JPH0314821Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for supplying a desired voltage or current to a load circuit, and particularly to a stabilizing circuit for the circuit.

FIG. 1 is a block diagram of a conventional voltage/current control circuit. A power amplifier 3 amplifies the input signal applied to the input terminal 1 and supplies the output signal to the load circuit 7 via the current detection resistor 5 (resistance value R _I ). The current flowing through the load circuit 7 is detected by the resistor 5 and the amplifier 11 and fed back to the input side of the amplifier 3. When current control is performed, the current flowing through the load circuit 7 is controlled to a desired value. Also, the voltage of the load circuit 7 is determined by the voltage follower 9
The voltage is fed back to the input side of the amplifier 3 via the voltage control circuit 7, and when performing voltage control, the voltage of the load circuit 7 is controlled to a desired value. That is, a signal for obtaining a desired load voltage or current is applied to the input terminal 1, and the entire circuit operates to obtain these desired values through the feedback operation described above. Whether to perform voltage control or current control is determined by the selection of the magnitude of the signal applied to input terminal 1 and by the amplifiers 11 and 9 described above.
It is only necessary to select which output signal to feed back. The details of this circuit are described in Japanese Unexamined Patent Publication No. 121812 of 1982, which was previously filed by the present applicant. From the above explanation, the feedback control operation is thought to be obvious to those skilled in the art, but to explain in more detail, since a differential amplifier (operational amplifier) is generally used in the power amplifier 3 for control, A signal for obtaining a desired load voltage or load current may be applied to one input terminal of the amplifier 3, and the output signal of the amplifier 11 or 9 may be selectively inputted to the other input terminal. It goes without saying that the gist of the present invention is not such a feedback control operation.

In the above circuit, in order to prevent noise from entering the coupling line between the current detection resistor 5 and the load circuit 7, a guard 13 is used to surround this coupling line. This guard 13 is connected to the output terminal of the voltage follower 9 and held at the same potential as the output terminal. Note that this guard 13 is especially necessary when a minute current is passed through the load circuit 7. In addition, considering that the load circuit 7 is supplied with a variable voltage over a wide range, the voltage follower 9 operates as a voltage follower, and power consumption is reduced, the reference potential B of the power supply of the voltage follower 9 is
is based on the output voltage of amplifier 3. Further, the reference potential A of the load circuit 7 is based on the reference potential of the power supply of the amplifier 3.

However, the conventional circuit has the following drawbacks. That is, the guard capacity 15 generated by the guard 13
The influence of this makes the current control system unstable, making it more likely to cause oscillation. If the guard capacitance value is Cg, the gain of the amplifier of the voltage follower 9 is _A5 , and the cutoff angular frequency is _ω5 , then an admittance Yc is equivalently entered in parallel with the current detection resistor 5. And Yc=jωCg/(1+A ₅ )=jωCg/{1
+(ω ₅ /jω)}, and in the band of ω < ω ₅ , Yc≒
jωCg・(jω/ω ₅ )=−ω ² Cg/ω ₅ . Afterwards,
Depending on the value of R _I , especially when R _I is large (minimum current), the total impedance of the current detection resistor may enter the negative region and cause oscillation.

The present invention has been devised to eliminate the above-mentioned drawbacks, and FIG. 2 is a block diagram showing one embodiment of the present invention. The same parts as in FIG. 1 are designated by the same reference numerals. The difference between the circuit in Figure 2 and that in Figure 1 is as follows:
A low-pass filter is provided between the output terminal of the voltage follower 9 and the reference potential point A, and the guard 13 is connected to the connection point between the resistor 17 and the capacitor 19.

FIG. 3 is an equivalent circuit of FIG. 2. An admittance Yi is connected to the load circuit 7 in parallel with the current detection resistor 5.
This means that admittance Y _X is inserted in parallel with . Here, Yi and _YX are expressed by the following formula.

Yi=jωCg・f(ω)/(1+A ₅ ) Yx=jωCg(1−f(ω)) f(ω)=1/1+jωC _F・R _F =1/1+(jω/ω
_FIL ) C _F is the capacitance value of capacitor 19, R _F is resistor 17
is the resistance value of

From the above formula, at ω<ω ₅ , Yi=jωCg・〓〓/1+(ω ₅ /jω)=jωCg・ω _FI
Since _L /ω ₅ , Yi is no longer in the negative region to begin with,
As a result, the factors that cause oscillation are removed.

Note that Y _X is input in parallel to the load circuit 7, and since the filter is a low-pass filter, as ω increases, fω approaches zero and Y _X approaches jωCg. Therefore, the guard capacitance is simply seen as a load and has no effect. Further, this capacitive load works so that the current flowing through the resistor 5 becomes phase advanced with respect to the output voltage of the power amplifier 3, so that the current control system is stabilized in this sense as well.

FIG. 4 is a block diagram showing another embodiment of the present invention. The difference from FIG. 2 is that the reference point of the power source of the voltage follower 9 is made the same as the reference point of the power source of the power amplifier 3. In this case, the guard capacity is 13
As in the case of Fig. 1, the effect appears in the form of being inserted in parallel to the load circuit 7, which worsens the stability of the voltage control system, but by connecting a low-pass filter, it can be reduced as in the case of Fig. 2. The above drawbacks are excluded.

As is clear from the above explanation, according to the present invention, the drawbacks of the conventional device can be eliminated without impairing the original guard function.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional voltage/current control circuit, FIG. 2 is a block diagram of a voltage/current control circuit according to an embodiment of the present invention, and FIG. 3 is a partial equivalent circuit diagram of FIG. FIG. 4 is a block diagram of another embodiment of the present invention. 3: Power amplifier, 5: Current detection resistor, 7: Load circuit, 9: Voltage follower, 13: Guard, 15:
Guard capacity.

Claims (1)

[Scope of utility model registration request] An output signal of a power amplifier that receives an input signal at one input terminal is supplied to a load circuit via a current detection resistor and a connection means having a guard, and the voltage between both terminals of the current detection resistor or the load voltage is The circuit selectively feeds back to the other input terminal side of the power amplifier to control the load current or load voltage to a desired value, the circuit comprising: a current detection amplifier for detecting the voltage between the two terminals; and an input side connected to the load circuit. Selecting a connected load voltage detection amplifier, a low pass filter connected between an output terminal of the load voltage detection amplifier and the guard, and an output signal of the current detection amplifier or the load voltage detection amplifier. 1. A voltage/current control circuit comprising: a switching means for feeding back to the other input terminal side of the power amplifier.