JPH05312852A - Electric power source voltage detecting cirucit - Google Patents

Abstract

PURPOSE:To prevent error operation of repeating on-off of an inner electric power source even if the battery voltage decreases near detection threshold level by additionally connecting a resistor which provides hysteresis to a voltage detecting circuit. CONSTITUTION:A PON terminal of a microcomputer 1 is connected to a base of a transistor Tr1 through a hysteresis resistor RH and also connected to a switching circuit which turns on and off of an inner electric power source. Consequently, the detection threshold voltage VTHON at the time of turning on the inner electric power source is set to be lower than the usual detection threshold voltage VTH and the threshold voltage VTHOFF at the time of turning off the inner electric power source is set to be higher than the threshold voltage VTH. When the inner power source is turned on, current runs and voltage decreases. In the case the input voltage VIN lowers less than the threshold voltage VTHON due to that, the inner power source is turned off by the microcomputer 1 and thus current does not run and as a result the voltage VIN returns to the initial level. However, since the voltage never reachs the threshold voltage VTHOFF, the inner power source becomes stable in off condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply voltage detection circuit, and more particularly, to a backup power supply for in-vehicle equipment, A
The present invention relates to a power supply voltage detection circuit for a CC power supply or the like.

[0002]

2. Description of the Related Art FIG. 3 shows a control unit from a battery.
FIG. 3 is a schematic diagram showing a circuit configuration when power is supplied to the printer.
It In the figure, 100 is a control unit and 103 is a bar.
The control unit 100 is shown in FIG.
The power supply voltage detection circuit 20 is internally provided, and the battery 103 has
A plus terminal 103a and a minus terminal 103b are provided.
Has been. The negative terminal 103b of the battery 103 is
B of the control unit 100
The positive terminal 103a is connected to the terminal b
1 to the Ba terminal of the control unit 100
Has been continued. The harness 101 is connected via the Ba terminal.
When entering the control unit 100, it branches into two, one of which
B_INConnected to the voltage detection circuit 20 via the terminal,
Is connected to other control circuits (not shown) etc.
It The resistance r shown in the figure is possessed by the harness 101.
It shows the resistance, I_ONFlows harness 101
Current, V_DROPIs I_ONIs generated by resistance r
It shows the voltage drop _B Indicates the battery voltage
is doing.

FIG. 4 is a circuit diagram showing the configuration of a conventional power supply voltage detection circuit 20. Figure 1 is a microcomputer - represents the data, microcomputer - the motor 1 is provided with P _ON terminal and DET pin, P _ON terminal causes the switching circuit (shown for turning on and off the internal power source of the equipment No)
Etc., and the DET terminal is connected to the collector of the transistor Tr ₁ . Also, the micro computer 1
Has one end grounded and the other end connected to V _CC (+5 V), and a resistor R _L is interposed between V _CC and the collector of the transistor Tr ₁ . The emitter of the transistor Tr ₁ is grounded, the base is grounded via the resistor R ₂ , and the resistor R ₁ and the Zener diode Z ₁ are grounded.
It is also connected to the B _IN terminal via. In FIG. 4, V _IN is the voltage applied to the terminal B _IN , V _Z is the voltage across zener diode Z ₁ , V _R2 is the voltage across resistor R ₂ , and V _BE is the transistor Tr. The voltage between the base and the emitter required to turn on ₁ is shown, and V _DET is the voltage applied to the DET terminal (= collector voltage of the transistor Tr ₁ ).

In the power supply voltage detection circuit 20 described above, V _IN
Is set to a predetermined value, that is, the detection threshold voltage V _TH or more, the transistor Tr ₁ is turned on. The detection threshold voltage V _TH in the power supply voltage detection circuit 20 is calculated as follows.

Input voltage V_INOn the other hand, Zener-Dio-
De Z₁ , Resistance R₁ , Resistance R₂ Are connected in series.
Therefore, the resistance R₂ Voltage V across_R2Is V_R2= (V_IN-V_Z ) × (R₂ / (R₁ + R₂ )). By the way, as can be seen from FIG._R2Is
Transistor Tr₁ Voltage between base and emitter of
But also. Therefore, the transistor Tr₁ Turned on
First, V_R2≧ V_BESo that (V_IN-V_Z ) Is resistance
R₁ And resistance R₂Must be divided by.
That is, {(V_IN-V_Z ) × (R₂ / (R₁ + R₂ ))} ≧ V_BE The relationship must be met. Where V from the formula
_INAnd ask for V_IN≧ V_Z + V_BE(1 + R₁ / R₂ ). From formula, transistor Tr₁ To turn on
Minimum required input voltage V _IN, That is, the detection threshold
-Voltage voltage V_THIs V_TH= V_Z + V_BE(1 + R₁ / R₂ ). As shown in the equation, the detection threshold hold
Voltage V_THIs V_Z And V _BEIs expressed using
To be kept.

As described above, the power supply voltage detection circuit 20 has
By the way, V_THIs maintained at a constant value, V _IN≧ V_THThen V
_R2≧ V_BEBecomes transistor Tr₁ To turn on
Circuit element (Z₁ And Tr₁ Etc.) is selected and configured
Has been. For example, backup power for in-vehicle equipment
In case of power supply voltage detection circuit for power source and ACC power supply,
Threshold voltage V_THIs about 8V,
The circuit element is selected and configured.

The operation of the power supply voltage detection circuit 20 will be described below separately for the case of V _IN ≧ V _{TH and} the case of V _IN <V _TH . When V _IN ≧ V _TH Voltage V _IN input to the B _IN terminal
Becomes equal to or higher than the detection threshold voltage V _TH , the transistor Tr ₁ is turned on as described above. When the transistor Tr ₁ is turned on, through a resistor R _L V _CC (+5
V), the collector current flows to the transistor Tr ₁ and the potential of the collector decreases, and the DE of the microcomputer 1 is reduced.
The voltage V _DET input to the T terminal becomes low level. V
_{When DET} goes low, the microcomputer 1 judges that V _IN ≧ V _TH and outputs a high level voltage from the P _ON terminal to turn on the internal power supply of the device.

When V _IN <V _TH Since the magnitude relation between V _R2 and V _BE does not satisfy the above equation, the transistor T
r ₁ is turned off, the collector potential becomes +5 V, and V _DET
Becomes a high level. When V _DET becomes high level, the microcomputer 1 determines that the voltage V _IN input to the B _IN terminal is less than the detection threshold voltage V _TH , and outputs a low level voltage from the P _ON terminal. Then turn off the internal power of the device.

[0009]

The power supply voltage detection circuit 2 described above.
The B _IN terminal of 0, as shown in FIG.
It is connected to the battery 103 via. Therefore, when the internal power supply is turned on and the device starts operating, a current I _ON flows from the battery 103 through the harness 101, so that the voltage appearing at the B _IN terminal is the battery voltage V
_It is a value obtained by subtracting the voltage drop I _ON × r generated in the harness 101 from _B. That is, B of the power supply voltage detection circuit 20
_The voltage V _IN applied to the _IN terminal becomes V _IN = V _B −V _DROP ... When the device starts operating. However, V
_DROP = I _ON × r.

Normally, V _IN is V _IN > V _TH , but if the battery is exhausted until V _B becomes V _TH <V _B <V _TH + I _ON × r, it is set to 8 V, for example. When V _B is consumed up to about 8.2 V with respect to V _TH , V _IN becomes V more than V _{B when the} device starts operating, as shown in the equation.
Since it drops by _DROP , V _B −V _TH <V _DROP and V _IN
<It becomes V _TH . When V _IN <V _TH , the transistor Tr ₁ is turned off and the internal power supply is turned off by the microcomputer ₁ as described above. That is, in the power supply voltage detection circuit 20, when the battery voltage V _B is consumed and drops to around V _TH as described above, when the device is operated, the voltage drop may cause V _IN <V _TH. There, in that case, even though it is actually a _{V iN <V TH <V B} , microcomputer - V _B by motor 1
I had been misjudged to be <V _TH .

FIG. 5 is a graph schematically showing the relationship between V _IN and V _TH when the voltage V _B of the battery is exhausted and drops to around the detection threshold voltage V _TH . The vertical axis represents the voltage and the horizontal axis represents the passage of time.
In FIG. 5, the dotted line parallel to the horizontal axis is the detection threshold.
Voltage V _TH , the dashed line parallel to the horizontal axis is the battery voltage V
_B and solid line graphs show V _IN , respectively _{, where} signs a and c are V _IN values at the time when the internal power supply is turned on, and signs b and d are values at the time when the internal power supply is turned off. The values of V _IN are shown respectively.

When the device is not operating, I _ON does not flow, so that V _IN = V _B. However, when the internal power source is turned on at point a and the device starts operating, a voltage drop V _DROP occurs as shown in the equation, and V _IN is the detection threshold voltage.
Voltage becomes lower than the threshold voltage V _TH , and in FIG.
Drop to the point. Since V _IN <V _TH at the point b, the internal power supply is turned off by the microcomputer 1. When the internal power supply is turned off, the current I _ON does not flow through the harness 101, so that the relationship of V _IN = V _B is restored and V _IN = V _B is restored.
_IN moves from point b to point c on the graph. When V _IN reaches the point c, V _IN = V _B > V _TH , so the internal power supply is turned on by the microcomputer 1. Thereafter, the above operation is repeated to turn on / off the internal power supply.

As described above, in the power supply voltage detection circuit 20, when the battery is exhausted and V _B drops to the vicinity of the detection threshold voltage V _TH , the voltage drop V _DROP of the harness 101 causes the micro voltage drop. Computer 1 has V _B <
There is a problem that the internal power supply is repeatedly turned on and off as described above by erroneously detecting V _TH .

The present invention has been made in view of the above problems, and prevents an erroneous operation in which the internal power supply is repeatedly turned on and off even when the battery voltage is exhausted and drops to around the detection threshold voltage. An object of the present invention is to provide a power supply voltage detection circuit capable of performing the above.

[0015]

In order to achieve the above object, the power supply voltage detection circuit according to the present invention is characterized in that a resistor for giving a hysteresis is additionally connected.

[0016]

According to the above construction, since the resistor for giving hysteresis is additionally connected, the set value of the detection threshold voltage is changed depending on whether the internal power source is turned on or off. That is, the detection threshold voltage V _THON when the internal power supply is turned on.
Is set lower than the conventional detection threshold voltage V _TH , and the detection threshold voltage V _{THOF F} when the internal power supply is turned off is set higher than the V _TH .

When the detection threshold voltage is set as described above, even if the internal power supply is turned on when the battery voltage is exhausted to the vicinity of the detection threshold voltage, the internal power supply is repeatedly turned on and off. Such an erroneous operation is prevented, and the internal power supply is set to either the on state or the off state.

[0018]

Embodiments of the power supply voltage detection circuit according to the present invention will be described below.
An example will be described with reference to the drawings. In addition, the same machine as the conventional example
The same symbols shall be attached to the functional components.
It FIG. 1 shows a power supply voltage detection circuit 10 according to an embodiment.
FIG. 1 is a circuit configuration diagram, in which 1 is a microcomputer
It is shown, and P is attached to the microcomputer 1._ONTerminal and
And a DET terminal are provided. P_ONTerminal is hysterical
Cis resistance R_H Through transistor Tr₁ Contact the base of
Switch on for turning on and off the internal power supply
The DET terminal is also connected to a switching circuit (not shown).
Register Tr ₁ Connected to the collector. Also,
One end of the icrocomputer 1 is grounded and the other end is V
_CCIt is connected to (+ 5V) and V_CCAnd transistor T
r₁ Resistor R between the collector of_L Is installed.

The emitter of the transistor Tr ₁ is grounded, and the resistor R ₁ and the resistor R ₂ are connected to the base in addition to the hysteresis resistor R _H. Transistor Tr
₁ of base - scan the resistor R ₁ and the Zener - diode - via the de Z ₁ is connected to the B _IN terminal, also connected to ground via a resistor R _2. Note that V _PON shown in FIG. 1 represents the voltage output from the terminal P _ON , and V _IN , V _Z , V _R2 , V _BE and V
The meaning of _DET is the same as that of the conventional example shown in FIG.

In the power supply voltage detection circuit 10 described above, V_IN
Is Zener diode Z₁ , Hysteresis resistance R_H ,
Anti-R₁ And resistance R₂ Is divided by V_R2≧ V_BE Where is
That is, V_INIs above the detection threshold voltage
Transistor Tr, if any ₁ Turns on and V_DET Is
-It becomes the level, and P of the micro computer 1_ONTerminal?
Output a high level voltage and the internal power of the device is turned on.
It is supposed to be done. Conversely, V_INIs a detection threshold
Below the hold voltage, V_R2<V_BEIf
Langista Tr₁ Turns off and V_DET Is a high level
, P of Microcomputer 1_ONLow level from terminal
Voltage is output and the internal power of the device is turned off.
Is becoming

As described above, the operation of the power supply voltage detecting circuit 10 is reversed at the time point when V _R2 = V _BE . However, in the embodiment, as shown in FIG. 1, the output V _PON of the microcomputer 1 is fed back to the power supply voltage detection circuit 10 via the hysteresis resistance R _H , so that if V _R2 = V _BE. The size of V _IN is not constant as in the conventional example, but V _PON is at a high level or low.
It depends on the level. Hereinafter, V _PON Gallo - divided into the cases of level and high level, V _R2 = V _BE become occupied V _IN, that is, the detection in the power supply voltage detection circuit 10 Suresshuho - field voltage V _THOFF (V _PON = b -Level)
And V _THON (V _PON = high level).

When V _{PON is} low level (when the internal power supply is off). Since V _PON = 0 volt,
The hysteresis resistance R _H and the resistance R ₂ are connected in parallel with V _IN . The combined resistance of R _H and R ₂ is R _2H
Then, R _2H = R ₂ · R _H / (R ₂ + _RH ). Then, the Zener diode Z ₁ , the resistor R ₁ , and the combined resistor R _2H are connected in series with respect to the input voltage V _IN . Therefore, the voltage V _R2 applied across the resistor R ₂ is V _R2 = (V _IN −V _Z ) × (R _2H / (R _2H + R ₁ )).
It becomes. The detection threshold voltage is V
_{Since R2} = V _BE, which is the size of V _IN , V in the formula
When determining the V _IN by replacing _R2 to V _BE, the _{V IN = V Z + V BE} (1 + R 1 / R 2H). Therefore, the detection threshold voltage V _THOFF when V _{PON is} low level is V _THOFF = V _Z + V _BE (1 + R ₁ / R _2H ).
Becomes Here, taking the difference between the equations, V _THOFF −V _TH = V _BE (R ₁ / R _2H −R ₁ / R ₂ ) = V _BE · R ₁ / _RH ... If a resistor R _H is additionally connected, V
_It can be seen that _TH OFF can be set higher by V _BE · R ₁ / _RH than the conventional detection threshold voltage V _TH .

When V _PON is at a high level (when the internal power supply is turned on). Since V _PON = 5V, a voltage of 5V is applied to both ends of the resistor R _H and the resistor R ₂ , and the resistor R ₁
A voltage of (V _IN −V _Z ) is applied across the resistor R ₂ . When the voltage V _R2 across the resistor R ₂ is obtained under this condition, V _R2 = 5 × R _12H / _RH + (V _IN −V _Z ) × R _12H / R ₁ ... However, here 1 / R _12H = 1 / R ₁ + 1 / R
_It represents ₂ + 1 / _RH . Next, in the same manner as described above, V _IN that V _R2 = V _BE is obtained from the equation, and V _IN is V _{TH ON}
In other _words , V _THON = V _Z + V _BE · R ₁ / R _12H −5 × R ₁ / _RH = V _Z + V _BE (1 + R ₁ / R _2H ) −5 × R ₁ / _RH ··· (10) Is obtained. As is clear by _{comparing the} equation (10) with the equation, V _THON becomes a value lower than V _{TH OFF} by 5 × R ₁ / _RH . Also, from the equation, the hysteresis resistance R _H
If adding V _THON than the _{V TH (5-V BE)} × R 1 /
It can be seen that the value can be set lower by R _H.

As described above, in the embodiment, the detection threshold voltage is changed depending on whether the internal power source is on or off.
_{Since THON} is set lower than V _THOFF by 5 × R ₁ / _RH, it is effective in the following cases. Figure 2
6 is a graph schematically showing the relationship between V _IN and V _THON and V _THOFF when the battery is exhausted and V _B is reduced to the vicinity of the detection threshold voltage. The vertical axis represents the voltage value and the horizontal axis represents the passage of time.

V_INIf the value of is A. Internal power supply at point e
If the power is turned on, it means that the internal power is turned on.
More current I_ONFlows, the voltage drop V_DROPOccurs. The V
_DROPBy V_INIs V_THOFF , V_THLower than
V_THONIt does not fall beyond the range. Therefore,
Unstable operation such as internal power being turned on and off repeatedly
Operation is prevented, the internal power supply is stable in the ON state, and V_INThe value of the
Is the voltage drop V from A _DROPStable at value C after subtracting
It

When the value of V _IN is B. If the internal power supply is turned on at point f, a current I _ON flows and a voltage drop V
_DROP occurs. The V _DROP causes V _IN to drop below V _THON . When it drops below V _THON , the internal power supply is turned off by the microcomputer 1. When the internal power supply is turned off, the current I _{ON stops} flowing, so that the relationship of V _IN = V _B is restored and V _IN rises to the initial value B. However, since B is lower than V _{THOF F} , the rise never reaches V _THOFF . Therefore, the internal power supply stabilizes in the off state, and V _IN stabilizes at the initial value B.

As described above, the power supply voltage according to the embodiment
In the detection circuit 10, the hysteresis resistance R_H Is added
It is connected and detects the threshold voltage when the internal power is turned on.
Pressure V _THONDetects the threshold voltage when the internal power is turned off.
Pressure V_THOFF Battery is set lower than
Exhausted V_B Up to near the detection threshold voltage
Even if the internal power is turned on when the voltage drops, the
Repeatedly turning on / off the internal power supply
There is no. That is, if the power supply voltage detection circuit 10 is used,
It is possible to stabilize the power supply in the on or off state.
It is possible to prevent the unstable operation. Moreover,
Hysteresis resistance R_H Simple configuration with additional connection
The addition of does not increase the cost.

[0028]

As described above in detail, in the power supply voltage detecting circuit according to the present invention, since the resistor for giving the hysteresis is additionally connected, the battery voltage is consumed and the voltage around the detection threshold voltage is increased. It is possible to prevent malfunctions such as repeated turning on / off of the internal power supply even when the power consumption drops to. Moreover, it is possible to add a simple configuration in which the resistor is additionally connected, and the cost does not increase.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a power supply voltage detection circuit according to the present invention.

FIG. 2 is a diagram illustrating a power supply voltage detection circuit according to an embodiment, in which V _IN
The detection Suresshuho - and field voltage V _THOFF, is a graph schematically showing the relationship between V _THON.

FIG. 3 is a schematic diagram showing a circuit configuration when power is supplied from a battery to the control unit.

FIG. 4 is a circuit configuration diagram showing a conventional power supply voltage detection circuit.

FIG. 5 is a graph schematically showing the relationship between V _IN and the detection threshold voltage V _TH in the conventional power supply voltage detection circuit.

[Explanation of sign]

1 Microcomputer 10 Power supply voltage detection circuit 101 Harness 103 Battery _RH Hysteresis resistance

Claims (1)

[Claims] 1. A power supply voltage detection circuit, wherein a resistance for giving a hysteresis is additionally connected.