JPH04111605U - Variable output power supply - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a variable output power supply device that allows output voltage to be easily and accurately controlled on and off using an external on and off signal. [Structure] A bias voltage V _E is applied to the electrode on the opposite side to the output side of the transistor, and the control electrode of the transistor is configured to be short-circuitable to control the output voltage on and off.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to a variable output power supply device, in particular, which can be easily turned on and off by an external signal. Control and output voltage can be varied, and stable and highly accurate constant voltage can be achieved. supply.

0002

[Conventional technology]

Electrophotographic fields such as plain paper copiers, laser beam printers, etc. In this case, a high voltage of several hundred volts is applied to the grid of a corotron for charge accumulation. child The high voltage of is a constant voltage, and constant voltage is obtained by using Zener diodes, varistors, etc. be able to. By the way, recently there have been improvements in print quality, such as adjusting print density. It is required to change.

0003 In addition, this high voltage is turned off when the device starts up, and is then turned off for a certain period of time after the power is turned on. It is required to apply this high voltage when the voltage has passed and a stable state has been reached. ing.

[0004]For this reason, consider a case where, for example, as shown in FIG. 3A, a transistor Q ₁ for output control is provided and a DC control voltage V _C is applied to the transistor Q ₁ to obtain a constant voltage output.

At this time, as shown in FIG. 3A, since there are resistors R ₁ and R ₂ connected to the base, ideally the following equation holds true. Here, V _out is the output voltage, and the transistor Q ₁ can be configured with a MOSFET or a power MOSFET.

[Math 1]

[0006]

[Problem that the idea aims to solve]

Actually, since there is a base-emitter voltage V _BE of the transistor Q ₁ , the following equation is obtained.

[Math 2]

[0007] Therefore, the output voltage V _out is expressed by the following equation.

[Math 3]

As can be seen from this equation, even if the external control voltage V _C is set to zero, the output V _out does not become zero. In the case of FIG. 3(A), V _out is a negative voltage, and V _BE is also a negative voltage. In this case, in order to make the output zero, V _out cannot be made zero unless a negative voltage is applied to V _C .

Moreover, as mentioned above, when a high voltage is applied to the corotron grid, the output current is on the order of μA, which is very small, and therefore the transistor Q ₁ cannot be turned on sufficiently. Therefore, a large V _BE exists.

In order to turn on Q ₁ sufficiently, for example, as shown in FIG. 3(B), a switching transistor Q _S is provided at the base of Q ₁ and an ON-OFF signal is applied to the base of Q _S to turn on Q ₁ . - There is a method to control OFF. However, the ON-OFF signal V _S in this case also requires a negative voltage, and the power supply V ₁ of Q _S also requires a negative voltage.

As described above, in the conventional example, as shown in FIG. 3 (A) or (B), in a constant voltage circuit that obtains a variable constant voltage output, there is no simple means to turn the output ON and OFF, and the control A voltage V _C and a power source with reverse polarity were required.

[0012] Accordingly, an object of the present invention is to provide a variable output power supply device in which the output of the transistor _Q1 can be turned on and off to zero.

[0013]

[Means to solve the problem]

In order to achieve the above object, in the present invention, as shown in FIG. 1(A), the emitter follower connected transistor _Q2 is connected to the emitter of the transistor _Q1 . Then, the applied voltage V _E applied to the base of the transistor Q ₂ is set to |V _E |≧|V _BE |, so as to cancel the V _BE of the transistor Q ₁ as described later.

[0014]

[Effect]

In FIG. 1(A), transistor Q₂+V on the base of_EApply and transition Star Q_SBy applying a positive turn-on voltage as an external signal to the base of transistor Q, ₁ The base of is at ground potential. transistor Q₂works with emitter follower This +V_Eis transistor Q₂emitter and resistor R₃at the connection point of output, which causes transistor Q₁The emitter of is +V_Ebiased towards. Of course theory + V_Elarger voltage V₁is the resistance R₃is applied to.

[0015] This results in +V₁-R₃-Q₁emitter Q_S- Sufficient current in the grounded circuit current, transistor Q₁is fully turned on and R₃-Q₁Emitter-Q_Sthrough Q due to the current flowing₁The emitter of will also be zero. Therefore, its output voltage V_out becomes zero. Of course, transistor Q_Sbase voltage to zero or negative, e.g. and transistor Q_SIf you turn off the transistor Q₁The predetermined output voltage V _out can be obtained.

Note that FIG. 1(B) shows a case where a positive output voltage +V _out having the opposite polarity to that of FIG. 1(A) is obtained. Since the operation is similar to that in FIG. 1(A), detailed explanation will be omitted.

In FIG. 1A, the external control voltage V _C , ON-OFF signal V _S , bias voltage V _E , and emitter follower circuit power supply V ₁ are all positive power supplies, and the configuration is extremely simple. Become. Similarly, in the case of FIG. 1(B), all voltages are negative and can be supplied with a simple configuration.

[0018]

【Example】

Another embodiment of the present invention will be described with reference to FIG.

FIG. 2 is equipped with a changeover switch SW consisting of fixed contacts C ₁ , C ₂ , C ₃ and a movable contact MC as means for making the output voltage V _out variable.

The constant voltage obtained by the Zener diode ZD is divided by resistors r ₁ , r ₂ , r ₃ , and r ₄ , and the outputs of r ₁ to _{r 3} are sent to the fixed contacts C ₁ to C ₃ of the changeover switch SW. As will be described later, the output control voltage V _C is made variable.

Further, the output of the resistor r ₄ is applied as the applied voltage V _E to the base of the transistor Q ₂ which operates as an emitter follower.

[0022] The output of the movable contact MC is input to an operational amplifier OP that operates as a buffer, and an output control voltage V _C is output. Therefore, as the movable contact MC sequentially contacts the fixed contacts C ₁ , C ₂ , and C ₃ , the output control voltage V _C decreases in magnitude as V _C1 →V _C2 →V _C3 .

[0023] Therefore, if the base-emitter voltage of transistor Q ₁ is V _BE , the following formula holds true.

[Math 4]

[0024] Therefore, the output voltage V _out is as shown in the following equation.

[Math 5]

At this time, since V _E is determined as described above so that V _E +V _BE becomes zero, the output voltage V _out is as follows. Note that at this time, V _E has the opposite polarity to the output voltage. V _out =V _C・R ₂ /R ₁

By making the output control voltage V _C variable as described above using the changeover switch SW, the output voltage V _out can be made variable.

[0027] Moreover, the external ON-OFF signal V_SThe switching transistor Q_S Turn on Q₁By passing a sufficient base current of Q₁can be turned on. Ma Bias voltage V_Eis the emitter follower circuit Q₂,R₃Since Q ₁ The base current of R does not flow indefinitely, and R₃Due to the voltage drop of Q₁of The emitter is Q₁becomes zero when it is ON. As a result, the output voltage V_outto zero can be done.

[0028] In this invention, instead of the transistor shown in the figure, a FET or a Darlington circuit is used. Composite elements can also be used.

[0029]

[Effect of the idea]

With this invention, the output of the transistor can be switched between zero and an output voltage of several hundred volts or more. On/off control is possible, and the output voltage can also be made variable. . In addition, since all of these control signals are DC voltages, they cannot be connected even if noise occurs. Noise can be removed by simple means such as connecting a ground capacitor. Easy to configure, stable, and highly accurate output that is virtually unaffected by noise. A variable power supply can be provided.

[Brief explanation of drawings]

FIG. 1 is two configuration diagrams showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of another embodiment of the present invention.

FIG. 3 shows a variable output power supply device when controlling the output voltage on and off.

[Explanation of symbols]

Q ₁ , Q ₂ , Q _S Transistor R ₁ , R ₂ , R ₃ Resistor ZD Zener diode

Claims (1)

[Scope of utility model registration request] Claim 1: In a variable output power supply device in which the control voltage of a transistor is short-circuited to control its output voltage to zero, an electrode on the opposite side to the output side of the transistor,
A variable output power supply device characterized by applying a bias voltage _VE .