JPH0443285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a current output device that supplies current to an electromagnet, an electromagnetic actuator, a linear motor, or the like.

Conventional configuration and its problems Current output devices that control load current using command signals are widely used in the above-mentioned industrial fields. FIG. 1 shows a conventional example of a typical configuration using transistors. The transistor Tr ₁ is a current control transistor, and its emitter current is detected by a current detection resistor R ₁ . The error between the current command signal a and the current detection signal b is amplified by the differential amplifier 1, and the base of the transistor _Tr1 is driven to cause the emitter current to follow the current command signal a. A load 2 is connected to the collector of the transistor Tr ₁ . In addition to reducing the power consumption of transistor Tr ₁ ,
In order to avoid saturation of Tr ₁ , the transistor is set so that the collector voltage follows the voltage of reference power supply 3.
Tr ₂ and amplifier 4 control the power supply voltage of load 2 . By setting the voltage of the reference power supply 3 to an appropriate value, it is possible to select an operating point at which the transistor Tr ₁ does not saturate. However, the configuration of FIG. 1 has the following drawbacks. In other words, the unsaturated collector-emitter voltage V _CE of transistor Tr ₁ changes depending on the load current, transistor temperature, transistor variations, etc., so the reference voltage is set high, or these It must be made to follow the fluctuation factors. If the reference voltage is set high, V _CE of transistor Tr ₁ will increase, and power consumption will increase. Furthermore, in order to make the reference voltage follow the fluctuation factors, the circuit configuration becomes complicated, leading to an increase in cost, which is disadvantageous from an industrial perspective.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks, and an object of the present invention is to provide a current output device that can control a load current using a control transistor with minimum power consumption.

Structure of the Invention In order to achieve the above object, a current output device of the present invention includes a voltage control means connected to one end of a load, a current control transistor connected to the other end of the load, and an emitter current of the current control transistor. a first current detection means for detecting the current control transistor; a first amplifier for amplifying the error between the output signal of the first current detection means and the current command signal; base and second
and a second amplifier that amplifies the difference between the output signals of the first and second current detecting means, the voltage being controlled by the output of the second amplifier. It is configured to control the means.

According to this configuration, the ratio of the emitter current to the base current of the current control transistor can always be kept constant, and the operating point at the minimum collector-emitter voltage at which the current control transistor is not saturated can be maintained at all times, while the command It becomes possible to output a current that follows the signal.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a circuit diagram of the current output device, in which the same components as those shown in FIG. 1 are given the same reference numerals. NPN transistor Tr ₁
Load 2 between the collectors of and PNP transistor Tr ₂
The emitter of the transistor Tr ₁ is grounded via a current detection resistor R ₁ and is also connected to the inverting input terminals of the current output type differential amplifier groups 1 and 5 . The output signal c of the amplifier 1 is connected to the collector of the diode-connected PNP transistor _Tr3 . PNP transistor Tr ₄ , Tr ₅
The bases of both are connected to the base of transistor Tr ₃ , and the emitters of transistors Tr ₃ to _{Tr 5} are connected to the power supply via resistors R ₂ to R ₄ , respectively, forming a current mirror. The collector of the transistor Tr ₄ is connected to the base of the transistor Tr ₁ , and the collector of the transistor Tr ₅ is connected to the ground via the current detection resistor R ₅ and connected to the amplifier 5.
is connected to the non-inverting side input terminal of The base of the transistor Tr ₂ is connected to the output terminal of the amplifier 5,
The emitter is connected to the power supply terminal 6. A non-inverting input terminal of the amplifier 1 is connected to a load current command signal input terminal 7.

Next, the operation will be explained. The emitter current of transistor Tr ₁ flows through resistor R ₁ and generates voltage V ₁ .
The difference between the voltages V ₂ and V ₁ at the input terminals 7 is amplified by the amplifier 1 and distributed to the outputs d and e by the current divider 8 composed of transistors Tr ₃ to _{Tr 5} . Since the output d is applied to the base of the transistor Tr ₁ , the negative feedback loop causes V ₁ and V ₂
The base current I ₁ b of the transistor Tr ₁ flows so that the voltage becomes equal to . Now, resistance R ₁ and resistance R
Let the values of R ₁ and R ₅ be respectively, and assume that the values of the resistors R ₂ to R ₄ are equal. A state in which a sufficient base current is not supplied to transistor Tr ₂ , that is, the collector current I ₂ c of transistor Tr ₂ , which is the current of load 2, is the collector current of transistor Tr _1.
When it is smaller than I ₁ c, the collector-emitter voltage V _CE of transistor Tr ₁ becomes low, transistor Tr ₁ approaches saturation, and the current amplification factor (h _FE ≡I ₁ c/
I ₁ b) decreases. Therefore, I ₁ b increases to equalize the difference between V ₁ and V ₂ . On the other hand, since the current having the same value as I ₁ b is distributed to the resistor R ₅ by the current mirror, the voltage V ₃ of the resistor R ₅ becomes V ₃ =I ₁ b×R ₅ . The emitter current of transistor Tr ₁ is I ₁ e
Then, V ₁ becomes V ₁ =I ₁ e×R ₁ . Amplifier 5 amplifies the difference between V ₃ and V ₁ ,
Since it drives the base of transistor Tr ₂ , V ₃ >
When _V1 , the output of the amplifier 5 increases and the collector current _I2c of the transistor _Tr2 also increases. As a result,
Collector-emitter voltage of transistor Tr ₁
V _CE increases and h _FE also increases. Then, the base current I ₁ b required to generate V ₁ decreases, V ₃ also decreases and approaches V ₁ , and eventually stabilizes in a state where they are equal. Due to this negative feedback loop, V ₃ =
Since V ₁ is maintained, I ₁ b×R ₅ =I ₁ e×R ₁ . In other words, h _FE ≡I ₁ e/I ₁ b-1 = R ₃ /R ₁ -1, and transistor Tr ₁ is h _FE determined by R ₅ and R ₁ .
It operates at _VCE , and outputs current to the load 2 in accordance with the current command signal a.

FIG. 3 depicts the relationship between V _CE and h _FE of the transistor Tr ₁ using I ₁ e as a parameter. As can be seen from FIG. 3, when h _FE is kept constant, V _CE increases as I ₁ e increases. This can be achieved by choosing h _FE appropriately.
It is shown that Tr ₁ can be operated at an operating point just before saturation. For example, if h _FE is constant at H, I ₁ e becomes I ₁ ′e
If V _CE just before saturation is V′, then I ₁ e
When increases to I ₁ ″e, V _CE also increases to V″, and I ₁ e
When I ₁ e, V _CE also becomes V, and the device always operates at an operating point just before saturation. This state changes automatically according to element variations and temperature.
Therefore, by choosing the values of R ₅ and R ₁ ,
The V _CE of the transistor Tr ₁ can be kept at the required minimum value, and the power consumption by the transistor Tr ₁ can be extremely reduced. In addition, by changing the ratio of the emitter resistances R ₂ to R ₄ of the current mirror, the collector currents of transistors Tr ₄ and Tr ₅ ,
That is, the distribution ratio of the distributor 8 can be changed,
h _FE can be arbitrarily set together with the ratio of R ₅ and R ₁ .

Next, another embodiment of the present invention will be explained using FIG. The connection relationships between the transistor Tr ₁ , the resistor R ₁ , the amplifier 1 divider 8, the resistor R ₅ , and the input side of the amplifier 5 are the same as those in the embodiment shown in FIG. 2, and therefore their explanation will be omitted. The output of the amplifier 5 is applied to the control circuit 10 of the switching mode power supply 9, and becomes an input for controlling the conduction state of the switching transistor _Tr6 . The collector of the transistor Tr ₆ is connected to the diode D ₁ and one end of the coil L ₁ . Koi
The other end of L ₁ is connected to capacitor C ₁ and serves as the output of switching mode power supply 9, to which one end of load 2 is connected. The other end of load 2 is a transistor
Connected to the collector of Tr ₁ .

Now, when the output voltage of the switching mode power supply 9 is low and the V _CE of the transistor Tr ₁ is low, the output of the amplifier 5 increases by the same operation as described above. This output serves to drive the control circuit 10 to lengthen the conduction time of the transistor Tr ₆ and to increase the output voltage of the switching mode power supply 9. Therefore, a negative feedback loop is formed, and the V _CE of the transistor Tr ₁ is divided by the divider 8, the resistor R ₅ and the resistor R ₁
h _FE is maintained at a constant value, and the power consumption of the transistor Tr ₁ is kept to the minimum necessary, and a current can be output to the load 2.

FIG. 5 shows another embodiment of the distributor used in the present invention. Transistor Tr ₇ constitutes a divider 11,
The input is applied to the base of transistor _Tr7 .
The emitter of transistor Tr ₇ is transistor Tr ₁
The collector of transistor Tr ₇ is connected to the bases of current mirror transistors Tr ₈ and Tr ₉ . The collector of current mirror transistor Tr ₉ is connected via resistor R ₅ . Assuming that the base current of transistor Tr ₇ is I ₇ b, the emitter current is I ₇ e, the collector current is I ₇ c, and the current amplification factor is h _FE7 , then I ₇ e = (1 + h _FE7 ) I ₇ b V ₃ = h _FE7・I ₇ b×R ₅ . Therefore, V ₃ = h _FE7 /1 + h _FE7・I ₇ e・R ₅ , and V _CE of transistor Tr ₁ can be set to the required minimum value by the same operation as explained using FIG. .

Note that, of course, various modifications and applications are possible without changing the gist of the present invention, such as operating the transistor Tr ₂ as an emitter follower in FIG. 2 or changing the conductivity of the transistor. .

Effects of the Invention As explained above, according to the present invention, the current control transistor is always operated at a constant DC current amplification factor with a simple configuration, and the power consumption is adjusted according to the temperature characteristics and variations in the elements. It can be set to a minimum, and its industrial value is extremely large.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional current output device, Fig. 2 is a circuit diagram of a current output device according to an embodiment of the present invention, and Fig. 3 is an explanatory diagram of the relationship between V _CE and h _FE of a current control transistor. , FIG. 4 is a circuit diagram of a current output device in another embodiment, and FIG. 5 is a circuit diagram of a distributor in yet another embodiment. 1, 5...Amplifier, 2...Load, 8...Distributor, 9...Switching mode power supply, Tr ₁ ...
Current control transistor, Tr ₂ ...transistor,
R ₁ , R ₅ ...Resistance.

Claims (1)

[Claims] 1. A voltage control means connected to one end of the load, a current control transistor connected to the other end of the load, and a first current detection means for detecting an emitter current of the current control transistor. , a first amplifier for amplifying the error between the output signal of the first current detection means and the current command signal;
and a second amplifier that amplifies the difference between the output signals of the first and second current detecting means, the voltage being controlled by the output of the second amplifier. A current output device configured to control means. 2. Claims in which a second transistor having conductivity different from that of the current control transistor is used as the voltage control means, and the conduction state of the second transistor is controlled by the output of the second amplifier. The current output device according to item 1. 3. The current output device according to claim 1, wherein a switching mode power supply is used as the voltage control means, and the output voltage of the power supply is controlled by the output of the second amplifier. 4. The current output device according to any one of claims 1 to 3, which is configured to use a two-output current mirror circuit as a distributor. 5 Using a third transistor as a distributor,
4. The current output device according to claim 1, wherein the collector and emitter of the third transistor are configured to serve as the output of the distributor.