JPS59175327A - Electronic 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 [Technical Field] The present invention relates to an overvoltage detection circuit frequently used in various electronic devices and an electronic circuit using the same.

[Background technology]

The overvoltage detection circuit detects fluctuations in the power supply voltage, and is used to prevent damage and burnout of electronic circuits such as amplifier circuits. Therefore, it does not operate when the power supply voltage is in a steady state, but operates when it becomes abnormally high.
Gives an abnormal signal.

Prior to the present invention, the present inventors investigated the case of protecting an amplifier circuit, etc. using a normally considered overvoltage detection circuit, and found that it is similar to so-called blocking oscillation, which repeats activation and non-operation states when overvoltage is detected. It has also been found that this phenomenon is often observed when the power supply voltage rises or falls slowly near the overvoltage detection level, and when the power supply voltage fluctuates up and down near the detection level.

It has also been found that when the above phenomenon occurs, an abnormally high or abnormally low power supply voltage is intermittently supplied to the electronic circuit, causing damage to the electronic circuit. Further, this problem is especially serious when the electronic circuit system includes a large inductive inductance.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to improve overvoltage detection when the power supply voltage fluctuates, thereby sufficiently reducing the image area of electronic circuits.

[Summary of the invention]

One proposal in this application to achieve the above purpose is to make the voltage detection level different when the power supply voltage rises to an abnormal state and when it returns to a steady state. To detect fluctuations in the power supply voltage, a predetermined current is supplied to the reference voltage element when the power supply voltage moves from a steady state to near the detection level, and the characteristics other than the rising part of the reference voltage element are It is possible to detect fluctuations in the power supply voltage due to the characteristics of good linearity (characteristics of the portion with small internal resistance), and to accurately and quickly detect abnormalities. [Example] Figures 1 and 2 are shown below. A first embodiment of an overvoltage protection circuit to which the present invention is applied will be described with reference to .

It is assumed that the overvoltage detection circuit 1 shown in FIG. 1 is constituted by a semiconductor integrated circuit (hereinafter referred to as IC).

The 1st terminal is an output terminal, and the 2nd terminal has +V. C power is supplied, and the No. 3 terminal is the ground terminal.

First, ten v. The steady state voltage level VCc of the ot source.

The following describes the circuit operation when the detection level approaches the detection level ■Co.

+v source, the reference voltage VRP,F becomes C
C occurs. Therefore, ■cc is vcc=v2+■B
The transistor Q1 is in the off state until F, , 1+vREF. (Here, V2 is Zener diode 2
The Zener voltage of D, VBEQI, is the voltage between the pace and emitter of transistor Q, which is normally 0.7V. ,
) In other words, in this state, the current flowing through the collector of Q is almost zero. Therefore, at this time, the pace current to transistor Q3 is almost zero, so transistor Q3
is in the off state. At this time, a base current is supplied to the transistor Q2 from the constant current circuit C8 via the resistor R8, and the transistor Q is in an on state.

Further, the current of the constant current circuit C8 is also supplied to the transistor Q4 via the resistor R4, and the transistor Q,
is also turned on, and the constant current circuit cs is turned on.

absorbs the current of Therefore, the voltage at output terminal 1 is V.

ut':O. Here, the power supply voltage ■. 0 is “C”
When C> vZ rises to the range of +VREF, a current flows to the collector of transistor Q, and as that current increases, at a certain point (E = 1), the pace potential of transistor Q increases. However, its pace emitter threshold voltage VBEQ3 (generally about 0.7
V)Y can be heard. At that time, the transistor Q turns on and drains the current of the constant current circuit cs, which increases the saturation voltage oV between the collector and emitter of the transistor Q3.
If oP,s is set to be lower than the pace emitter voltage VBE (0.7V) of transistor Q4 (generally about 0.2V), transistors Q and Q will be turned off. , the current of the constant current circuit cs1 flows out from the terminal 1, indicating an abnormal state.

Here, the point where the transistor Q3 changes from off to on, that is, the point where the voltage becomes I, is the detection level VCCI when the power supply voltage increases from the steady state to the abnormal state. The current flowing through RA is the above current■
The current amplification rate of transistor Q is sufficiently smaller than 11, and therefore its base current is sufficiently smaller than 11, and the collector-emitter resistance 'cs when transistor Q is turned on is sufficiently smaller than R2/J%. Furthermore, assuming that the base current required to turn on the transistor Q3 is also sufficiently smaller, the detection level Vcc1 can be derived from the following equation.

Vocl”:=V,,,+V2+I,R1+V,,,
1・-・・・-fl）VA'I、R、・・・old...
・・・・・・Yamamachi・・・・・・Old・＋21
Therefore, VCCI ””REF +VZ +VA! ! '10V
R, FIEQ1°°゛°゛° (3) In the above equations (11 to (3)), VRE F is the voltage level of the reference power supply, ■ is the Zener voltage of the Zener diode ZD, and vA is the voltage level when the transistor Q is turned off. The on-state voltage "BEQI" is the pace-to-emitter voltage of transistor Q.

Assuming that t is the time point at which Equation 31 holds true, as is clear from the above explanation, the voltage 4 will turn on the transistor Q, and the output current of the constant current circuit C8 will pass through the transistor Qsk to the ground line. Then, transistor Q!

No base current is supplied to Q, and they will be in the off state, so the collector voltage of transistor Q4, in other words, the output signal ■. The voltage level of U increases as at time 12 shown in FIG.

On the other hand, +V. Steady state (■) occurs from a voltage equal to or higher than the voltage level V shown in formulas 1 and 3) above. When CI decreases to CO, the circuit operation as described below is performed.Once the power supply voltage cc exceeds vcc1, transistor Q is turned off, so almost all of the collector current of transistor Q1 is transferred to the transistor Q1. Q,
Therefore, the power supply voltage for turning off transistor Q and turning on transistors Q, , Q, flows into the base of Q. . , and the collector current of the transistor Q1 at this time, that is, the transistor Q.

If the base current of is , then +Voc, '? VR,, 10V2+J, R,+V,
, 1・−・−+41. To simplify the explanation here, in this case L)■, that is, ■+ R+ >> I
It can be seen as t R+, therefore, formula (4) is compared with formula ill, assuming I, R, χO, v = v + v + v ・・・・・・・・・
・・・・・・・・・ (5) CC2REF z
It can be seen as BEQI.

Therefore, +VcotS, the voltage gradually decreases, and
CC2” ■REF When the voltage level is lower than +v2+VBEQI, transistor Q.

The voltage to maintain the on state can no longer be obtained,
Transistor Q3 is turned off. Therefore, constant current circuit C8! The output current is supplied to the base of transistor Q2 via resistor R8, and at the same time, is supplied to the base of transistor Q4 via resistor Ra'l. As a result, transistor Q.

Q4 is turned on again. And the output signal vout
The voltage level drops again as shown at time 12 in FIG.

In the manner described above, a hysteresis characteristic as shown in FIG. 2 can be obtained.

In this case, the width of hysteresis is l”cct −v
CC21 can be expressed by the equation (31) (approximately V since it can be expressed as a difference of 57) By providing hysteresis to the detection level of the overvoltage detection circuit in this way, it becomes possible to perform good retention.

In addition, in this embodiment, although the resistor RAk is added,
This is to improve the rise and fall characteristics at the time of tll'2.

That is, by providing the resistor RA, VoC>■2
If this happens, current will always flow from the Zener diode ZD to the reference power supplies RF and F via the resistor RA. Therefore, when the transistor Q operates in the on state or the off state and the above-mentioned hysteresis operation is performed, the V-■ characteristic of the Zener diode ZD does not operate at the point where the internal resistance is large in the rising part, and the V- Using the part of the I characteristic where the current changes rapidly even if the voltage changes minutely, that is, the part where the internal resistance is small, h tl +
The operation at time tt will be performed.

Therefore, the rise and fall characteristics of the hysteresis characteristics shown in FIG. 2 become extremely good.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that the overvoltage detection circuit 1 shown in FIG. 1 has the same configuration as the circuit described in the first embodiment, so a description thereof will be omitted.

FIG. 3 shows an example of an audio amplifier implemented as an IC, and an audio signal VIN is supplied to the 11th terminal. +Vcc power supply voltage is supplied to terminal 12,
Output signal from terminal 13■. is obtained. Terminal 14 is a ground terminal. In addition.

It is assumed that the overvoltage prevention circuit 1 is supplied with +cctR from the 12th terminal, although not particularly shown.

11 is a bias circuit, 12 is a voltage amplifier, and a diode D.
,,D! is a level shift diode. Darlington connected transistor Q1. .

Qu is a '#L source side output transistor, and transistor Q+s is a ground side output transistor. Further, capacitor C1 is a DC blocking capacitor, and sp is a speaker connected as a load.

And the output signal ■ of the overvoltage prevention circuit 1. ut is supplied to each base of transistor Q +41 Q +5. Let's say it's 10V. If the C power supply is at a normal voltage level, the output signal vout
is at a low level. In this case, transistor Q 141
Q +s is in the off state. As a result, the bias circuit 11 operates normally, and a predetermined bias voltage is supplied to the base of the transistor QB and other circuits (not shown) such as the amplifier 12. Also, transistor Q7. Since the transistor QI! is in the off state, the transistor QI! The base of is never grounded.

In this state, when the audio signal 1N is supplied, it is amplified by the amplifier 12. Then, corresponding to the polarity of the output signal of the amplifier 12, the output transistor Qu+Q
+ or the output transistor Q+s are driven alternately. When the output transistor Qll+Q+t is in the operating state, the output signal ■. should rise above -“'- due to the alternating current component (order 4 signal).
When s is on, the output signal V. is lower than -1 due to the AC component (audio signal). and,
Is capacitor C8 only for the above AC component, i.e. audio signal? Supply it to the speaker Sp and obtain the audio output in response to the input signal ■1N.

By the way, while the above circuit operation is being performed, +■
When co gradually rises and exceeds the voltage level shown in Equation 31 above, the voltage level of the output signal . A base current is supplied to Q+s, and each operates in the on state.Then, the bias circuit 11 is switched to the off state, and the bias voltage p- necessary for the amplification operation cannot be obtained.In addition, the output transistor Q+2 The pace becomes grounded.

Transistor Q+2 is forced into a disabled state.

As a result of the above circuit operation, the output transistor Q
+P is of course an output transistor. Excessive current will not flow through +3. This prevents the output transistor Q H+Q 1* from being destroyed. Furthermore, if the above-mentioned operation of the overvoltage detection circuit 1 is performed suddenly as described in the first embodiment, the voltage level of the transistor Q 141 Q +g near the voltage level shown by the above equation (3) is
does not repeat unstable on-state or off-state,
Therefore, destruction of the output transistor X/Q+21Q13 can be accurately prevented.

On the other hand, ten v. , when the source voltage drops below the voltage level shown in the above equation t5i, the output signal V is generated by the circuit operation described above. As a result of ut rising again, the input signal V1
The amplification operation for N is performed again, and an audio signal is obtained from the speaker SP. In this case, too, the transistors Q, , , and Q do not operate unstablely near the voltage level shown at t5+ above. .

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the above-mentioned overvoltage prevention circuit 1 is applied to a motor control circuit. Although FIG. 4 shows a control circuit for a single motor coil L1, in the case of a three-phase motor, three systems of limiting circuits are provided. At this time, the overvoltage detection circuit 1 may be provided for each motor control circuit, but it is provided for one system as in this embodiment, and the overvoltage detection circuit 1 is provided for each motor control circuit. Application of UL to two pond systems 1. But that's fine.

H2 is a Hall element that detects the rotational position of the rotor that constitutes the motor. The detection signal Hv is.

Taking a three-phase motor as an example, this is an AC signal obtained every 12 degrees. Reference numeral 21 denotes an amplifier, and transistors Q, .

Assume now that the transistor Q□ is in the on state and the transistor Qvt is in the off state.

The transistor Q□ is turned on by the base current supplied from the transistor Qy+ and the current supplied between the emitter and the paste of the transistor Qt< and further through the resistor Rn. On the other hand, transistor Q! 6 is not supplied with base current and is in an off state. Therefore, +
Vcc1! From the source, transistor Q24, terminal 24,
Motor coil L, Terminal 25, Transistor 25.
Current II+ flows to the ground line.

On the other hand, the output signal AV of the amplifier 21 causes the transistor Q7. operates in the on state, the transistor Q
N operates in an off state and transistor Q26 operates in an on state. That is, the transistor Qya is the transistor Q
, 2 and the base current supplied from transistor Q2.
The transistor is turned on by the collector current supplied between the emitter and base of the transistor and further through the resistor R7. Therefore, a current 112 flows from the 10 VCC power supply to the transistor Qts, the 25th terminal, the coil L1, the 24th terminal, and the transistor Qte+earth line. Current ■+I+112
flow in opposite directions.

In the case of a three-phase motor, the same operation as described above is performed for the other 2W4 motor coils (not shown) in accordance with the rotational position of the motor.

The motor is sequentially energized to rotate in a predetermined direction and continues to rotate smoothly.

By the way, while the above control operation is being performed, +V
When the OC power supply voltage exceeds the voltage level shown in Equation 31 above, the following circuit operation is performed. That is, the transistor Q is turned on by the output signal Vout of the overvoltage protection circuit 1. In this case, the output current of the constant current circuit CS, , flows to the ground line via the transistors Q and 7.
The emitter voltage of +Qu decreases, and even if the output signal AV of the amplifier 21 is supplied, the amplifier 21 no longer operates. Therefore, an excessive current does not flow through the transistors Qts to Qu and further to the coil L1, and the transistors Qys to Q78
．． Unexpected accidents such as damage and burnout of the coil L are prevented.

In addition, when the power supply voltage 10 Vc gradually decreases from the above-mentioned increased voltage level and becomes below the voltage level shown in equation 51 above, the voltage level of the output signal V.ul decreases again.As a result, the voltage level of the output signal V.ul decreases again. ] is turned off, and the control operation as described above will be performed thereafter.

Then, the transistor Qtt is suddenly switched to the on state or off state by the output signal ou1 of the overvoltage prevention circuit 1. Therefore, during the above switching, unstable control operations are not performed.

〔effect〕

(11) By configuring the overvoltage detection circuit to have hysteresis characteristics, a stable protection effect can be achieved against fluctuations in the power supply voltage.

(2) By detecting overvoltage while a predetermined current is flowing through a constant voltage element such as a Zener diode,
It is possible to obtain good detection characteristics.

(3) The overvoltage detection circuit 1 is configured to detect the rise and fall of overvoltage while a predetermined current is flowing through a constant voltage element such as a Zener diode, thereby improving the rise and fall of hysteresis characteristics. The effect of improving the characteristics can be obtained.

(4) According to the first embodiment, the circuit configuration for obtaining the effects of il+(2) and (3) is extremely simple, and it is easy to integrate the circuit into a semiconductor integrated circuit.

(5i) In an electronic device to which the overage detection circuit 1 of the present invention is applied, the bias voltage and control signal are quickly cut off in response to fluctuations in the power supply voltage, so the H of the electronic device can be maintained reliably. Although the invention made by the present inventors has been described in more detail than would be possible, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the invention. be.

For example, the resistor RA described for the overvoltage detection circuit 1 does not necessarily have to be connected between the base and emitter of the transistor Q1.

That is, the resistor RA may be connected between the base and emitter of the transistor Q. In this case, the resistance value of the resistor RA is equal to the resistor R in relation to the current 1.

It is desirable that the resistance value is sufficiently larger than the resistance value of .

Further, the present invention is not limited to the circuit shown in FIG. 1, and other circuits may be used as long as they can provide at least hysteresis to the detection level.

[Application field]

In the above explanation, the invention made by the present inventors will be mainly described as the field of application of the amplifier circuit 57-
Although the case where the present invention is applied to the main control circuit has been described, the present invention is not limited to the above.

For example, it could be applied to a power supply stabilization circuit provided after a rectifier circuit.

Furthermore, it is suitable for electronic devices such as car radios, where the power source t)E fluctuates rapidly.

The present invention can be applied at least when it is desired to protect electronic equipment from fluctuations in power supply voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the overvoltage detection circuit to which the present invention is applied, FIG. 2 is a hysteresis characteristic diagram for explaining the circuit operation of the overvoltage detection circuit, and FIG. 3 is a circuit diagram of the overvoltage detection circuit according to the present invention. FIG. 3 is a circuit diagram of an amplifier circuit showing a second embodiment. FIG. 4 is a circuit diagram of a motor drive circuit showing a third embodiment of the present invention. 1... Overvoltage detection circuit, Q, , Q, , Q3. Q number + Q
+41Q I 5 r Q t? ...transistor,
R1+Rz+Rs+ R41RA...Resistance, ■REF
...Reference voltage, ■Yo...Voltage, Vout...Output signal of the overvoltage prevention circuit, tl...At the rise of the hysteresis characteristic, t2...At the fall of the hysteresis characteristic, I
I I II +I+2...Current. Agent Patent Attorney Akio Takahashi 1st plan... Figure 2 Figure 3 C

Claims (1)

[Claims] 1. The power supply voltage rises from a steady state to an abnormal state. An electronic circuit including an overvoltage detection circuit, characterized in that when returning to a steady state after a certain time, the power supply voltage detection level at the time of the increase and at the time of return are made different. 2. Claim 1 above, characterized in that the signal transmission path is not switched to a non-operating state when the power supply voltage fluctuates.
Electronic circuit as described in section. 3. The electronic circuit according to claim 1, wherein the electronic circuit prevents energization to the load of the semiconductor integrated circuit when the power supply voltage fluctuates.