JPH04111606U - Variable output constant voltage circuit - Google Patents

Abstract

(57) [Summary] [Purpose] The output voltage can be easily varied according to an external control signal, the influence of noise can be controlled, and a stable and highly accurate constant voltage can be output. Provides a variable output power supply device. [Configuration] Control voltage V _C is applied to the control electrode of transistor Q ₁
The present invention is characterized in that it is provided with a DC voltage output source that outputs.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention relates to a variable output constant voltage circuit, and in particular, the output voltage can be easily adjusted by an external signal. It is variable and provides a stable and highly accurate constant voltage. .

0002

[Conventional technology]

using electrophotographic processes such as plain paper copiers and laser beam printers. In the equipment, a charger is used to charge the photosensitive drum. Normally, chargers have high It is used by applying a voltage, but in order to keep the amount of charge on the photosensitive drum constant, the charger is The potential of the grid is kept constant. Constant voltage elements such as Zener diodes and varistors A constant voltage is obtained by connecting a constant voltage circuit to the grid.

0003 By the way, recently, in order to improve print quality such as adjusting print density, paper quality and usage environment have been changed. It is required to be variable in response to the environment.

0004 For this reason, in the past, as shown in FIG. Connect the diode ZD and apply the current I to the transistor._LWhile flowing, the resistance R₁,R ₂ and on the other hand, for example, a resistor R₁is made variable and the output voltage V_outadjust the there was.

That is, when the Zener voltage of the Zener diode ZD in FIG. 4 is V _ZD , the following formula holds true.

[0006]

[Math 1]

[0007] That is, the resistance R₁,R₂Or Zener voltage V_ZDBy appropriately choosing , any output voltage V_outcan be obtained. and resistance R₁or R₁can be externally By deforming the output voltage V_outcan be made variable. Figure 4 shows the resistance R ₁ Here is an example of making variable.

[0008]

[Problem that the idea aims to solve]

By the way, when configuring the resistor R ₁ or R ₂ to be made variable so that at least one of them is taken out to the outside, the following problem exists.

[0009] In the case of a corotron hybrid circuit, a high voltage and a small current on the order of μA are required. The circuit shown in FIG. 4 has extremely high impedance. For that reason It is easily affected by noise, which deteriorates the accuracy of the output voltage. like this In order to avoid this, it is possible to create a structure that allows the resistance to be varied by remote control, which would reduce the cost. Become something.

0010 Therefore, the purpose of the present invention is to have a simple configuration, which can be easily varied by external signals, and An object of the present invention is to provide a stable and highly accurate constant voltage circuit.

[0011]

[Means to solve the problem]

To achieve the above object, in the present invention, as shown in FIG. 1A, a resistor _R1 and a control voltage _Vc are inserted into the base of the transistor _Q1 , and a resistor _R2 is connected between the base and the collector. As a result, since the emitter potential is 0, if the output voltage is set to V _out , the following formula holds true.

0012

[Math 2]

[0013] Therefore, V _out =-V _C R ₂ /R ₁ .

[0014]

[Effect]

By making the control voltage V _C variable in this manner, the output voltage V _out can be made variable. Since the control voltage V _C is a direct current, the influence of noise can be removed by connecting a capacitor in parallel with it, so it is stable and highly accurate, and can also be controlled remotely. Can provide voltage power. Furthermore, by changing the control voltage V _C , the output voltage can be changed linearly.

[0015]

【Example】

Other embodiments of the invention will be described below.

FIG. 1(B) shows that in the first embodiment shown in FIG. 1(A), a plurality of fixed resistors r ₁ and r ₂ are used as the resistor R ₁ , or one of them is replaced with a variable resistor r ₃ . It is also possible to use a plurality of fixed resistors r ₄ and r ₅ as the resistor R ₂ in the same way as the resistor R ₁ , or to make one of them a variable resistor r ₆ . It is shown that. It is also shown that a power MOSFET or a normal MOSFET can be used as the transistor _Q1 .

[0017] In order to further improve the breakdown voltage, an element E is inserted on the collector side, and a resistor R is inserted as the element E. ₀ (more than one is possible), Zener diode ZD, varistor, etc. can be used. are doing.

Similar to FIG. 1A, the output voltage V _out can be made variable by adjusting V _C . Note that the power supply voltage is not shown in FIGS. 1A and 1B.

[0019] Figure 1(C) shows the output voltage V_outIndicates the case where is positive. In this case, transistor Q ₁ ’ control voltage V_C′ has negative polarity, and by making it variable, As in the previous case, the output voltage V_outcan be made variable.

A second embodiment of the present invention will be explained based on FIG. 2. In reality, however, the right side of the relational expression between V _out and V _C does not become zero, but becomes the base-emitter voltage V _BE of the transistor, resulting in the following equation.

[0021]

[Math 3]

[0022]

[Math 4]

[0023] Therefore, even if the control voltage V _C is zero, the term V _BE remains and does not become zero.

The embodiment of FIG. 2 improves this by applying a bias voltage _VE to the emitter in order to cancel this V _BE . By applying this bias voltage _VE , the following equation is established.

[0025]

[Math 5]

[0026]

[Math 6]

[0027] Therefore, if (V _E +V _BE ) becomes zero, the influence of the base-emitter voltage V _BE of the transistor Q ₁ can be canceled. Actually, a voltage such that V _E ≧−V _BE is applied to the emitter of the transistor Q ₁ . Note that this V _E provides a polarity opposite to the output voltage V _out . In this way, the output voltage V _out can be controlled from zero using the control voltage V _C .

Note that FIG. 2B shows a case where the output voltage V _out is positive. At this time, the bias voltage V _E ' has a negative polarity opposite to the output voltage V _out .

[0029] The specific circuits in FIGS. 2A and 2B will be explained with reference to FIGS. 3A and 3B.

FIG. 3A shows an example in which the output voltage V _out is negative -V _out , and the transistor Q ₂ is operated as an emitter follower. +V ₁ is applied to the emitter of transistor Q ₂ via resistor R ₃ , and the emitter of transistor Q ₂ is connected to the emitter of transistor Q ₁ .

[0031] When a positive voltage V _E smaller than V ₁ is applied to the base of the transistor Q ₂ , a sufficient current flows between the emitter and base of the transistor Q ₂ via V ₁ -R ₃ . V _E is applied to the emitter of transistor Q ₂ , that is, the emitter of transistor Q ₁ , which cancels out the V _BE of transistor Q ₁ , and the output voltage V _out is reduced to zero based on V _C by the following equation. It can be controlled from

[0032]

[Math 7]

FIG. 3B shows a case where the output voltage V _out is positive. In this case, transistor Q ₂ ' is connected to the negative voltage -V ₁ via resistor R ₃ . Since its operation is the same as that shown in FIG. 3(A), detailed explanation will be omitted.

FIG. 3(C) is an example in which a potential obtained by dividing the external control voltage V _C by resistors R ₄ and R ₅ is used as V _E in FIG. 3(A).

Further, FIG. 3(D) is an example in which V _C is used as +V ₁ in the case of FIG. 3(C).

FIG. 3(E) is the simplest configuration of the specific circuit in FIG. 2(A), and utilizes the constant voltage characteristics of a Zener diode, which is obtained by inserting a Zener diode into the emitter of transistor _Q1 . The purpose is to add a potential to the emitter of _Q1 .

In the case of FIG. 3(B), it is clear that a configuration similar to that of FIGS. 3(C) _, (D) _, and (E) can be achieved, so a detailed explanation will be omitted.

[0038] In this way, by using the external control voltage V _C , it is possible to configure a constant voltage power supply that can be easily varied.

[0039] In addition, in this invention, instead of transistors, composites such as FETs and Darlington circuits are used. elements can also be used.

[0040]

[Effect of the idea]

According to the present invention, since a DC voltage can be used as the control voltage V _C , noise can be easily removed by means such as connecting a capacitor in parallel. Therefore, it is possible to apply the control voltage V _C from the outside, and a constant voltage circuit can be obtained with a stable, highly accurate, and simple circuit. Moreover, the output can be controlled linearly by changing V _C .

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing the principle configuration of a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 shows a conventional constant voltage circuit.

[Explanation of symbols]

Q ₁ , Q ₁ ′ Transistor R ₁ , R ₂ Resistor V _C , V _C ′ Control potential

Claims (4)

[Scope of utility model registration request] [Claim 1] In a constant voltage circuit using a control element,
The constant voltage output terminal and the control terminal of the control element are connected through a resistor, and a DC voltage is applied to the control terminal through the resistor to obtain a constant voltage output corresponding to the DC voltage. Variable output constant voltage circuit. 2. The variable output constant voltage circuit according to claim 1, wherein a transistor is used as the control element. 3. The variable output constant voltage circuit according to claim 1, wherein an FET is used as the control element. 4. The variable output constant voltage circuit according to claim 1, wherein a bias voltage V _E having a polarity opposite to the output voltage is applied to a terminal of the control element opposite to the constant voltage output end.