configuration of the energy recovery circuit 30 is combined with the configuration of the inductive load driving circuit 100. In the inductive load drive circuit 1 shown in FIG. 1, the decrease in the solenoid current when the solenoid was stopped was measured, and the fall characteristics were compared. The results are shown in the graph of FIG.

  Fig. 2 shows the current value (A) along the elapsed time on the vertical axis on the horizontal axis, which is the time axis, when the solenoid is stopped (when the current supply is stopped) from the state where the solenoid current is constant. It is.

  As is clear from FIG. 2, the energy recovery circuit 30 causes the solenoid to start up with respect to the current value change curve X in the case of the inductive load drive circuit as a control that does not have the energy recovery circuit 30 and does not recover the electromotive force of the solenoid. In the current value change curve Y in the inductive load drive circuit 1 of FIG. 1 from which power is recovered, it can be seen that the decrease (falling) speed of the solenoid current is large and the response is very high.

  Further, the recovery power when the solenoid current decreases in the recovery of the back electromotive force measured in FIG. 2 is measured over time, and the change is obtained by taking the recovery power (W) on the vertical axis with respect to time: horizontal axis (msec). Curve Z is shown in the graph of FIG. From FIG. 3, it is clear that the recovered power increases rapidly immediately after the start of the decrease of the solenoid current, and the recovery of the electromotive force by the energy recovery circuit 30 contributes to the high response when the solenoid current decreases. is there.

  In the energy recovery circuit 30 of FIG. 1, when the back electromotive force recovery progresses and the current decreases, the voltage across the large resistance primary coil LP1 decreases, and the recovery also decreases. Therefore, based on the configuration of the energy recovery circuit 30 shown in FIG. 1, a second recovery control element (FET) 41 arranged in series with the large resistance primary coil LP1 is further provided as shown in FIG. By adopting the configuration of the energy recovery circuit 40, this problem can be solved.

  That is, in the energy recovery circuit 40, the second recovery control is performed on the current flowing through the large resistance primary coil LP1 so that the voltage when the recovery control element 32 of the small resistance primary coil LP2 is turned off is constant. Since it can be limited by the element 41, this suppresses a decrease in the amount of transmission to the recovery secondary coil RLS even if the voltage across the large resistance primary coil LP1 decreases, and the second recovery control element Due to the loss of 41, the decrease rate of the solenoid current can be increased.

1, 100: Inductive load drive circuit 10: Switching power supply circuit 11, 111: Solenoid (inductive load)
12, 112: Supply power supply 13, 113: Bridge diode 14, 114: Smoothing capacitor (primary side)
15, 115: switching element 16, 116: switching transformer LP, Lp: primary coil LS, Ls: secondary coil 17, 35, 117: rectifier diode 18, 118: smoothing capacitor (secondary side)
20: control circuit 21, 121: command signal 24, 124: pulse signal generator 25, 125: current sensor 30, 40: energy recovery circuit 31: recovery transformer LP1: large resistance primary coil LP2: small resistance primary coil RLS: secondary coil for recovery 32: recovery control element 33: second pulse signal generator 41: second recovery control element

Claims (2)

A rectifying bridge diode that rectifies alternating current from a power source, a primary side smoothing capacitor that smoothes the rectified direct current, and a period based on the pulse signal from the pulse signal generating means that smoothes the direct current smoothed by the primary side smoothing capacitor. A switching transformer that transforms the pulse wave converted to alternating current by on / off switching of the switching element into a predetermined alternating voltage and transmits it to the secondary side, and rectifies the alternating current transmitted to the secondary side Based on a switching power supply circuit comprising a secondary side diode to perform, a secondary side smoothing capacitor for further smoothing and outputting the rectified direct current, and a command signal and a detection result on the output side of the switching power supply circuit ON / OFF switching of the switching element by adjusting the pulse width of the pulse signal by the pulse signal generator And Gosuru control circuit, in inductive load driving circuit having,
An energy recovery circuit for recovering while generating a counter electromotive force of the inductive load when the current of the inductive load is reduced;
The energy recovery circuit includes two primary coils having different resistance values connected in series with the inductive load in opposite polarities and one secondary coil connected to the primary side of the switching transformer. A second pulse based on a recovery command signal from the control circuit, which is arranged in series with a recovery transformer having the same iron core and a small resistance primary side coil having a relatively small resistance value among the two primary side coils. A recovery control element that operates in response to a pulse signal from the signal generator and controls a current flowing through the small-resistance primary coil;
The control circuit adjusts the pulse width of the pulse signal by the second pulse signal generator with respect to the recovery control element when the current of the inductive load is reduced, and controls the recovery control element to be off for a certain period of time. While generating the back electromotive force of the inductive load, the current is passed through the large resistance primary side coil having a relatively large resistance value of the recovery transformer to change the core magnetic flux and transmit the energy to the corresponding secondary side coil. An inductive load driving circuit characterized by being a thing.   A current flowing through the large resistance primary side coil is arranged in series with the large resistance primary side coil of the recovery transformer, and the voltage when the recovery control element of the small resistance primary side coil is turned off is made constant. The inductive load drive circuit according to claim 1, further comprising a second recovery control element for limiting.

Images