JP2888915B2 - Power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention rectifies a voltage from an AC power supply, and smoothes the rectified output after performing pulse width modulation with a chopper circuit. The present invention relates to a power supply device that converts a voltage into an AC voltage by an inverter circuit, amplifies the voltage, converts the voltage to DC, and outputs the DC to a load.

(Prior Art) In recent X-ray CT apparatuses, an inverter type X-ray high voltage apparatus is often used as a power supply for supplying a high voltage to an X-ray tube for emitting X-rays.

Conventionally, as such an X-ray high voltage device, for example, a device described in Japanese Patent Application No. 1-443494 is known. This conventional device is shown in FIG. 4, in which an AC voltage from an AC power supply 1 is rectified by a rectifier circuit 2, then smoothed by a smoothing capacitor C1, and a transistor Tr1 as a switching element of a chopper circuit. Is applied to

When the control signal S1 is supplied from the controller 3 to the base B of the transistor Tr1, the transistor Tr1
Tr1 operates on and off, and a chopper voltage is obtained at the output of the transistor Tr1. Thereafter, the chopper voltage is smoothed by the smoothing coil L1 and supplied to the middle point of the primary winding L2 of the transformer 4.

One end of the primary winding L2 is connected to a transistor Tr2 as a switching element of the inverter circuit, and the other end is connected to the transistor Tr3. When the control signals S2 and S3 are supplied from the controller 3 to the bases of the transistors Tr2 and Tr3, the DC voltage from the smoothing coil L1 is converted to an AC voltage.

Thereafter, the AC voltage is boosted by the transformer 4 and the AC voltage obtained in the secondary windings L3, L4 is converted into DC voltage by the rectifier circuits 5a, 5b, respectively, and the DC voltage is supplied to the X-ray tube 6 as an X-ray source. High voltage is applied.

Thus, during the period when the transistor Tr1 is operated by the control signal S1, X-rays are emitted from the X-ray tube 6 to the subject (not shown).

Also, in this conventional device, when the voltage supply is stopped, the coil L1
In order to prevent device damage due to abnormal voltage generated by the current stored in the controller 3, the controller 3 first stops the control signal S1 to the transistor Tr1 when stopping the X-ray exposure.
Is turned off to shut off the transistor Tr1. Thereafter, after a lapse of a predetermined time, the control signals S2 and S3 to the transistors Tr2 and Tr3 are turned off, and the transistors Tr2 and Tr3 are stopped.

As a result, the current accumulated in the smoothing coil L1 when the transistor Tr1 is turned off is output to the transformer 4 via the transistors Tr2 and Tr3, and the occurrence of an abnormal voltage can be prevented.

(Problems to be Solved by the Invention) In such a conventional apparatus, when the power supply is regularly shut down by the operator's intention, it is possible to operate safely while preventing the occurrence of abnormal voltage. However, when the drive power supply of the controller 3 itself is cut off, for example, during a stop or an emergency, predetermined control cannot be performed, and the transistors Tr1, Tr2, and Tr3 are cut off at the same time.

For this reason, the current stored in the smoothing coil L1 at the time of cutoff has no place to go, and an abnormally high voltage is generated, and this abnormal voltage exceeds the maximum rating of the transistor Tr1. As a result, there was a problem that Tr1 was damaged.

The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide an electric power supply capable of preventing occurrence of abnormal voltage even during a power failure or emergency and protecting a chopper circuit. It is to provide a device.

[Means for Solving the Problems] To achieve the above object, the present invention rectifies a voltage from an AC power supply, smoothes the rectified output after pulse width modulation with a chopper circuit, and In a power supply device for converting a smoothed voltage into an AC voltage by an inverter circuit, amplifying the AC voltage, exchanging the DC voltage, and outputting the DC voltage to a load, the chopper circuit and the inverter circuit are connected to each other when a drive power supply of the inverter circuit is cut off. And chopper control means for controlling to turn off the switching element of the chopper circuit.

Further, the switching element is a transistor,
The inverter control means is a transistor drive circuit having a positive power supply and a negative power supply that can be selectively supplied to the transistor, and is characterized in that when the cutoff of the drive power supply is detected, the negative power supply is turned off first. is there.

Further, the switching element is a transistor,
The chopper control means is a transistor drive circuit having a positive power supply and a negative power supply that can be selectively supplied to the transistor, and is characterized in that when the cutoff of the drive power supply is detected, the positive power supply is turned off first. is there.

(Operation) With the configuration described above, the negative power supply is turned off before the positive power supply in the inverter control means when the drive power supply is cut off. Therefore, the transistor operated by the inverter control means is turned on when the power is turned off.

In the chopper control means, the plus power supply is turned off before the minus power supply. Therefore, the transistor operated by the chopper control means is turned off when the power is turned off.

As a result, the current accumulated in the smoothing coil provided on the output side of the inverter circuit is consumed via the transistor of the inverter circuit. Therefore, no abnormal voltage is generated when the drive power of the chopper circuit and the inverter circuit is cut off.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a circuit configuration of the apparatus of the embodiment, and a rectifier circuit 2 shown in FIG. 1 is configured with a diode as a bridge circuit and performs full-wave rectification of AC from an AC power supply 1.

The smoothing capacitor C1 smoothes the rectified output from the rectifier circuit 2 and supplies it to the transistor Tr1.

The transistor Tr1 operates as a switching element of the chopper circuit. When a control signal is given to the base B of the transistor Tr1 from a power supply circuit described later, the transistor Tr1 is turned on or off at a frequency sufficiently higher than the frequency of the AC power supply 1. Then, the smoothed voltage output is subjected to pulse width modulation and output to the smoothing coil L1.

The smoothing coil L1 smoothes the output voltage from the transistor Tr1 and outputs it to the middle point of the primary winding coil L2 of the transformer 4. One end of this coil L2 is a transistor
Tr2 and the other end are connected to a transistor Tr3, respectively.

The transistors Tr2 and Tr3 operate as switching elements of the inverter circuit, and convert a DC voltage from the smoothing coil L1 into an AC voltage according to a control signal from a power supply circuit described later.

The rectifier circuit 5 (5a, 5b) has the same configuration as the rectifier circuit 2 described above, and rectifies an AC voltage generated in the secondary windings L3, L4 of the transformer 4 and applies the rectified voltage to both ends of the X-ray tube 6. It is.

FIG. 2 shows a power supply circuit for supplying a control signal to a transistor Tr1, which is a switching element of the chopper circuit.

The power supply circuit shown in FIG.
, A positive power supply section 9, a negative power supply section 10, and an operational amplifier 11, which alternately output a positive voltage and a negative voltage in synchronization with a predetermined control signal.

The positive power supply unit 9 obtains a positive DC voltage from an AC voltage generated on the secondary side of the transformer 8, and includes a fuse F1, a rectifier circuit 13, and a smoothing capacitor C3. Then, the generated positive DC voltage is supplied to a positive input terminal of the operational amplifier 11 via a contact K1 operated by an output of a relay Ry1 described later. In addition, a stabilizing resistor Rx is connected to this positive input terminal, which prevents the operation of the operational amplifier 11 from becoming unstable when the positive input terminal is opened when the contact K1 is opened. Work as you do.

The negative power supply unit 10 obtains a negative DC voltage from the AC voltage generated on the secondary side of the transformer 8, and includes a news F2, a rectifier circuit 14, and a smoothing capacitor C4. The voltage is supplied to the negative input terminal of the operational amplifier 11. Further, a relay Ry1 is provided on the AC side of the minus power supply unit 10, and when the voltage supply from the AC power supply 7 is cut off, the relay Ry1 operates so as to open the contact K1 immediately.

When the control signal is input, the operational amplifier 11 alternately outputs a plus voltage and a minus voltage in synchronization with the control signal. The output voltage of the operational amplifier 11 is
T1, and through the base limiting resistor R _B, it is supplied to the base of the transistor Tr1 as a control signal.

FIG. 3 shows a power supply circuit for supplying a control signal to a transistor Tr2 which is a switching element of the inverter circuit.

The power supply circuit shown in FIG. 2 has substantially the same configuration as the power supply circuit shown in FIG. 2, except that the contact K2 of the relay Ry2 attached to the AC side of the negative power supply 10 is
Is different on the DC side. Further, the stabilizing resistor Rx is connected to the negative input terminal of the operational amplifier 11. Control signal output from the operational amplifier 11 is the terminal T2, and via the base limiting resistor R _B, is supplied to the base of the transistor Tr2.

The control signal supplied to the transistor Tr3 is obtained by inverting the polarity of the control signal supplied to the transistor Tr2. The power supply circuit has the same configuration as that shown in FIG. I do.

 Next, the operation of the present embodiment will be described.

Now, when a predetermined control signal is given to each of the transistors Tr1, Tr2, and Tr3 from each power supply circuit and the voltage is constantly supplied to the X-ray tube 6, the AC power supply 7 of the power supply circuit is cut off for some reason. Then, in the chopper power supply circuit shown in FIG. 2, the relay Ry1 detects this and stops the relay output. As a result, the contact K is immediately opened,
As for the voltage supplied to the operational amplifier 11, the plus voltage stops earlier than the minus voltage.

For this reason, the control signal supplied to the transistor Tr1 stops when this signal is a negative voltage,
The transistor Tr1 operates to cut off the supply voltage from the smoothing capacitor C1.

On the other hand, in the power supply circuit of the inverter shown in FIG. 3, when the AC power supply 7 is cut off, the relay Ry2 detects this, and
Stop the relay output. As a result, the contact K2 is immediately opened, so that the negative voltage of the voltage supplied to the operational amplifier 11 stops earlier than the positive voltage.

Therefore, the control signal supplied to the transistor Tr2 stops when the signal is a positive voltage, and the transistor Tr2 operates to make the supply voltage from the smoothing coil L1 conductive. Similarly, the transistor Tr3 operates to make the supply voltage conductive.

Therefore, the current accumulated in the smoothing coil L1 is supplied to the load via the transistors Tr2 and Tr3.

As described above, in this embodiment, even when the AC power supply 7 is cut off at the time of a power failure or emergency,
Since Tr1 becomes non-conductive and the transistors Tr2 and Tr3 become conductive, the current accumulated in the smoothing coil L1 can be reliably consumed. Therefore, generation of an abnormal voltage can be prevented, and the transistor Tr1 is not damaged.

[Effects of the Invention] As described above, in the present invention, when the drive power of the chopper circuit and the inverter circuit is cut off, the switching element of the inverter circuit conducts and the switching element of the chopper circuit becomes non-conducting. The current accumulated in the coil provided on the output side of the chopper circuit can be consumed on the load side.

For this reason, the occurrence of abnormal voltage can be prevented, and the problem of damaging the switching element of the chopper circuit is eliminated.

[Brief description of the drawings]

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a power supply circuit of a shopper, FIG. 3 is a block diagram showing a power supply circuit of an inverter, and FIG. FIG. 9 ... Positive power supply unit, 10 ... Negative power supply unit 11 ... Operational amplifier Tr1, Tr2, Tr3 ... Transistor L1 ... Smoothing coil Ry1, Ry2 ... Relay K1, K2 ... Contact

Claims (3)

(57) [Claims] A rectified voltage from an AC power supply, a pulse width modulation of the rectified output by a chopper circuit, and smoothing. The smoothed voltage is converted to an AC voltage by an inverter circuit, amplified, and then exchanged for DC. An inverter control means for controlling a switching element of the inverter circuit to be conductive when a driving power supply of the chopper circuit and the inverter circuit is cut off, and a switching element of the chopper circuit. And chopper control means for controlling so as to shut off the power supply. 2. The switching element is a transistor, and the inverter control means is a transistor drive circuit having a positive power supply and a negative power supply that can be selectively supplied to the transistor, wherein the cutoff of the drive power supply is detected. The power supply device according to claim 1, wherein the negative power supply is turned off first. 3. The switching element is a transistor, and the chopper control means is a transistor driving circuit having a positive power supply and a negative power supply that can be selectively supplied to the transistor, wherein the cutoff of the driving power is detected. 2. The power supply device according to claim 1, wherein the plus power supply is turned off first.