JPS60186140A - Power-on state detecting circuit - Google Patents

Abstract

PURPOSE:To obtain a power source turning-on and resetting circuit which has good temperature characteristics and is suitable for IC-implementation by utilizing a band gap reference voltage generating circuit as the reference input supply circuit for the comparator of the power-on state detecting circuit. CONSTITUTION:The band gap reference voltage generating circuit BC has a constant current source I which is hard to depend upon a source voltage V, and when the power source is turned on, the source voltage V rises linearly and the current I flows in the circuit BG and rises faster than the voltage V rises, so the rising characteristics of the circuit BG are compensated. The voltage V is applied to turn on transistors (TR)1, 2, and 3. When the voltage V is lower than VE at the intersection of the terminal voltage V2 of a voltage dividing resistance R10 and the output voltage V1 of the circuit BG in a case where the voltage V rises linearly on power-on operation, V1>V2 and the output of a comparator COMP3 is L; when the voltage V rises above VE, V1<V2 and the output of the COMP3 is H. Temperature coefficients of the difference DELTAVBE between base-emitter voltages of the TRs 1 and 2 and VBE of the TR3 are positive and negative respectively, so excellent temperature characteristics are obtained.

Description

Detailed Description of the Invention (a) 9 Technical Fields of the Invention The present invention relates to a power-on (turn-on) detection circuit, and particularly to an initial setting of a logic circuit when power is turned on to a digital system device composed of logic circuits. This relates to a circuit that detects power-on for the purpose of

(b) Problems with the prior art According to the prior art, the power-on detection circuit used for the above purpose uses a Zener diode and the time constant of a resistor and capacitor. There are two ways to do this.

FIG. 1 is a diagram showing a power-on detection circuit using a Zener diode, and FIG. 2 is a diagram showing a power-on detection circuit using a time constant of a resistor and a capacitor.

In Figures 1 and 2, R1-R7 are resistors, Z is a Zener diode, C is a capacitor, COMP 1,
COMP2 is a comparator.

In the case of FIG. 1, the power supply voltage terminal (2) is applied when the power is turned on. The power supply voltage (2) increases linearly and gradually from OV at the same time as the power is turned on, and reaches a specified value.

Therefore, when such a power supply voltage +■ is applied, the resistance R3
The terminal voltage increases linearly from 0■ in proportion to the power supply voltage (■).

However, the terminal voltage of the Zener diode Z quickly becomes a constant voltage value. Therefore, when the terminal voltage of resistor R3 becomes higher than the terminal voltage of Zener Gouion Z after the power is turned on, the comparator COMP1 operates, and the output of comparator COMP1 becomes "Low" as shown in the figure. ” to Hi
This output voltage resets the logic circuit in the device.

In the case of FIG. 2, it is the same as J1. In this case, when there is no capacitor C, the terminal voltage of resistor R5 is higher than the terminal voltage of resistor R7 (set it. When the power is turned on, the terminal voltage of resistor R7 is linear from 0 in proportion to the power supply voltage 1). However, since the capacitor C is present, the voltage of the resistor R5 increases with a delay in time.

However, since the terminal voltage of the resistor R5 is set to be higher than the terminal voltage of the resistor R7, after a period of time, the terminal voltage of the resistor R5 becomes higher than the terminal voltage of the resistor R7. At this time, the comparator COMP2 operates, and as shown in the figure, the comparator COMP2
The output changes from ``LOW'' to ``High'', and this output voltage resets the logic circuit in the device 71-.
do.

The method shown in Figure 1 that uses a Zener diode has the disadvantage that it is difficult to incorporate it into an IC and the detection voltage fluctuates depending on the temperature, and the time constant of a resistor and capacitor is used. The method shown in FIG. 2 does not follow a slow voltage rise and also has the disadvantage that a capacitor must be placed outside the IC.

(C)0Object of the invention The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art,
It is an object of the present invention to provide a power-on detection circuit that has good temperature characteristics and is suitable for IC implementation.

(d)0 Structure of the Invention According to the present invention, the above-mentioned object is composed of a band gap reference voltage generation circuit, a resistive voltage dividing circuit, and a voltage comparator circuit, and applying a power supply voltage to the resistive voltage dividing circuit. The output of the resistor voltage divider circuit is applied to the voltage comparator circuit, the power supply voltage is applied to the Hunt Gap reference voltage generation circuit, and the output of the Hunt Gap reference voltage generation circuit is applied to the voltage comparator circuit. Characterized by being connected to human power.
This is achieved by providing a power-on detection circuit.

(e) 1 Embodiment of the Invention The present invention utilizes a hand gap reference voltage generation circuit as a reference input supply circuit for a comparator of a power-on detection circuit, thereby providing a power-on system with good temperature characteristics and adaptable to IC implementation.・This is an attempt to obtain a reset circuit.

FIG. 3 is a diagram showing the transient characteristics of the band gap reference voltage generating circuit according to the present invention.

FIG. 4 is a diagram showing an embodiment of a power-on detection circuit using a band/gear reference voltage circuit according to the present invention. In the figure, BG is a hand gear 7B reference voltage generation circuit (
(encircled by a dotted line)-COMP3 is a comparator, R9-R13 are each a resistor, Tr1 to Tr3 are each an l-transistor, J
For example, it is a constant current source.

Hunt gap reference voltage generation circuit BG surrounded by dotted line
has a constant current source J that is hardly dependent on the power supply voltage, and a constant current l flows into the hand gap reference voltage generation circuit BG.

The present invention will be described in detail with reference to FIG. 4 below.

When the power is turned on, the power supply voltage +V increases linearly, and the current I flows into the band gap reference voltage generation circuits B and G, and this current I has a fast rise characteristic compared to the increase in the power supply voltage '→-■. , which compensates for the rise characteristics of the Hunt Gap reference voltage generation circuit BG.

Now, by applying the power supply voltage +V, 1-range disk Tr1 (
In this case, the transistor (which is diode-connected) is turned on, and therefore the l-landisk Tr 2 is also turned on. In the hand gear knob reference voltage generation circuit BG, resistor R11
The value of O is a low resistance of several hundred ohms, for example, the current r1 is set to be relatively large, and the value of the resistor R12 is set to be at least 10 times the value of the resistor R11, so the current I2 is the current 1
It is about 1i10.

In this case, the difference ΔVbe between the voltages between each of the transistors Tr1 and Tr2 becomes the voltage drop across the resistor R2. Therefore, ΔVbe=R1,l ] 2 If the current gain of transistor Tr2 is large, then
The voltage drop across resistor R12 is also proportional to ΔVbe.

Therefore, the output voltage (1) of the transistor Tr3 is the sum of the voltage (1)be between the bases and emitters of the transistors 1 to Tr3 and the voltage drop across the resistor R12.

V l =Vbe+R127I 2 -Vbe+R12・(ΔVbe+R13)=Vbe+
Δvbe·(R12÷RI3).

In this case, ΔVbe is a positive temperature coefficient, but Vbe is a negative temperature coefficient, so by appropriately selecting the values of R12 and R13, the output voltage 1 of the transistor Tr 3 can be prevented from changing due to temperature. It can be done.

Figure 3 is a graph showing the temporal changes in the terminal voltage +V2 of the resistor RIO and the output voltage V1 of the band gap reference voltage generation circuit f18BG when the power supply voltage +■ increases linearly when the power is turned on. be.

If the value of the power supply voltage +V when the curves of this terminal voltage +■2 and the output voltage +v1 intersect is Ve, then the power supply voltage is Ve.
In the following cases, +v1>+y2, the output of comparator COMP3 becomes L, o w'', and when the power supply voltage is higher than Ve, +v1<→-v2, the output of comparator COMP3 becomes o
ut becomes "High" and resets the logic circuit.

Moreover, since the output voltage (1) of the band gap reference voltage generation circuit BG does not change due to changes in temperature, a stable reset can always be supplied.

(f) 0 Effects of the Invention As explained in detail above, the present invention has good temperature characteristics and 1. This has the great effect of realizing a power-on detection circuit that is compatible with C.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a conventional power-on detection circuit using a Zener diode. FIG. 2 is a diagram showing a conventional power-on detection circuit that utilizes the time constants of a resistor and a capacitor. FIG. 3 is a diagram showing the transient characteristics of the band gear knob reference voltage generation circuit according to the present invention. FIG. 4 is a diagram showing an embodiment of a power-on detection circuit using a band gap reference voltage circuit according to the present invention. In the figure, R1-R13 are resistors, Z is a Zener diode, C is a capacitor, COMP 1, COMP2, C
OMP3 is a comparator, Tr, '1'-Tr3 are transistors, J is a constant current source, and BG is a band gap reference voltage generation circuit. District 4

Claims (1)

[Claims] It is composed of a band/gear knob reference voltage generation circuit, a resistor voltage divider circuit, and a voltage comparator circuit, and the power supply voltage is applied to the resistor voltage divider circuit to convert the output of the resistor voltage divider circuit into the voltage comparator circuit. A power-on detection circuit characterized in that a power supply voltage is applied to the hand gear knob reference voltage generation circuit, and the outputs of the band gap reference voltage generation circuit are respectively connected to the voltage comparator circuit.