JPS59204305A - Insulation type current amplifier - Google Patents

Abstract

PURPOSE:To obtain an insulation type current amplifier which outputs a large output and is manufactured in simple constitution by providing a differential amplifier, current control element, switching means, and feedback control. CONSTITUTION:A signal S1 when outputted by a D/A converter 4 is voltage- amplified by the differential amplifier 13 and current-amplified by the current control element 14 to obtain a signal S2. Therefore, the waveform of the signal S2 is equal to that of the signal S1. The S2 flows through the center tap of the primary winding of a transistors (TR) 15 and 16, and feedback means in order when a TR16 is on or through the center tap of the primary winding, a TR17, and the feedback means 18 in order when the TR17 is on. When currents flowing in the collectors of the TRs 16 and 17 are signals S3 and S4, the S3 and S4 are signals which alternate a section of the same waveform with the S2 and a section of level 0. Consequently, the waveform obtained by the full-wave rectification 25 of the secondary-side output of the TR15, i.e. the waveform of the voltage across a load resistance Rl is the same with the signal S1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an isolated current amplifier that isolates and amplifies analog signals.

When converting the results of calculations by an electronic circuit such as a microcomputer into an analog signal and driving an external device using this analog signal, separate isolation means is required to prevent the power from the logic circuit side from being drawn outside. is taken. Figures 1 and 2 are block diagrams showing examples of the configuration of general isolation means. - Figure 1 shows %IJX2rI! when a photocoupler is used. J shows the case where an isolated amplifier is used. In the example shown in Figure 1, the CPU
(Central processing unit) After the output data of l is latched by the latch circuit 2, it is transferred to the D/A converter 4 via the photocoupler 3.
The analog output of the D/A converter 4 is supplied to external equipment via the amplifier 5. In addition, the example shown in Figure 8g2 (
In this case, the output of the latch circuit 2 is isolated and amplified by the isolation amplifier 6, and then supplied to external equipment via the amplifier 5.

By the way, in the configuration shown in FIG.
Since the output signal is small, an amplifier 5 is required, and in order to achieve high precision, a large number of high-speed photocouplers must be used, making the configuration complex and expensive. Next, the configuration shown in FIG. 2 has the disadvantage that the isolated amplifier 6 itself is expensive and has a small output, requiring the amplifier 5. in this way,
In the configuration examples shown in FIGS. 1 and 2, there is a problem in that an amplifier 5 is also required, and a power source for operating both amplifiers 5 must be provided separately.

In view of the above-mentioned circumstances, the present invention provides an isolated current amplifier that can provide a large output and that can be manufactured at low cost with a simple configuration. a current control element that controls the current in response to the output signal of the differential amplifier, and a current control element that alternately switches the direction of the output current of the current control element to control the output current of the transformer. and a feedback means for feeding back the primary side current of the transformer to the other input terminal of the differential amplifier, rectifying the secondary current of the transformer and supplying it to the load. It is characterized by

Examples of actual weaving of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the structure of one embodiment of the present invention, and parts corresponding to those in FIG. 2 are given the same reference numerals.

In this figure, 8 is a differential amplifier 1 along with resistors 9 to 12.
3, and the operational amplifier 8's ■
An analog output signal S1 of the D/A converter 4 is supplied to the input end via a resistor 9. The output signal of the differential amplifier 13 is supplied to the base of a transistor 14, and the collector of this transistor 14 is supplied with the power supply vcc. The emitter of transistor 14 is connected to the center tap of the primary winding of transformer 15, and both ends of this primary winding are connected to the collectors of transistors 16 and 17, respectively. The emitters of the transistors 16 and 17 are both connected to one end of the variable resistor 18, and the other end of the variable resistor 18 is grounded.The voltage obtained between the sliding terminal of the variable resistor 18 and the ground is connected to the operational amplifier 8. It is fed back through the θλ input terminal resistor 11 of .

20 is an oscillator that outputs a rectangular signal s5 shown in FIG. A signal S5 is supplied to each of the transistors 17 through the resistor 22, so that the transistors 16 and 17 are alternately turned on and off. Also, transistor 16.
The switching means 23 is composed of the 17% resistors 21 and 22 and the oscillator 20. On the other hand, %24 is an external device and has a full-wave rectifier 25. ~ is full wave rectifier 25
is the load resistance connected between the output terminals of

In the above configuration, when the signal S1 shown in FIG. 4(a) is output from the D/A converter 4, this signal S
The current is amplified at , and becomes the signal S2. Therefore, the waveform of signal S2 shown in FIG. 4(b) is equal to signal S0. This signal S2 causes the transistor 16 to turn off.
When it is N, the flow follows the path of transformer; The current flows through the path from F to variable resistor 18. Therefore, the currents flowing into the collectors of transistors 16, 17, respectively, are connected to signals S3. S4, the signals S and S4 are shown in Fig. 4 (e) and (e), respectively.
As shown in FIG. 2, the signal is a signal that alternately repeats sections of the same waveform as the signal S2 and sections of 0 level. As a result,
The waveform obtained by full-wave rectification of the secondary side output of the transformer 15, that is, the voltage waveform at both ends of the load resistor ~ has the same waveform as the signal S1 (FIG. 4(A)) as shown in i@4 (G).

Note that in the above configuration, the transistors 16 and 17
If each fr is replaced with a Darlington-connected transistor,
Since the pace current can be reduced, the current flowing through the variable resistor 18 and the value of the signal S2 match with high precision, thereby making it possible to improve the precision of circuit operation.

However, according to this embodiment, since current amplification is performed, it is possible to compensate for the lower part of the forward voltage in the full-wave rectifier 25, and also to prevent poor contact in external equipment after the secondary side of the transformer 15. If this happens, the secondary voltage increases, which has the effect of preventing poor contact.

As explained above, according to the present invention, there is provided a differential amplifier to which an analog signal is supplied to one input terminal.

A current control element that controls the current in response to the output signal of the differential amplifier, and a switching means that alternately switches the direction of the current control element output current and supplies it to the primary side of the transformer. , and a feedback means for feeding back the primary current of the transformer to the other input terminal of the differential amplifier, which has the advantage that it can be manufactured at low cost with an hour wheel configuration and that a large output can be extracted. can get.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing the configuration of conventional isolation means, FIG. 3 is a block diagram showing the configuration number of an embodiment of the present invention, and FIGS. ) is the third
FIG. 3 is a waveform diagram showing waveforms of various parts of the circuit shown in the figure. 13... Differential amplifier% 14... Transistor (current control element), 18... Variable resistor (
feedback means), 23...switching means, 25
...Full wave rectifier. Japanese Patent Publication No. 59-204305 (3)

Claims (1)

[Claims] a differential amplifier to which an analog signal is supplied to one input terminal; a current control element that controls the current in response to the output signal of the differential amplifier; and a current control element that alternately switches the direction of the output current of the current control element. and a feedback means that feeds back the primary side current of the transformer to the other input terminal of the differential amplifier, and includes switching means that supplies the primary side current of the transformer to the other input terminal of the differential amplifier, An isolated current amplifier that rectifies waves and supplies them to the load.