JP3362666B2 - Circuit that controls the output current of the inverter circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit that controls the output current of an inverter circuit that converts direct current into alternating current.

[0002]

2. Description of the Related Art Inverter circuits that convert the output of a DC power supply into AC are widely used. For example, in order to use an electric appliance connected to a commercial power supply (here, an effective value of voltage is 100 Vrms AC) in an automobile or the like, an AC equivalent to the commercial power supply is output from the battery. An inverter circuit for generating is needed.

FIG. 7 is a block diagram of an example of a conventional inverter circuit. Here, an inverter circuit using an H bridge circuit will be described as an example.

The H-bridge circuit 101 includes four switching elements (for example, MOS transistors) S1 to S4.
And a DC voltage VH is supplied. Control circuit 102
Generates a control signal for controlling the states of the switching elements S1 to S4. The current detection circuit 103 detects the current supplied to the load 104 and outputs the detection result to the control circuit 10.
Notify 2. The control circuit 102 includes a current detection circuit 103.
If the load current detected by S1 is larger than a predetermined value (that is, if an overcurrent occurs), the current is reduced or S1 to S4 is set to stop the current.
To control.

The operation of the above-configured inverter circuit will be described with reference to FIG. The control circuit 102 is generally configured such that the H bridge circuit 101 has a first state (a state in which S1 and S3 are turned on and a state in which S2 and S4 are turned off) and a second state (in which the S1 and S3 are turned off, and S2
And a state in which S4 is turned on) are alternately repeated to output a control signal. Here, when the control signals for S1 to S4 are at "H" level, the corresponding switching elements S1 to S4 are turned on. In the period of the first state, the switching element S1 → the load 10
The current flows in the direction of 4 → switching element S3, while in the period of the second state, switching element S
A current flows in the direction of 2 → load 104 → switching element S4. In this way, the alternating current is supplied to the load 104. The inverter circuit usually has an overcurrent prevention function. That is, when an overcurrent (the load current exceeds the limit value) occurs in the inverter circuit, the control circuit 102 forcibly stops the H bridge circuit 101 to reduce the load current. Here, the control circuit 102 suspends the current supply to the load 104 by turning off all the switching elements S1 to S4. If the load current returns below the limit value,
The control circuit 102 outputs the control signal for causing the H bridge circuit 101 to repeat the first state and the second state again.

[0006]

Some electrical appliances are called capacitive loads. The capacitive load means a load having a large capacitor, and corresponds to, for example, a television. A capacitive load is generally used with the capacitor charged. Therefore, in order to quickly activate the capacitive load, it is necessary to charge the capacitor in a short time. In order to charge the capacitor having a predetermined capacity in a short time, it is necessary to increase the supplied current value. That is, when starting a capacitive load, a large current is usually required until the capacitor is charged.

However, the inverter circuit usually has the above-mentioned overcurrent preventing function. Therefore, when the capacitive load demands a large current at the time of its activation, the overcurrent prevention function of the inverter circuit operates, and the inverter circuit cannot sufficiently supply the current required by the capacitive load.
As a result, the rise time of the capacitive load becomes long. Of course, it is possible to quickly start a capacitive load by using a large capacity inverter circuit, but using an inverter circuit that far exceeds the rated power in the normal operating state causes a cost and accommodation space. The disadvantages are large. It is desirable for the user to be able to quickly start the load with an inverter circuit having the smallest capacity.

[0008] Some devices have a protection function that prevents them from accepting subsequent inputs if they cannot be activated within a predetermined time after the power is turned on. If such a device has a capacitive load, even if the rating of the device is within the rating range of the inverter circuit, if the startup time becomes long, the protection function will work and the device itself will not operate. It can happen.

As described above, when a capacitive load is connected to the inverter circuit, it takes a long time to activate the load, or in some cases, the load cannot be activated.

The above-mentioned problem is not only related to the capacitive load but also occurs at the time of starting the motor or turning on the power of the lamp. That is, in the case of a motor load, the startability is not good unless a sufficient current can be supplied at the time of starting, and in the case of a lamp load, the filament cannot be quickly warmed immediately after the power is turned on.

An object of the present invention is to solve the above problems and to provide a control circuit for realizing an inverter circuit capable of quickly and reliably starting a capacitive load or the like. In particular, the capacitive load or the like can be started quickly and reliably without increasing the electric capacity of the inverter circuit itself.

[0012]

The control circuit of the present invention is a circuit for controlling the output current of an inverter circuit for converting direct current into alternating current, and has the following means.

The threshold value output means outputs a first threshold value corresponding to a predetermined current value or a second threshold value corresponding to a current value larger than the predetermined current value. The comparison means compares the current supplied to the load with the threshold value output by the threshold value output means. In the suppressing means, the current supplied to the load is the first
Alternatively, when the comparison means determines that the current is larger than the second threshold value, the current supplied to the load is suppressed.
The control means sets the second threshold value to the threshold value output means when the current supplied to the load becomes larger than the first threshold value while the threshold value output means is outputting the first threshold value. Output only for time.

With the above arrangement, the threshold value for monitoring overcurrent becomes larger than the normal threshold value only when the load current momentarily increases. As a result, a large current is momentarily supplied to the load.

Further, in the control circuit of the present invention, the first state is set by turning on the power source or a reset signal generated upon turning on the power source, and the threshold value output means sets the second threshold value by the instruction of the control means. Second when the output period ends
It is also possible to further provide a latch means for setting the state of, and the control means not to send the instruction to the threshold value output means during the period when the second state is set in the latch means.

With such a configuration, the threshold value becomes larger than the threshold value in the normal state only for the first overcurrent after the inverter circuit is reset. Therefore, it is possible to supply a sufficient current to a load that requires a large current at the time of startup, such as a capacitive load.

Further, the control circuit of the present invention may reset the first state in the latch means after a lapse of a predetermined time after shifting from the first state to the second state.
With such a configuration, a current larger than the first threshold value is repeatedly supplied to the load. At this time, the interval at which the large current is permitted is maintained for a predetermined time or longer.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of a control circuit of this embodiment. This control circuit is the control circuit 1 shown in FIG.
Corresponds to 02. That is, this control circuit converts the direct current into the alternating current and supplies the alternating current to the load 104 by controlling the H bridge circuit 101 while referring to the output of the current detection circuit 103 shown in FIG. 7. Although the H-bridge circuit 101, the current detection circuit 102, and the load 104 are omitted in FIG. 1, they may be referred to in the following description.

The control circuit of this embodiment is composed of the current control unit 10
And a duty control unit 30. The current control unit 10 monitors the current supplied to the load 104, and when detecting an overcurrent, notifies the duty control unit 30 of that fact. The duty control unit 30 generates a control signal for converting the output of the DC power supply into an AC having an effective value of 100 V, and supplies the control signal to the switching elements S1 to S4 of the H bridge circuit 101. When the duty control unit 30 receives a notification from the current control unit 10 that an overcurrent has occurred, the duty control unit 30 receives the load 1
A control signal for suppressing (decreasing or stopping) the current supplied to 04 is generated and supplied to the switching elements S1 to S4.

The current control unit 10 differs from the existing overcurrent detection circuit in the following points. That is, the existing overcurrent detection circuit
The load current is compared with a predetermined threshold value (limit current), and the overcurrent is detected depending on whether or not the load current exceeds the threshold value. On the other hand, the current control unit 10 has at least two threshold values for comparison with the load current, and monitors the overcurrent while switching the threshold values as needed.
In this embodiment, two thresholds are used. These two threshold values correspond to different current values, and the threshold value corresponding to a small current will be referred to as a first threshold value, and the threshold value corresponding to a large current will be referred to as a second threshold value.

The current controller 10 normally monitors the overcurrent by using the first threshold value. Then, when the load current exceeds the first threshold value, the threshold value to be compared with the load current is changed from the first threshold value to the second threshold value. At this time, the current control unit 10 does not notify the duty control unit 30 that an overcurrent has occurred. Further, the period in which the second threshold value is used as the threshold value to be compared with the load current is only a predetermined time period, and after that period, the threshold value is returned to the first threshold value.

According to the above configuration, the second threshold value is larger than the first threshold value, so that the inverter circuit is operated within a predetermined period immediately after the load current exceeds the first threshold value.
A large current can be supplied to the load 104. When the load current exceeds the second threshold, the current controller 10 notifies the duty controller 30 that an overcurrent has occurred.

The current control unit 10 uses the second threshold value when the load current exceeds the first threshold value, as described above.
In this way, the second threshold value is used only when the load current exceeds the first threshold value only after the power is turned on or after resetting. The reason for introducing such a configuration is as follows. That is, assuming that a capacitive load such as a television is connected as the load 104, it is when the load is started that a large current equal to or higher than the rating is required. Therefore, in this case, it is only necessary to supply a large current for a predetermined period after the power is turned on (the period until the capacitor included in the capacitive load is charged). For this reason, the second threshold value is used only when the load current exceeds the first threshold value for the first time after power-on or reset. As a matter of course, if the threshold value is switched to the second threshold value every time the load current exceeds the first threshold value, there is substantially no point in providing the first threshold value.

As described above, the control circuit for controlling the output current of the inverter circuit of this embodiment increases the allowable value of the overcurrent only at the time of starting the load, and the inverter circuit can supply a large current to the load in the meantime. .

Next, the configurations and operations of the current controller 10 and the duty controller 30 will be described in detail.

The comparator 11 is a current detection circuit 103.
The load current detected by and the output of the threshold value output circuit 12 are compared, and when the load current exceeds the threshold value, the "L" level is output. The output of the comparator 11 is transferred to the duty control unit 30 via the transistor Q2, and its logical value is inverted and input to the NAND circuit 13.

The threshold output circuit 12 includes a transistor Q3,
And resistors R1 to R3. Transistor Q
3 is controlled by the Q output of the one-shot circuit 14. The output of the threshold output circuit 12 is the transistor Q3.
It changes according to the state of. That is, the threshold value output circuit 12 has the first threshold value V1 = when the transistor Q3 is in the off state.
Outputs Vcc · R2 / (R1 + R2). On the other hand, when the transistor Q3 is on, ignoring the on-resistance of the transistor Q3, the resistors R1 and R3 are connected in parallel.・ Output R2 / (Ra + R2). Ra = R1.R3 / (R1 + R3). Here, since R1> Ra, V1 <V2. That is, when the threshold output circuit 12 receives the “H” level from the one-shot circuit 14, it raises the output from V1 to V2.

The Q output of the one-shot circuit 14 is input to the other terminal of the NAND circuit 13. Then, the output of the NAND circuit 13 is transferred to the input terminals of the one-shot circuits 14 and 15 and the clock terminal of the flip-flop 16.

When detecting the falling edge, the one-shot circuit 14 sets its Q output to the "H" level for a time determined by the resistance value of the connected resistor and the capacitance of the capacitor. That is, when the output of the comparator 11 is switched from the “H” level to the “L” level and the load current increases, the one-shot circuit 14 outputs Q for a predetermined time in a state where the output of the flip-flop 17 has not cleared it. The output is set to "H" level. The inverted Q output of the one-shot circuit 14 is transferred to the clock terminal of the flip-flop 17.

The one-shot circuit 15 basically operates the same as the one-shot circuit 14. However, the time constant of the one-shot circuit 15 is sufficiently shorter than the time constant of the one-shot circuit 14. These time constants will be described later. The Q output of the one-shot circuit 15 is input to the base terminal of the transistor Q1 and the clear terminal of the flip-flop 34.

The flip-flop 16 outputs the "L" level when the reset signal is input. The reset signal is generated when the power supply for supplying power to this control circuit is turned on. And the flip-flop 16
When a rising edge is input to the clock terminal,
After that, the output is held at the “H” level. The output of the flip-flop 16 is input to the control terminal of the transistor Q2.

The flip-flop 17, like the flip-flop 16, receives "L" when a reset signal is input.
Output level. Further, the inverted Q output of the one-shot circuit 14 is connected to the clock terminal of the flip-flop 17, and the flip-flop 17 holds the “H” level thereafter when it detects a rising edge at the clock terminal. That is, when the load current rises and the output of the comparator 11 switches from the “H” level to the “L” level, and the one-shot circuit 14 outputs a pulse having a predetermined pulse width accordingly, the flip-flop is output at the end timing of the pulse. The output of group 17 becomes "H" level. The output of the flip-flop 17 is input to the clear terminals of the one-shot circuits 14 and 15. Therefore, when the output of flip-flop 17 is switched to the "H" level as described above, one shot circuits 14 and 15 will no longer perform the pulse generating operation.

The transistor Q1 is a one-shot circuit 1
5 output. The transistor Q1 switches whether to erase the triangular wave used when determining the duty of the pulse signal (control signal) that controls the H-bridge circuit 101. When the transistor Q1 is in the on state, the duty controller 30 causes the triangular wave to disappear. The transistor Q2 is controlled by the output of the flip-flop 16. The transistor Q2 switches whether to transmit the output of the comparator 11 to the duty control unit 30. When the transistor Q2 is off,
Even if the overcurrent is detected, the fact is not transmitted to the duty control unit 30.

The duty control section 30 basically operates in the same manner as the existing technology. However, the operation when the load current first exceeds the first threshold value after reset is different from the existing technology. First, a part that basically operates in the same manner as the existing technology will be described. The amplifier 31 is an error amplifier, compares the DC voltage VH supplied to the H bridge circuit 101 with a predetermined reference voltage Vref, amplifies the difference, and outputs it. While the DC voltage VH is constant,
The output of the amplifier 31 is also constant. As shown in FIG. 2, the oscillator 32 generates a pulse signal instructing the timing of alternately inverting the direction of the load current and a triangular wave (sawtooth wave) used when determining the duty. The pulse signal and the triangular wave are synchronized with each other. The comparator 33 compares the output of the amplifier 31 with the triangular wave, outputs “L” level when the output level of the amplifier 31 is higher, and outputs “H” level when the output level of the amplifier 31 is lower. Output level. The time ratio between the “H” level and the “L” level of the output of the comparator 33 is called “duty”. Alternatively, the ratio of the “H” level time of the output of the comparator 33 and the sum of the “H” level time and the “L” level time is called “duty”.

The flip-flop 34, based on the pulse signal output from the oscillator 32, includes one set of switching elements S1 and S3 or one set of switching elements S2 and S4.
A signal is generated to bring each switching element belonging to one of the groups into a conductive state. For example, in Figure 2.
In, the switching elements S1 and S3 are in the conductive state during the period from the pulse P1 to the pulse P2, and the switching elements S2 and S4 are in the conductive state during the period from the pulse P2 to the pulse P3. Whether or not each of the switching elements S1 to S4 is actually turned on (conductive state) in the conductive state is determined by the output of the comparator 33. That is, each switching element S1 to S4
Are respectively in the conductive state and the comparator 3
When the output of 3 is at "H" level, it is turned on. Then, when the switching elements S1 and S3 are in the ON state, the voltage of the first polarity is applied to the load 104, and when the switching elements S2 and S4 are in the ON state, the voltage of the polarity opposite to the first polarity is applied to the load 104. Is applied.

By receiving the Q output of the one-shot circuit 15, the duty control section 30 operates differently from the existing technology. That is, the flip-flop 34 is reset when the Q output of the one-shot circuit 15 becomes "H" level. The flip-flop 34 outputs the “L” level as the Q output and the “H” level as the inverted Q output during the reset period. As a result, the switching elements S1 and S3 are forcibly rendered conductive, and the switching elements S2 and S4 are forcibly rendered non-conductive.

The triangular wave input to the comparator 33 turns on the transistor Q1 when the Q output of the one-shot circuit 15 becomes "H" level, and the oscillator 3
The capacitor connected to 2 discharges and disappears. That is, when the Q output of the one-shot circuit 15 becomes "H" level, the oscillator 32 is substantially initialized.

Next, the operation of the control circuit having the above configuration will be described with reference to FIG.

First, when the control circuit is powered on, a reset signal is generated and input to the flip-flops 16 and 17. As a result, the outputs of the flip-flops 16 and 17 are at the "L" level. Therefore, the transistor Q2 is turned off. Also,
The one-shot circuits 14 and 15 include the comparator 11
Of the Q output, the Q output is at the “L” level and the inverted Q output is at the “H” level. Therefore, the transistors Q1 and Q3 are in the off state. Therefore, the threshold output circuit 12 uses V1 as the threshold.
= Vcc · R2 / (R1 + R2) is output.

Current flowing in load 104 (current detection circuit 1
The output of 02) is smaller than the threshold value (the output V1 of the threshold value output circuit 12), the one-shot circuits 14 and 15, the flip-flops 16 and 17, the threshold value output circuit 11, and the transistors Q1 and Q2 hold the initial state. . Therefore, the current control unit 10 monitors the overcurrent by comparing the load current with the threshold value V1. Further, the duty control unit 30 generates a control signal for driving the H-bridge circuit 101 according to the operation shown in FIG. 2 while the overcurrent is not detected.

In the above state, it is assumed that a capacitive load is connected as the load 104 and the capacitive load is activated. The capacitive load has a large capacitor as described above, and is generally used with the capacitor charged. Therefore, when starting the capacitive load, a large current is required until the capacitor is charged.

When the load current exceeds the threshold value V1 due to the activation of the capacitive load or the like, the output of the comparator 11 switches from "H" level to "L" level. This falling edge is transmitted to the one-shot circuits 14 and 15 via the NAND circuit 13. When detecting this edge, the one-shot circuit 14 sets the Q output to the “H” level for a predetermined time. When the Q output of the one-shot circuit 14 becomes "H" level, the transistor Q3 is turned on, and the threshold output circuit 11 sets V2 = Vcc.R2 / (Ra +) as a threshold.
R2) is output. Ra = R1 · R3 / (R1 + R
3). Similarly, when the one-shot circuit 15 detects the edge, the one-shot circuit 15 sets its Q output to "H" level for a predetermined time. When the Q output of the one-shot circuit 15 becomes "H" level, the transistor Q1 is turned on and the flip-flop 34 is cleared. When the transistor Q1 is turned on, the triangular wave disappears when the capacitor connected to the oscillator 32 is completely discharged. When the triangular wave disappears in this way, the output level of the amplifier 31 is substantially constant, so the output of the comparator 33 is fixed at the “L” level. This state continues until the oscillator 32 outputs the next pulse for switching the direction of the load current. On the other hand, in the clear state, the flip-flop 34 fixes its Q output to the “L” level and its inverted Q output to the “H” level.
Fixed to level. Therefore, the duty control unit 30
Outputs a signal for turning on the switching elements S1 and S3 and turning off the switching elements S2 and S4 as a control signal for the H-bridge circuit 101. The pulse width of the pulse output by the one-shot circuit 15 is set to such a time that the capacitor connected to the oscillator 32 can be sufficiently discharged.

When the duty control section 30 outputs the above-mentioned control signal, the H-bridge circuit 101 causes a current to flow through the path of the switching element S1 → the load 104 → the switching element S3. At this time, since the threshold value for detecting the overcurrent is set to the threshold value V2 larger than the threshold value V1 in the threshold value output circuit 12, the threshold value V1 is set to the load 104.
Can supply a larger current. However, the load current cannot be larger than the threshold value V2.

According to the above structure, a large current exceeding the threshold value V1 does not flow through the switching elements S2 and S4, but always flows through the switching elements S1 and S3. Therefore, if the current capacity of the switching elements S1 and S3 is increased (for example, the threshold value V
2), and the switching elements S2 and S4 having a small current capacity (for example, the threshold value V
1) can be used.

When the load current exceeds the threshold value V1 due to the activation of the capacitive load or the like, the output of the comparator 11 switches from "H" level to "L" level, but at this time, the transistor Q2 is in the off state. The fact that the load current exceeds the threshold value V1 is not notified to the duty control unit 30. Therefore, a current larger than the threshold value V1 can be supplied to the load 104.

When the load current becomes smaller than the threshold value due to the threshold value rising to the threshold value V2, the output of the comparator 11 returns from the "L" level to the "H" level. This rising edge is transmitted to the flip-flop 16 via the NAND circuit 13. Upon detecting this edge, the flip-flop 16 outputs the "H" level to turn on the transistor Q2. When the transistor Q2 is turned on, the output of the comparator 11 is transmitted to the duty controller 30. That is, after the threshold value is once set to the threshold value V2, when the comparator 11 detects the overcurrent, the duty control unit 30 is notified of that fact.

The duty control section 30 outputs a control signal for turning on the switching elements S1 and S3 and turning off the switching elements S2 and S4 until any one of the following three events occurs. Continue to output. (1) The load current exceeds the threshold value V2. (2) The output of the amplifier 31 becomes smaller than the level of the triangular wave.
(3) The level of the triangular wave reaches the peak (a pulse signal for switching the direction of the load current is received from the oscillator 32). In the case of (1) or (2) above, the comparator 3
The output of 3 becomes "H" level, and the switching element S1
The control signals for ~ S4 are all at the "L" level.
Therefore, the switching elements S1 to S4 are all turned off, and no current flows through the load 104. on the other hand,
In the case of the above (3), the Q output and the inverted Q output of the flip-flop 34 become the “H” level and the “L” level, respectively, and the switching elements S2 and S4 are in the energizable state. At this time, since the triangular wave is output as in the normal state, the H bridge circuit 101 performs a normal operation.

When the one-shot circuit 14 detects a falling edge of the comparator 11 due to the load current exceeding the threshold value V1 at the time of starting the capacitive load and a predetermined time elapses, the Q output becomes "L". Then, the inverted Q output is returned to the "H" level. When the Q output of the one-shot circuit 14 becomes "L" level, the transistor Q3 is turned off, and the threshold value output circuit 12 outputs the threshold value V1 as the threshold value. Therefore, thereafter, the comparator 11 monitors the overcurrent using this threshold value V1. Further, when the inverted Q output of the one-shot circuit 14 becomes “H” level,
The Q output of the flip-flop 17 becomes "H" level until it is reset. Then, when the Q output of the flip-flop 17 becomes "H" level, the one-shot circuit 14
And 15 are cleared and go dormant. That is, after the time set as the time constant of the one-shot circuit 14 has elapsed, the one-shot circuits 14 and 1
5 ignores the edge even if the output of the comparator 11 has an edge due to the generation of the overcurrent. In other words,
The current control unit 10 makes the threshold value higher than the normal time only when the first overcurrent is detected after the reset (after the power is turned on), but thereafter, even if the overcurrent occurs, the threshold is shaving e4e4e46cV.
It remains unchanged at 1.

The time constant and threshold value V2 of the one-shot circuit 14 are set so that the switching elements S1 and S3 operate within the stable operation region. Also,
If the time constant of the one-shot circuit 14 is set to be, for example, about the same as the period of the triangular wave, the switching element S1 is in the period in which the load current may exceed the normal threshold value (threshold value V1).
And S3 are limited to the ON state, and a large current exceeding the threshold value V1 does not flow through the switching elements S2 and S4.

In the above embodiment, as the threshold value for monitoring overcurrent, a first threshold value corresponding to a certain current value and a second threshold value corresponding to a current value larger than the first threshold value are prepared. The configuration in which the second threshold value is used only when the load current exceeds the first threshold value after the power is turned on or reset is shown, but the present invention is not limited to this configuration. In the following, a configuration that allows the threshold value for monitoring the overcurrent to be periodically switched from the first threshold value to the second threshold value will be described.

FIG. 4 is a circuit diagram of a current controller according to another embodiment of the present invention. Although the duty control unit 30 is not shown in FIG. 4, its configuration and operation are as described with reference to FIG.

The current control unit shown in FIG. 4 is different from the current control unit 10 shown in FIG. 1 in that the flip-flop 16 and the transistor Q2 are removed, and one-shot circuits 18 and 19 are newly provided. . The one-shot circuit 18 outputs one pulse by using the rising edge of the inverted Q output of the one-shot circuit 14 as a trigger. Further, the one-shot circuit 19 outputs one pulse triggered by the rising edge of the inverted Q output of the one-shot circuit 18. And the Q output of the one-shot circuit 19 is
It is input to the clear terminal of the flip-flop 17. When at least one of the reset signal and the Q output of the one-shot circuit 19 becomes "H", the flip-flop 17 thereafter outputs "L" until the rising edge from the one-shot circuit 14 is detected. Hereinafter, the operation of the current controller shown in FIG. 4 will be described with reference to the timing chart shown in FIG.

When the load current exceeds the threshold value V1 for the first time after receiving the reset signal, the threshold value output circuit 12
The operation up to the output of the threshold value V2 is basically the same as the operation of the current controller 10 shown in FIG. After that, in the current controller shown in FIG. 4, the one-shot circuit 14
The one-shot circuit 18 sets its inverted Q output to “L”, triggered by the switching of the inverted Q output of “L” from “H”. The time for which the one-shot circuit 18 sets the inverted Q output to “L” (hereinafter, referred to as “cycle time”) is
It is determined by the resistance value of the resistor connected to the one-shot circuit 18 and the capacitance of the capacitor. Here, at the timing when the inverted Q output of the one-shot circuit 14 is switched from “L” to “H”, the output of the threshold value output circuit 12 is the threshold value V.
This is the timing of returning from 2 to the threshold value V1. Therefore,
The one-shot circuit 18 outputs "L" from when the threshold value for monitoring the load current returns from the threshold value V2 to the threshold value V1 until the cycle time elapses.

When the cycle time has elapsed, the one-shot circuit 18
The one-shot circuit 19 generates a pulse when the inverted Q output of the signal changes from "L" to "H". This pulse is a reset signal for the flip-flop 17. Therefore, the flip-flop 17 includes the one-shot circuit 19
When it receives a pulse from, it outputs "L". When the output of the one-shot circuit 19 becomes "L", the reset state of the one-shot circuits 14 and 15 is released. That is, when the cycle time elapses from the time when the threshold value for monitoring the load current returns from the threshold value V2 to the threshold value V1, the flip-flop 17 is reset and the one-shot circuits 14 and 15 receive the signal from the comparator 11 respectively. Enter the accepting state. Here, the “state in which a signal from the comparator 11 is accepted” means that when the comparator 11 detects an overcurrent,
A state in which it is possible to instruct to switch the threshold value from the threshold value V1 to the threshold value V2.

When an overcurrent occurs in the above state, that is, when the load current exceeds the threshold value V1, the one-shot circuit 1
4 instructs the threshold value output circuit 12 to switch its output from the threshold value V1 to the threshold value V2, whereby the threshold value output circuit 12 outputs the threshold value V2. Then, the comparator 11 monitors the overcurrent by using this threshold value V2. As described with reference to FIG. 1, the period during which the threshold value output circuit 12 outputs the threshold value V2 is determined by the time constant of the one-shot circuit 14. Further, after the threshold value for monitoring the overcurrent returns from the threshold value V2 to the threshold value V1, the above-mentioned processing is repeated.

As described above, in the current control unit shown in FIG. 4, after allowing a large current by increasing the threshold value for detecting the overcurrent, the cycle time determined by the time constant of the one-shot circuit 18 elapses. Until that time, the threshold is fixed at a small value. Then, after the cycle time has elapsed, the threshold value can be increased as necessary. This cycle time is set to a time in which the switching elements S1 to S4 (especially S1 and S3) that generate heat due to a large current flowing during a period when the threshold value is large are sufficiently cooled.

When the configuration shown in FIG. 4 is introduced, when the load demands more current even though the inverter circuit instantaneously supplies a large current to the load, the inverter circuit again supplies a large current. Can be supplied. At this time, the large current is supplied for a short time, and the interval from the supply of a certain large current to the allowance of the next large current is set so that the load is not destroyed. ing. As a result, the ability to activate the load is improved while preventing destruction of the load.

The current controller shown in FIG. 4 may have a temperature detecting function. The temperature detection function, for example,
Switching element S1 connected to this inverter circuit
Includes a temperature sensor 41 provided near S4. The output of the temperature sensor 41 is, as shown in FIG.
Is input to the clear terminals of the one-shot circuits 14 and 15 via. The temperature sensor 41 is "H" when the detected temperature exceeds a predetermined temperature.
To reset the one-shot circuit 14.

Further, as shown in FIG. 6 (b), even when the temperature sensor 41 detects that the temperature exceeds a predetermined temperature, the output of the comparator 33 is set to "H". Good.

According to the above configuration, the switching element S1
When the temperature of S4 rises, the inverter is not allowed to flow a large current even when the load requires it. As a result, the switching elements S1 to S4
Are protected from overcurrent or the associated heat generation.

As another structure for protecting the switching elements S1 to S4, it may be possible to provide a function of limiting the number of times a large current flows. This function is provided with a counter 43 for counting the number of pulses output from the one-shot circuit 19, as shown in FIG. 6C, and the one-shot circuit 14 is provided when the count value of the counter exceeds a predetermined value. It is realized by a circuit that resets.

[0062]

The threshold value for monitoring the load current is controlled so as to be larger than the threshold value during normal operation for the first overcurrent after power-on or reset, so that a large current is required at startup. Sufficient current can be supplied to loads, and such loads can be activated reliably and quickly. In addition, since the threshold value is returned to the original value in normal times, it is not necessary to increase the capacity of the inverter itself.

In the structure in which a large instantaneous current is allowed to flow repeatedly, the interval at which the large current is permitted is limited to a predetermined time or longer, so that the load can obtain a large current within a range that does not cause breakdown.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a control circuit of this embodiment.

FIG. 2 is a diagram illustrating a basic operation of a duty control unit.

FIG. 3 is a timing diagram illustrating the operation of the control circuit of the present embodiment.

FIG. 4 is a circuit diagram of a current controller according to another embodiment of the present invention.

5 is a timing diagram illustrating the operation of the current controller shown in FIG.

6A to 6C are examples of additional circuits of the current control unit shown in FIG.

FIG. 7 is a configuration diagram of an example of a conventional inverter circuit.

8 is a timing diagram illustrating the operation of the inverter circuit shown in FIG.

[Explanation of symbols]

10 Current control section 11 comparator 12 Threshold output circuit 14,15 One shot circuit 16,17 flip flops 18, 19 One-shot circuit 30 Duty control circuit 32 oscillators 33 Comparator 34 flip-flops 101 H bridge circuit 102 control circuit 103 Current detection circuit 104 load

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 H02M 7/5387

Claims (3)

(57) [Claims] 1. An inverter circuit for converting direct current to alternating current
A control circuit for controlling an output current, the first threshold value corresponding to a predetermined current value, or a predetermined threshold value thereof.
Output the second threshold value corresponding to the current value that is larger than the current value
Threshold output means , the current supplied to the load and the threshold output means
And a current supplied to the load is higher than the first or second threshold value.
If it is judged to be large by the above comparison means, the negative
Suppressing means for suppressing the current supplied to the load, and the period during which the threshold output means outputs the first threshold
The current supplied to the load is greater than its first threshold
When the second threshold is reached, the second threshold is output to the threshold output means.
The first state is set by the control means for outputting only for a fixed time and the reset signal generated upon power-on or power-on, and the threshold value output means sets the second threshold value by the instruction of the control means. It has a latching means second state is set when the period of outputting is completed, the control means, a period in which the second state is set to the latch means, with respect to the threshold output means A control circuit characterized by not sending a threshold change instruction. 2. An inverter circuit for converting direct current into alternating current
A control circuit for controlling an output current, the first threshold value corresponding to a predetermined current value, or a predetermined threshold value thereof.
Output the second threshold value corresponding to the current value that is larger than the current value
Threshold output means , the current supplied to the load and the threshold output means
And a current supplied to the load is higher than the first or second threshold value.
If it is judged to be large by the above comparison means, the negative
Suppressing means for suppressing the current supplied to the load, and the period during which the threshold output means outputs the first threshold
The current supplied to the load is greater than its first threshold
When the second threshold is reached, the second threshold is output to the threshold output means.
A first state corresponding to a control means for outputting only for a fixed time and a state in which the control means is permitted to send a threshold value changing instruction to the threshold value output means or the control means is the threshold value output means. Latch means for setting a second state corresponding to a state in which it is not permitted to send a threshold value change instruction to the latch means, and a first state for the latch means after a lapse of a predetermined time from the end of the first state. It has a state setting means for setting a condition, the control means, and characterized by sending threshold change instruction against the threshold output means only during a period in which the first state is set to the latch means control circuit to be. 3. The inverter circuit is an H-bridge circuit including four switching elements, and the four switching elements are included in at least a part of a period in which the threshold output unit outputs the second threshold. and forcibly turned on a predetermined two switching elements in the, according to claim 1 or 2 further comprising a switch control means for generating a signal for forcibly turning off the other two switching elements Control circuit.