JP3076414U - High voltage generation circuit of toner type printing device - Google Patents

Abstract

(57) [Problem] To protect a transistor even when a protection diode is omitted. A voltage control circuit for transmitting a voltage control signal generated based on a voltage detection signal indicating a voltage of a secondary side output to a terminal of an auxiliary coil, the voltage control circuit comprising: By changing the signal 14 to control the oscillation amplitude of the transistor Q1, the secondary output 13
And the secondary side output 13 is guided to the high voltage application section of the toner type printing section in the voltage control circuit 1
And a base current limiting resistor R8 connected between the terminal of the auxiliary coil L3 and the terminal of the auxiliary coil L3.
The resistance is set to a value close to the maximum value among the resistance values in a range satisfying the maximum value of the base current required for the transistor Q1.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a toner-type printing apparatus that performs printing using toner, such as a laser-type printer or a copier, and more specifically, to a high-pressure generation for generating a high pressure required for toner-type printing. It is related to the circuit.

[0002]

[Prior art]

 One of the conventional techniques for protecting the output when the output is short-circuited in a power supply that obtains a secondary output by switching a current flowing through a primary coil is a technique disclosed in Japanese Patent Publication No. 7-79444. That is, in this technique, an overcurrent detecting means for detecting an overcurrent flowing through the control transistor, an intermittent operating point setting means for setting an intermittent operating point, an output of the overcurrent detecting means and an output of the intermittent operating point setting means. And comparing means for comparing with. Therefore, when the output is short-circuited, the PWM circuit generates an intermittent pulse based on the output of the comparing means. As a result, even when the output is short-circuited, the current flowing through the control transistor and the coil is limited, and the element is protected from destruction (referred to as a first conventional technique).

[0003] Further, there is a conventional technique proposed as Japanese Patent Application Laid-Open No. 9-121537. In this technique, when an output is short-circuited, information indicating the short-circuit is fed back to a primary circuit via a photocoupler. ing. On the other hand, on the primary circuit side, when information indicating a short circuit is led, the supply of the switching pulse for driving the switching transistor is stopped by turning on the thyristor. Therefore, when a short circuit occurs in the output, the operation of the switching transistor is stopped, and this stopped state is maintained thereafter, so that the element is protected from heat generation and destruction (the second conventional technology). Do).

[0004] As in the switching method in the above-described technology, a method in which the switching element is in a saturated state when the switching element is turned on requires efficient conversion when the output power is large. Can be. However, if the output power is small, as in the case of a high-voltage generating circuit of a toner-type printing device, the conversion efficiency deteriorates and the operation becomes unstable. For this reason, in the high-voltage generation circuit of the toner-type printing device, a configuration is adopted in which the transistor connected to the primary coil is always operated in the unsaturated region and the output voltage is stabilized by controlling the oscillation amplitude. Have been. That is, a configuration is employed in which the output voltage is stabilized by a principle different from those of the first and second prior arts. For this reason, when protecting a transistor, it is used in the first prior art and the second prior art, that is, in a configuration in which the switching element is saturated when the switching element is turned on. It has been difficult to apply protection methods.

FIG. 5 shows an electrical connection of a high-voltage generating circuit that stabilizes an output voltage by controlling the amplitude of oscillation of a transistor. That is, the collector of the transistor Q1 is connected to the primary coil L1, and the base is connected to one terminal of the auxiliary coil L3. The output of the OP amplifier 3 that generates a voltage control signal based on the output voltage on the secondary side is led to the other terminal of the auxiliary coil L3. Therefore, the transistor Q1 increases the oscillation amplitude when the voltage of the voltage control signal sent from the OP amplifier 3 increases, and decreases the oscillation amplitude when the voltage of the voltage control signal decreases. On the other hand, the OP amplifier 3 lowers the voltage of the voltage control signal when the voltage of the secondary output becomes higher than the set value, and decreases the voltage control signal when the voltage of the secondary output becomes lower than the set value. Increase the voltage of For this reason, the voltage of the secondary output is stabilized to the voltage set by the voltage setting signal 22 (21 is a path for supplying a reference voltage for setting the operating point of the OP amplifier 3). .

In the above configuration, that is, in the configuration in which the voltage of the secondary output is stabilized by controlling the amplitude of oscillation, the first and second conventional methods are used to protect the output when the output is short-circuited. A different method from that of the technology (the case where the switching element shifts to the saturation state when turned on) is adopted. That is, in the configuration shown in FIG. 5, when a short circuit occurs in the output, the voltage of the voltage control signal sent from the OP amplifier 3 increases. On the other hand, a resistor R21 is inserted between the output terminal of the OP amplifier 3 and the other terminal of the auxiliary coil L3, and a clamp circuit including diodes D5 and D6 is provided between the resistor R21 and the auxiliary coil L3. It is connected. Therefore, the voltage of the other terminal of the auxiliary coil L3 is suppressed to about 1.3 V even when the output voltage of the OP amplifier 3 increases. As a result, the increase in the base current of the transistor Q1 is limited, and the increase in the collector current is suppressed, so that the transistor Q1 is protected from destruction (the third conventional technique).

[0007] The capacitor C3 is an element for grounding the other terminal of the auxiliary coil L3 at high frequency. The resistor R9 is an element for suppressing a decrease in impedance connected to the auxiliary coil L3 when a base current flows through the transistor Q1, and has a value of about 100Ω (the reason for this will be described later). Detailed)). The value of the resistor R21 is set to about several kΩ in order to supply a sufficient base current to the transistor Q1 when the output voltage of the OP amplifier 3 is 1.3 V or less.

FIG. 6 shows a configuration in which a method different from the method shown in FIG. 5 is employed to protect the transistor Q1. That is, the portion consisting of the resistor R21 and the diodes D5 and D6 in FIG. 5 is replaced by the resistor R22 and the Zener diode D7 (the other portions are the same as the configuration shown in FIG. 5). . Therefore, in the case of this configuration, the voltage of the other terminal of the auxiliary coil L3 is shifted to a side lower than the output voltage of the OP amplifier 3 by the Zener voltage of the Zener diode D7. Therefore, the voltage of the other terminal of the auxiliary coil L3 is suppressed to a low voltage even when the output voltage of the OP amplifier 3 increases. As a result, the increase in the base current of the transistor Q1 and the increase in the collector current are limited, so that the transistor Q1 is protected from breakdown. The value of the resistor R22 is set to 20 kΩ to 30 kΩ in order to enable a sufficient base current to be supplied to the transistor Q1 even when the output voltage of the OP amplifier 3 is shifted to a low voltage by the Zener diode D7. (The fourth prior art).

[0009]

[Problems to be solved by the invention]

 However, in the third conventional technique, the transistor Q1 is protected when the secondary output is short-circuited by using two diodes D5 and D6. In the fourth prior art, the use of one Zener diode D7 protects the transistor Q1 when the secondary output is short-circuited. On the other hand, since the diodes D5 and D6 and the Zener diode D7 are semiconductor elements, the element prices are high. Further, the number of elements used increases due to the diodes D5 and D6 or the Zener diode D7. As a result, there has been a problem that the cost of parts increases.

The present invention has been made in order to solve the above-mentioned problem, and an object of the present invention is to insert an auxiliary coil between a voltage control circuit for transmitting a voltage control signal for controlling the oscillation amplitude of a transistor and an auxiliary coil. When the voltage of the voltage control signal rises, the resistance of the transistor connected to the primary coil is set to a large value within the range that satisfies the maximum value of the base current required for the transistor. To provide a high-voltage generation circuit of a toner-type printing apparatus capable of protecting a transistor even when a protection diode is omitted by limiting a maximum value of a base current to a current value at which a transistor is not destroyed. It is in.

[0011] In addition to the above objects, by using an NPN transistor as the transistor connected to the primary coil, even when the omission of the semiconductor element and the reduction in the number of elements are performed, the same transformer as the conventional transformer can be used. An object of the present invention is to provide a high voltage generating circuit of a toner type printing apparatus which can be used.

[0012]

[Means for Solving the Problems]

 In order to solve the above problems, the high voltage generating circuit of the toner type printing apparatus according to the present invention includes a transformer in which at least a primary coil, a secondary coil, and an auxiliary coil are wound, a collector connected to the primary coil, and a base. A transistor connected to one terminal of the auxiliary coil, and a voltage control circuit for sending a voltage control signal generated based on a voltage detection signal indicating a voltage of the secondary output to the other terminal of the auxiliary coil, The control circuit stabilizes the voltage of the secondary side output by changing the voltage control signal and controlling the oscillation amplitude of the transistor, and the secondary side output is guided to the high voltage application section of the toner type printing section. Applied to the high voltage generation circuit of the toner type printing device, it has a base current limiting resistor connected between the voltage control circuit and the other terminal of the auxiliary coil, and the value of the base current limiting resistor By limiting the maximum value of the base current of the transistor when the secondary output is short-circuited by setting the resistance near the maximum value among the resistance values in a range satisfying the maximum value of the base current required for the transistor. ing.

That is, when the hfe of the transistor varies to the side with the smallest value and the current value of the secondary output becomes the maximum value on the setting, the base current required for the transistor becomes the maximum. Therefore, if the value of the base current limiting resistor is set so as to be close to the largest resistance value in a range where the above-described base current can flow, a short circuit occurs in the secondary side output, and the level of the voltage control signal is reduced. Also when the maximum value is reached, the increase in the base current is suppressed. Therefore, even when a short circuit occurs in the secondary output, an increase in the collector current is suppressed, so that an increase in the amount of heat generated by the transistor is suppressed.

In addition to the above configuration, the transistor is an NPN transistor.

That is, the base current can be suppressed even when a transformer having the same configuration as the transformer in the configuration that suppresses the increase in the base current is used by the diode clamp circuit or the Zener diode.

[0016]

[Embodiment of the invention]

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the electrical connection of the first embodiment of the high-voltage generating circuit of the toner type printing apparatus according to the present invention. For example, the output voltage can be changed at a voltage near -1100V. The possible configurations are shown. Elements having the same configuration as that shown in FIG. 5 are given the same reference numerals as those in FIG.

In FIG. 1, a reference voltage source 7 is a block that outputs a voltage precisely stabilized at, for example, 10V. The voltage setting unit 8 is a block for setting the voltage of the secondary output 13, and sets the voltage of the secondary output 13 based on the duty ratio of the output pulse signal. Note that the output of the voltage setting unit 8 is an open drain output.

The transformer 4 is a transformer in which a primary coil L1, a secondary coil L2, and an auxiliary coil L3 are wound. One terminal of the primary coil L1 is connected to, for example, a positive power supply P of 20 V. It is connected. An NPN transistor Q1 (hereinafter simply referred to as a transistor Q1) having a collector connected to the other terminal of the primary coil L1, a base connected to one terminal of the auxiliary coil L3, and an emitter grounded is connected to the primary coil L1. The element performs self-excited oscillation using the magnetic coupling formed between the coil and the auxiliary coil L3 as a feedback path.

The diode D1 and the capacitor C4 form a block for rectifying and smoothing the high voltage generated in the secondary coil L2, and the rectified and smoothed secondary output 13 is applied to the high-voltage applying section of the toner type printing section. (Detailed later). One terminal of a resistor R9 is connected to the other terminal of the auxiliary coil L3, and the other terminal of the resistor R9 is grounded via a capacitor C3.

The voltage control circuit 1 serves as a block for sending a DC voltage control signal 14 generated based on a voltage detection signal 18 indicating the voltage of the secondary output 13 to the other terminal of the auxiliary coil L3. I have. The voltage of the secondary output 13 is stabilized to the voltage set by the voltage setting unit 8 by changing the voltage of the voltage control signal 14 and controlling the oscillation amplitude of the transistor Q1.

The base current limiting resistor R8 connected between the output of the voltage control circuit 1 (the output terminal of the OP amplifier 3) and the other terminal of the resistor R9 limits the maximum value of the base current of the transistor Q1. Device. For this reason, the value of the base current limiting resistor R8 is set to a value near the resistance value at which the value becomes the largest within a range that satisfies the maximum value of the base current required for the transistor Q1.

FIG. 3 is an explanatory diagram schematically showing a toner type printing unit. The toner-type printing section includes a toner roller 51, a developing roller 52, a charging roller 53, a photosensitive drum 54, a transfer roller 55, a doctor blade 56, and a cleaner blade 57. That is, the charging roller 53 applies a uniform charge to the surface of the photosensitive drum 54. Further, the toner roller 51 applies the toner in a toner storage unit (not shown) to the surface of the developing roller 52. The developing roller 52 transfers the toner to a portion where the charge has been erased because the surface of the photosensitive drum 54 has been irradiated with the laser beam 58. Further, the transfer roller 55 transfers the toner transferred on the surface of the photosensitive drum 54 to the printing paper 59 side.

The doctor blade 56 makes the thickness of the toner applied on the surface of the developing roller 52 uniform. Further, the cleaner blade 57 removes the toner remaining on the surface of the photosensitive drum 54 without being transferred to the printing paper.

The present embodiment is an apparatus for applying a high voltage to a high voltage application unit (the rollers 51 to 53, 55, blades 56, 57, or the photosensitive drum 54 of the toner type printing unit described above). I have. For this reason, the actual device is configured to generate a plurality of types of voltages. However, in FIG. 1, the configuration for generating a secondary output having a voltage different from that of the secondary output 13 is not illustrated. Have been.

Returning to FIG. 1, the details of the voltage control circuit 1 will be described. One terminal of the resistor R3 is connected to the output of the reference voltage source 7, and the other terminal of the resistor R3 is connected to the output of the voltage setting unit 8. That is, the resistor R3 is an element that pulls up the output of the voltage setting unit 8 to the voltage of the reference voltage source 7 when the output of the voltage setting unit 8 is turned off.

One terminal of the resistor R 4 is connected to the reference voltage source 7. One terminal of the resistor R5 is connected to the output of the voltage setting unit 8. The other terminal of the resistor R4 and the other terminal of the resistor R5 are connected to each other and to the non-inverting input of the OP amplifier 3. Further, a capacitor C2 is connected between the other terminal of the resistor R5 and the ground level in order to convert a signal appearing at the other terminal of the resistor R5 into DC.

From the above, when the resistance R4 is neglected, when the duty ratio of the output of the voltage setting unit 8 changes in the range from 0% to 100%, the voltage of the other terminal of the resistance R5 becomes , 0V to 10V. The value of the resistor R4 is set to be about seven times the value of the resistor R5. Therefore, assuming that there is no resistor R7, the duty ratio of the output of the voltage setting unit 8 changes in the range of 0% to 100%, assuming that the resistor R7 does not have the resistor R7. At this time, it changes in a range from about 1.25V to 10V.

The resistors R 1 and R 2 are elements that divide the voltage of the reference voltage source 7 to 、 and send the divided voltage to the inverting input of the OP amplifier 3. A series circuit composed of the capacitor C1 and the resistor R6 and connected between the inverting input and the output terminal of the OP amplifier 3 is for preventing parasitic oscillation of the OP amplifier 3. A resistor R7 connected between the secondary output 13 and the non-inverting input divides the voltage of the secondary output 13 at an extremely high ratio, and outputs the divided output to the voltage detection signal 18. As an element applied to the non-inverting input.

The OP amplifier 3 is operated by a single power supply. For this reason, a positive power supply P of 20 V is connected to the positive power supply terminal, and the negative power supply terminal is grounded.

The voltage control circuit 1 has the above-described configuration. Therefore, when the voltage of the secondary output 13 decreases, the level of the voltage detection signal 18 shifts to the 0V side, and the level of the non-inverting input increases, so that the output level of the OP amplifier 3 increases. When the output level of the OP amplifier 3 increases, the oscillation amplitude of the transistor Q1 increases, so that the voltage of the secondary output 13 increases (increases in the negative direction). Therefore, the level of the non-inverting input of the OP amplifier 3 falls, and the rise of the output level of the OP amplifier 3 stops. As a result, the voltage of the secondary output 13 is stabilized at a voltage determined by the duty ratio of the output of the voltage setting unit 8.

In the following, the transistor Q1 performs self-excited oscillation. At this time, the transistor Q1 operates in an unsaturated region. For this reason, the voltage waveform of the collector changes as a sine wave, as shown at 15 in FIG. Similarly, the voltage generated in the auxiliary coil L3 shows a change approximating a sine wave. The level of the connection point between the base current limiting resistors R8 and R9 is shown in FIG. 17 because one terminal of the auxiliary coil L3 is grounded via a diode between the base and the emitter of the transistor Q1. So, it will be a minus level. When the level of the output 14 of the OP amplifier 3 changes, the amplitude (oscillation amplitude) 61 of the collector of the transistor Q1 changes, so that the voltage of the secondary output 13 changes.

Hereinafter, the operation of the resistor R 9 will be described. When a base current flows through the transistor Q1, the impedance of the transistor Q1 as viewed from the auxiliary coil L3 has an extremely small value. The capacitor C3 is an element that grounds the other terminal of the auxiliary coil L3 in an AC manner. Therefore, at the oscillation frequency of the transistor Q1 (about 90 kHz), the impedance of the capacitor C3 is small. Therefore, when a base current flows through the transistor Q1, the impedance connected to the auxiliary coil L3 is equivalently substantially equal to the value of the resistor R9.

On the other hand, when the impedance connected to the auxiliary coil L 3 is short-circuited, the resonance waveform in the transformer 4 is disturbed. The resistor R9 prevents the short circuit described above (therefore, the resistor R9 may be connected between one terminal of the auxiliary coil L3 and the base of the transistor Q1).

On the other hand, the current generated in the auxiliary coil L3 flows through the resistor R9. Therefore, as the value of the resistor R9 increases, the feedback ratio of the transistor Q1 decreases, and the oscillation becomes unstable. From the above, a value of about 100Ω is adopted as the value of the resistor R9. That is, for the resistor R9, by making its value sufficiently large, the effect of the element for limiting the base current of the transistor Q1 cannot be doubled.

That is, in order to limit the base current of the transistor Q 1, it is necessary to connect the base current limiting resistor R 8 between the connection point between the capacitor C 3 and the resistor R 9 and the voltage control circuit 1.

The operation of the base current limiting resistor R8 will be described below. The maximum value of the base current required for the transistor Q1 is the same as that when the hfe of the transistor Q1 varies to the side where the value is the smallest and the current value of the secondary output 13 becomes the maximum value on the setting. It is defined as a peak value when the set voltage can be output from the side output 13 with a margin (hereinafter, referred to as a virtual maximum state). Therefore, the value of the base current limiting resistor R8 is set to a value close to the largest resistance value in a range where the maximum value of the base current can flow (in this embodiment, a value close to 100 kΩ). And).

Now, assuming that the minimum value is min and the maximum value is max among the variations in hfe of the transistor Q 1, when the value of the base current limiting resistor R 8 is set as described above, a short circuit occurs in the secondary output 13. Therefore, even when the output level of the OP amplifier 3 is maximized, the collector current of the transistor Q1 is equal to (max) of the collector current of the transistor Q1 in the virtual maximum state, regardless of the value of hfe of the transistor Q1. / Min) times less. Therefore, even when a short circuit occurs in the secondary output 13, the amount of heat generated by the transistor Q1 does not become too large. As a result, even when a short circuit occurs, destruction of transistor Q1 is prevented.

FIG. 2 is a circuit diagram showing the electrical connection according to the second embodiment, and shows a configuration in which a voltage detection signal indicating the voltage of the secondary output 13 is taken out differently. For this reason, FIG. 1 shows only a portion related to the voltage detection signal (a portion not shown is the same as the configuration shown in FIG. 1).

When compared with the transformer 4, the transformer 5 has a configuration in which a detection coil L 4 is added in order to take out a voltage detection signal indicating the voltage of the secondary output 13 on the primary side. Also, a diode D3 and a capacitor C6 are added to extract the voltage detection signal 19 by rectifying and smoothing the output of the detection coil L4. Therefore, the level of the voltage detection signal 19 increases when the voltage of the secondary output 13 increases.

Further, since the voltage detection signal 19 is a signal that gives a positive feedback, in the voltage control circuit 2, the voltage detection signal 19 is divided by the resistors R11 and R12, and then divided by the OP amplifier. 3 inverting input.

The second embodiment has the same configuration as the first embodiment except for the above difference. Therefore, when the level of the voltage detection signal 19 rises because the voltage of the secondary output 13 has risen, the voltage control circuit 2 lowers the output level of the OP amplifier 3 so that the secondary output 13 Voltage is lowered. Further, when the voltage of the secondary output 13 drops and the level of the voltage detection signal 19 drops, the voltage of the secondary output 13 is increased by increasing the output level of the OP amplifier 3. Therefore, the voltage of the secondary output 13 is stabilized at a voltage corresponding to the DC level of the path 12.

The operation of the base current limiting resistor R8 is the same as the operation in the first embodiment.

[0043]

[Effect of the invention]

 As described above, the high-voltage generating circuit of the toner-type printing apparatus according to the present invention includes the transistor having the collector connected to the primary coil and the base connected to one terminal of the auxiliary coil, and the voltage of the secondary output. And a voltage control circuit for transmitting a voltage control signal generated based on a voltage detection signal indicating the following to the other terminal of the auxiliary coil, wherein the voltage control circuit changes the voltage control signal and controls the oscillation amplitude of the transistor. In this configuration, the voltage of the secondary output is stabilized, and the secondary output is connected to the high-voltage application section of the toner type printing section, and is connected between the voltage control circuit and the other terminal of the auxiliary coil. Base current limiting resistor, and the value of the base current limiting resistor is set to a value close to the maximum value among the resistance values in a range satisfying the maximum value of the base current required for the transistor. By limiting the maximum value of the base current of the transistor during a short circuit of the secondary side output. Therefore, even when a short circuit occurs in the secondary output and the output level of the voltage control circuit is maximized, the increase in the base current of the transistor is suppressed, and the increase in the collector current is also suppressed. For this reason, even when a short circuit occurs in the secondary output, the increase in the amount of heat generated by the transistor is suppressed, so that the transistor can be protected even when the protection diode is omitted.

Further, the transistor is an NPN transistor. Therefore, even when using a transformer having the same configuration as the transformer in the configuration in which the increase in the base current is suppressed by a clamp circuit using a diode or a Zener diode, the base current can be suppressed. The same transformer as the transformer in the conventional technology can be used when performing the above.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an electrical connection of a first embodiment of a high voltage generation circuit of a toner type printing apparatus according to the present invention.

FIG. 2 is a circuit diagram illustrating an electrical connection according to a second embodiment.

FIG. 3 is an explanatory view schematically showing a toner type printing unit.

FIG. 4 is an explanatory diagram showing signal waveforms at main points.

FIG. 5 is a circuit diagram showing a conventional electrical connection.

FIG. 6 is a circuit diagram showing a conventional electrical connection.

[Explanation of symbols]

 1, 2 Voltage control circuit 4, 5 Transformer 13 Secondary output 14 Voltage control signal 18, 19 Voltage detection signal L1 Primary coil L2 Secondary coil L3 Auxiliary coil Q1 Transistor R8 Base current limiting resistor

Claims (2)

[Utility model registration claims] A transformer having at least a primary coil, a secondary coil and an auxiliary coil wound thereon; a transistor having a collector connected to the primary coil and a base connected to one terminal of the auxiliary coil; A voltage control circuit that sends a voltage control signal generated based on a voltage detection signal indicating an output voltage to the other terminal of the auxiliary coil, wherein the voltage control circuit changes the voltage control signal and causes the oscillation amplitude of the transistor to change. In the high voltage generation circuit of the toner type printing device in which the secondary side output is guided to the high voltage application section of the toner type printing section by controlling the voltage of the voltage control circuit and the auxiliary coil, A base current limiting resistor connected to the other terminal, the value of the base current limiting resistor being within a range satisfying the maximum value of the base current required for the transistor. A high-voltage generating circuit for a toner-type printing apparatus, wherein the maximum value of the base current of the transistor when the secondary output is short-circuited is limited by setting a value near the maximum value among the resistance values in the box. 2. The high-voltage generation circuit according to claim 1, wherein the transistor is an NPN transistor.