JPS6276812A - Hysteresis circuit - Google Patents

Abstract

PURPOSE:To attain a low voltage drive and to specify an accurate output by connecting a transistor (TR) to an output terminal of the 1st current mirror circuit, connecting the 2nd current mirror circuit to the collector and making an output of the current mirror circuit flow to the 1st current mirror circuit. CONSTITUTION:In the process of the increase in an input voltage Vin, when the result of subtraction of a current Iref from a current Ia flowing from a collector of a TR Q12 to a connecting point (a) of TRs Q14, Q19 reaches twice the current flowing to a TR Q13 from the collector of a TR Q11, TRs Q15, Q16 are balanced. On the other hand, in the process of the decrease in the input voltage Vin, when the current Ia reaches twice of the current Ib, the balancing of the TRs Q15, Q16 is released. Thus, a hysteresis circuit where the low voltage drive is attained and the output current is decided accurately to a prescribed value is offered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a hysteresis circuit used for an input switch of a D drive circuit, etc.

[Technical background of the invention]

For example, an input switch for an LED drive circuit is required to have hysteresis characteristics.

In other words, in the process of increasing the input level, the output state changes from an unmanned state to a steady state only when the input level increases to a certain value, and even if this input level changes, the output state does not change and the input In the process of decreasing the level, the input level when the output state changes from the unmanned state to the steady state in the above input increasing process has the characteristic that the output state changes from the steady state to the unmanned state at a small input level. It is required to have. The reason why such characteristics are required is that once the LED is turned on, it is necessary to prevent the LED from turning off even if the input level fluctuates somewhat.

FIG. 3 shows a conventional hysteresis circuit having the characteristics described above.

In Fig. 3, transistor Q1*Qts constant current source I
1 constitutes a differential amplifier circuit. The load of this circuit is a current mirror circuit constituted by transistors QspQa having mutually different emitter areas. In this case, the transistor Q having a smaller emitter area is diode-connected, and the collector of the transistor Q4 having a larger emitter area is used as a current output terminal. The base of a transistor Q is connected to this output terminal. The collector of this transistor Q is connected to a constant current source I8 and a current input terminal of a current mirror circuit constituted by transistors Q@ to Q$. In this current mirror circuit, the collector of one of the two output transistors Qy=Qs is connected to the collector of transistor Q, and the collector of the other transistor Q is used as a current output terminal.

The operation in the above configuration will be explained. First, when unmanned,
Since the collector currents of transistors Q□ and Q are equal,
Transistor Q4 becomes saturated. As a result, no base current flows through transistor Q, so transistor Q is turned on. Then, the current I of the constant current source I2. Most of f flows through transistor Q. As a result, a current equal to the current Ir@f of the constant current source (2) attempts to flow through the transistor QyyQs. As a result, transistor Q is turned on.

However, transistor Q7 is in a saturated state.

Next, consider the process in which the input voltage Vin increases from Ov. Now, the ratio of the emitter areas of transistors Q and Q4 is 1
: Assume that it is 2. Assuming this, the input voltage V
As in increases, the collector current IC2 of the transistor Q and the collector current IC1 of the transistor Q1 become as follows: IC2=2 Ic1+Ir@f −(1
), transistors Qs and Q
4 equilibrium state is established. This results in r1 transistor Q
4 exits the saturation region and operates in the forward region.

In this state, if the input voltage Vin increases slightly,
Transistor Q draws out the base current of transistor Q, turning on transistor Q. For this,
A current obtained by multiplying the base current of transistor Q by β (forward current amplification factor) flows into transistor Q and constant current source (2). As a result, the current flowing through the transistors Q6 to Q is . It becomes less than f. Then, in equation (1), the terms Ir and f are replaced with smaller values. The difference leads to an increase in the base current of transistor Q, so transistor Qs is a constant current source! , the current flowing into increases. When this operation is completed and the state becomes stable, transistor Q is turned on and transistors 91 to 9 are turned off. In the process of increasing the input voltage Min, the transistor Q has a current I. f changes from a flowing state to an off state.

Next, consider the process by which the input voltage vin decreases from this state. In this case, transistor Q.

Ignoring the base current of IC2'' 2 IC1・When (2) holds true, transistors Q and Q4 tend to deviate from the equilibrium state. Therefore, the input voltage Vin is slightly different from this state. As it decreases, transistor Q will no longer draw the base current of transistor Qs.As a result,
Transistor Q11 attempts to shift to the off state rapidly. As a result, the current ref of the constant current source I flows to the transistors 6 to Q, thereby accelerating the off operation of the transistor Qs. When this operation is completed and stability is achieved, transistor Qi is turned off, and current flows through transistors Q6 to Qa. f is flowing. In other words, 1 input terminal v
In the process of decreasing ln, the transistor Qs changes from an off state to a state in which a current "ref flows."

To summarize the above, the hysteresis width is expressed by formula (1).

(2) Determined by a relatively small current Iref.

[Problems with background technology]

However, in the conventional hysteresis circuit described above,
There was a problem that low voltage drive was not possible. That is,
Constant current source 1111. If we replace it with a transistor, the operating power supply voltage is at least Vex(sat) + VaK(oN) + vag(
oN)≧0.2 + 0.7 + 0.7 = 1.6
(:V) It is impossible to drive at a low voltage of less than 1V, which is necessary.

Furthermore, the conventional circuit has a problem in that the output current cannot be accurately defined. That is, during unmanned operation, the transistor Q4 is saturated, the transistor Qs is turned off, and most of the current Iref flows through the transistor Q@. What about this, transistor Q? is saturated, the parasitic transistor Tr is turned on. As a result, this transistor Tr
The base current of transistor Qs decreases by the base current of , and the output current becomes ■. ut decreases.

Therefore, the output current I. ut no longer matches the current I□.

[Purpose of the invention]

The present invention has been made to address the above-mentioned circumstances, and an object of the present invention is to provide a hysteresis circuit that can be driven at a low voltage and can accurately define an output current.

[Summary of the invention]

In order to achieve the above object, the present invention uses a resistive load as the load of the incrementing amplifier circuit, converts each differential output voltage into a current using a transistor with a common base, and supplies the current to a first current mirror circuit. A transistor driven by a constant current source is connected to the current output terminal of the first current mirror circuit, and a second transistor driven by the constant current source is connected to the collector of this transistor.
In this book, a current mirror circuit is connected, and the output current of this current mirror circuit is made to flow to the output or input of the first current mirror circuit.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, NPN transistor Q1! .

Ql2 and constant current source Ill form a differential amplifier circuit. That is, the bases of the transistors QxteQtz are connected to one and the other of the differential input terminals 11 and 12, respectively, and the emitters are commonly connected to the constant current source Ill.

The load of the differential amplifier circuit is a resistive load. That is, the collectors of transistors Qll + Qti are resistors R11l R1!, respectively. It is connected to the power supply VCE via.

The collectors of the transistors Qst + Ql are further connected to the emitters of the respective PNP transistors Qts + Ql4. These transistors Q1m1Q
14 has a base-grounded configuration in which a constant voltage source Vtt is commonly connected to the base thereof.

The collectors of transistors Qls+Ql4 are each connected to the collectors of NPN transistors Qts*Qts. Transistors Qllll #Ql- form a current mirror circuit. In this case, transistor Q
Ill constitutes a transistor on the input side and is diode-connected. The emitter area of transistor Q16 is set to be twice that of transistor Qli. That is, the current mirror ratio is set to 1:2.

The emitters of transistors QIII and Q16 are each grounded via a resistor 'Rts l R14. Also, the collector of the transistor Qts is an NPN transistor Ql? connected to the base of. The emitter of this transistor Q17 is grounded, and the collector is the constant current source 11.
Connected to 2.

The collector of transistor Q17 is NPN. The collector of transistor Qss and NPN transistor Q11+Q.
,. connected to the base of. These transistors Q
ll-Q! 6 constitutes a current mirror circuit.

In this case, the transistor Q18 on the input side is diode-connected across the resistor R15, and its emitter is grounded. Also, one transistor Qx on the output side
The collector of s is connected to the collector of transistor Q12, and the emitter is grounded. Also, the other transistor Qm on the output side. The collector is connected to the output terminal 13, and the emitter is grounded.

The operation in the above configuration will be explained.

First, let us consider the case of unmanned operation, that is, the case where the input voltage vln is OV. In this case, the transistor Qll e QlN
Since the collector currents of are equal, the transistor Qrs is saturated and the transistor Q17 is turned off. This results in
A current mirror circuit made up of transistors Qu to Q and o is driven by a current Iref from a constant current source Ill.

Next, a process of increasing the input voltage Vin will be explained. However, if the base potential of transistor Q1t is plus, transistor Q1! Let the base potential of be negative.

Now, when the input voltage Vin starts to rise above Ov, the collector current of the transistor Qll increases, and conversely, the collector current of the transistor Q1z decreases. Then, the current flowing through transistor Q13 decreases, and the current flowing through transistor Q14 increases. Transistor (hs
The current flowing through r Ql4 is the current flowing through transistor Q1, respectively.
s r Flows to Qts. Here, transistor Q16
As mentioned above, the emitter surface of the transistor Q1B
Therefore, the current mirror circuit constituted by the transistor Q15*Qts becomes in an equilibrium state when the collector current of the transistor Qta becomes twice the collector current of the transistor Q15. In this state, if the input voltage v1n further increases, supply of base current to the transistor Q1y is started. As a result, υ, -transistor Q17 turns on and draws a current β times its base current from constant current source I1m, so the current flowing through the current mirror circuit constituted by transistors Q xs -Q to rapidly decreases. . Since the transistor Qu draws current from the resistor R11, this decreasing operation is accelerated. When this operation is completed, the transistor Q1γ is turned on and the transistors Qrs to Ql11 are turned off.

Next, a process in which the input voltage vln decreases will be explained.

In this case, as the input voltage vln decreases, the collector current of the transistor (ht) decreases, and the collector current of the transistor Q12 increases.
The base current of sy decreases. After this, transistor Q
When ls r Qts goes out of equilibrium, transistor Q17 turns off and transistors Q1s-Q2G turn on.

In summary, in the process of increasing the input voltage v1°, the transistor Q1! The collector of transistor Q1
4 * When the current I& flowing into the connection point a of Qts minus the current "ref" becomes twice the current Ib flowing into the transistor Qts from the collector of the transistor Qll, the transistor Qls + Ql is in an equilibrium state. On the other hand, in the process of decreasing the input voltage Vin, when the current Iref becomes twice the current Xb, the equilibrium state of the transistors Qss + Qts is released.Therefore, in FIG. A hysteresis characteristic with a width defined by is obtained.

According to this embodiment described in detail above, since the transistor Q19 corresponding to the transistor Q7 in FIG. 3 does not become saturated, the output current I. ut can be made to accurately match the current Iref.

The reason why the transistor Q7 is not saturated is that the collector of the transistor Q7 is connected to the collector of the saturated transistor Q4. The VCE of transistor Q4 is VCFI(sat) = 0.
Similarly, the VcW of the nitransistor Q is at a potential that should enter saturation.

On the other hand, the VCE of transistor Qle is always 0.2
This is because it is less than v.

Furthermore, by appropriately setting constants, the operating power supply voltage can be set to approximately 1V. That is, in FIG. 1, ■CC:vBE15+vCE13(aat)+lR11
1R11= 0.7 + 0.2 + IiN・R11
= 0.9 +IR11°R11 holds true, so by setting lR11·R11 to 0.1v or less, vcc<1v can be obtained.

FIG. 2 is a circuit diagram showing another embodiment of the invention. In FIG. 2, the same parts as in the previous embodiment are given the same reference numerals.

In FIG. 3, the collector of transistor Q1G is PN
P Connected to the current input terminal of a current mirror circuit consisting of transistors Q and Qts.

The two output transistors Q of this current mirror circuit!
The collector of one of the transistors I r Qzs (hz) is connected to the collector of transistor Qt3.

Even in such a configuration, the same operation as in the previous embodiment can be obtained. That is, in the previous embodiment, the input voltage v
In the process of increasing ln, the transistor Q15 * Q
The input current of the current mirror circuit consisting of 16 is set as I, -I, and the output current is I, -I. f, the width is I
A hysteresis characteristic determined by ref was obtained. On the other hand, this embodiment obtains exactly the same hysteresis characteristic by setting the above-mentioned input current to Ib and ref, and setting the output current to 8.

Hikoo, in Figure 2, terminal 1 is used as the current output terminal.
In addition to 3, terminal 14 can also be used. Which one to use may be selected as appropriate depending on the input form of the next stage.

〔Effect of the invention〕

According to the present invention, it is possible to provide a hysteresis circuit that can be driven at a low voltage and whose output current is accurately determined to a predetermined value.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a circuit diagram showing the structure of another embodiment of the present invention, and FIG. 3 is a circuit diagram showing the structure of a conventional hysteresis circuit. Qll~Qzs...transistor, R11~R15・
...Resistance, ■111112... Constant current source, Vll...
・Constant voltage source. Applicant's agent Patent attorney Takehiko Suzue-17=

Claims (1)

[Claims] A differential amplifier circuit that differentially amplifies an input signal; 1. a second PNP transistor; a third NPN transistor that is diode-connected and whose connection point is connected to the collector of the first PNP transistor; and a third NPN transistor whose collector is connected to the collector of the second PNP transistor; and a fourth PNP transistor forming a current mirror circuit of the third PNP transistor, and a fifth NPN whose base is connected to the collector of the fourth PNP transistor and whose collector is connected to a constant current source.
a sixth NPN transistor which is diode-connected and whose connection point is connected to the collector of the fifth NPN transistor; a current mirror circuit is formed with the sixth NPN transistor, and whose collector is connected to the collector of the third NPN transistor; , a seventh NPN transistor connected so as to cause the constant current source current to flow through the input or output of the current mirror circuit constituted by the fourth NPN transistor.
A hysteresis circuit comprising: a PN transistor; and an eighth NPN transistor forming a current mirror circuit with the sixth NPN transistor and having a collector connected to a current output terminal.