JPH0315190B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for fixing toner images formed in image forming apparatuses such as copying machines and facsimile machines.

[Technical background]

In image forming apparatuses such as copying machines and facsimile machines, a visible image is formed by fixing a toner image formed by development onto an image support made of paper or the like. As a method for fixing toner images, a heating roller fixing method using a heating roller is conventionally known.
However, this heating roller fixing method requires waiting time at the beginning of image formation until the temperature of the heating roller rises to the temperature required for fixing the toner, and in particular, fixing the toner image on a large area image support. Since this requires a large amount of heat, there is a problem that the standby time is considerably long.

[Prior art]

For this reason, a method has been developed in which a toner image is fixed by using a flash lamp and irradiating light energy from the flash lamp. According to such a method, the flash lamp can be turned on instantly, and has the advantage that it can be fixed immediately without requiring any waiting time.

To emit light from the flash lamp, the main capacitor for energy supply is charged via a power transformer and a rectifier to the set voltage required for toner fixation, and after charging is completed, the primary side of the power transformer is connected to a switching element made of, for example, a semiconductor. Charging is temporarily stopped by cutting off the power, and then the charging energy of this main capacitor is supplied to the flash lamp. For example, in a copy machine, B4 size or A3 size
In order to fix the entire large-area toner image transferred onto a transfer paper of various sizes, it is necessary to repeatedly emit light from the flash lamp about four times or more in a short cycle.

[Problem that the invention seeks to solve]

However, each time such light emission is repeated, the main capacitor is charged and discharged repeatedly in a short time, but if the light emission is repeated at a high speed of 500 msec or less, charging of the main capacitor may start. Sometimes, the impedance on the secondary side of the power transformer is extremely small, and inrush current tends to flow into the primary side of the power transformer.
Moreover, at the end of charging when the charging voltage of the main capacitor reaches the set voltage, the power transformer is likely to be magnetically saturated and a biased magnetism phenomenon appears.As a result of this biased magnetism, a considerably large inrush current flows at the start of the next charging, which flows through the primary of the power transformer. There is a problem in that the switching element inserted on the side is destroyed, making it impossible to charge the main capacitor.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and its purpose is to prevent the magnetization phenomenon of the power transformer and safely charge the main capacitor without causing a large inrush current to flow. To provide a toner fixing method capable of fixing toner at high speed by repeatedly emitting light from a flash lamp in a short period of time.

[Means for solving problems]

The toner fixing method of the present invention charges an energy supply capacitor through a power transformer and a rectifier, supplies the charging energy of the main capacitor to a flash lamp to emit light, and uses the light energy at this time to fix the toner. In the fixing method, a first switch circuit including a series circuit of an impedance element and a switching element and a second switch circuit including a switching element are inserted on the primary side of the power transformer to charge the main capacitor. With the second switch circuit open and the first switch circuit closed, the power supply transformer is energized via the impedance element to start charging the main capacitor, and then, after a delay, the second switch circuit is closed.
The first switch circuit is closed and the impedance element of the first switch circuit is short-circuited, and the current is continued.
When the detection voltage of the voltage detector that detects the voltage corresponding to the charging voltage of the main capacitor exceeds the second reference voltage, which is lower in level than the first reference voltage, the second switch circuit is activated by the second comparator. The switch is opened and the power transformer continues to be energized via the impedance element of the first switch circuit, and after a delay, the detected voltage of the voltage detector becomes a voltage corresponding to the set voltage of the main capacitor necessary for fixing the toner. When a certain first reference voltage is reached, the first
The first switch circuit is opened by the comparator to stop the power supply to the power transformer, and then the charging energy of the main capacitor is supplied to the flash lamp to emit light, and the flash lamp is emitted repeatedly to fix the toner. It is characterized by carrying out the following.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram schematically showing an example of a toner fixing device that can be used in the present invention, and 1 is a flash lamp made of, for example, a xenon flash lamp.
is a lamp cover 2 with a reflective mirror surface formed on the inner surface.
1, and a transparent cover glass 22 is provided on the lower opening surface thereof. 11 is a trigger wire, which is arranged so as to extend along the outer wall surface of the flash lamp 1. Reference numeral 23 denotes a conveyance belt for transferring a transfer paper, which is a support for the transferred toner image, and the transfer paper is conveyed in the direction of arrow A by this conveyance belt 23.

When the transfer paper, on which the toner image has been transferred, is conveyed in the direction of arrow A by the conveyor belt 23, a conveyance detector 24 provided at the entrance of the fixing section sends a control signal CHG1 for the electric circuit section, which will be described later. ，
The timing of CHG2 and trigger signal TG is set. When the transfer paper enters the fixing area,
Until the trailing edge of the transfer paper finishes passing through the fixing area, the flash lamp 1 is repeatedly emitted every time the transfer paper advances the distance of the effective fixing width to fix the entire area. When the transfer paper leaves the fixing area, the discharge detector 25 cancels the timing settings of the control signals CHG1, CHG2 and the trigger signal TG.

FIG. 2 is an explanatory diagram showing an example of an electric circuit portion for causing the flash lamp 1 to emit light.

3 is a step-up power transformer whose secondary voltage is approximately 2 to 3 KV; 4 is a rectifier; 5 is a main capacitor for energy supply; and 6 is a trigger circuit for triggering the flash lamp 1.

7 is a first switch circuit, 8 is a second switch circuit, and these first switch circuit 7 and second switch circuit are connected to each other.
The switch circuits 8 are inserted, for example, in parallel with each other on the primary side of the power transformer 3. The first switch circuit 7 includes an impedance element 71 made of, for example, a resistor and a solid state relay, for example.
The second switch circuit 8 is made up of a series circuit of switching elements 72 made of SSR or the like, and the second switch circuit 8 is made up of a switching element 81 made of, for example, a solid state relay SSR. In this example, switching elements 72 and 81 switch terminals 72B and 72C while high level (H level) signals are input to input terminals 72A and 81A, respectively.
The terminals 81B and 81C are electrically conductive, and are cut off during a period when a low level signal is input. The impedance of the impedance element 71 is set in consideration of the characteristics of the power transformer 3, the magnitude of power consumption, and other conditions, and for example, it is about 1 to 10 Ω.

9 is a voltage detector for detecting the charging voltage of the main capacitor 5, and is composed of, for example, two voltage dividing resistors. In this voltage detector 9, there is only one charging voltage detection point, and the detection voltage V ₂ of this detection point 91 is the inverting input terminal 10 of the first comparator 101 in the first control circuit 100, which will be described later.
1A and an inverting input terminal 201 of a second comparator 201 in a second control circuit 200 to be described later.
Commonly input to A.

Reference numeral 100 indicates the opening/closing operation of the switching element 72 in the first switch circuit 7, a detection voltage V ₂ of the charging voltage of the main capacitor 5, a high-level first reference voltage V ₃ to be described later, a control signal CHG1, and a trigger signal TG. This is a first control circuit that controls based on the first comparator 101 and the first
a timer circuit 102 and a first comparator 10
a transistor 103 for cutting off the output of the first switching element 72 for a time set by the first timer circuit 102 and inputting an L level signal to the input terminal 72A of the first switching element 72 during that period; and a transfer paper. control signal generated in synchronization with the conveyance of
Transistor 1 turned on by CHG1
04, a resistor 105, and a comparator protection resistor 106.

The first comparator 101 has an inverting input terminal 1
When the magnitude of the detection voltage V ₂ inputted to 01A is less than the value of the high-level first reference voltage V ₃ inputted to the non-inverting input terminal 101B, its output V ₅
is at H level, and when the magnitude of the detection voltage _V2 exceeds the value of the high level first reference voltage _V3 , the output
_V5 becomes L level. First timer circuit 102
is the so-called "555" timer IC31
, resistors 32 and 33, and capacitors 34 and 35. When the trigger signal TG is input, the output V ₇ becomes H for a time T ₁ corresponding to the time constant determined by the resistor 33 and the capacitor 34. At other times, the output _V7 is at L level.
The transistor 103 is connected to the first timer circuit 102
When the output V ₇ is at L level, it is in the on state, and when the output V ₇ is at H level, it is in the off state. The transistor 104 is off when the control signal CHG1 is at the H level, and is on and short-circuits the resistor 105 when the control signal CHG1 is at the L level.

Reference numeral 200 controls the opening/closing operation of the switching element 81 in the second switch circuit 8 using a detection voltage V ₂ of the charging voltage of the main capacitor 5, a low-level second reference voltage V ₄ to be described later, a control signal CHG2, and a trigger signal TG. This is a second control circuit that controls based on the second comparator 201 and the second
a timer circuit 202 and a second comparator 20
A transistor 203 for cutting off the output of the second switching element 81 for a time set by the second timer circuit 202 and inputting an L level signal to the input terminal 81A of the second switching element 81 during that period, and a transfer paper. control signal generated in synchronization with the conveyance of
Transistor 2 turned on by CHG2
04, a resistor 205, and a comparator protection resistor 206.

The second comparator 201 has an inverting input terminal 2
When the magnitude of the detection voltage V ₂ input to 01A is less than the value of the low-level second reference voltage V ₄ input to the non-inverting input terminal 201B, its output V ₆
is at H level, and when the magnitude of the detection voltage _V2 exceeds the value of the second low level reference voltage _V4 , the output
_V6 becomes L level. Second timer circuit 202
is the so-called "555" timer IC41
, resistors 42, 43, and capacitors 44, 45, and when the trigger signal TG is input, the output _V8 becomes H for a time _T2 corresponding to the time constant determined by the resistor 43 and capacitor 44. At other times, the output _V8 is at L level.
The transistor 203 is connected to the second timer circuit 202
It is in the on state when the output _V8 of is at the L level, and is in the off state when the output _V8 is at the H level. The transistor 204 is off when the control signal CHG2 is at the H level, and is on and short-circuits the resistor 205 when the control signal CHG2 is at the L level.

The timings of the control signals CHG1 and CHG2 are respectively set by the conveyance detector 24 when the transfer paper enters the fixing section. Although the details are omitted, in this example, the control signal CHG1 is first set by an appropriate timing setting mechanism.
is set to a high level, and after a delay of time τ, the control signal CHG2 is set to a high level. This time τ
is approximately half a cycle to two cycles or more of the AC power input to the power transformer 3, for example, at a frequency of 50
When using a Hz AC power source, the time is approximately 10 msec or more.

By the first timer circuit 102 its output V ₇
The length of time T ₁ during which T is at H level is the second
The timer circuit 202 makes the output V ₈ smaller than the length of time T ₂ during which it is at H level, and the difference T ₂ −T ₁ is equal to half the cycle of the AC power supply AC input to the power transformer 3. It is said to be about 2 cycles,
For example, it is set equal to the time τ from when the control signal CHG1 becomes high level until the control signal CHG2 becomes high level.

300 and 400 are reference voltage sources, respectively. The first reference voltage source 300 at a high level is connected to the non-inverting input terminal 101B of the first comparator 101, and the second reference voltage source 400 at a low level is connected to the second reference voltage source 400. The non-inverting input terminal 20 of the comparator 201 of
Connected to 1B. The high-level first reference voltage V ₃ set by the high-level first reference voltage source 300 is determined when the charging voltage V ₁ of the main capacitor 5 reaches the set voltage required for fixing the toner. The magnitude is set to be exactly equal to the magnitude of the detection voltage V ₂ at the detection point 91. The magnitude of the low-level second reference voltage V ₄ set by the low-level second reference voltage source 400 is determined just before the charging voltage of the main capacitor 5 reaches the set voltage necessary for fixing the toner. Detection voltage V ₂
set equal to the level of Practically speaking, the detection voltage V ₂ is set to a second reference voltage V ₄ at a low level.
During the period from when the above detection voltage V ₂ reaches the high-level first reference voltage V ₃ , the power supply transformer 3 supplies power for, for example, about one cycle to the main capacitor 5 . reference voltage of
V ₃ and the second reference voltage V ₄ are adjusted.

Using the apparatus configured as described above, toner is fixed in the following manner. First, when a transfer paper carrying an unfixed toner image on its surface is conveyed to the fixing section, the leading edge of the transfer paper causes a conveyance detector 24 to be detected.
turns on, which causes the control signals CHG1 and CHG2 to
and the timing of the trigger signal TG is set. As shown in Figure 3, first the control signal is
CHG1 becomes H level, which turns off transistor 104 in first control circuit 100, releases the short-circuited state of resistor 105, and switches output _V9 from L level to H level.
At this time, an H level signal is inputted from the output V ₉ to the input terminal 72A of the switching element 72 of the first switch circuit 7, and as a result, conduction occurs between the terminals 72B and 72C of the switching element 72, and the first Impedance element 71 of switch circuit 7
A current flows through the power transformer 3 and charging of the main capacitor 5 is started. Next, after a delay of time τ, the control signal CHG2 becomes H level, and as a result, in the second control circuit 200, the transistor 204 is turned off, the short-circuited state of the resistor 205 is released, and the output V ₁₀ changes from the L level. Switches to H level. At this time, the output V ₁₀ is input to the input terminal 81A of the switching element 81 of the second switch circuit 8.
An H level signal is input to the switching element 81, which causes conduction between the terminals 81B and 81C of the switching element 81, short-circuiting the first switch circuit 7 including the impedance element 71, and supplies current to the power transformer 3. Charging of the capacitor 5 continues.

Just before the charging voltage V ₁ of the main capacitor 5 reaches the set voltage, the detection voltage V ₂ at the detection point 91 of the voltage detector 9 exceeds the low level first reference voltage V ₄ , and the second control circuit 200 The output V ₆ of the second comparator 201 is inverted from the H level to the L level, the output V ₁₀ is switched from the H level to the L level, and the input terminal 81A of the switching element 81 of the second switch circuit 8 receives an L level signal. When a signal is input, terminals 81B and 81 of switching element 81
C is cut off, the short-circuited state of the first switch circuit 7 is released, and current is again supplied to the power transformer 3 via the impedance element 71 to continue charging the main capacitor 5.

When the charging voltage V ₁ of the main capacitor 5 reaches the set voltage, the detection voltage V ₂ of the detection point 91 of the voltage detector 9 reaches the high level first reference voltage V ₃ .
In the first control circuit 100, the output _V5 of the first comparator 101 is inverted from H level to L level, the output _V9 is switched from H level to L level, and switching element 7 of first switch circuit 7 is inverted.
An L level signal is input to the input terminal 72A of the switching element 72, and the terminals 72B and 72C of the switching element 72 are cut off, the supply of current to the power transformer 3 is stopped, and charging of the main capacitor 5 is stopped.

If the charging voltage V ₁ of the main capacitor 5 reaches the set voltage and the charging voltage decreases before the trigger signal TG is generated, the detection voltage V ₂ and the high level first reference voltage V ₃ and the first comparator 10 of the first control circuit 100 based on
1, the first switch circuit 7 is repeatedly opened and closed, and the charging voltage _V1 is automatically controlled to be maintained at the set voltage.

Next, the first trigger signal is generated between when the leading edge of the transfer paper enters the fixing area and when it leaves the fixing area.
TG is generated, whereby a high voltage pulse is supplied from the trigger circuit 6 to the trigger wire 11,
At this time, the charging energy of the main capacitor 5 is supplied to the flash lamp 1 to generate a flash of light. The light energy at this time fixes the toner image in a first area corresponding to the effective fixing width on the leading edge side of the transfer paper.

On the other hand, the trigger signal TG is applied to the first timer circuit 102 and the second timer circuit in the first control circuit 100.
The second timer circuit 20 in the control circuit 200 of
2 simultaneously, the first timer circuit 102
and the second timer circuit 202 each start operating. That is, when the trigger signal TG is input, the set times T ₁ and
Outputs V ₇ and V ₈ are at H level only during T ₂ , during which transistors 103 and 203 are turned off, thereby cutting off outputs V ₅ and V ₆ of first comparator 101 and second comparator 201, As a result, the outputs V ₉ and V ₁₀ are at the L level for the set times T ₁ and T ₂ , respectively, and the outputs are switched to the first switch circuit 7 and the second switch circuit 8.
Both are opened, and the supply of current to the power transformer 3 is stopped. In this way, the main capacitor 5
This prevents current from being supplied from the power transformer 3 during the discharge period, thereby making it possible to stop the sustained discharge after the flash occurs and preventing damage to the electrodes.

After the flash occurs, the time from the occurrence of the trigger signal TG
After T ₁ has elapsed, the first timer circuit 10
The output V ₇ of V 2 returns to the L level again, which turns the transistor 103 on, and at this time the main capacitor 5 is discharged and the detection voltage V ₂
is lower than the high-level first reference voltage V ₃ , so the output V ₅ of the first comparator 101
is at H level, and thus the output _V9 becomes H level. When this output _V9 becomes H level, the first
The switch circuit 7 is closed in the same manner as described above, and current is again supplied to the power transformer 3 via the impedance element 71, and charging of the main capacitor 5 is restarted.

Next, in the second timer circuit 202, the difference is determined when the time _T2 has elapsed since the generation of the trigger signal TG, that is, when the output _V7 has switched to the L level.
The output V ₈ returns to the L level after a delay of T ₂ - T ₁ , which turns on the transistor 203, and at this time the detection voltage V ₂ returns to the low level second level.
Since it is lower than the reference voltage _V4 , the output _V6 of the second comparator 201 is at the H level, which causes the output _V10 to be at the H level. This output
When V ₁₀ reaches the H level, the second switch circuit 8 is closed in the same manner as described above, and current is supplied to the power transformer 3 with the impedance element 71 short-circuited to continue charging the main capacitor 5.

After the charging of the main capacitor 5 is completed in the same manner as described above, the second trigger signal TG is generated before the rear end of the fixed first area of the transfer paper leaves the fixing area, and the second trigger signal TG is generated as described above. In the same manner as above, the toner image is fixed in the second area following the first area of the transfer paper.

Such an operation is repeated a number of times depending on the length of the transfer paper in the conveying direction, and the fixing of the entire toner image on the transfer paper is completed. When the paper discharge detector 25 detects that the trailing edge of the transfer paper has left the fixing area after the final flash has been generated, a control signal is sent.
When the timing settings of CHG1, CHG2 and the trigger signal TG are canceled and the conveyance detector 24 is turned on by the next conveyed transfer paper, the timing of the control signals CHG1, CHG2 and the trigger signal TG are newly set. , the toner image is fixed in the same manner as described above.

According to the method described above, since charging of the main capacitor 5 is started by first supplying current to the power transformer 3 via the impedance element 71, the peak of the rush current flowing to the primary side of the power transformer 3 is reduced. Then, when a short time has elapsed from the start of charging, the second switch circuit 8 short-circuits the impedance element 71 to continue charging, so that the loss of power consumed by the impedance element 71 is small, and the main During the period from just before the charging of the capacitor 5 is completed until the charging is completed, current is again supplied to the power transformer 3 via the impedance element 71 to perform charging, so the impedance element 71 causes the peak of the current to rise. As a result, the power transformer 3 operates stably without magnetic saturation, and the biased magnetic phenomenon is reduced. Therefore, when charging of the main capacitor 5 is started again at a short time interval after the occurrence of a flash, the power transformer 3's primary In addition to the inrush current flowing to the side becoming smaller, the ripple after rectification is also small, and the charging voltage matches the set voltage with high precision.As a result, charging of the main capacitor 5 on the primary side of the power transformer 3 is started. Switching element 7 inserted for stopping
The impedance element 7 can be operated stably without destroying the main capacitor 2, and the main capacitor 5 can be repeatedly charged and discharged in a short time.
1 can be reduced, and as a result, the main capacitor 5 can be charged and discharged stably and economically, and the flash lamp 1 can be caused to emit light repeatedly in a short period of time, thereby fixing toner at high speed. .

Since the voltage detector 9 has one detection point for the charging voltage of the main capacitor 5, and the detection voltage at this detection point is commonly input to the first comparator 101 and the second comparator 201, The magnitude of the set voltage at the time of completion of charging of the main capacitor 5 is set to a high level first reference voltage.
It can be independently selected by appropriately adjusting the size of _V3 . The opening and closing timings of the first switch circuit 7 and the second switch circuit 8 are set using a high-level first reference voltage V ₃ .
This can be done by adjusting the magnitude of the second reference voltage _V4 , which is at a low level relative to the voltage, so that the above-mentioned timing can be arbitrarily adjusted.

[Modified example]

The first switch circuit 7 and the second switch circuit 8 may be connected as shown in FIG. 4, for example. That is, in this example, the impedance element 71 and the switching element 72 are connected in series to the primary side of the power transformer 3, and the impedance element 71
A switching element 81 constituting the second switch circuit 8 is connected in parallel to the switching element 81.

The first charging voltage source at a high level and the second reference voltage source at a low level are, for example, as shown in FIG.
A resistor 501 and a Zener diode 502 are connected in series to a common DC power source 500, and voltage dividing resistors 503, 504,
505, voltage dividing resistor 503 and voltage dividing resistor 50
A high level first reference voltage from connection point 506 of
Take out V ₃ and connect voltage dividing resistor 504 and voltage dividing resistor 50
5 from the connection point 507 of the low level second reference voltage.
It may also be configured to take out _V4 . The DC power source 500 may also be configured to use a power source for driving the timer ICs 31 and 41.

The first control circuit 100 and the second control circuit shown in FIG.
The specific configuration of the control circuit 200 is an example, and
A configuration for providing similar control functions may be freely selected.

〔Effect of the invention〕

As explained in detail above, the present invention charges a main capacitor for energy supply via a power transformer and a rectifier, supplies the charged energy of the main capacitor to a flash lamp to emit light, and generates light energy. A toner fixing method for fixing toner by a first switch circuit including a series circuit of an impedance element and a switching element on the primary side of the power transformer;
A second switch circuit consisting of a switching element is inserted, and in charging the main capacitor,
With the second switch circuit open and the first switch circuit closed, electricity is supplied to the power transformer via the impedance element to start charging the main capacitor,
Then, after a delay, the second switch circuit is closed and current is continued with the impedance element of the first switch circuit short-circuited, so that the detection voltage of the voltage detector that detects the voltage corresponding to the charging voltage of the main capacitor reaches the first switch circuit.
When the level reaches or exceeds the second reference voltage, which is lower than the reference voltage of
The first switch circuit is opened and the power transformer continues to be energized via the impedance element of the first switch circuit, and after a delay, the detected voltage of the voltage detector corresponds to the set voltage of the main capacitor required for fixing the toner. When the voltage reaches a first reference voltage, which is the voltage to
After that, the charged energy of the main capacitor is supplied to the flash lamp to cause it to emit light, and the toner is fixed by repeating the flash lamp's light emission. To provide a toner fixing method that can safely charge a main capacitor without causing a large inrush current by preventing this phenomenon, and can cause a flash lamp to emit light repeatedly in a short period of time to fix toner at high speed. can do.

[Brief explanation of the drawing]

FIG. 1 is an explanatory sectional view schematically showing an example of a toner fixing device that can be used in the present invention, FIG. 2 is an explanatory circuit diagram showing an example of an electric circuit portion for causing a flash lamp to emit light, and FIG. Figure 3 is the second
An explanatory time chart showing the output state of each part of the electric circuit shown in the figure, Fig. 4 is an explanatory circuit diagram showing a modification of the first switch circuit and the second switch circuit, and Fig. 5 is a reference voltage source. It is an explanatory circuit diagram showing a modification of . 1... Flash lamp, 11... Trigger wire, 21... Lamp cover, 23... Conveyance belt, 24... Conveyance detector, 25... Paper discharge detector,
3... Power transformer, 4... Rectifier, 5... Main capacitor for energy supply, 6... Trigger circuit, 7... First switch circuit, 71... Impedance element, 72... Switching element, 8...
...Second switch circuit, 81...Switching element, 9...Voltage detector, 91...Detection point, 100
...first control circuit, 101...first comparator, 102...first timer circuit, 200...
Second control circuit, 201... Second comparator, 202... Second timer circuit, 300... High level reference voltage source, 400... Low level reference voltage source, 500... DC power supply, 502 ... Zener diode, 503, 504, 505... Voltage dividing resistor.

Claims (1)

[Claims] 1. A main capacitor for energy supply is charged via a power transformer and a rectifier, and the charged energy of this main capacitor is supplied to a flash lamp to emit light, and the toner is fixed by the light energy at this time. The toner fixing method includes a first circuit including a series circuit of an impedance element and a switching element on the primary side of the power transformer.
A switch circuit and a second switch circuit consisting of a switching element are inserted, and when charging the main capacitor, the second switch circuit is opened and the first switch circuit is closed, and the power is supplied via the impedance element. The transformer is energized to start charging the main capacitor, and then the second switch circuit is closed after a delay, and energization is continued with the impedance element of the first switch circuit short-circuited to generate a voltage corresponding to the charging voltage of the main capacitor. When the detection voltage of the voltage detector detecting the voltage exceeds the second reference voltage, which is lower in level than the first reference voltage, the second comparator opens the second switch circuit and the first switch circuit is switched on again. The power transformer continues to be energized through the impedance element, and after a delay, the detected voltage of the voltage detector reaches a first reference voltage, which is a voltage corresponding to the set voltage of the main capacitor necessary for fixing the toner. At times, the first comparator opens the first switch circuit to stop energizing the power transformer, and then the charging energy of the main capacitor is supplied to the flash lamp to cause it to emit light, and such flash lamp light emission is repeated. A toner fixing method characterized in that the toner is fixed by using the toner fixing method.