JPH01232808A - Voltage amplifier with low voltage current limit - Google Patents

Abstract

PURPOSE:To set an optical voltage amplification factor and to limit optionally its output current at the same time by connecting a base of a 2nd transistor(TR) to the base of a 1st TR so as to regulate the operation of the 1st TR by the 2nd TR when an output current of a differential amplifier circuit reaches a prescribed value or over. CONSTITUTION:The circuit is constituted by connecting a base of a TR Q6 to a base of a TR Q5, connecting a collector of the TR Q6 to a current source 3 and also to a base of a TR Q7, and connecting an emitter of the TR Q7 to a base of the TR Q5. Through the constitution above, the voltage amplification factor of an open loop is set higher by the TR Q5. Moreover, the sink current is limited by a current of a current source 2 and the source current is limited by a current of the current source 3. That is, with a current over a current 2I2 flowing to the collector of the TR Q6, the base potential of the TR Q5 rises to limit the output current. Thus, both the source and sink output currents are limited in this circuit by using the current I2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage amplification circuit that operates at low voltage and is additionally provided with a current limiting function.

[Conventional technology]

FIG. 3 shows a conventional voltage amplifier circuit operating at a low voltage. This circuit is composed of a differential amplifier circuit made up of transistors Q1 and Q2, and has a current mirror circuit made up of transistors Q3 and Q4 as a load. 1 is a current source of current ■1.

The output current in this circuit can be limited by the current 11 for both the sink and source. However, the voltage amplification degree between input and output is low, and the voltage amplification degree is 1. Therefore, any voltage amplification degree or current 1
It is difficult to set +.

The circuit shown in FIG. 4 takes this point into consideration, and adds a transistor Q5 to the output side to make the voltage amplification sufficiently high. 2 is a current source of current 2, and C is a phase compensation capacitor.

[Problem to be solved by the invention]

In this circuit, the sink current can be limited by the current ■2, but the source current is the product of the current amplification factor of the transistor Q5 and the current ■1, and it is extremely difficult to take an arbitrary value. .

An object of the present invention is to be able to set an arbitrary voltage amplification degree and at the same time to arbitrarily limit the output current.

[Means to solve the problem]

For this purpose, the present invention provides a voltage amplification circuit in which a first transistor with a common collector is connected to the output side of the differential amplification circuit, and a constant current source is connected to the collector side of the first transistor. A base of a second transistor is connected to a base of the transistor, and when the output current of the differential amplifier circuit exceeds a predetermined value, the second transistor regulates the operation of the first transistor. did.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing a voltage amplifying circuit according to one embodiment.

In this embodiment, the base of the transistor Q6 is connected to the base of the transistor Q5 in FIG. The emitter of is connected to the base of transistor Q5.

In this circuit, the open loop voltage amplification degree can be set sufficiently high by the transistor Q5. In addition, the sink current can be limited by the current of current source 2,
The source current can be limited by the current of the current source 3. That is, a current 2IZ is applied to the collector of the transistor Q6.
When the above current flows, the emitter potential of transistor Q7 rises, raising the base potential of transistor Q5,
Limit the output current. As described above, in this circuit, both the source and sink output currents can be limited by the current I2.

Figure 2 (al to (C)) shows the circuit shown in Figure 1, that is, the circuit in which the voltage amplification degree of the oven loop is sufficiently high, as a single voltage amplifier A, and any voltage amplification degree can be set by appropriately setting the feedback amount. 1 is a diagram configuring an amplifier circuit that can realize the following.It is possible to operate with a supply voltage of 0.9V.

(a) is configured as a buffer circuit, and the same voltage as the input voltage Vi is output regardless of the load resistance RL.

('b) is configured as an inverting amplifier, and the input voltage V
The phase of i is inverted and output. The voltage amplification degree is set by the feedback loop resistors Ra and Rb. (C) is configured as a non-rotating amplifier, and the voltage amplification degree is similarly set by the resistance RC% Rd of the feedback loop.

In this way, it can be used almost in the same way as an operational amplifier circuit at a low voltage, and output current can also be limited by the current It. Also, if the load resistance RL is made relatively small within a range where the supply voltage does not limit the output voltage, then the load resistance R
Output voltage can also be limited by L and current (2).

〔Effect of the invention〕

As described above, according to the present invention, it is possible to limit the output current, and the degree of voltage amplification can also be arbitrarily set by setting the amount of feedback.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a voltage amplification circuit according to an embodiment of the present invention, Figure 2 18) to (e) are circuit diagrams of various circuits using the circuit of Figure 1, and Figures 3 and 4 are circuit diagrams of various circuits using the circuit of Figure 1. FIG. 2 is a circuit diagram of a conventional voltage amplification circuit. Agent Patent Attorney Tsuneaki Nagao

Claims (1)

[Claims] (1) In a voltage amplification circuit in which a first transistor with a common collector is connected to the output side of the differential amplification circuit, and a constant current source is connected to the collector side of the first transistor, the base of the first transistor is A base of a second transistor is connected to the differential amplifier circuit, and when the output current of the differential amplifier circuit exceeds a predetermined value, the second transistor regulates the operation of the first transistor. A low voltage and current limiting voltage amplification circuit.