JPH04364398A - Current controller for inductive load - Google Patents

Abstract

PURPOSE:To eliminate a flywheel diode, to obviate a subject of generation of a heat and to stably supply a current to an inductive load by composing a closed loop only of the load and a second switch, and controlling ON, OFF first, second switches in reverse phases to each other. CONSTITUTION:When a command signal becomes 'H', a transistor 3 is turned ON, and a current flows in a first circuit of a loop of a positive electrode of a DC power source 1, an inductive load 2, the transistor 3, a current detector 4 and a negative electrode of the power source 1. When the transistor 3 is turned OFF soon, a current flows in a second circuit of a closed loop of a transistor 5 and the load 2. Then, a current alternately flows in the first circuit, the second circuit and the first circuit. Thus, a flywheel diode is eliminated, generation of heat can be reduced, a current ripple rate is reduced, and an operating state of the load can be stabilized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductive load current control device for intermittently exciting an inductive load.

0002

2. Description of the Related Art FIG. 3 shows a circuit configuration of a conventional inductive load current control device. 1 is a DC power supply whose (-) pole side is grounded, 2 is an inductive load whose one end is connected to the (+) pole side of the DC power supply 1, and 3 is an inductive load 2 whose other end is connected to the collector which is the input end. a transistor as a first switch;
Reference numeral 4 denotes a current detection resistor as a current detector connected between the emitter, which is the output terminal of the transistor 3, and ground.

5 is a transistor as a second switch;
Reference numeral 6 denotes flywheel diodes, which are connected in series and in parallel to the inductive load 2. 7 is a Zener diode provided between the collector of the transistor 3 and the ground to absorb the surge voltage applied to the collector; 10 is a reference voltage; and 11 is a comparator that compares the voltage of the current detection resistor 4 with the reference voltage 10. .

Reference numeral 12 denotes an AND which takes the logical product of a command signal for starting and stopping the device (current), the output of the comparator 11, and the output of a monostable flip-flop (hereinafter referred to as monostable FF) 15, which will be described later. In the circuit, the output is given to the transistor 3 via the base resistor 13 and monostable FF1.
5 is given as input. 16 is an inverter circuit that inverts the command signal and supplies it to the transistor 5 via the base resistor 17.

FIG. 4 is a waveform diagram of signals at various parts of the current control device for an inductive load having the above configuration. The current signal S4 is the signal of the output part b of the inverter circuit 16, S5 is the current signal of the transistor 5, and S6 is the current signal of the inductive load 2.

Next, the operation will be explained. The command signal is “
When the level is "L" (hereinafter referred to as "L"), the output of the AND circuit 12 is "L" and the transistor 3 is in the OFF state.At this time, the output of the inverter circuit 16 is "H" level. (hereinafter referred to as "H"), and the transistor 5 is also in the OFF state. In this state, the current detection resistor 4
Since no current flows through the comparator 11, the output of the comparator 11 is “H”.
Therefore, the output of monostable FF15 is also “H” on the stable side.
It has become.

Next, when the command signal becomes "H", the output of the AND circuit 12 becomes "H", and the transistor 3 is turned on. As a result, the (+) pole side of DC power supply 1 → inductive load 2 → transistor 3 → DC detection resistor 4 → DC power supply 1
Current begins to flow in the first circuit of the loop on the (-) side of
It increases at a value determined by the inductance, resistance value, and power supply voltage of this first circuit.

During the rise of this current, the voltage applied to the current detection resistor 4 becomes higher than the reference voltage 10, so the output of the comparator 11 becomes "L" and the output of the AND circuit 12 also becomes "L". Therefore, transistor 3 is turned off. As a result, the current to the current detection resistor 4 becomes 0, and the output of the comparator 11 returns to "H", but due to the fall of the output of the AND circuit 12, the output of the monostable FF 15 becomes "L" for a certain period of time tOFF. . Therefore, during this "L" period, the output of the AND circuit 12 continues to be "L", and therefore the transistor 3 is in the OFF state.

On the other hand, when the command signal is in the "H" state, the output of the inverter circuit 16 is "L" and the transistor 5 is in the ON state, so the transistor 3 is turned OFF.
Then, the current flowing through inductive load 2 becomes
-> Transistor 5 -> Flywheel diode 6 -> Inductive load 2 -> flows through the second circuit of the loop. Eventually, after a certain period of time tOFF during which the monostable FF 15 outputs "L" has elapsed, the output of the AND circuit 12 becomes "H", the transistor 3 is turned on, and current flows in the first circuit.

As shown in FIG. 4, when the command signal S1 is
"Sometimes, by repeating the above operation, a current flows intermittently in the first circuit (current signal S3 of transistor 3), and conversely, current also flows intermittently in the second circuit (current signal S3 of transistor 5)." The current signal S5) and the current S6 flowing through the inductive load 2 are controlled to a substantially constant current.

Note that the flywheel diode 6 provided in the second circuit is connected to the transistor 3 and the transistor 5.
This is to prevent excessive current from flowing in the path of DC power supply 1 → transistor 5 → transistor 3 → current detection resistor 4 even if the transistors turn on at the same time.

0012

Problem to be Solved by the Invention Since the conventional inductive load current control device is constructed as described above, the second
When operating in this circuit, there is a large voltage drop due to the flywheel diode 6, and this part consumes a large amount of power and releases heat, which poses an unfavorable problem in terms of thermal design of the device.

Furthermore, when the power consumption by the flywheel diode 6 is large, the current drop while the current is flowing through the second circuit is large, and the ripple rate of the current signal flowing through the inductive load 2 becomes large. When the inductive load 2 is a solenoid, there are problems such as not being able to bring it into a stable operating state.

[0014] This invention was made to solve the above-mentioned problems, and by eliminating the need for a flywheel diode, the problem of heat generation can be solved, and moreover, current can be stably passed through an inductive load. The purpose of this invention is to obtain a current control device for an inductive load that is capable of controlling the current of an inductive load.

[0015]

[Means for Solving the Problems] The inductive load current control device of the present invention includes a first circuit in which a DC power supply, an inductive load, and a first switch are connected in series, and a second switch and an inductive load. A second switch is connected in parallel to an inductive load in a device that alternately supplies current to a closed loop configured at the time of a start command,
and a second control means for controlling ON/OFF of the second switch in reverse to the first switch at the time of the start command based on the comparison result of the voltage at the input and output terminals of the second switch and the command signal. It is something that

[0016]

[Operation] The inductive load current control device in this invention has the following features:
Since the closed loop is configured with only the inductive load and the second switch, the voltage drop during energization is only at the second switch, which reduces loss and reduces the ripple rate of the current in the inductive load.
In addition, the first and second switches can be turned on and off in opposite phases to each other.
Since they are controlled, they are not turned on at the same time to prevent excessive current from flowing.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration of an inductive load current control device according to an embodiment of the present invention. In FIG.
to 13, 15, and 17, and their explanations will be omitted. However, the transistor 5 serving as the second switch is connected in parallel to the inductive load 2.

18 is a NAND circuit that multiplies the command signal and the output signal of a comparator 19 (described later), negates the product, and outputs the result; 19;
is the power supply voltage of the DC power supply 1 and the voltage at the connection point e between the other end of the inductive load 2 on the opposite side to the side connected to the DC power supply 1 and the emitter of the transistor 5, that is, the input/output terminal of the transistor 5. This is a comparator that compares the emitter and collector voltages. Note that components 10 to 12, and 15 constitute a first control means that controls ON/OFF of the transistor 3, and components 18 and 19 constitute a second control means that controls ON/OFF of the transistor 5. It consists of

FIG. 2 shows the waveforms of signals from each part of the device shown in FIG. The signal of the c section which is the output section of the NAND circuit 18, S
5 is a current signal of the transistor 5, and S6 is a current signal of the inductive load 2.

Next, the operation of one embodiment will be explained with reference to FIGS. 1 and 2. However, parts that overlap with the operations of the conventional example explained in FIG. 3 will be omitted.

When the command signal is “L”, the NAND circuit 1
8 is "H", the transistor 5 as the second switch is in the OFF state, and similarly to the conventional example, the transistor 3 as the first switch is also in the OFF state. No current flows through the circuit No. 1 (the loop labeled 1→2→3→4→1) and the second circuit (corresponding to the loop labeled 2→5→2).

When the command signal becomes "H", the transistor 3 turns on as in the conventional example, and the (
A current flows through the first circuit of the (-) pole side loop of the +) pole side→inductive load 2→transistor 3→current detection resistor 4→DC power supply 1. At this time, the voltage at section e is lower than the power supply voltage of DC power supply 1 by the voltage drop caused by inductive load 2, so the output of comparator 19 that compares these voltages is "L", so the output of NAND circuit 18 is At "H", transistor 5 is in the OFF state.

When the amount of current flowing through the first circuit increases and eventually the transistor 3 switches from the ON state to the OFF state as in the conventional example, e
The voltage of the DC power source 1 rises instantaneously and becomes higher than the power supply voltage of the DC power supply 1. As a result, the output of the comparator 19 becomes "H" and the output of the NAND circuit 18 becomes "L", so the transistor 5 is turned on, and the inductive load 2 → transistor 5
→A current flows through the second circuit of the closed loop of the inductive load 2. The period during which the current flows at this time is the fixed time tOF during which the output of the monostable FF 15 is "L", as in the conventional example.
It is F. Thereafter, as described above, the current alternately flows by repeating the sequence from the first circuit to the second circuit to the first circuit.

[0024] When current is flowing in the second circuit,
Although a voltage drop occurs due to the transistor 5, it does not pose a problem because it is much smaller than that of the flywheel diode used in the conventional example. In this invention, since the power loss of the flywheel diode is reduced compared to the conventional example, the current drop in the second circuit during the constant OFF time of the transistor 3 is small, that is, the current reduction rate {in FIG. When the peak current amount of S6 is Ip and the current amount after the current drop is Ib, (Ip − Ib
)/Ip } is smaller than that of the conventional example (see S6 in FIG. 4).

In the above embodiment, the monostable FF 15 inputs the output of the AND circuit 12, but instead, the monostable FF 15 inputs the output of the AND circuit 12.
Even if the output of 1 is input, the same effect as in the above embodiment can be obtained.

[0026]

As described above, according to the present invention, the first switch connected in series with the inductive load is Since the second switch is configured to be ON/OFF controlled in the opposite way to the ON/OFF control of the switch start command, a flywheel diode is no longer required, resulting in less heat generation and equipment downsizing. In addition, since the temperature rise inside the device is reduced, this has the effect of improving the reliability of other parts.

[0027] Also, since the power loss due to the flywheel diode is reduced, the OF of the first switch
Rate of current decrease during a certain period of time at F {(Ip - Ib)
/Ip} becomes smaller, that is, the ripple rate of the current flowing through the inductive load becomes smaller, so that, for example, when a solenoid is used as the inductive load, the operating state of the solenoid becomes more stable.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of an inductive load current control device according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram of each part of the circuit in FIG. 1;

FIG. 3 is a circuit configuration diagram of a conventional device.

FIG. 4 is a signal waveform diagram of each part of the circuit in FIG. 3;

[Explanation of symbols]

1 DC power supply 2 Inductive load 3 Transistor (first switch) 4 Current detection resistor (current detector) 5 Transistor (second switch) 10 Reference voltage 11 Comparator 12 AND circuit 15 Monostable FF 18 NAND circuit 19 Comparator

Claims (1)

[Claims] 1. A first circuit in which a DC power source, an inductive load, a first switch, and a current detector are connected in series, a second switch forming a closed loop with the inductive load, and a second switch for starting and stopping. a first control means that controls ON/OFF of the first switch based on a command signal to command and a detection signal of the current detector; and a second control that controls ON/OFF of the second switch. In the current control device for an inductive load, the second switch is connected in parallel to the inductive load, and the second switch is connected in parallel to the inductive load, and the second switch is connected in parallel to the inductive load. The second control means turns on the first switch at the time of the start command based on the comparison result of the voltage at the input and output terminals of the second switch and the command signal.
- A current control device for an inductive load, characterized in that the second switch is controlled to turn on and off, contrary to turning it off.