JPH0254031B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a high voltage generation circuit using a transistor inverter suitable for generating high voltage for charging, transferring, and eliminating static electricity in an electronic copying machine or for an electrostatic precipitator. In particular, it is intended to make the high voltage output constant voltage and current.

(b) Prior Art Figure 1 shows a conventional inverter type high voltage generation circuit with constant voltage output. In this figure, 1 is the primary coil of the transformer T of the oscillation output circuit, 2 is the secondary output coil, 3 is the feedback coil, 4 is the starting resistor, 5 is the base resistor, 6 is the DC blocking capacitor, and 7 is for oscillation. A base bias diode for the transistor 8; 9 a bias control diode for the oscillation transistor 8; 10 a capacitor for smoothing the AC bias signal taken out from the bias control diode 9;
11 is an oscillation control transistor, 12 is a Zener diode for reference voltage, 13 is a variable resistor for adjusting voltage division of the load voltage detection circuit, 14 is a smoothing capacitor,
15 is a load voltage circuit rectifier, 16 and 19 are high voltage smoothing capacitors, 17 and 18 are high voltage rectifiers, 20
is the discharge resistance.

The operation of the conventional circuit shown in FIG. 1 is as follows.
When the base current flows through the starting resistor 4 and the bias diode 7, the oscillation transistor 8 becomes 1
Next, a collector current is applied to coil 1. Therefore, the voltage induced in the feedback coil 3 causes the base current to increase through the base resistor 5 and the DC blocking capacitor 6, and the collector current flowing through the primary coil 1 is saturated. Then, the induced voltage in the feedback coil 3 disappears, and the transistor 8 is turned off. Next, the induced voltage in the feedback coil 3 due to the ringing of the primary coil 1 causes a base current to flow, thereby turning on the transistor 8, and a collector current flows through the primary coil 1. By the switching operation of the oscillation transistor 8 as described above, oscillation at approximately 35 KHz continues, and a high AC voltage is induced in the secondary output coil 2.

This alternating current voltage is
It is rectified and smoothed by 7, 18, and 19, and supplies high DC voltage to the load. The discharge resistor 20 is connected to the high voltage capacitor 1 when the power is turned off under no load.
This is a resistor for discharging the voltage accumulated in 6 and 19. On the other hand, the voltage induced in the feedback coil 3 is supplied to a load voltage detection circuit composed of a rectifier 15, a smoothing capacitor 14, and a variable resistor 13 for adjusting voltage division. The voltage is then compared with the reference voltage of the Zener diode 12, and a control signal is applied to the base of the control transistor 11.

Now, when the load becomes lighter and the high voltage output voltage increases, the voltage of the feedback coil 3 also increases, and the rectifier 15
The voltage rectified and smoothed by the smoothing capacitor 14 becomes higher. Therefore, the voltage of the variable resistor 13 becomes higher than the reference of the Zener diode 12, and the base current of the control transistor 11 increases. Therefore, the collector current of the control transistor 11 increases, the impedance between the collector and emitter decreases, the bias of the oscillation transistor 8 decreases, and the base current decreases. Then, since the collector current of the oscillation transistor 8 decreases, the current in the primary coil 1 decreases, and the current in the secondary coil 2 decreases.
voltage decreases. In this way, the output voltage is controlled by operating up to a constant value equal to the reference voltage of the Zener diode 12.

As described above, the conventional circuit performs a constant voltage ratio of the output voltage, and FIG. 2 shows this output characteristic. The horizontal axis is the output current, and the vertical axis is the output current. As you can see from this diagram, in conventional circuits, when the load becomes heavy, the power consumption of the load increases significantly.
There is a risk of heat generation and fire. Also, when a certain limit is exceeded, the output voltage becomes unstable, and the voltage supplied to the load,
Current fluctuates greatly.

FIG. 3 is a circuit diagram showing another conventional example, and the circuit shown in this figure is an inverter type high voltage generation circuit having constant voltage and constant current characteristics. In this figure, 48 is the primary coil of the transformer of the oscillation circuit, 49
is a feedback coil, 50 is a load voltage detection coil, 51
is a high voltage secondary coil. 52 is an oscillation transistor, 53 is a starting resistor, 54 and 56 are DC blocking capacitors, 57 is a bridge rectifier, 58 is a protective rectifier for the oscillation transistor 52, 59 is a load voltage detection rectifier, 60 is a smoothing capacitor, and 61 is a load voltage This is a variable resistor for adjusting the voltage division of the detection circuit. 64 is a constant voltage Zener diode, 62 is a power supply resistor to the Zener diode 64, 63 is a comparison transistor, 67 is a variable resistor for adjusting voltage division for detecting load current, 68 is a smoothing capacitor, and 65 and 66 are reverse potential blocking rectifiers. It is. 69 is a high voltage rectifier, 70 is a high voltage smoothing capacitor, 71 is a discharge resistor, and 55 is a base resistor of the oscillation transistor 52.

To explain the operation of this circuit, first, the oscillation of the oscillation transistor 52 causes the secondary coil 5 to
A high voltage is induced in 1 and applied to the load.
Further, a voltage is also induced in the load voltage detection coil 50, and a detected voltage is output to the variable resistor 61. This voltage passes through diode 65 and enters the base of comparison transistor 63. The current flowing through the load flows through the variable resistor 67 and returns to the high voltage secondary coil 51.
This resistor performs current-to-voltage conversion, and this detected voltage passes through a diode 66 and enters the base of a comparison transistor 63. The voltage applied to the base of the comparison transistor 63 is compared with the Zener voltage of the Zener diode 64, and the comparison transistor 63 is connected to the bridge rectifier 57.
control. By controlling the bridge rectifier 57, it is possible to control the oscillation force of the oscillation transistor 52, and the output voltage and current can be controlled, so that a constant voltage ratio and constant current can be achieved.

However, a drawback of this conventional example is that the transformer requires a large number of windings, making it difficult to downsize the transformer T. Furthermore, since the output current detection section captures a portion of the output current into the base of the control transistor 63, when the output voltage is small, the constant current performance deteriorates and the control may not work.

For example, in this circuit, if the output current is about 200 μA, the control will hardly work, and there will be no constant current property of 200 μA.

(c) Purpose of the Invention The present invention has been made in view of the drawbacks of the above-mentioned circuit, and is intended to prevent abnormal overheating due to an increase in load, as well as to reduce the size of the transformer and stabilize the small output current. be.

(d) Structure of the Invention The present invention provides a feedback coil between the base and emitter of an oscillation transistor connected to a DC power source via the primary winding of an oscillation transformer whose output is taken out from the secondary winding. A base return circuit is formed, and a diode and a capacitor are provided to rectify and smooth the signal of this feedback circuit so that it becomes a negative voltage with respect to the ground, and this potential is connected to a feedback voltage detection circuit and This high voltage generation circuit compares the reference voltage of the Zener diode through comparison transistors provided in each of the load current detection circuits, and directly controls the regeneration force of the base circuit of the oscillation transistor using the amplified detection signal.

(e) Examples FIG. 4 is a circuit diagram showing an example of the present invention.

In this figure, 21 is the primary coil of the oscillation circuit converter T, 22 is the feedback coil, 23 is the output secondary coil, 24 is the oscillation transistor, 25 is the starting resistor,
26 is a DC blocking capacitor, and 27 is a base resistance of the oscillation transistor 24. 28 is a protection rectifier for the oscillation transistor 24, 29 is a diode for the feedback voltage (load voltage) detection circuit, 30 is a smoothing capacitor, 31 is a bias control diode for the oscillation transistor 24, and 32 is taken out from the bias control diode 31. A capacitor 33 smoothes the AC bias signal, and a comparison transistor 33 is used to control oscillation. 34 is a Zener diode for reference voltage, 35 is a variable resistor for adjusting the voltage division of the load voltage detection circuit, 36 is a bias control diode for the oscillation transistor 24, and 37 is for smoothing the AC bias signal taken out from the bias control diode 36. A capacitor, 38 is a comparison transistor for oscillation control, 39 is a Zener diode for reference voltage, 40 is a variable resistor for adjusting the voltage division of the load current detection circuit, 41 is a smoothing capacitor, and 42 is a diode for preventing backflow of the collector current of the comparison transistor 38. be. And 43 and 46 are high voltage smoothing capacitors,
44 and 45 are high voltage rectifier diodes, and 47 is a discharge resistor.

When the power is turned on, the starting resistor 25 causes the base current of the oscillation transistor 24 to flow.
Therefore, the collector current flows through the primary coil 21, and the feedback coil 2 coupled to the primary coil 21
DC blocking capacitor 2 due to the voltage induced in 2
6. Oscillation transistor 24 via base resistor 27
The base current of increases. Therefore, the collector current further increases, and the oscillation transistor 24 is turned on. This increase in the collector current is saturated when the base current reaches its peak point, so that the magnetic flux of the transformer T no longer changes, and the induced voltage in the feedback coil 22 decreases. Therefore, the base current decreases, the collector current also decreases rapidly, and the oscillation transistor 24 is turned off. Such an oscillation transistor 2
Due to the switching action of 4, the high frequency high voltage output induced to the output secondary coil 23 via the transformer T is rectified and smoothed by high voltage diodes 44, 45 and smoothing capacitors 43, 46, and high voltage DC output is supplied to the load. That will happen.

Next, constant current and constant voltage control, which is the main point of the present invention, will be explained. Fluctuations in the load voltage are detected using a feedback coil 22 to detect the load voltage, and rectified to a negative voltage with respect to ground by a diode 29.
The voltage is smoothed by a smoothing capacitor 30, adjusted to a desired value by a variable resistor 35, and supplied to the base of a comparison transistor 33 through a reference voltage diode 34. On the other hand, the load current is converted into a voltage by a variable resistor 40, and this potential is compared with the base bias potential of the oscillation transistor 24, which has been rectified and smoothed by a diode 36 and a smoothing capacitor 37. The amplified detection signals compared by the comparison transistors 33 and 38 are applied to the base of the oscillation transistor 24, and the base current of the oscillation transistor 24 is directly controlled in parallel by this voltage signal and current signal to provide constant current and constant current of the load circuit. The voltage characteristics will be obtained. Note that the diode 42 prevents malfunctions due to current flowing from the collector to the base of the comparison transistor 38 to the diode 39 when the potential at the anode of the diode 39 becomes lower than the negative potential rectified by the feedback coil 22. It is designed to prevent.

Now, let us consider a case where the load voltage decreases. At this time, the voltage induced in the feedback coil 22 decreases, the negative potential DC signal voltage rectified and smoothed by the diode 29 and the capacitor 30 decreases, and the potential on the anode side of the diode 29 increases. This increase in potential is detected by the variable resistor 35, and the Zener diode 3
4 will be compared. Due to the potential increase, the Zener current of the Zener diode 34 decreases, and the base current of the comparison transistor 33 also decreases. Therefore, the collector current of the comparison transistor 33 also decreases,
The bias of the oscillation transistor 24 increases. Therefore, the base current of the oscillation transistor 24 increases, the voltage of the secondary coil 23 increases, and the load voltage also increases. By such an operation, the load voltage is controlled to increase until it is balanced with the reference voltage of the Zener diode 34. Next time the load voltage increases,
In contrast to the above effect, control is performed to lower the base bias of the oscillation transistor 24, reduce the load voltage, and maintain desired constant voltage characteristics.

Next, constant current control of this circuit will be explained.
Detection of the load current is performed using the potential of a voltage dividing variable resistor 40 for adjusting the detection circuit connected in series with the load circuit;
A Zener diode 39 compares the base bias of the oscillation transistor 24 with the potential smoothed and rectified by a diode 36 and a capacitor 37 . The comparison transistor 38 directly controls the base bias current of the oscillation transistor 24.

FIG. 5 is an output characteristic diagram in this example,
The horizontal axis is the high voltage output current, and the vertical axis is the high voltage output voltage. As is clear from this figure, even if the output voltage increases, the output current remains constant over a wide range.

In addition, in this embodiment, the starting resistance 25 is
560KΩ, base resistance 27 is 1KΩ, variable resistance 35
The setting resistance is 5KΩ, and the setting resistance of variable resistor 40.
50KΩ, and the discharge resistance 47 is 150MΩ.
Also, the DC blocking capacitor 26 is 0.01 μF, the smoothing capacitor 30 is 3.3 μF, and the smoothing capacitor 32 is
3.3μF, smoothing capacitor 37 is 0.001μF, smoothing capacitor 41 is 0.022μF, smoothing capacitor 43 is
330PF and the high voltage smoothing capacitor 46 is 330PF.

(F) Effects of the Invention In the present invention, since the high voltage output is made constant current and voltage by directly controlling the base circuit of the oscillation transistor, abnormal heating during overload can be prevented. In addition, since the output voltage detection section rectifies the feedback coil voltage to a negative potential and uses this potential as the reference potential of the control section to control the oscillation transistor, the transformer can be miniaturized with only three windings. can be achieved.

[Brief explanation of the drawing]

Figures 1 to 3 show conventional examples, Figure 1 is a circuit diagram showing one conventional example, Figure 2 is an output characteristic diagram of the circuit shown in Figure 1, and Figure 3 shows another conventional example. It is a circuit diagram. 4 and 5 show an embodiment of the present invention, where FIG. 4 is a circuit diagram and FIG. 5 is an output characteristic diagram. T...Transformer, 21...Primary coil, 22...
Feedback coil, 23... Secondary coil, 24... Oscillation transistor, 25... Starting resistor, 29... Diode, 30... Capacitor, 33, 38... Comparison transistor, 34, 39... Zener diode, 35, 40...variable resistance.

Claims (1)

[Claims] 1. An oscillation transistor 24 connected to a DC power supply via the primary winding 21 of an oscillation transformer T whose output is taken out from a secondary winding 23, and between the base and emitter of this oscillation transistor 24. A base feedback circuit is formed and includes a feedback coil 22, and a diode 29 and a capacitor 3 that rectify and smooth the signal of this base feedback circuit to output a negative voltage.
0, a first comparison transistor 33 that compares this negative voltage with a reference voltage and controls the base bias of the oscillation transistor 24 based on the comparison output, and a load current detection resistor 40 connected in series to the load circuit. and a PNP whose base electrode is connected to the resistor 40 via the Zener diode 39, whose collector electrode is supplied with the negative voltage, and whose emitter electrode controls the base bias of the oscillation transistor 24.
A high voltage generation circuit comprising: a second comparison transistor 38 of the type;