JPH0710406Y2 - Voltage / current generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a voltage / current generator capable of generating standard voltages and currents of arbitrary values according to set values.

[Conventional technology]

In this type of generator, a switch is used to switch between a voltage mode and a current mode. However, when a standard voltage and current are generated with high accuracy, the contact resistance of the changeover switch poses a problem. Therefore, in the conventional generator, a mechanical contact such as a relay is generally used as the changeover switch, but there are various problems such as size, price, and life.

[Problems to be solved by the invention]

The present invention uses a semiconductor element as a changeover switch, and has improved the circuit so that an error does not occur due to the semiconductor changeover switch. Therefore, it is a compact, low-priced, high-precision standard voltage / current generator with a long life. The purpose is to provide a device.

[Means for solving problems]

The present invention separates the switching of the load current path and the switching of the reference common potential side, and uses an operational amplifier to absorb the circuit current of the reference voltage generation circuit, thereby providing a signal ground of the same potential as the reference common potential. The above-mentioned object is achieved by providing it so that the current of the reference common potential line becomes zero. Hereinafter, examples will be described in detail.

〔Example〕

FIG. 1 is a connection diagram of an embodiment of the voltage / current generator according to the present invention. In the figure, VS is a reference voltage generating circuit that generates a reference voltage whose value is variable according to a set value. In the embodiment, VS generates a variable analog reference voltage Er according to the set value S given by a digital signal. It is composed of a digital-analog converter. This reference voltage generator VS
A schematic equivalent circuit of is shown in FIG. In FIG. 3, S is a setting means and U is an operational amplifier. The voltage Er corresponding to the set value is taken out from the output terminal of the operational amplifier U by the setting means S. Returning to FIG. 1, Dz is a Zener diode used as a reference voltage generating element of the reference voltage generating circuit VS, to which a power source + V is added together with the reference voltage generating circuit VS.

A1 is an error amplifier to which the output of the reference voltage generating circuit VS is added to its inverting input terminal, and RG is an error amplifier to its control terminal r.
It is a regulator to which the output of A1 is added and which controls the output voltage of the power supply + V according to the output of A1. H and L are high-side and low-side input terminals to which the load LO is connected, and the output terminal of the regulator RG is connected to the terminal H. S1 and S2 are switches composed of field effect transistors (hereinafter referred to as FET
The terminal H is connected to the non-inverting input terminal of the error amplifier A1 via the switch S1, and the terminal L is connected to the non-inverting input terminal of the error amplifier A1 via the switch S2.

Q1 and Q2 are semiconductor switches for mode switching that switch between voltage mode and current mode. Both switches are composed of transistors. The collector electrode of the transistor switch Q1 is connected to the terminal L, and the emitter electrode thereof is connected to the common potential point COM. RS is a reference resistor, one end of which is connected to the terminal L and the other end of which is connected to the common potential point COM via the transistor switch Q2.

OP is an operational amplifier added especially by the present invention. The output terminal of the operational amplifier OP is connected to the inverting input terminal of this operational amplifier, and the output terminal is connected to the above-mentioned reference voltage generating circuit VS via the signal ground line SG '. The non-inverting input terminal of the operational amplifier OP is connected to the connection point between the reference resistor RS and the transistor Q2 via the reference common potential line SG.

In the voltage / current generating device according to the present invention having such a configuration, for example, when the voltage mode is set, the reference voltage generating circuit VS generates a desired reference voltage Er according to the set value, and the FET switch S1 and the transistor Turn on both switches Q1 (turn off S2 and Q2). By turning on the FET switch S1, the error amplifier A1 is connected to the regulator RG in its forward circuit and the FET switch S1 in the feedback circuit.
1 is connected to form a buffer amplifier that receives the reference voltage Er as an input. As a result, this error amplifier A1 has terminals H and L
In between, a standard voltage Eo corresponding to Er is generated. Due to this voltage Eo, the current passing through the load LO flows to the common potential point COM via the transistor switch Q1. On the other hand, the voltage generated at the terminal L is the reference common potential line SG in which the reference resistance RS is connected in series.
Is added to the non-inverting input terminal of the operational amplifier OP via. As a result, the operational amplifier OP operates so that the potential of the signal ground line SG 'becomes equal to the reference common potential line SG.

Next, to switch to the current mode, turn on both FET switch S2 and transistor switch Q2 (turn off S1 and Q1). Reference voltage Er generated by the reference voltage generator VS corresponding to the set value
Is applied to the inverting input terminal of error amplifier A1. switch
The output current of the error amplifier A1 obtained via the regulator RG by turning on S2 and Q2 is
Flow through the reference resistance RS connected to the terminal L
And to the common potential point COM through the series circuit of the transistor switch Q2 in the ON state. This load current is the resistance R
The flow of S causes a voltage drop in RS, and this voltage drop is applied to the inverting input terminal of the error amplifier A1. As a result, the error amplifier A1 controls the value of the load current so that the voltage drop across the resistor RS becomes equal to the reference voltage Er. On the other hand, the potential at the connection point between the reference resistor RS and the transistor Q2 is applied to the non-inverting input terminal of the operational amplifier OP via the reference common potential line SG, and this operational amplifier has the same signal ground line SG as in the voltage mode. ′ Potential is the reference common potential line
Operates equal to SG. Therefore, the output voltage Er of the reference voltage generation circuit VS has a value based on the potential of the reference common potential line SG.

Here, in the present invention, transistors Q1 and Q2 which are semiconductor switches are used as changeover switches for switching between the voltage mode and the current mode. The voltage drop of a transistor switch is larger than that of a mechanical switch such as a relay. In this regard, the present invention is configured so that the path (transistors Q1, Q2) through which the load current flows and the reference common potential are separated by the reference common potential line SG. In this case, in order that the voltage drop of the transistors Q1 and Q2 does not affect, it is necessary that the circuit current of the reference voltage generation circuit VS that generates the reference voltage Er or the current flowing through the Zener diode Dz does not flow into the reference common potential line SG. Is. As a means for solving this, in the present invention, the operational amplifier OP is provided as described above, and the output terminal of this operational amplifier is used as the signal ground SG ', and the potential of this signal ground SG' and the reference common potential SG are made equal. While keeping it, the circuit current of the reference voltage generating circuit VS or the current flowing through the Zener diode Dz is absorbed by this operational amplifier from the output terminal of the operational amplifier OP, whose output impedance can be regarded as zero, as shown by the dotted line in the figure. Potential line SG
It doesn't flow to. As described above, in the present invention, even if the transistor switch is used for switching the voltage / current mode, it is not affected by the voltage drop of the switch. Since no current flows in the FET switches S1 and S2, there is no influence of the voltage drop of these switches.

FIG. 2 is a connection diagram of another embodiment of the voltage / current generator according to the present invention. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals as those in FIG. 1 and their re-explanation is omitted. In FIG. 2, Q3 is a transistor switch, SW1,
SW2 is a changeover switch which has contacts a and b and works together. The transistor Q3 is connected between the output end of the regulator RG and one end of the reference resistor RS. The switch SW1 is connected to the terminal H and the switch SW2 is connected to the terminal L.
Is connected to the output terminal of the regulator RG, the contact b is connected to the voltage dividing point of the reference resistance RS, the contact a of SW2 is the connection point of the transistor Q3 and the reference resistance RS, and the contact b is the connection of the reference resistance RS and the transistor Q2. They are connected to each other. Transistor Q3 is Q2
It turns on in synchronization with.

In the circuit of FIG. 2 having such a configuration, the switches SW1, SW
When both 2 are connected to the contact a side, the transistors Q2 and Q3 are turned off, and S1 and Q1 are turned on, the circuit of FIG. 2 becomes the same as in the voltage mode of FIG. On the other hand, switches SW1 and SW2
Is connected to the contact b, and the transistors Q2, Q3 are turned on and Q1 is turned off, the output current of the regulator RG passes through the paths of Q3, RS, Q2 as shown by the dotted line in the figure. In this case, switch SW
By connecting the contacts of 1 and SW2 to b, operation is performed so that the voltage across RS becomes equal to the reference voltage Er as in the case of the current mode in FIG. Here, if one resistance value is RS1 and the other is RS2 with the voltage dividing point of the reference resistor RS as the boundary, when the contacts of the switches SW1 and SW2 are connected to b, the circuit of FIG.
The divided voltage (stable mV voltage) represented by S2 / (RS1 + RS2) can be obtained between terminals H and L.

[Effect of the present invention]

As described above, in the present invention, even if a semiconductor element is used as a voltage mode / current mode changeover switch in a voltage / current generator, the circuit is improved so that an error does not occur due to the semiconductor changeover switch element. As a result, it is possible to obtain a small-sized, low-priced, high-precision voltage / current generator with a long life.

[Brief description of drawings]

1 and 2 are connection diagrams of an embodiment of the device according to the present invention, and FIG. 3 is a schematic equivalent circuit diagram of the reference voltage generating circuit used in FIGS. 1 and 2. VS ... Reference voltage generation circuit, A1 ... Error amplifier, H, L ... terminals, Q
1, Q2 ... Transistor, RS ... Reference resistance, OP ... Operational amplifier,
SG: Reference common potential line, SG ': Signal ground.

Claims (1)

[Scope of utility model registration request] 1. A reference voltage generating circuit VS for generating a variable reference voltage according to a set value, H and L terminals to which a load is connected, and an output terminal of the reference voltage generating circuit VS is connected to one input terminal. An error amplifier whose output terminal is connected to the H terminal and whose H terminal is connected to the other input terminal through the semiconductor switch S1 and the L terminal through the semiconductor switch S2, respectively. A semiconductor switch Q connected between COM and turned on in synchronization with the semiconductor switch S1.
1, a semiconductor switch Q2 connected between the other end of the reference resistor RS whose one end is connected to the L terminal and a common potential point COM and turned on in synchronization with the semiconductor switch S2, and its inverting input terminal and output terminal With a connected operational amplifier OP,
A reference common potential line is provided between the connection point between the reference resistor RS and the semiconductor switch Q2 and the other input terminal of the operational amplifier OP.
A voltage / current generator characterized in that the output terminal of the operational amplifier OP and the reference voltage generating circuit VS are connected by a signal / ground line SG 'while being connected by SG.