JPH03232005A - Start-up circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application)] This invention relates to a starting circuit for a transistor circuit used in particular in a bipolar integrated circuit.

(Prior Art) A bandgap current source is known as a current source that operates stably at low voltage. A starting circuit is required to start this circuit.

FIG. 3 is a circuit diagram showing the configuration of the band gap type current source and a conventional starting circuit for starting the same. In the figure, the right side surrounded by a broken line is the band gap type current source A, and the left side is the starting circuit C.

Bandgap current source A is configured as follows. The emitters of the PNP transistors 11 and 12 are each connected to the power supply voltage Vcc, and their bases are connected in common and to the collector of the transistor 12. The collector of transistor II is connected to the collector of NPN l-transistor 13, and the collector of transistor 12 is connected to the collector of NPN h-transistor 14. The bases of these transistors 13 and 14 are commonly connected. The emitter of transistor 14 is connected to ground voltage GND, and the emitter of transistor 13 is connected to ground voltage GND via resistor 15.

The base of a PNP l-transistor 16 is connected to the connection point between the collectors of the transistors 11 and 13. The emitter of this transistor 16 is connected to the power supply voltage V
cc, and its collector is connected to the collector of the N P N +- transistor 17 . The base of this transistor 17 is connected in common with the bases of the transistors 13 and 14, and also connected to the collector, and the emitter is connected to the ground voltage GND. The base of the transistor 16 has an emitter connected to the power supply voltage VCC.
A PNP I-transistor connected to 18. +9 bases are connected, and a constant current is taken out from the collectors of these transistors 18 and 19.

A conventional starting circuit C for starting such a band gap type current source A is configured as follows. NPN
The bases of transistors 21, 22 are connected in common,
The collector of the transistor 21 is connected to the base and to the power supply voltage Vcc via the resistor 23, and the emitter is grounded. The emitter of the transistor 22 is connected to the ground voltage GND via a resistor 24.

These NPN l-transistors 21 and 22 constitute a current mirror circuit 25. The collector of transistor 22 is connected to the collectors of transistors 11 and 13 in bandgap current source A.

A connection point between the emitter of the transistor 22 and the resistor 24 is connected to the collector of a PNP transistor 2B. The emitter of this transistor 26 is connected to the power supply voltage VCC.
, and its base is connected to the common base of transistors 11 and 12 in the bandgap current source A.

The operation of the circuit with the above configuration will be explained. The transistor 21 in the starting circuit C turns on and the current mirror circuit 25
is activated. The collector current of the transistor 22 is the transistor 1B in the bandgap current source A, 18.1
The base current is 9. Conduction of transistor 16 turns on transistor 17, which turns on transistor 13.
14 turns on. In the current mirror circuit of transistors 11 and 12, when the currents flowing through the transistors 13 and 14 become equal, a stabilized current can be extracted from the collectors of transistors 18 and 19.

This band gap type current source A has VT (Vt-kT/
Q: Proportional to Q: electron charge, T: absolute temperature, and Boltzmann's constant), and a stable constant current can be obtained.

By the way, the starting circuit C is a means for stably operating this band gap type current source A, and once the band gap type current source A is started, the starting circuit C does not need to be used. Therefore, after starting the bandgap current source A, it is necessary to turn off the transistor 22.

Conventionally, the collector current of the transistor 2B is used to connect the resistor 24.
A large amount of current is caused to flow through the resistor 24, and a potential that can turn off the transistor 22 is applied to the resistor 24, thereby turning off the transistor 22.

However, in the above configuration, the transistor 2
In order to turn off transistor 2, a large collector current must flow through transistor 2B, resulting in an increase in current consumption. For example, if vCC is 1.2V, the resistance value of resistor 23 is 39
Assuming that the resistance value of the resistor 24 is 15Ω, the collector current of the transistor 26 is required to be about 40 μA in order to turn off the transistor 22.

(Problems to be Solved by the Invention) As described above, the conventional current source startup circuit has the drawback of large current consumption.

This invention was made in consideration of the above circumstances, and its purpose is to provide a starting circuit with low current consumption.

[Structure of the Invention] (Means for Solving the Problems) A starting circuit of the present invention includes a first transistor from which a starting current for starting a transistor circuit is output from a first terminal, and this first transistor. a second transistor connected in cascode to a second terminal of the transistor; first circuit means for supplying a direct current bias voltage to the gates of the first and second transistors; and second circuit means for turning off the first transistor.

(Function) In the starting circuit of the present invention, the current for turning on the first transistor is set to a minute value by the first circuit means. After activation of the current source, the second circuit means increases the emitter potential of the first transistor to turn it off.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 1, the right side surrounded by a broken line is a band gap type current source A, and the left side is a starting circuit B for the current source of the present invention. Since the band gap type current source A is the same as that shown in FIG. 3, the same reference numerals are given and the description thereof will be omitted.

The starting circuit B of the present invention is constructed as follows. N
The emitter of the PN transistor 1 is connected to the ground voltage GND, and the collector is connected via the resistor 2 to the power supply voltage Vcc. The base of transistor 1 is connected to the collector and to the base of transistor 3. The collector of this transistor 3 is connected to the connection point of the collectors of transistors 11 and 13 in the bandgap return current source A.

The bases of the NPN transistors 4.5 are connected in common,
The collector of the transistor 4 is connected to its base, and is also connected to the common base of the transistor 13 via a resistor 6. The emitter of this transistor 4 is connected to ground voltage GND. The collector of transistor 5 is connected to the emitter of transistor 3, and the emitter is connected to ground voltage GND via resistor 7.

The base of an NPN transistor 8 is connected to the connection point between the emitter of the upper transistor 3 and the collector of the transistor 5. The emitter of this transistor 8 is connected to the ground voltage GND, and the collector is connected to the base and to the collector of a PNP transistor 9. The emitter of this transistor 9 is connected to the power supply voltage VCC, and the base is connected to the common base of transistors 11 and 12 in the bandgap current source A.

Next, the operation of the starting circuit will be explained.

A small current flows through the transistor 5 biased by the resistors 2 and 6 and the transistors 1 and 4. This minute current flows through transistor 3 to transistor 16 in bandgap return current source A. This becomes the base current of ill 19. Therefore, transistors 1B and 18°19 are turned on. In the current mirror circuit of transistors 11 and 12, when the currents flowing through transistors 13 and 14 become equal, transistors 18 and 18. A stabilized current can be extracted from the collector of 19.

In this manner, when the bandgap current source A is activated, the emitter voltage of the transistor 3 increases due to the collector current of the transistor 9, the transistor 3 is turned off, and the activation circuit B is stopped.

That is, in order to turn off transistor 3, the current flowing through transistor 9 only needs to be larger than the current flowing through transistor 5. Therefore, it is possible to turn off the transistor 3 with a small amount of current consumed by the transistor 9. Note that the transistor 8 is a diode connected to prevent the transistor 9 from becoming saturated when current flows through the transistor 9.

FIG. 2 shows the current characteristic curve of the starting circuit of the above embodiment, and the curve a shows the current I3 of the transistor 3 with respect to the current 2 flowing through the resistor 2 when starting the current source A. This is a current characteristic curve showing the current I2 flowing through the resistor 2 and the current 2 required to turn off the transistor 3.

At this time, the resistance values of resistors 2 and 6.7 are 100Ω, 18Ω, and 18Ω, respectively, resistor 15 in bandgap current source A is 3.6Ω, and transistor 13 is for stabilization. Therefore, the area ratio with other transistors was quadrupled.

As shown in FIG. 2, a base current of about 1 μA at most is sufficient to turn off the transistor 3.

Although the above embodiment has been described as a starting circuit for a bandgap current source, it can also be used as a starting circuit for other current source circuits or voltage source circuits. Further, as a countermeasure against the early effect, an emitter resistor may be added to each transistor constituting the circuit of FIG. In addition, although the transistor i11.19 is shown as a transistor for extracting a constant current, only one transistor 18 is shown.
Alternatively, a large number of transistors may be added so that a large number of transistors can be extracted.

[Effects of the Invention] As described below, according to the present invention, the transistor for starting the transistor circuit can be turned off with a small amount of current, so it is possible to provide a starting circuit with low current consumption.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a configuration according to an embodiment of the present invention. Second
The figure shows a current characteristic curve of a part of the circuit of FIG. 1, and FIG. 3 is a circuit diagram for explaining a conventional starting circuit. 1.3, 4.5.8...NPN transistor, 2.6.
7...Resistor, 9...PNP transistor.

Claims (3)

[Claims] (1) a first transistor whose first terminal outputs a starting current for starting the transistor circuit; a second transistor connected in cascode to a second terminal of the first transistor; 1. A first circuit means for supplying a DC bias voltage to the base of a second transistor, and a second circuit means for turning off the first transistor in response to activation of the transistor circuit. Starting circuit. (2) The first circuit means includes a third transistor whose collector and base are connected to the base of the first transistor, and a collector and base connected to the base of the second transistor, and a third transistor whose collector and base are connected to the base of the second transistor. 2. The startup circuit according to claim 1, further comprising a fourth transistor to which a base potential lower than the base potential of the fourth transistor is applied. (3) The second circuit means is operated by a control current of a fifth transistor which supplies a part of the current flowing after the transistor circuit is activated to a control terminal. starting circuit.