JP2001218462A - Controllable power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain control of the frequency and level of output AC finely, setting of the frequency and the level of the output AC with one electric pulse from a controller, and simplification, miniaturization, and cost reduction in an electric circuit. SOLUTION: This controllable power supply circuit 70 generates a clock C in a differentiation circuit 30 from the electrical pulse A and rectangular waves D, E or a sine wave F in a waveform generating circuit 41, or 42, boosts the wave with an amplifier circuit 50 and a booster transformer 60 to obtain AC high voltage, converts a duty Td/Ts of the electric pulse A into an analog signal B in an integration circuit 20, and controls the conductivity of a transistor 51 corresponding to the level of the signal B to change the primary drive voltage in the booster transformer 60. The primary of the booster transformer 60 is switched with the rectangular wave (FIG. 1) or the sine wave is AC- amplified 54 to feed it to the primary (FIG. 2). The secondary winding of the booster transformer 60 is DC-biased in DC booster circuits 71-73.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device capable of controlling an AC output level and a frequency, and more particularly, but not exclusively, to varying an output frequency and an output voltage or current used in an electrophotographic apparatus. The present invention relates to an AC high-voltage power supply that can be used.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, in a contact charging in which a DC biased AC voltage is applied to a charging roller in contact with a photosensitive member, the frequency and / or level of the AC voltage is adjusted. For example, Patent No. 282
In the specification of Japanese Patent No. 2702, a target value data of an AC voltage is supplied from a CPU to a D / A converter, and a deviation of a feedback signal of an AC voltage applied to the contact charging roller with respect to an output voltage of the D / A converter is determined by a comparator. There has been proposed a power supply device that calculates, amplifies by adding the deviation to the sine wave reference level, and applies the amplified voltage to the primary winding of the step-up transformer. The specification of Japanese Patent No. 2822702 mentions the selection of an AC frequency, but does not disclose a means for adjusting the AC frequency. Japanese Patent No. 2826918 discloses an AC power supply device that automatically adjusts an AC frequency so as to resonate with the electric capacity of a charging roller. Also, JP-A-11-5
Japanese Patent Publication No. 2684 discloses a power supply device which includes two AC power supplies having different frequencies and two AC power supplies having different peak voltages, and selects an output of one of the power supplies by a switch at an output stage and supplies the output to a load. ing.

[0003]

The above-mentioned Japanese Patent No. 28227 is disclosed.
No. 02 describes that a target value of the AC voltage is input from the CPU, a predetermined AC high voltage is obtained in response thereto, and the frequency is switched in two stages. Although there is no description on the method of switching the frequency, the normal frequency switching requires the provision of two oscillators in the high-voltage power supply, and the configuration is complicated, large, and expensive. Further, it is difficult to perform frequency switching in multiple stages. Japanese Patent No. 2826918 discloses that a duty (Duty) 50 from a port of a CPU.
% High frequency sine wave
There is no means for changing the output level (level). Japanese Patent Application Laid-Open No. H11-52684 requires two AC power supplies having different frequencies and two AC power supplies having different peak voltages, and the configuration is complicated, large, and expensive. In order to switch the high voltage output stage, large and expensive switch means are required, and the device becomes expensive and large. In addition, the high voltage switch means has a short life and cannot ensure reliability.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a power supply device capable of finely adjusting the frequency and level of an output voltage, wherein the frequency and level of the output voltage are set by one control signal from a control circuit. A second object is to provide a power supply device that can be obtained, and a third object is to provide a power supply device that has a simple, small, and low-cost electric circuit.

[0005]

(1) Means (20) for converting the duty of an electric pulse (A) as a control signal into a voltage level (B); and the electric pulse (A) and the voltage level
(B), in response to the electric pulse (A), a frequency proportional to the frequency, the AC level generating means for generating an AC voltage of a level proportional to the voltage level (B) (30,41 / 42,50, 60); a controllable power supply comprising:

[0006] In order to facilitate understanding, the reference numerals of the corresponding elements or corresponding items of the embodiment shown in the drawings and described later are added for reference in parentheses. The same applies to the following.

The level of the output voltage is defined by the duty of the electric pulse (A) which is a control signal.
The frequency of the output voltage is defined by the frequency (A). The duty and frequency of the electric pulse (A) are determined by the pulse generation period (Ts) and the high-level H period (Td), both of which can be finely and easily adjusted. The frequency and level of the output voltage can be finely adjusted. Further, the frequency and level of the output voltage can be set by one control signal from the control circuit (10), that is, the electric pulse (A). The number of signal lines to the control circuit is minimized.

The duty of the electric pulse (A) is changed to the voltage level
The means (20) for converting to (B) can be, for example, an integration circuit having a relatively simple configuration as in the embodiment described later,
Further, the AC generating means (30, 41/42, 50, 60) is, for example, mainly a step-up transformer (60), in addition thereto, in synchronization with the electric pulse (A), as in the embodiment described later. A clock generation circuit (30) and a waveform generation circuit (41/42) for generating a square wave or a sine wave, and a square wave or a sine wave proportional to the voltage level (B) applied to the primary winding of the step-up transformer (60). An amplifier circuit (50) for supplying a current obtained by amplifying a wave can be provided, so that the power supply circuit can be simplified, small, and low in cost.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (2) The AC generating means (30, 41/4)
Means for generating an energization signal (D, E / F) having a frequency proportional to the frequency of the electric pulse (A) (30, 41/42); and the voltage level (B) Means for generating an AC voltage having a level proportional to the voltage level (B) and a frequency proportional to the frequency of the energization signal (D, E / F) in response to the energization signal (D, E / F) ( 50,60);

The means (30, 41/42) for generating an energizing signal (D, E / F) having a frequency proportional to the frequency of the electric pulse (A) is, for example, an electric pulse (A, It can be composed of a clock generation circuit (30) that generates a clock (C) synchronized with A) and a waveform generation circuit (41/42) that generates a square wave or a sine wave in synchronization with the clock (C). Means to occur
(50,60) is a current obtained by amplifying the rectangular wave or the sine wave in proportion to the voltage level (B) in the step-up transformer (60) and its primary winding,
And an AC generator (30, 41/42, 50, 60) that is simple, small, and low in cost.

(3) The means (50, 6) for generating the AC voltage
0) is to apply a drive voltage according to the voltage level (B) to the step-up transformer (60) and its primary winding (61), and energize in synchronization with the energization signal (D, E / F). Amplifying means (50). The means (50, 60) for generating the AC voltage can be simple, small, and low in cost.

(4) The step-up transformer of the amplifying means (50)
The means for applying a drive voltage according to the voltage level (B) to the primary winding (61) of (60) is provided between the primary winding (61) and a DC power supply line (24 V) for supplying power thereto. And a semiconductor element (51) that conducts according to the voltage level (B). The semiconductor element (51) is a transistor 51 in an embodiment described later.
It is. The voltage level (B) is an analog voltage, and it suffices to define the output voltage level. The primary current that defines the output voltage level of the step-up transformer (60) is determined by a relatively simple electric circuit using the transistor 51. Can be determined.

(5) The energization signal generating means (30, 41)
A square wave (D, E) having a frequency proportional to the electric pulse (A) is generated, and the energization signal (D, E) is applied to the primary winding (61) of the boosting transformer (60) of the amplifying means (50). The means for energizing in synchronization with E) includes switching elements (52, 53) that are turned on / off by the rectangular waves (D, E). Thereby, the amplification means (50)
Simple, small, and low cost.

(6) The energization signal generating means (30, 42)
A sine wave (F) having a frequency proportional to the electric pulse (A) is generated, and a primary winding of a step-up transformer (60) of the amplifying means (50) is generated.
(61) means for energizing the energizing signal (F) in synchronization with the energizing signal (F) includes an AC amplifier (54) that is fed by the semiconductor element (51) and amplifies the sine wave (F), and outputs the output from the primary winding Line (6
Includes a capacitor (55) that feeds 1). This allows amplification means
(50) can be simplified, small, and low in cost.

(7) In the AC high-voltage power supply (70) for outputting an AC high voltage, the duty ratio of the pulse signal (A) is set at a frequency synchronized with the input pulse signal (A) from the control circuit (10). An AC high-voltage power supply device characterized in that a proportional output is obtained.

According to this, the frequency and voltage level of the output AC voltage can be freely varied with one signal (A) from the control circuit (10), so that the signal line with the control circuit (10) is minimized. No problem. In addition, since the control circuit (10) only needs to output a signal (A) having a predetermined frequency and a predetermined duty, the output can be freely changed in fine steps. Further, with such a configuration, the AC high-voltage power supply circuit can be simple, small, and low in cost.

(8) Means (30) for generating a clock signal (C) synchronized with the input signal (A), and an oscillation signal from the clock signal (C)
Means (41/42) for generating (D, E / F), means (52, 53, 60) for boosting the oscillation signal (D, E / F), and the duty of the input signal (A) is converted to an analog value (B Means), and the analog value
An AC high-voltage power supply device comprising: means (51) for changing the drive voltage of the means for increasing the voltage (52, 53, 60) according to (B).

A clock signal (C) is generated from the input signal (A),
Then, an oscillating waveform (D, E / F) is created and boosted to obtain an AC high voltage. In order to set the duty of the input signal (A) as the target value of the output value, an analog value corresponding to the duty is used.
(B), and booster means (52,
53, 60), which can change the drive voltage of the step-up transformer (60), and can provide a high-voltage power supply that can freely change the frequency and level of the output voltage with a simple configuration, small size and low cost.

(9) Means for creating clock signal (C) (30)
Is a differentiating circuit (30:31 to 34). Since the input signal (A) is converted into the clock (C) by the differentiating circuit (30), the means (30) is
Simple, small, and low cost.

(10) The means (20) for setting the duty of the input signal (A) to the analog value (B) is an integrating circuit (20: 21 to 28). Since the input signal (A) is converted into the analog value (B) by the integration circuit (20), the means (20) can be made simple, small, and low in cost.

(11) Means for generating oscillation signal (D, E / F) (41/4
2) is a waveform shaping circuit (41/42) that generates a square wave (D, E) or a sine wave (F) synchronized with the clock signal (C), and a means for applying a drive voltage to the step-up transformer (60). Is a DC amplifier (5
1), including an AC amplifier (54) and a capacitor (55), a DC amplifier (51) feeds the AC amplifier (54) in proportion to the analog value (B), and the AC amplifier (54) supplies a capacitor (55). The power is supplied to the step-up transformer (60) via.

(12) A rectangular wave (D, E) or a sine wave (F) is created from the clock (C) by the waveform shaping circuit (41/42), and the resulting signal is amplified by the AC amplifiers (51, 54) and then the capacitor. Input to the step-up transformer (60) by coupling and the amplification factor of the amplifiers (51, 54)
A simple, low-cost, compact AC high-voltage power supply circuit that varies the frequency and voltage level of the AC output voltage with a configuration that changes the analog value (B) representing the duty of (A).

(13) The means for generating the oscillation signal is a waveform shaping circuit (41) for generating rectangular waves (D, E) synchronized with the clock signal (C), and means for driving the step-up transformer (60). Are the transistors (52, 53), and the means for changing the drive voltage connected to the step-up transformer (60) is a transistor (5) for changing the input voltage of the step-up transformer (60) according to the analog value (B).
1). Square wave (D, E) waveform shaping circuit from clock (C)
(41), thereby driving the transistors (52, 53) connected to the step-up transformer (60), and changing the input voltage of the step-up transformer (60) to an analog value proportional to the duty of the input signal (A).
Since the AC high-voltage output can be varied by the configuration changed in (B), the AC high-voltage power supply circuit can be made simple, low-cost, and compact.

(14) The above-mentioned AC high-voltage power supply (70) is used for charging or developing bias of the electrophotographic apparatus, and the control circuit (10) of the electrophotographic apparatus is adapted to environmental fluctuations, aging fluctuations and image forming conditions. In accordance therewith, the required AC high voltage frequency and output voltage value are determined, and the corresponding control signal (A) is output to the AC high voltage power supply (70). According to this, an AC high voltage of a necessary frequency and voltage value can be obtained freely, so that an electrophotographic apparatus with high image quality and high reliability can be realized.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1A shows a first embodiment of the present invention. The controllable power supply circuit 70 of this embodiment applies a charging voltage to a charging roller of a contact charging type electrophotographic apparatus. A control signal A for specifying the frequency and voltage value of this voltage is supplied from the controller 10 for controlling the image forming process of the electrophotographic apparatus to the controllable power supply circuit 70.

The electrophotographic apparatus includes a photosensitive member, a charging roller,
Image exposure unit, developing unit, transfer unit, fixing unit, operation / display unit,
Various motors, solenoids, clutches, sensors, lamps,
An electric element such as a heater and a controller 10 for controlling these operations are included. An AC high voltage of a rectangular wave or a sine wave is applied to the contact charging roller that applies a charge to the photoconductor by the controllable power supply circuit 70 shown in FIG. 1 (first embodiment) or FIG. 2 (second embodiment). . Alternatively, the controllable power supply circuit 70 shown in FIG. 3 (third embodiment) applies a high voltage in which a rectangular or sine wave AC high voltage and a DC high voltage are superimposed.

A high voltage obtained by superimposing a rectangular wave or a sine wave AC high voltage or a DC high voltage on the AC voltage is also applied to the controllable power supply circuit 70 shown in FIG.
Is applied from a controllable power supply circuit having the same configuration as that of.

The frequency and voltage value of the AC high voltage, and similarly the output voltage or output current of the DC high voltage, vary depending on the ambient temperature, humidity, developer density, image exposure light amount, and fatigue deterioration of the photosensitive member. It is appropriately adjusted and set in accordance with various intentions, such as a change in physical conditions, an image to be formed with what characteristics, suppression of ozone and AC noise, and the like.

The controller 10 is a microcomputer system which reads the states or instruction inputs of the various electric elements described above, starts an image forming process, and controls the progress of the image forming process. The microcomputer system mainly includes a CPU, a ROM, a RAM, and an input / output interface. Yes, specifically, control of motor speed, rotation direction, ON / OFF timing, ON / OFF timing control of solenoids and clutches, reading of sensor output and change of control conditions based thereon, control of lamp voltage, heater temperature And control of the output frequency, output voltage, output current and ON / OFF timing of the high voltage power supply.

In this embodiment, the CPU (not shown) in the controller 10 controls the frequency and voltage value of the AC voltage to be output from the controllable power supply circuit 70 (the cycle value data Ts defining the frequency and the voltage value). High-level H-width data Td) is determined, and these cycle value data Ts and high-level H-width data Td are transferred to the controller 10 via an address bus, a data bus, and a control signal line (not shown). The data is loaded into a PWM timer (timer IC) 11 included in the output interface. That is, the data Ts and Td are stored in the PWM timer 1
1 to switch the clear signal CLR from the clear instruction level L to the timer operation instruction level H.

In response to this switching, the PWM timer 11
Latches the data Ts and Td in itself, switches the signal level of the output port from the low level L to the high level H, and starts timing each time represented by the data Ts and Td. Thereafter, when the time represented by the data Td has elapsed, the signal level of the output port is returned from the high level H to the low level L. When the time represented by data Ts has elapsed, the signal level of the output port is switched from low level L to high level H, and data Ts and Td are again output.
Start timing each time represented by. Clear signal CLR
During the timer operation instruction level H, the PWM timer 11 repeats such an operation, so that the output port of the PWM timer 11 outputs an electric pulse A having a waveform shown in FIG. The frequency of the pulse A is 1 / Ts Hz when Ts is in seconds, and the duty is Td /
Ts [(Td / Ts) × 100% in percentage expression].

When the CPU of the controller 10 switches the clear signal CLR from the timer operation instruction level H to the clear instruction level L, the PWM timer 11 restricts its output to a low level L and stops the above-described timer operation.

Electric pulse A generated by PWM timer 11
Is amplified by the amplifier 12 and is controlled by the D
/ V (duty / voltage) conversion circuit 20 and synchronous clock generation circuit 30.

The D / V conversion circuit 20 is a kind of integrating circuit, and when the electric pulse A is at a high level H, the input transistor 22 is turned on, whereby the charging transistor 25 is turned on.
Conducts and charges the integrating capacitor 26. While the electric pulse A is at the low level L, since the transistors 22 and 25 are off (non-conductive), the integrating capacitor 26 is not charged and is gradually discharged through the resistor 27. While the electric pulse A is pulsating (high and low fluctuations), the charging voltage of the integrating capacitor 26 is equal to the duty (Td) of the electric pulse A.
/ Ts). This charging voltage is used as a signal (AC voltage instruction signal) B representing the duty of the electric pulse A as the base (control) of the transistor 51 inserted between the 24 V DC power supply line and the primary winding 61 of the step-up transformer 60. Terminal). Accordingly, the conductivity (conductivity) of the transistor 51 is proportional to the duty of the electric pulse A via the signal B. The transistor 51 outputs an output voltage proportional to the base voltage from the emitter to supply power to the primary winding 61 of the step-up transformer 60.

The synchronous clock generating circuit 30 is a kind of differentiating circuit. When the level of the electric pulse A rises from a low level L to a high level H, a resistor 31 and a capacitor 3 are connected.
A capacitor charging current flows through the resistor 2 and the resistor 33, and a pulse voltage C appears on the resistor 33. Conversely, when the level of the electric pulse A falls from the high level H to the low level L, the capacitor 32 discharges toward the amplifier 12, but since the discharge at this time flows through the diode 34 in the forward direction, The signal C has substantially no voltage fluctuation.

From the low level L to the high level H of the electric pulse A
The pulse signal C synchronized with the rising edge of the waveform is applied to the waveform generation circuit 41. In this embodiment, the waveform generating circuit 41 is an IC that generates a pair of rectangular waves D and E having a duty of substantially 50% and a phase difference of 180 ° in synchronization with the pulse signal C. Switching transistor 52,
53, and these transistors 52,
Numeral 53 turns on when the rectangular waves D and E are at the high level H and turns off when the rectangular waves D and E are at the low level L.

FIG. 1B shows the relative timing between the electric pulse A supplied from the controller 10 to the controllable power supply circuit 70 and the electric signals B to E generated by the controllable power supply circuit 70.

The transistor 51 of the amplifier circuit 50 supplies a current proportional to the duty Td / Ts of the electric pulse A to the primary winding 61 of the step-up transformer 60, and the switching transistors 52 and 53 supply the electric current to the electric pulse A. It is turned on / off at a frequency (cycle) proportional to the frequency (reciprocal cycle Ts). Accordingly, the secondary winding 62 of the step-up transformer 60 has a frequency proportional to the frequency of the electric pulse A,
An AC high voltage having a voltage level proportional to the duty Td / Ts of the electric pulse A is generated. Since the waveform generation circuit 41 outputs a rectangular wave, a rectangular wave high voltage is obtained at the output of the step-up transformer 60.

Second Embodiment FIG. 2A shows a second embodiment of the present invention, and FIG. 2B shows an electric signal of each part. In the second embodiment,
It is the same as the first embodiment shown in FIG. 1 in that the electric pulse A is integrated to obtain a drive voltage proportional to the duty of the electric pulse A from the emitter of the transistor 51.
The obtained drive voltage is supplied to the AC amplifier 54 as a power supply. The synchronous clock generating circuit 30 for generating the clock signal C from the electric pulse A is the same as in the first embodiment shown in FIG. The waveform shaping circuit 42 outputs a sine wave F synchronized with the clock signal C and inputs the sine wave F to the AC amplifier 54. The output of the AC amplifier 54 is applied to the primary winding 61 of the step-up transformer 60 via the capacitor 55. Step-up transformer 60
Secondary winding 62 generates a sinusoidal high voltage. Primary winding 61
A resistor 56 and a capacitor 57 between the terminals constitute a snubber circuit and also perform waveform shaping. In the second embodiment, a sine wave AC high voltage synchronized with the frequency of the electric pulse A, which is a control signal, and an AC high voltage of an output voltage or current proportional to the duty of the electric pulse A can be obtained.

Third Embodiment FIG. 3 shows a third embodiment of the present invention. This embodiment outputs a high voltage obtained by superimposing a DC voltage and an AC voltage. The configuration of the electric circuit that generates the AC high voltage is the same as that of FIG. The DC high voltage is generated by the DC high voltage generation circuits (71 to 73) in response to an electric pulse G which is a control signal provided by the controller 10. Electric pulse G
Is the CPU of the controller 10 like the electric pulse A.
Is generated by the PWM timer 13 based on the periodic data Ts ′ and the high-level section width data Td ′ given by The electric pulse G drives the transistor 71 connected to the primary side of the step-up transformer 72, and the high voltage obtained on the secondary side is converted into a DC high voltage by the rectifying and smoothing circuit 73, and the AC high voltage G
It is superimposed on the ND side, that is, one end of the secondary winding 62 of the step-up transformer 60.

The output DC voltage of the rectifying / smoothing circuit 73 is stepped down by a voltage dividing resistor 74 and applied to a light emitting diode of an insulating coupler 75 composed of a photocoupler. The signal is amplified by an interface amplifier, applied to an A / D conversion port in the controller 10, converted into digital data, and read by the CPU in the controller 10. This is the feedback of the DC output voltage.
The CPU calculates the duty of the electric pulse G for matching the output DC voltage of the rectifying and smoothing circuit 73 to the target DC voltage from the feedback data and the target DC voltage, and sets Ts ′ and Ts ′ to a value representing the calculated duty. Change Td '. That is, the DC high voltage generation circuits (71 to 73) are controlled so as to obtain a predetermined DC output. The target value of the DC output is set to a predetermined value depending on the temperature, humidity, elapsed time, image forming conditions, and the like.

In each of the embodiments described above, the transistor may be an FET. In this case, the terms base, emitter and collector are replaced with gate, source and drain. The waveform generation circuits 41 and 42 include TI
TL494 manufactured by Maxim Corporation or MAX038 manufactured by Maxim Corporation can be used. Alternatively, it may be constituted by a general-purpose logic IC or the like. The AC amplifier 54 has a LA6
500 or the like can be used.

[Brief description of the drawings]

FIG. 1A is an electric circuit diagram showing a configuration of a first embodiment of the present invention, and FIG. 1B is a time chart showing electric signals of respective parts of the controllable power supply circuit 70 shown in FIG.

FIG. 2A is an electric circuit diagram showing a configuration of a second embodiment of the present invention, and FIG. 2B is a time chart showing electric signals of each part of the controllable power supply circuit 70 shown in FIG.

FIG. 3 is an electric circuit diagram showing a configuration of a third embodiment of the present invention.

[Explanation of symbols]

 60: step-up transformer 61: primary winding 62: secondary winding 72: step-up transformer 74: voltage dividing resistor

Claims (6)

[Claims] Means for converting the duty of an electrical pulse, which is a control signal, to a voltage level; and, in response to the electrical pulse and the voltage level, a frequency proportional to the frequency of the electrical pulse being proportional to the voltage level. Controllable power supply device comprising: AC generation means for generating an AC voltage of a predetermined level. 2. The apparatus according to claim 1, wherein said AC generating means generates an energizing signal having a frequency proportional to a frequency of said electric pulse; and a level proportional to said voltage level in response to said voltage level and said energizing signal. 2. The controllable power supply according to claim 1, further comprising: means for generating an AC voltage having a frequency proportional to the frequency of the energization signal. 3. The means for generating an AC voltage includes a step-up transformer and an amplifying means for applying a drive voltage according to the voltage level to a primary winding thereof and energizing in synchronization with the energization signal. The controllable power supply according to claim 2. 4. The amplifying means for applying a drive voltage corresponding to the voltage level to a primary winding of a step-up transformer is interposed between the primary winding and a DC power supply line for supplying power to the primary winding. 4. The controllable power supply device according to claim 3, further comprising a semiconductor element that is turned on according to the voltage level. 5. The energizing signal generating means generates a rectangular wave having a frequency proportional to the electric pulse.
The controllable power supply device according to claim 4, wherein the means for energizing the primary winding of the step-up transformer in synchronization with the energization signal includes a switching element that is turned on / off by the rectangular wave. 6. The energizing signal generating means generates a sine wave having a frequency proportional to the electric pulse.
The means for energizing the primary winding of the step-up transformer in synchronization with the energization signal includes an AC amplifier that is supplied by the semiconductor element and amplifies the sine wave, and a capacitor that provides an output thereof to the primary winding. Item 5. A controllable power supply according to item 4.