JPS6349801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a load power stabilizing device that always keeps the load power in an exposure lamp of a copying machine or the like constant regardless of fluctuations in the power supply or the like.

[Conventional technology]

For example, load power stabilizing devices (lamp regulators) used in lighting circuits for exposure lamps in copying machines have conventionally been of the following types.

(A) The average value of the voltage or current of the lamp is detected by an averaging circuit, and the phase of the power supply to the lamp is controlled according to the error between the detected average value and the reference value to keep the supplied power constant. This method keeps the amount of light from the lamp constant.

(B) Detects the approximate effective value of the lamp voltage using the nonlinearity of a diode, etc., and supplies power to the lamp by controlling the phase according to the error between the detected approximate effective value and the reference value. A method of keeping the power constant, thereby keeping the lamp light intensity constant.

(C) The effective value of the voltage or current of the lamp is detected using the fact that the amount of heat generated or light emitted by the lamp is proportional to the effective value of the applied voltage or current, and the error between the detected effective value and the reference value is A method that adjusts the phase of the power supply to the lamp to keep the supplied power constant, thereby keeping the amount of light from the lamp constant.

However, the lamp regulators according to each of the above methods (A) to (C) have the following drawbacks (A) to (C), respectively.

(b) In order to keep the lamp light intensity constant, it is necessary to keep the effective value of the lamp voltage or current constant;
If the AC waveform does not change, the ratio of the effective value to the average value (waveform ratio) is constant, so the same effect can be obtained even if the average value is kept constant.

However, since the method (A) performs phase control, the AC waveform changes and the waveform rate changes, making it impossible to keep the lamp light amount constant using the average value.

(B) In method (B), accuracy approximately equivalent to the effective value detection method can be obtained in a narrow range of phase changes, but sufficient accuracy cannot be ensured over a wide range of phase changes, and The circuit itself is complex.

(C) In method (C), the response is poor because detection takes time, and when detecting lamp light emission using a light receiving element, a separate pilot lamp that is lit under the same conditions as the exposure lamp is used. Therefore, maintenance is required to prevent lamps from burning out and dirt.

Another possibility is to calculate the effective value using effective value conversion using the steepest descent method, which is used in measuring instruments, but the calculation circuit is complicated and there is a cost problem.

In view of this background, the present applicant has previously proposed that the effective value or root mean square value of the voltage or current of the load can be obtained by matching the source bias voltage with the pinch-off voltage between the input and output of a field effect transistor. A load that is detected using the square-law characteristic of , and that maintains the load power constant by controlling the phase of the power supply to the load according to the error between the detected effective value or root mean square value and a preset reference value. A power stabilizing device was proposed in Japanese Patent Application No. 156656/1983 (Japanese Patent Application No. 79310/1983).
A patent application has been filed as No.

The square-law characteristic of the electric field transistor used in the invention will be explained with reference to FIG.

Drain (output) current _ID and gate current of N-channel field effect transistor (FET) 1
The relationship I _D = I _DSS (V _GS /V _P −1) ² ...(1) holds between the input voltage V _GS between the sources.

In addition, in equation (1), I _DSS is the gate G of FET1
When shot between the source S and the drain saturation current (V _GS = 0), V _P is the pinch-off voltage (I _D =
value of |V _GS | to become 0).

Since the input voltage V _GS is the value obtained by subtracting the gate input voltage V _G from the source bias voltage V _S , (1)
The formula is ID=I _DSS (V _S /V _P −V _G /V _P −1) ² ...(2).

In this equation (2), if V _S =V _P , then I _D =I _DSS /V _P ² ·V _G ² =KV _G ² (3). Note that K=I _DSS /V _P ² is constant.

Therefore, for example, by adjusting the variable resistor R _S that constitutes the bias circuit, the source bias voltage V _S
If I make it match the pinch-off voltage V _P of FET1, the output current I _D of FET1 will be equal to the gate input voltage
It is proportional to the square of V _G , and its output voltage V ₀ is also shown in equation (4), V ₀ = V _DD −I _D・R _D = V _DD −K・R _D・V _G ² ……( 4) Contains a component proportional to the square of the input voltage V _G. Note that R _D in formula (4) is the resistance value of the drain resistance.

Therefore, by inputting a DC voltage corresponding to the lamp voltage into the square circuit consisting of FET 1 set in this way and averaging the output using an integrating (smoothing) circuit, it is possible to obtain a value corresponding to the root mean square value of the lamp voltage. A value is obtained, and by taking the square root of the value, a value corresponding to the effective value can also be obtained.

If this is applied to a load power stabilizing device, the root mean square value or effective value of the load voltage or current can be detected quickly and accurately over the entire phase change range with a very simple circuit configuration. The power supplied to the lamp can also be controlled with high precision, and the amount of light from the lamp can always be kept constant.

[Problem to be solved by the invention]

However, the above-mentioned squaring circuit has the following drawbacks.

That is, the pinch-off voltage V _P of the FET 1 generally has a positive temperature coefficient, and the value increases as the temperature rises. Therefore, if the source bias voltage V _S of FET1 is constant, V _S = V _P due to temperature change.
As a result, the squared output V ₀ will change even if the gate input voltage V _G is constant.

This invention has been made in view of the above points, and is intended to maintain the condition that Vs = Vp at all times even when the temperature changes in a load power stabilizing device using the effective value or root mean square value detection circuit as described above. It is an object of the present invention to satisfactorily detect the effective value or root mean square value of the voltage or current of a load, and to maintain the load current constant.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a square characteristic between the input and output of a field effect transistor, which is obtained by making the effective value or root mean square value of the voltage or current of the load match the source bias voltage and the pinch-off voltage. In addition to detecting using
In a load power stabilizer that keeps the load power constant by controlling the phase of the power supply to the load according to the error between the detected effective value or root mean square value and a preset reference value, there is a A source bias circuit is provided that applies an output voltage obtained from the collector of a transistor whose emitter and collector are connected via an emitter load and a collector load, respectively, to the field effect transistor as a source bias voltage. is selected to have the same polarity as the temperature coefficient of the pinch-off voltage of the field-effect transistor, and by varying the ratio of the collector load and emitter load of this transistor, the temperature coefficient of the output voltage and the pinch-off voltage of the field-effect transistor can be adjusted. a first adjusting means for adjusting the collector load or the emitter load so as to match the temperature coefficient of the transistor; and adjusting the operating point of the transistor by changing the base potential of the transistor, and A second adjustment means is provided for adjusting the voltage to match the pinch-off voltage of the effect transistor.

[Effect]

With this configuration, the first adjustment means adjusts the temperature coefficient of the output voltage obtained from the collector of the transistor of the source bias circuit and the pinch-off voltage Vp of the field effect transistor to match, and the second adjustment means By adjusting the operating point of the transistor so that the output voltage matches the pinch-off voltage Vp of the field effect transistor, the output voltage is applied to the source of the field effect transistor as the source bias voltage Vs, so that the temperature increases. Even if the voltage changes, Vs and Vp change in the same way, and the relationship of Vs=Vp is always maintained.

Therefore, the above-mentioned problem is solved, and the effective value or root mean square value of the voltage or current of the load can be accurately detected and the load power can be kept constant.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3 of the drawings.

FIG. 2 is a block circuit diagram showing an embodiment in which the load power stabilizing device according to the present invention is applied to a lamp regulator of an exposure lamp of a copying machine.

In FIG. 2, the lamp 2 is connected to a bidirectional three-terminal thyristor (hereinafter referred to as "TRIAT") which is turned on by a trigger pulse _SP from a trigger pulse generation circuit 14 (described later), which is supplied with voltage from an AC power supply (AC200V) 4. )3 and is applied with phase control.

After this lamp voltage Vout is insulatedly detected by the lamp voltage detection transformer 5, the rectifier circuit 6
Both waves are rectified by

Next, the DC voltage Va that pulsates at twice the power supply frequency obtained in this way is squared by a squaring circuit 7 that also performs a temperature correction function to obtain a voltage V ₀
(V ₀ ∝Va ² ) is obtained.

This squaring circuit 7 consists of resistors R ₃ and R ₄ connected in series between the output terminals of the rectifier circuit 6, and a gate G connected to a resistor.
The drain D is connected to the power supply terminal d to which DC voltage (+12V) V _DD is supplied via the resistor R _{D ,} and the source S is connected to the ground via the capacitor C to the _four connection points a of R 3 and R, respectively. N-channel field effect transistor (FET) 1 and source bias voltage V _S
and a source bias circuit 8 that outputs.

This source bias circuit 8 consists of a variable resistor R ₁ and a resistor R ₂ connected in series between a power supply terminal d to which a DC voltage V _DD is supplied and the ground, a base connected to the connection point b, and an emitter connected to the emitter. The source bias circuit 8 consists of a transistor 9 connected to a power supply terminal d via a variable resistor Re serving as a load, and to ground via a resistor Rc serving as a collector load whose collector is connected in parallel to a capacitor C. It also acts as a compensator.

Note that the DC voltage V _DD supplied to the power supply terminal d
is supplied via a constant voltage circuit (not shown), so there is no voltage fluctuation and is constant.

Also, the resistance value of resistors R ₃ and R ₄ is the connection point a
The peak value of the gate input voltage V _G output from the gate is set to a value that does not exceed the gate-source voltage V _GS .

Furthermore, the capacitor C is connected to the gate input voltage V _G
This is provided to bypass the frequency component twice the power supply frequency.

Here, the source bias circuit 8, which performs a temperature compensation function, will be explained.

The output voltage of the source bias circuit 8 is output from the collector of the transistor 9 and is applied to the source of the field effect transistor as a source bias voltage V _S . Therefore, this source bias voltage
V _S is expressed as: V _S = Rc/Re(r・V _DD − V _BE )...(5) However, r=R ₁ /R ₁ + R ₂ , V _BE : Can be expressed as the voltage between the base and emitter of the transistor. The temperature coefficient ΔV _S /ΔT is
If the temperature coefficient of the DC voltage V _DD is zero, it can be expressed as ΔV _S /ΔV=−Rc/Re·ΔV _BE /ΔT (6) from equation (5).

In equation (6), the temperature coefficient ΔV _BE /ΔT of the transistor base-emitter voltage V _BE is a negative value (approximately -2 mV/°C), so the temperature coefficient ΔV _S /ΔT of V _S is , pinch-off voltage of FET1
Similar to the temperature coefficient of V _P , it is positive. Moreover, Rc/
By varying the value of Re, the temperature coefficient ΔV _S /ΔV
can be set arbitrarily.

Therefore, by varying the resistance value of the variable resistor Re, the temperature coefficient ΔV _S /ΔT of the source bias voltage V _S can be changed as follows.
Temperature coefficient of pinch-off voltage V _P of FET1 ΔV _P /ΔT
(for example, 4 mV/℃), and V _S =
If the resistance value of the variable resistor R ₁ is _varied and r (r=R ₁ /R ₁ +R ₂ ) is selected so that the pinch-off voltage V _p changes due to temperature change, Since the source bias voltage V _S changes accordingly,
The relationship _VS = _VP can always be maintained.

Thereby, the voltage V _G input to the gate G of the FET 1 is accurately squared according to the principle explained in FIG.

As is clear from the above explanation, in the bias circuit 8 shown in FIG.
The variable resistor R1 also serves as a first adjusting means for adjusting the temperature coefficient of Vp to match the temperature coefficient of the transistor 9, and the variable resistor _R1 adjusts the output voltage of the transistor 9 so that the output voltage Vs of the transistor 9 matches the pinch-off voltage Vp of the FET1.
This is a second adjustment means for adjusting the operating point of the transistor by changing its base potential.

Next, the output voltage V ₀ of this square circuit 7 is averaged by an averaging circuit 10 consisting of a smoothing circuit, etc., and the voltage
A DC voltage V _L (V _L ∝Vout ² ) proportional to the root mean square value of V _G , that is, the root mean square value of the lamp voltage Vout is obtained.

Then, if we take the square root of this DC voltage V _L , we get
A DC voltage proportional to the effective value of the lamp voltage Vout can be obtained, but once the value of the DC voltage _VL is determined, the relationship with its square root is constant, and the lamp regulator is not a measuring instrument but an effective value. In this embodiment, the direct current voltage V _L is used as it is, since it is sufficiently effective even without obtaining the value itself.

This DC voltage V _L and a reference voltage V _REF outputted from a reference voltage selection circuit (not shown) in accordance with a copy density signal from a control section of the copying machine are input to an inverting differential amplifier 11, and V _REF It increases or decreases depending on the voltage level of , and decreases as the difference between the two increases,
Obtain the error voltage V _ER that increases as it becomes smaller.

Next, this error voltage V _ER is combined with the sawtooth wave voltage V shown in FIG. _T is compared by the comparator 12, and at the time when V _ER = _V
Obtain the signal Sc to determine the firing angle of the triator 3.

Then, this signal Sc is input to the _trigger pulse generation circuit 14 to form a trigger pulse S _P shown in FIG. Triack 3 is applied to the gate of
is turned on, thereby controlling the phase of the supply voltage waveform to lamp 2.

In this way, if the lamp voltage Vout increases for some reason, the voltage V _G will also increase. Voltage V _G
rises, the output V ₀ of the squaring circuit 7 increases to the voltage V ² _G
(see equation (4)), and the output V _L of the averaging circuit 10 also decreases.

Then, when the reference voltage V _REF is constant and the voltage V _L decreases, the error voltage output from the differential amplifier 11
Since V _ER increases, the trigger pulse generation circuit 14
The generation phase of the trigger pulse S _P output from is delayed.

That is, the cut-off phase angle .theta. (shown in FIG. 3C) of the triax 3 increases, and the voltage Vout applied to the lamp 2 decreases.

Further, when the lamp voltage Vout decreases, the cut-off phase angle θ of the triax 3 decreases, contrary to the above case, and the lamp voltage Vout increases.

Thus, the voltage Vout applied to the lamp 2
When Vout changes, it returns to its original value, so the root mean square value of the lamp voltage Vout is always kept constant. In other words, the effective value voltage of the lamp voltage becomes constant.

As a result, the lamp power becomes constant, and the amount of lamp light also becomes constant. Therefore, since the color temperature of the lamp is constant, the color rendering properties of copies can always be constant.

In the above embodiment, a method of detecting the root mean square value of the lamp voltage has been described, but a method of detecting the root mean square value or the effective value of the lamp current may also be used.

Further, in the above embodiment, the present invention was applied to a lamp regulator of an exposure lamp of a copying machine, but it goes without saying that the invention can also be applied to a regulator of an AC load other than a lamp.

〔Effect of the invention〕

As explained above, in the load power stabilizing device according to the present invention, the source bias voltage is changed in accordance with the fluctuation of the pinch-off voltage due to temperature in the squaring circuit that utilizes the squaring characteristic of the field effect transistor, and both of them are Since the voltage is generated by a bias circuit that has a temperature compensation function that always matches the voltage, the effective value or root mean square value of the voltage or current of the load can be accurately detected and controlled even if the environmental temperature changes. .

Therefore, it is possible to perform power control with high accuracy of approximately ±1%.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of a squaring circuit used in a load power stabilizing device, which is the premise of this invention. Second
The figure is a block circuit diagram showing an embodiment of the present invention. 3A to 3C are signal waveform diagrams for explaining the operation of FIG. 2. 1... Field effect transistor (FET), 2...
Lamp, 3...triax, 7...square circuit,
8... Source bias circuit, 9... Transistor, 10... Average circuit, 11... Differential amplifier, 1
2... Comparator, 13... Sawtooth wave generation circuit, 14
...Trigger pulse generation circuit, 15...Pulse transformer, Re...Variable resistor (emitter load, first adjustment means), _R1 ...Variable resistance (second adjustment means).

Claims (1)

[Claims] 1. The effective value or root mean square value of the voltage or current of the load is determined by using the square characteristic between the input and output of the field effect transistor obtained by matching the source bias voltage with the pinch-off voltage. In a load power stabilizing device that detects the detected effective value or root mean square value and controls the phase of the power supply to the load according to the error between the detected effective value or root mean square value and a preset reference value to keep the load power constant. , a source bias circuit is provided between the power supply and the ground for applying an output voltage obtained from the collector of the transistor whose emitter and collector are connected via an emitter load and a collector load, respectively, to the field effect transistor as a source bias voltage; By selecting the temperature coefficient of the output voltage to have the same polarity as the temperature coefficient of the pinch-off voltage of the field effect transistor, and varying the ratio of the collector load and emitter load of this transistor, the temperature coefficient of the output voltage and a first adjusting means for adjusting the collector load or emitter load so as to match the temperature coefficient of the pinch-off voltage of the field effect transistor; and adjusting the operating point of the transistor by changing the base potential of the transistor. and a second adjusting means for adjusting the output voltage to match the pinch-off voltage of the field effect transistor.