JPS58217786A - Inverter circuit for inverter pump - Google Patents

Abstract

PURPOSE:To prevent damage of an output circuit when an inverter pump is locked, by stopping production of output from the output circuit when it is detected that the voltage between the drain and the source of an MOS type field- effect transistor (MOS FET) is higher than a prescribed value. CONSTITUTION:An inverter circuit for an inverter pump of this invention is composed of a DC power source 1, a switching circuit 2, an output circuit 3 having switches of MOS type field-effect transistors (called hereinafter MOS FET), an AC motor 4 and a stop circuit 6 which detects the voltage drop VDS between the drain and the source of an MOS FET 3h in synchronism with energization of the MOS FET 3h and gives a signal to the switching circuit 2 to stop the output of the output circuit 3 when it is detected that the voltage drop VDS is greater than a prescribed value. With such an arrangement, MOS FETs in the output circuit 3 can be protected against burn-out even if the inverter pump is used under unexpectedly unfavorable conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter circuit for an inverter pump, and more particularly to an improvement of an inverter circuit for an inverter pump that is built into a pump body and drives an AC motor using a DC power source as a power source.

As an inverter circuit for an inverter pump of this type, the one shown in FIG. 1 is known. FIG. 1 is a block diagram showing a conventional inverter circuit for an inverter pump. In FIG. 1, 1 is a DC power supply, 2 is a switching control circuit, 3 is each transistor 3a, 3b,
3c, 3d.

3e and 3f are output circuits with switches, 4 is an AC motor, 5 is a resistor with a low resistance value for converting the magnitude of the current flowing through the output circuit 3 into the magnitude of voltage, and 6 is the resistor 5. This is a stop circuit that detects a voltage drop occurring across both ends, and sends a signal to the switching control circuit 2 to stop the output of the output circuit 3 when this voltage remains at a predetermined value or higher for a certain period of time. Therefore, the resistor 5 and the stop circuit 6 are used to protect the transistors 33 to 3f, which are the switches of the output circuit 3, from being burnt out when a mechanical abnormality occurs in the pump (not shown). belongs to.

Next, the operation shown in FIG. 1 will be explained. If the pump locks due to a mechanical abnormality, the AC motor 4
is stopped, and a large current flows through each transistor 3a to 3f of the output circuit 3. If this large current flows for a longer period than a predetermined period, the power consumption of each transistor 33 to 3f increases and may burn out. In order to prevent this, the current flowing through the output circuit 3 is converted into voltage by the resistor 5,
When this voltage is detected by the stop circuit 6 and flows to the output circuit 3 for more than the limit time T when the pump is locked,
Each of the transistors 3a to 3f of the output circuit 3 is configured to be turned off. Here, the above-mentioned limit time T is determined based on the maximum ambient temperature at which the inverter circuit is arranged, the allowable junction temperature of each transistor 3a to 3f, and the cooling effect of each transistor 3a to 3f by the liquid flowing through the inverter pump. It is selected from the allowable power consumption in 3a to 3f.

By the way, the inverter circuit for a conventional inverter pump is configured as described above, so if the impark pump is used in a more adverse environment than expected, for example, the inverter pump may be run dry, that is, the liquid flowing through the pump may be If the pump is operated in the absence of the
The junction temperature of transistors 33 to 3f becomes extremely high, and each transistor 33 to 3f eventually burns out.

The present invention has been made in order to eliminate the drawbacks of the conventional ones as described above, and is an inverter circuit for an inverter pump that is built into the pump body and drives an AC motor using a DC power supply. A configuration in which a MO8 type field effect transistor is used, a voltage between the drain and source of the MO8 type field effect transistor is detected, and when a voltage equal to or higher than a predetermined value is detected, the output of the output circuit is stopped. The inverter pump is used in a harsher environment than expected.

An object of the present invention is to provide an inverter circuit for an inverter pump, which prevents the MO8 type field effect transistor of the output circuit from burning out even when the output circuit is operated.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing an inverter circuit for an impark pump according to an embodiment of the present invention.

In FIG. 2, 1 is a DC power supply, 2 is a switching control circuit, and 3 is each MO8 type field effect transistor (hereinafter referred to as M
3' + 3h +
31゜3j, 3, output circuit with 31 as a switch, 6
is synchronized with the conduction of MOS P”ET 3h, and this M
Drop voltage between drain D and source S of O8FET3h ■
This is a stop circuit that detects voltage VD8 and sends a signal to the switching control circuit 2 to stop the output of the output circuit 3 when a voltage higher than a predetermined value of the voltage VD8 is detected.

Next, the operation shown in FIG. 2 will be explained. Now, the second
When the inverter circuit shown in the figure is in the operating state, the current flowing through each MO8FE, :T3f~31 of the output circuit 3 is equal;
They have the same characteristics, and the voltage between the drain and source when conducting is the same for the same drain current. The stop circuit 6 synchronizes with the signal of the gate G of the MOS FET 3 h, and the drain D- of the MOS FET 3 h when it is conductive.
The voltage between the source S and Ds is detected, but this drain D
- voltage vD8 between source S is ~108 PET 3
Find the drain current flowing through h.

If the ON resistance of MOS PET 3h is RD8, ■
D8”'D×R'DS.The above ON resistance horse is MO
Since it is proportional to the chip temperature of S FET3h, each MO8
Assuming that the ON resistance of the FET3, 3h chip at the maximum allowable temperature is RDa, and the current flowing through the MOS PET3h when the inverter pump is locked is ■,
Since the electric current at the time of locking can be considered to be almost constant, when the inverter pump is locked, the voltage detected by the stop circuit 6 is D8=horse. IQ is MOS PE
The chip temperature of T 3 h will be detected. Therefore, the level voltage of the detection voltage vD8 that outputs a stop signal to the stop circuit 6 or the switching control circuit 2 is the same. If we set VI) s=: l-1, I,', then
It is possible to protect each MO8FET 3y-31, which is a switch of the output circuit 3 in the inverter circuit, from burning out.

As described above, with the inverter circuit for an inverter pump according to the present invention, for example, MOS can be used as a switch of the output circuit.
Ii"ET is used to detect the drain-source voltage proportional to the chip temperature of this MOS F'ET,
Since the configuration is such that the output circuit is protected, the output circuit can be effectively protected from burnout no matter what environmental conditions the inverter pump is used in. It is effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional inverter circuit for an inverter pump, and FIG. 2 is a block diagram showing an inverter circuit for an inverter pump according to an embodiment of the present invention. 1...DC power supply, 2...Switching control circuit, 3...Output circuit, 4
・・・・・・・・・AC motor, 6・・・・・・・・・
Stop circuit, 37 to 31..."MO8 type" LM08 FET,). Shin -8- 117-

Claims (1)

[Claims] In an inverter pump inverter circuit that is built into the pump body and drives an AC motor using a DC power supply, an MO8 type field effect transistor is used as a switch in the output circuit, and the voltage between the drain and source of the MO8 type field effect transistor is and when a voltage equal to or higher than a predetermined value is detected, the output of the output circuit is controlled to be stopped, and when the inverter pump is locked, the MO8 field effect transistor is An inverter circuit for an inverter pump, characterized in that the inverter circuit is prevented from burning out due to large current flowing through the inverter pump.