JPH08242588A - Ac high voltage generating circuit - Google Patents

Abstract

PURPOSE: To provide an AC high voltage generating circuit which performs protecting (stopping) operation only during the short-circuit of load and performs no protecting operation during no-load and outputs a high voltage by oscillating normally. CONSTITUTION: This circuit comprises a constant voltage control circuit 1, an oscillating circuit 2 receiving a supply of the constant voltage from said control circuit 1 and having a primary winding for a transformer T, a high voltage circuit 3 boosting the oscillating output by a secondary winding coupling with the primary winding of said oscillating circuit 2, a detecting circuit 4 connected in series to this high voltage circuit 3 and a load 5. This AC high voltage generating circuit also contains an inverting circuit 6 connected to the output side of this detecting circuit 4, a DA converting circuit 7 for converting the size of the output pulse width of this inverting circuit 6 to the size of analog amplitude voltage, a comparing and detecting circuit 8 for judging the output of this DA converting circuit 7, and an ON.OFF circuit 9 for controlling the control circuit 1 by means of the output from the comparing and detecting circuit 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC high voltage generating circuit used in an electrostatic copying machine or the like.

[0002]

2. Description of the Related Art A conventional high voltage generating circuit is shown in FIG. In the figure, reference numeral 11 denotes a constant voltage control circuit, which is composed of current amplification transistors Q ₁₁ and Q ₁₂ in Darlington connection and an operational amplifier 0P ₁₁ for performing feedback voltage control.
Reference numeral 12 is an oscillation circuit of a separately excited flip-flop, which is composed of transistors Q ₁₃ and Q ₁₄ connected between both ends of the primary winding of the transformer T, and is supplied with a constant voltage from the control circuit 11. Reference numeral 13 is a high-voltage circuit, and a high voltage obtained by boosting the oscillation output of the oscillation circuit 12 by the secondary winding of the transformer T is applied to the load 1
Supply to 4. A detection circuit 15 is composed of a resistor R and is connected to the high-voltage circuit 13 in series with the load 14. Then, the magnitude of the current flowing through the load 14 is output as the magnitude of the voltage drop. Reference numeral 16 denotes a comparison detection circuit, which rectifies the AC output of the detection circuit 15 with a diode D ₁₁ and a capacitor C ₁₁ , and judges the rectified DC voltage with the threshold value of the Zener diode D ₁₂ , and makes the transistor Q ₁₅ conductive or non-conductive. Then, the control circuit 11 is controlled via the ON / OFF circuit 17.

Next, the mode of operation of this conventional high voltage generating circuit will be described. 1) During normal operation of load 14 Connection point 1 of resistance R of detection circuit 15 with comparison detection circuit 16
Detection voltage 5a is high, the rectified output voltage of the detection voltage becomes equal to or higher than the threshold voltage of the Zener diode D _12, the transistor Q ₁₅ conducts and the transistor Q ₁₆ of the ON · OFF circuit 17 becomes nonconductive. Therefore, the control circuit 1
The first transistor Q ₁₂ and Q ₁₁ are turned on, and the normal oscillation operation is continued.

2) When the load 14 is short-circuited: The connection point 1 between the resistance R of the detection circuit 15 and the comparison detection circuit 16
The detection voltage of 5a is low, the rectified output voltage of this detection voltage becomes lower than the threshold voltage of the Zener diode D ₁₂ , the transistor Q ₁₅ becomes non-conductive, and the ON / OFF circuit 17
Transistor Q _{16 of} is conductive. Therefore, the transistors Q ₁₂ and Q ₁₁ of the control circuit 11 become non-conductive, the control circuit 11 becomes non-conductive, and the oscillation of the transmission circuit 12 is stopped.

3) No load of load 14 Connection point 1 of resistance R of detection circuit 15 and comparison detection circuit 16
The detection voltage of 5a is not generated, the circuit operation is the same as when the load 14 is short-circuited in 2) above, the transistor Q ₁₅ becomes non-conductive, the transistor Q ₁₆ becomes conductive, and the control circuit 11 becomes non-conductive. The oscillation of the transmission circuit 12 is stopped.

[0006]

In the conventional AC high voltage generating circuit described above, the control circuit 1 is operated when the load is short-circuited.
Since 1 operates to stop the oscillation of the oscillation circuit 12, there is no problem, but there is a problem that the oscillation of the oscillation circuit 12 stops even when there is no load. This is because, depending on the needs of the market, there is a case where an operation in a state close to no load (this is called a no load operation) is required.

Therefore, according to the present invention, the protection (stop) operation is performed only when the load is short-circuited, the protection operation is not performed when there is no load, and the AC high voltage that normally oscillates and outputs the high voltage as in the load is output. An object is to provide a generating circuit.

[0008]

In order to achieve the above object, the present invention provides a constant voltage control circuit and an oscillation circuit which receives a constant voltage supply from the control circuit and uses a primary winding of a transformer. , A high-voltage circuit that boosts the oscillation output by a secondary winding that is coupled to the primary winding of this oscillation circuit, a detection circuit and a load that are connected in series to this high-voltage circuit, and the output side of this detection circuit. An inverting circuit, a DA conversion circuit for converting the size of the bandwidth of the inverting circuit into a size of the analog amplitude voltage, a comparison detection circuit for determining the output of the DA conversion circuit, and the control by the output of the comparison detection circuit. It is characterized by comprising an ON / OFF circuit for controlling the circuit.

[0009]

The detection voltage of the detection circuit connected in series with the load in the high voltage circuit of the secondary winding coupled to the primary winding of the oscillator circuit has its waveform depending on the time of load, short circuit of load or no load. Be different. That is, the bandwidth is small and the amplitude is large when the load is present, the bandwidth is large and the amplitude is small when the load is short-circuited, and the bandwidth and the amplitude are zero when there is no load.

Of these, since the bandwidth becomes small when the load is applied, the output voltage of the DA conversion circuit has a small amplitude, there is no output of the comparison detection circuit, and the ON / OFF circuit does not conduct. Therefore, the control circuit The oscillator circuit continues normal oscillation without being controlled.

Since the bandwidth is large when the load is short-circuited, the output voltage of the DA conversion circuit has a large amplitude, the output of the comparison detection circuit is present, the ON / OFF circuit becomes conductive, and the control circuit is controlled. The oscillator circuit stops oscillating.

When there is no load, the amplitude and bandwidth are zero, the same operation as that under load is performed, the amplitude of the output voltage of the DA conversion circuit is small, there is no output of the comparison detection circuit, and O
Since the N-OFF circuit does not conduct, the control circuit is not controlled and the oscillation circuit continues normal oscillation.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention.
The block circuit is as follows.

A constant voltage control circuit 1, an oscillator circuit 2 which is supplied with a constant voltage from the control circuit 1 and which has a primary winding of a transformer T, and a coupling circuit which is coupled to the primary winding of the oscillation circuit 2. A high-voltage circuit 3 that boosts the oscillation output by the next winding,
The detection circuit 4 and the load 5 connected in series to the high voltage circuit 3, the inverting circuit 6 connected to the output side of the detection circuit 4, and the size of the bandwidth of the inverting circuit 6 are changed to the analog amplitude voltage. DA conversion circuit 7 for converting respectively, and this D
It comprises a comparison detection circuit 8 for judging the output of the A conversion circuit 7, and an ON / OFF circuit 9 for controlling the control circuit 1 by the output of the comparison detection circuit 8.

The internal configuration of the block circuit will be described in detail below. The control circuit 1 comprises a transistor Q ₁ and an operational amplifier OP ₁ . The collector of the transistor Q ₁ is connected to a power source (not shown), and the emitter is the next-stage oscillator circuit 2
Is connected to the midpoint of the primary winding of the transformer T. Although the operational amplifier OP ₁ is not shown in the form of connection, it receives the voltage from the tertiary winding (not shown) of the transformer T as an input and compares it with the reference voltage to feed back the high voltage output of the high voltage circuit 3. Control is applied to the base of transistor Q ₁ .

In the oscillator circuit 2, the collectors of the transistors Q ₃ and Q ₄ are connected to both ends of the primary winding of the transformer T, and the emitter of the transistor Q ₁ of the pre-stage control circuit 1 is located at the midpoint of the primary winding. It is connected. The emitters of the transistors Q ₃ and Q ₄ are commonly connected,
Connected to ground. Transistor Q ₃ ,
Q _{4 are,} are external clock voltage on their base input constitute a flip-flop oscillator circuit of another excitation.

The high-voltage circuit 3 obtains a boosted high-voltage output from the secondary winding of the transformer T, and the high-voltage side of this secondary winding serves as a high-voltage terminal 3a via a protection resistor R ₁ . .
A load 5 is connected between the high voltage terminal 3a and the ground.

The resistor R ₂ constituting the detection circuit 4 has one end connected to the low voltage side of the secondary winding of the transformer T via a capacitor C and the other end connected to the ground. Therefore, the load 5 and the resistor R ₂ are connected in series on both sides of the secondary winding of the transformer T via the ground.

The inverting circuit 6 is composed of transistors Q ₅ and Q ₆ whose emitters are grounded, and an operational amplifier OP ₂ . The output of the detection resistor R ₂ and a connection point between the capacitor C 4a of the detecting circuit 4 is connected to the base of the transistor Q _5, the collector of the transistor Q ₅ is connected to the base of the next transistor Q _6, transistor The collector output of Q ₅ is inverted by transistor Q ₆ . The collector output of the transistor Q ₆ is input to the operational amplifier OP ₂ which functions as a buffer amplifier.

The DA conversion circuit 7 includes an operational amplifier OP ₃ , a feedback capacitor C ₁ , a time constant capacitor C ₂ and a resistor R.
As shown in FIG. 2, the size of the bandwidth of the operational amplifier OP ₂ of the inverting circuit 6 is converted into the size of the analog amplitude voltage. That is, FIG. 2A shows that the large bandwidth voltage from the operational amplifier OP ₂ is transferred to the operational amplifier OP _2.
Converted to analog voltage with large amplitude by ₃ . In FIG. 2B, the voltage with a small pulse width from the operational amplifier OP ₂ is converted into an analog voltage with a small amplitude by the operational amplifier OP ₃ . The DA conversion circuit 7 functions as a pulse width (bandwidth) / amplitude modulator.

The comparison detection circuit 8 includes a Zener diode D.
₁ and its cathode is connected to the output side of the operational amplifier OP ₃ and its anode is connected to the base of the transistor Q _{7 in} the next stage. This Zener diode D ₁
Determines the magnitude of the amplitude of the output voltage of the DA conversion circuit 7 based on a preset threshold value, and outputs a voltage equal to or higher than the threshold value to the ON / OFF circuit 9 of the next stage.

The ON / OFF circuit 9 comprises a transistor Q ₇ , whose collector is the transistor Q _{1 of the} control circuit _1.
And the emitter is connected to ground. This transistor Q ₇ becomes conductive or non-conductive by the output of the Zener diode D ₁ and is input to the base of the transistor Q ₁ of the control circuit 1 at the next stage, so that the transistor Q 7
You will control ₁ .

In this embodiment, the detection circuit 4 to ON / O
Up to the FF circuit 9 becomes a protection circuit. The relationship between the circuit blocks and the constituent elements in the circuit blocks have been described above. Next, the protection operation will be described.

The voltage waveform at the connection point 4a of the detection circuit 4 is shown in FIG. FIG. A shows a case of normal load, FIG. B shows a case of load short circuit, and FIG. C shows a case of no load.

1. In the case of normal load As shown in FIG. 3A, the bandwidth of the voltage at the connection point 4a is small and the amplitude is large. The transistor Q ₅ of the inverting circuit 6 is conductive only during the period of the small bandwidth, and the transistor Q ₆ is inverted and becomes nonconductive during this period.
Therefore, the voltage of the small bandwidth is applied to the operational amplifier OP ₂ . Since the operational amplifier OP ₂ is a buffer amplifier, it outputs the input voltage as an output voltage to the operational amplifier OP ₃ of the DA conversion circuit in the next stage. The input voltage of the operational amplifier OP _{3 is} the voltage of the small bandwidth, that is,
Since the voltage has a small bandwidth shown in FIG. 2B, the converted output voltage is an analog voltage with a small amplitude. Since the Zener diode D ₁ of the comparison detection circuit 8 of the next stage is set so as not to conduct at the voltage of this small amplitude, the Zener diode D ₁ is non-conductive, and the transistor Q ₇ of the ON / OFF circuit 9 of the next stage. Also becomes non-conductive, and the transistor Q ₁ of the control circuit 1 of the next stage is not controlled by the transistor Q ₇ and becomes conductive and supplies a constant current to the oscillation circuit 2 of the next stage, and the oscillation circuit 2 normally oscillates to a high voltage. The circuit 3 outputs a high voltage.

2. In the case of load short circuit As shown in FIG. 3B, the bandwidth of the voltage at the connection point 4a is large and the amplitude is small. The transistor Q ₅ of the inverting circuit 6 is conductive only during the period of the large bandwidth, and the transistor Q ₆ is inverted and becomes non-conductive only during this period.
Therefore, the voltage of the large bandwidth is applied to the operational amplifier OP ₂ . Since the operational amplifier OP ₂ is a buffer amplifier, it outputs the input voltage as an output voltage to the operational amplifier OP ₃ of the DA conversion circuit in the next stage. The input voltage of the operational amplifier OP _{3 is} the voltage of the large bandwidth, that is,
Since the voltage has a large bandwidth shown in FIG. 2A, the converted output voltage is an analog voltage having a large amplitude. Since the Zener diode D ₁ of the comparison detection circuit 8 in the next stage is set to conduct at a voltage of this large amplitude, the Zener diode D ₁ conducts and the transistor Q ₇ of the ON / OFF circuit 9 in the next stage also. The transistor Q of the control circuit 1 in the next stage is turned on.
₁ is controlled by transistor Q ₇ and becomes non-conductive,
No constant current is supplied to the oscillator circuit 2 in the next stage, the oscillator circuit 2 stops oscillating, and the high voltage circuit 3 does not output a high voltage.

3. In the case of no load As shown in FIG. 3C, the bandwidth and amplitude of the voltage at the connection point 4a are zero. Therefore, the transistor Q ₅ of the inverting circuit 6 becomes non-conductive, and the transistor Q ₆ inverts and becomes conductive. The input / output voltage of the operational amplifier OP ₂ and the operational amplifier OP ₃ of the DA conversion circuit 7 becomes zero, and the Zener diode D ₁ of the comparison detection circuit 8 and the transistor Q ₇ of the ON / OFF circuit 9 are also non-conductive. Therefore, the transistor Q ₁ of the control circuit 1 is not controlled by the transistor Q ₇ and conducts to supply a constant current to the oscillation circuit 2, the oscillation circuit 2 normally oscillates, and the high voltage circuit 3 outputs a high voltage. Therefore, the case of no load is the same as the case of normal load.

As described above, according to the present invention, the oscillator circuit 2 normally oscillates under load and no load, the high-voltage circuit 3 operates normally, and the oscillator circuit 2 stops only when the load is short-circuited. Stops outputting high voltage.

[0029]

According to the present invention, a DA conversion circuit is provided in the protection circuit, and this DA conversion circuit converts the magnitude of the bandwidth (pulse width) of the input voltage into the magnitude of the amplitude of the analog voltage and outputs it. Even when there is no load, the operation is similar to that under load, the comparison detection circuit and the ON / OFF circuit do not operate, the control circuit conducts, and the oscillation circuit continues normal oscillation. Therefore, no load operation is possible, and the protection operation is performed only when the load is short-circuited.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an AC high voltage generating circuit according to an embodiment of the present invention.

FIG. 2 is an input / output amplitude characteristic diagram of a DA converter circuit according to the embodiment shown in FIG.

FIG. 3 is an output amplitude characteristic diagram of the detection circuit in the embodiment shown in FIG.

[Fig. 4] Conventional AC high voltage generation circuit diagram

[Explanation of symbols]

 1 Control circuit 2 Oscillation circuit 3 High voltage circuit 4 Detection circuit 4a Connection point 5 Load 6 Inversion circuit 7 DA conversion circuit 8 Comparison detection circuit 9 ON / OFF circuit

Claims (1)

[Claims] 1. A constant voltage control circuit, an oscillator circuit that receives a constant voltage supply from the control circuit and uses a primary winding of a transformer, and a secondary winding that is coupled to the primary winding of the oscillator circuit. A high-voltage circuit that boosts the oscillation output, a detection circuit and a load that are connected in series to this high-voltage circuit, an inverting circuit that is connected to the output side of this detection circuit, and the size of the bandwidth of this inverting circuit are the analog amplitude voltage. Of the DA conversion circuit, a comparison detection circuit that determines the output of the DA conversion circuit, and an ON / OFF circuit that controls the control circuit by the output of the comparison detection circuit. AC high voltage generation circuit.