JPH0311174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application and Prior Art The present invention relates to a regenerative voltage clamp circuit that bypasses overvoltage due to regenerative energy of an electric motor through a resistor.

When an electric motor is driven from an AC power source through a rectifier circuit, a gradually decreasing voltage is generated in the armature until the armature completely stops rotating when the electric motor is stopped. This regenerated energy at the time of stoppage is applied to the rectifier circuit, but since the rectifier circuit has unidirectional characteristics, there is no part to bypass the regenerated energy, and the voltage may rise above the rated voltage.

Since such an overvoltage poses a problem in terms of withstand voltage of various parts, a structure shown in FIG. 1, for example, described in Japanese Patent Publication No. 58-29698, has been proposed. In the figure, T is a transformer, REC is a rectifier circuit, CMP1 is a comparator with a hysteresis function, C1 and C2 are capacitors, R1 to R4 are resistors, D1 is a diode, and Q1 is a transistor. When DC current is supplied from the rectifier circuit REC to the load via diode D1, the comparator
Since the forward voltage of diode D1, for example, about 0.7V, is input to CMP, the comparator
The output of CMP becomes zero, and transistor Q1 is in an off state.

The voltage generated in an inductive load such as an electric motor is rectified by a rectifier circuit.
When the voltage exceeds the output voltage of REC, diode D1
When a reverse voltage is applied to , this reverse voltage is input to the comparator CMP, so the transistor Q1 is turned on by the output of the comparator CMP1, and the overvoltage is removed by the low resistance value resistor R4. It is possible to bypass the current caused by the voltage and suppress the voltage rise.

However, in such a conventional circuit, a large current flowing to the load flows through the diode D1, so
It is necessary to use a diode with a large allowable current. In addition, capacitor C1 that creates the reference voltage of comparator CMP1 must have a large capacitance; a small capacitance capacitor will not be able to provide sufficient smoothing because it will be drawn into the load circuit, causing ripples. There was a risk that the device CMP1 would malfunction.

Therefore, the conventional regenerative voltage clamp circuit requires a large space due to the diodes and capacitors, and is expensive.

Purpose of the Invention The present invention improves the above drawbacks of the prior art in a regenerative voltage clamp circuit that prevents overvoltage by bypassing regenerative energy generated in an inductive load such as an electric motor, and provides a capacitor and a capacitor for detecting overvoltage. The purpose of the present invention is to provide a regenerative voltage clamp circuit that has a small diode capacity and is inexpensive and compact.

Composition of the Invention The present invention provides a circuit for rectifying alternating current voltage with a rectifier circuit and supplying direct current to a load such as a motor.
A capacitor that obtains the peak voltage of the output voltage of the rectifier circuit through a diode and a resistor and is charged with the peak voltage, a comparator that compares the charging voltage of the capacitor with the positive side potential of the load, and a A regenerative voltage characterized by comprising a transistor that outputs an output from the comparator and is turned on when the side potential exceeds a charging voltage of the capacitor, and a resistor connected in series with the transistor between the output terminals. This is a clamp circuit.

Embodiment FIG. 2 is a circuit diagram of an embodiment of the present invention,
REC is a rectifier circuit, CMP2 is a comparator with hysteresis function, Q2 is a transistor, C3, C4
is a capacitor, D2~D4 are diodes, R5~
R9 is a resistor. One input of the comparator CMP2 receives the positive output of the rectifier circuit REC connected to the load, and the other input receives the diodes D2 to D.
The peak voltage of the rectifier circuit REC is obtained through the resistor R5 and the resistor R5, and the charging voltage of the capacitor C3 charged with the peak voltage is input. Further, the output of the comparator CMP2 is input to the base of the transistor Q2.

When current is supplied to the load from the AC power supply via the rectifier circuit REC, the capacitor C3 is charged to a constant voltage through the diodes D2 to D3 and the resistor R5, and this charged voltage is applied to the comparator.
It is input to the other terminal of CMP2 and constitutes a reference voltage. Since the input impedance of comparator CMP2 is very large, capacitor C
3. The current flowing through the diodes D2 to D4 is small. Therefore, the diodes D2 to D4 can be diodes with a small allowable current. Further, since there is no current drawn into the load circuit as in the prior art, the capacitor C3 may be a small capacitor.

Therefore, when the voltage generated in an inductive load such as an electric motor exceeds the charging voltage of the capacitor C3, that is, when the voltage input to one terminal of the comparator CMP2 exceeds the reference voltage input to the other terminal. , an output is output from the comparator CMP2, turning on the transistor Q2, bypassing the current that would cause an overvoltage due to the low resistance value R9, and suppressing the voltage rise.

Effects of the Invention As described above, the regenerative voltage clamp circuit of the present invention extracts the peak voltage of the rectifier circuit through the diode, rectifies this peak voltage with the capacitor, and uses the charging voltage of the capacitor as the reference of the comparator. Input as voltage.

Therefore, since the input impedance of the comparator is very large, the current flowing through the capacitor is small, and the current flowing through the diode is also small. Also, since there is no draw into the load circuit, the capacitance of the capacitor is reduced. Furthermore, a diode with a very small allowable current can be used as the diode. Therefore, unlike conventional methods, there is no need for a diode with a large allowable current to pass the load current, or a capacitor with a large capacity to smooth the output of the rectifier circuit and create a reference voltage, so it can be made smaller in space and cheaper. An inexpensive regenerative voltage clamp circuit can be obtained.

[Brief explanation of the drawing]

Figure 1 shows a conventional regenerative voltage clamp circuit,
The figure shows an embodiment of the regenerative voltage clamp circuit of the present invention. REC... Rectifier circuit, R1~R9... Resistor, C1~
C4...Capacitor, Q1, Q2...Transistor,
D1 to D4...Diode, CMP1, CMP2...Comparator.

Claims (1)

[Claims] 1. In a circuit that rectifies an alternating current voltage with a rectifier circuit and supplies direct current to a load such as a motor, a capacitor that obtains the peak voltage of the output voltage of the rectifier circuit through a diode and a resistor and is charged with the peak voltage. , a comparator that compares the charging voltage of the capacitor with the positive potential of the load, and a transistor that outputs an output from the comparator and is turned on when the positive potential of the load exceeds the charging voltage of the capacitor. A regenerative voltage clamp circuit comprising: a resistor connected in series with the transistor between output terminals.