JPS5914816Y2 - constant current circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a minute constant current circuit that generates a current of several hundred μA to several hundred times without using any special elements.

FIG. 1 shows a conventional constant current circuit using an operational amplifier.

This circuit has a reference voltage Vr applied to the non-inverting input 2.
and the emitter of the transistor T as a control means and GND.
Stable output current ■ by comparing the voltage drop that occurs across the current detection resistor R1 connected between (ground) and controlling to eliminate the difference.

I am getting . ■The value of o is given by Vr/R1, so■
.

To make it smaller, the reference voltage Vr should be made smaller or the resistor R1 should be made larger.

However, there is a limit to reducing Vr depending on the performance of the operational amplifier, and even if R1 is increased, there is a limit that the error due to the input bias current of the operational amplifier becomes relatively large, so it is recommended to make R1 larger than that. If so, an operational amplifier with a small input bias current (for example, an operational amplifier with FET input) must be used.

The difficulty of the above two methods becomes apparent when attempting to form an IC chip.

For example, the resistance that can be formed on an IC chip is 100 to 200.
The limit is Ω, and if you try to make an FET, not only will the number of steps increase, but the chip area will also be much larger than that of a bipolar element.

The purpose of the present invention is to provide a simple, slightly inconstant current circuit that does not require the use of special elements (operational amplifiers, transistors, resistors, etc.).

According to the present invention, the difference between the reference voltage and a voltage drop occurring across a current detection resistor connected to a control means controlled by the output of an operational amplifier whose non-inverting input is connected to a reference voltage, A minute constant current circuit is provided in which the current flowing through the control means is controlled to be constant, and the minute constant current circuit is characterized in that the control means are provided in parallel.

Next, the present invention will be explained by giving examples.

FIG. 2 is a circuit connection diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals.

In the figure, the output 3 of the operational amplifier OP is connected to the bases of a group of transistors T1 to Tn whose bases and emitters are common, and the collectors of T1 to Tn-1 are connected to voltage 1.

An inverting input 1 of the operational amplifier OP is connected to the emitters of T1 to Tn and a resistor R1, and a non-inverting input 2 is supplied with a reference voltage Vr.

Here, the output current ■o becomes 1 of the conventional constant current circuit.
can be the value of

Input bias voltage n The influence of the flow also becomes a sweetfish.

If the output current is to be further reduced, a resistor may be connected between the Tn emitter and the common emitter.

Furthermore, if formed on an IC chip, a stable constant current circuit with good thermal balance can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing an example of a conventional constant current circuit, and FIG. 2 is a circuit connection diagram showing an embodiment of a minute constant current circuit according to the present invention. Vr...Reference voltage, OP...Operation amplifier, I. ...Output current, T, T1~T, ...Transistor, R1...Current detection resistor, ■+...
...Positive power supply, ■1...Constant current, 1...
...Inverting input, 2...Non-inverting input, 3...
...OP output.

Claims (1)

[Scope of utility model registration request] Three or more transistors whose emitters are commonly connected to each other and their bases are commonly connected to each other, and a resistor is connected between the common emitter connection point of these transistors and a reference potential point, and the voltage drop across this resistor is constant. In a constant current circuit having a means for feeding back the voltage change appearing on this resistor to the base of each transistor, the collector of only one transistor is connected to the current output terminal, and the collectors of the remaining transistors are commonly connected to the voltage supply terminal. A constant current circuit characterized in that the constant current circuit is connected to the current output terminal and obtains a minute constant current from the current output terminal.