JPH023184Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a battery detection circuit that detects whether the voltage of a battery used in a portable measuring device or the like is higher than a predetermined value.

Generally, portable measuring instruments display whether the battery voltage is higher than the operating voltage of the circuit, and the battery detection circuits used in such measuring instruments use the battery voltage as a reference voltage. The comparison is made and a liquid crystal display, a light emitting diode, etc. are driven according to the results. However, in such devices, the reference voltage used to compare battery voltages is based on the positive or negative power supply line, but the reference voltage mainly required in measurement circuits, etc. Since the common line was used as the reference level, it was necessary to have two different reference voltages within the measuring instrument.

The present invention eliminates the drawbacks of the conventional device as described above and realizes a battery detection circuit with a simple configuration that can detect the magnitude of battery voltage using a reference voltage with the common line as the reference level. The purpose is to

The figure is a configuration diagram showing an embodiment of the battery detection circuit of the present invention. In the figure, MS is the measurement circuit, DP is the display circuit, V _B is the battery that supplies power to the measurement circuit MS, etc., A ₁ and A ₂ are operational amplifiers, and R ₁ to R ₇
is a resistor and D _Z is a zener diode. l ₊ and l _- are positive and negative power supply lines, and l _C is a common line. The potential of the common line _lC is stabilized by the operational amplifier _A1 , and the zener diode _DZ generates a reference voltage _VZ based on the common line _lC , and the measurement circuit
Applied to MS. Operational amplifier _A2 constitutes a comparator that detects the magnitude of battery voltage.

The operation of the battery detection circuit of the present invention configured as described above is as follows. Common line l _C when negative power supply line l _- is referenced
When the potential of is Va, the potential of the cathode side of the Zener diode D _Z is (Va+V _Z ). here,
One input terminal (+) of the operational amplifier A ₂ has a potential on the cathode side of the Zener diode D _Z connected to the resistor R ₄ ,
Since the voltage is divided by R ₅ and applied, the input voltage V ₁ is expressed as the following equation.

V ₁ = R ₅ / R ₄ + R ₅ (Va + V _Z ) (1) Also, resistors R ₆ and R ₇ are connected between the positive power supply line l ₊ and the common line l _C , and the voltage at the midpoint V ₂ is applied to the other input terminal (-) of operational amplifier A ₂ , so its input voltage V ₂ is: V ₂ = Va + R ₇ / R ₆ + R ₇ (V _B - Va) = R ₇ / R ₆ + R ₇ V _B +R ₆ /R ₆ +R ₇ Va (2). Therefore, the difference between the input voltages V ₁ and V ₂ applied to the operational amplifier A ₂ is: V ₁ −V ₂ = (R ₅ /R ₄ +R ₅ −R ₆ /R ₆ +R ₇ )Va + R ₅ /R ₄ +R ₅
V _Z −R ₇ /R ₆ +R ₇ V _B (3), and if the circuit conditions are R ₅ /R ₄ +R ₅ = R ₆ /R ₆ +R ₇ , then V ₁ −V ₂ = R ₅ /R ₄ +R ₅ V _Z −R ₇ /R ₆ +R ₇ V _B (4). As is clear from the above equation (4), the lower limit of the circuit operating voltage V _B is set to V _BO , and the resistance R is set so that R ₅ /R ₄ +R ₅ V _Z =R ₇ /R ₆ +R ₇ V _BO. By determining the values of ₄ to _R7 , when the battery voltage V _B reaches its lower limit value V _BO , the operational amplifier
The output of _A2 will be inverted and will generate the detection signal S _B. The detection signal S _B is transmitted to the display circuit D _P ,
Displays the decrease in battery voltage _VB .

As explained above, the battery detection circuit of the present invention uses a reference voltage based on the common line, and the potential difference between the negative power supply line and the positive power supply line and the common line at this reference voltage is calculated as follows. Since the voltages are divided at an appropriate ratio and compared, it is possible to realize a battery detection circuit with a simple configuration that can detect the magnitude of battery voltage using a reference voltage with the common line as the reference level. Can be done.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an embodiment of the battery detection circuit of the present invention. MS...Measurement circuit, D _P ...Display circuit, V _B ...Battery, _A1 , _A2 ...Operation amplifier, _R1 to _R7 ...Resistance,
D _Z ... Zener diode.

Claims (1)

[Scope of utility model registration request] A battery that supplies operating voltage through the positive and negative power lines, a zener diode that is inserted between the positive power line and the common line and generates a reference voltage with the common line as a reference level, and this zener a first voltage divider circuit inserted between the cathode side of the diode and the negative power supply line; a second voltage divider circuit inserted between the positive power supply line and the common line; A battery detection circuit comprising: a comparator that compares the output voltage of the voltage divider circuit with the output voltage of the second voltage divider circuit and generates a detection signal.