JPS6030965B2 - DC stabilized power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC stabilized power source used, for example, as a power source for heating a filament of an X-ray tube.

A switching type DC stabilized power supply conventionally used for heating an X-ray tube is constructed as shown in FIG.

That is, in the figure, 1 is a bridge circuit that full-wave rectifies the AC power supply E, 2 is a chopping transistor that chops the DC output obtained by this bridge circuit 1, and 3
4 is a smoothing circuit consisting of a diode D, a coil L, and a capacitor C that smooths the intermittent energy contained in the DC output after the chopping; 4 is a voltage dividing circuit that divides the voltage of the DC output smoothed by the smoothing circuit 3; 5 is a reference power supply, 6 is an error amplifier that compares the output of the voltage dividing circuit 4 with reference to the voltage of this reference power supply 5 and generates a difference voltage, 7 is a switch for connecting and disconnecting the reference power supply 5, and 8 is a predetermined frequency. 9 is a pulse width modulator that generates a signal with a pulse width corresponding to the output of the error amplifier 6 using this AC signal as a reference; 10 is driven by the output pulse of this pulse width modulator 9; This is a drive circuit that generates a drive signal corresponding to the pulse width and applies it to the chopping transistor 2 to operate it, and the above is the DC stabilized power supply section. Reference numeral 11 denotes an inverter transformer whose primary intermediate tap is provided with a DC output smoothed by the smoothing circuit 3, and 12 and 13 are switching devices connected to the ends of the primary winding of the inverter transformer 11, respectively. It is a transistor for

Further, 14 is an X-ray tube, and the secondary side output of the inverter transformer 11 is supplied to the cathode side of the X-ray tube to heat it. Next, to explain the operation, first, the transistors 12, 1
Pulses of mutually opposite phases are applied to the bases of the inverter transformer 11, and when a DC voltage is applied to the intermediate tap on the primary side of the inverter transformer 11, the inverter operates.

Next, when the READY switch of the X-ray control device (not shown) is pressed, the switch 7 is turned on and the reference power supply 5 is applied to the error amplifier 6, and an output corresponding to the potential of the reference power supply 5 is output from the error amplifier 6. A pulse width modulator 9 is provided. Since the reference pulse signal is applied to the pulse width modulator 9 from the oscillator 8, this pulse signal is pulse width modulated by the output of the error amplifier 6, and a signal with a pulse width corresponding to the output of the error amplifier 6 is sent to the drive circuit 101. I'll give you this. Then, a drive signal is generated for a time corresponding to the pulse width of the drive circuit 1 and is applied to the chopping transistor 2. As a result, the chopping transistor 2 operates and chops the DC output of the bridge circuit 1.
After this chopped DC output is smoothed by a smoothing circuit 3, it is input to the intermediate tap of an inverter transformer 11, and its potential is input to an error amplifier 6 through a voltage dividing circuit 4. Therefore, from now on, the chopping transistor 2 is operated with the pulse width of the difference between the potential from the voltage dividing circuit 4 and the potential of the reference power supply 5, and the DC stabilized power supply is controlled so that the potential is set by the reference power supply 5. It will be operated. The inverter transformer 11 to which the smoothed DC output is applied has its primary winding switched by alternately switched transistors 12 and 13, and the secondary output generated thereby is sent to the X-ray tube 14. The filament of the x-ray tube 14 is heated. At this time, depending on the residual magnetism state of the inverter transformer 11 and the timing at which the switch 7 closes, the chopping transistor 2, the smoothing circuit 3, and the inverter transformer 11
In many cases, a large inrush current will flow through the circuit, including the primary side of the device.

This inrush current may cause deterioration or damage to the chopping transistor 2 and the switching transistors 12 and 13. To prevent this, it is necessary to provide sufficient margin for such elements or to close the switch 7. It is necessary to take measures such as inserting a circuit that prevents the negative phase input of the error amplifier 6 from rising slowly when the error amplifier 6 is turned on. This causes the circuit configuration to become more complicated and the uncertainty of the device to increase, and moreover, there is a possibility that the circuit configuration becomes uneconomical. The present invention has been made in view of the above circumstances, and is a switching regulator type in which a bidirectional three-terminal thyristor (TRIAC) is connected as a chopping element to the negative terminal of the output side of a rectifier circuit, and a non-polar capacitor and a DC A charging circuit consisting of a power source and a control element for current control, such as a transistor, is provided to apply the charging potential of the capacitor to the triac to cause a breakover to ignite the triac, and to charge the capacitor with reverse polarity. The charging circuit is controlled by the correction signal of the circuit which attempts to extinguish the arc with a potential and also compares the smoothed output of the rectifier circuit with a reference voltage and outputs the difference signal as a correction signal so that the smoothed output becomes the set potential. By controlling transistors, constant voltage control and inrush current resistant structure are achieved, and direct current stabilization eliminates problems such as complication of circuits that had arisen to protect switching elements due to inrush current. The purpose is to provide power.

An embodiment of the present invention will be described below with reference to FIG.

In the figure, B is an AC power source, 21 is a rectifier circuit for full-wave rectification of this AC power source E, 22 is a smoothing capacitor connected between the output terminals of this rectifier circuit 21, and 23 is the positive output of this rectifier circuit 21. A smoothing choke transformer 24 is connected in series to the terminal, and 24 is a smoothing capacitor provided on the output side of this choke transformer 23, and the other devices are grounded. 25 is a bleeder resistor whose one end is connected to the input side of the choke transformer 23, that is, the connection side of the rectifier circuit 21, and the other end is grounded; 26 is a bleeder resistor that divides the rectified output after smoothing by the choke transformer 23 and the smoothing capacitor 24; 27 is a reference power source; 28 is an error amplifier that compares the divided voltage output of the voltage dividing resistor 26 with the potential of the reference power source 27 as a reference, and outputs the difference voltage as a correction signal; 29 is the reference power source; A switch for opening and closing the power supply 27, 30
is a non-polar capacitor which has one end grounded and the other end connected to the positive side of the DC power supply 31, and 32 has its emitter side grounded and is connected to the negative side of the DC power supply 31 via the collector side resistor r, and the base. is a PN for current control to which a correction signal output from the error amplifier 28 is applied.
These are P-type transistors, and 30, 31, and 32 form a current control type charging circuit.

Reference numeral 33 designates a tri-hook having one end connected to the negative output terminal of the rectifier circuit 21 and the other end connected to the DC power supply 31 connection side of the capacitor 30. It is used by firing at breakover.

Next, the operation of this apparatus having the above configuration will be explained.

When the switch 29 is turned on, the error amplifier 28 outputs a difference signal between the reference power supply 27 and the divided voltage of the voltage dividing resistor 26 as a correction signal. This correction signal is applied to the base of the PNP type transistor 32, and the transistor 32 is turned on.
2, its internal resistance increases or decreases. Due to this effect, the current flowing into the capacitor 301 from the DC power supply 31 is controlled, so that the charging time of the capacitor 30 to be charged is controlled according to the correction signal. On the other hand, Triack 33
Since the sum of the terminal voltages of the smoothing capacitor 32 and the non-polar capacitor 30 is added to
The triac 33 is fired when the voltage exceeds the breakover potential at the gate zero potential.

As a result of ignition, the non-polar capacitor 301 is connected to the DC power supply 31.
Since a voltage is applied to the reverse conductivity during charging, this capacitor 30 is charged with an electric charge with a polarity opposite to that at the time of breakover of the triac 33, and the triac 33 is extinguished at the time of being charged up. And the speed is far when the load is heavy, and slow when the load is light.
When the triac 33 is extinguished, the non-polar capacitor 30 is charged again by the DC power supply 31, and the above-described operation is repeated. The principle by which the output voltage can be stabilized by this device is that when the rectified output after smoothing is smaller than the potential of the reference power supply 27, the correction signal level becomes large, so the charging time of the capacitor 30 by the DC power supply 31 becomes longer, and the triac 33 reaches the breakover potential quickly.

Therefore, the switching operation of the triac 33 becomes frequent and the rectified output potential after smoothing is increased. Conversely, when the rectified output potential after smoothing is larger than the reference potential, the correction signal level becomes low, and the capacitor 30 by the DC power supply 31
Since charging is slower, the time required to reach the breakover potential is delayed, and the switching operation of the triac 33 is therefore less frequent. Note that the switching repetition period differs depending on the load. That is, the on/off duty of the triac 33 changes, and the rectified output potential is maintained at the set value. The bleeder resistor 25 is provided to ensure that the current flowing through the triac 33 exceeds the latching current when the triac 33 is ignited. Without this, due to the choke transformer 23, it would be impossible to obtain a load current greater than the latching current at the same time as the ignition, and the ignition would be extinguished again, making it difficult to perform normal operation. As mentioned above, since chopping is performed by a triac, DC stabilization has the characteristics of being resistant to deterioration and damage due to inrush current, eliminating the need for a flywheel diode, and simplifying the circuit. power source.

Note that the present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications within the scope of the gist thereof. For example, the present invention may be implemented by using an avalanche SCR instead of a triax It is possible to implement

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 21... Rectifier circuit, 22, 24... Smoothing capacitor, 23... Choke transformer, 25... Frieder resistor, 26... Voltage dividing resistor, 27... Standard Power supply, 28...Error amplifier, 30...
・Non-polar capacitor, 31...DC power supply, 3
2...Transistor, 33...Triack. Figure 1 Figure 2

Claims (1)

[Claims] 1. A chopping element using a triac or avalanche SCR is connected in series to the output terminal of the full-wave rectifier circuit, and a charging circuit consisting of a non-polar capacitor, a DC power source, and a control element for controlling the current is provided, and the non-polar capacitor is connected in series to the output terminal of the full-wave rectifier circuit. The capacitor is connected in series to the chopping element, and the potential of this capacitor is applied to the chopping element.The smoothed output potential of the full-wave rectifier circuit is compared with the reference voltage setting potential, and correction is made according to the difference. A DC stabilized power supply comprising a circuit that generates a signal and controls the control element by applying it to the control element.