JPS587170B2 - power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit used in portable equipment such as a camera, and more specifically to a power supply circuit used in an analog amplification circuit.

In recent years, there has been a demand for shortening the photometry time in photometering circuits for cameras, and there is a tendency to use light-responsive elements with fast light response as light-receiving elements.

For this reason, light receiving elements with extremely fast photoresponsiveness, such as silicon photocells SPC, are often used in photometry circuits, thereby shortening the photometry time.

However, since the output current of the silicon photocell SPC is very small, it is necessary to amplify it, and currently an operational amplifier is generally used as the amplification circuit, and the current circuit also supplies the midpoint potential to the operational amplifier. The circuit and the need to do it are required.

Conventionally, a constant voltage circuit using a constant voltage element such as a Zener diode has been used as a circuit for supplying a midpoint potential to an operational amplifier, but these constant voltage circuits always require a constant voltage of several mA to obtain stable voltage characteristics. This is inconvenient because it requires a current of several tens of milliamps to flow, consuming a lot of power, and requires a small capacity power source for portable equipment such as cameras.

Also, when the power supply voltage fluctuates, the overall width of the linear region, which is the effective operating range of the operational amplifier, changes, so in order to maximize the operational range of the operational amplifier, the midpoint potential of the operational amplifier should always be set within the operational range. The potential must be a constant ratio to the entire width of the .

For example, when the power supply voltage is 6V, the linear region of the operational amplifier is 4V, that is, between 1V and 5V.At this time, if the midpoint potential is set to 3V, the upper and lower operating regions can be used by 2V, but as the power supply voltage fluctuates, In this case, the linear region of the operational amplifier will be between 1V and 3V, and if the midpoint potential is left at 3.5V, the upper operating region will be zero, which is actually disadvantageous.

On the other hand, if the midpoint potential is set to a potential that has a constant ratio to the width of the linear region regardless of fluctuations in the power supply (in this case, an intermediate voltage with respect to the linear region), the power supply voltage will be Even when the voltage is 4V, it is at the midpoint of the linear region, that is, 2V, so the operating range of the operational amplifier becomes 1V above and below, and it is possible to effectively maintain the operating range at all times.

In the conventional method of supplying the midpoint potential using a constant voltage circuit, a constant midpoint potential is always provided even when the power supply voltage fluctuates, resulting in the above-mentioned result, which is difficult for cameras and other devices that cannot use a large power supply voltage. This was a major drawback in portable equipment.

In view of this point, the present invention has developed a portage follower circuit as a power supply circuit that supplies the midpoint potential of an amplifier circuit.The power consumption is extremely small on the order of micro-watts, and the power consumption is constantly maintained at a constant rate with respect to fluctuations in the power supply voltage. The present invention provides a power supply circuit that eliminates the above-mentioned drawbacks by configuring a circuit that provides a point potential to provide a midpoint potential.

Next, a power supply circuit according to the present invention will be explained using the drawings.

FIG. 1 is a circuit diagram showing an embodiment in which the power supply circuit according to the present invention is used in an A-D converter for photometric value conversion. The switches R1 and R2 are voltage dividing resistors, and the resistance value of R1 is the same as that of R2.

OP1 is an operational amplifier with an almost infinitesimal output impedance and serves as a voltage follower.

D1 is a photodetector for TTL photometry, OP2 is an operational amplifier,
D2 is a diode connected between the inverting input terminal and the output terminal of the operational amplifier OP2, forming a photometry and logarithmic compression circuit (2).

R4 to R8 are resistors, and OP3 is an operational amplifier having a transistor Tr1 as a part of the feedback circuit. Together with the resistors R4 to R8, they form an amplifier whose gain can be varied according to the input signal of the transistor Tr1.

OP4 is an operational amplifier that forms an operational amplifier together with resistors R9 to R12, and connects the photometry signal from the photometry circuit ■ to D-A, which will be described later.
The outputs from the converters are summed and amplified, and the summed signal is transmitted to one input terminal of the comparator OP5.

The comparator OP5 is set to “1” or “1” depending on the thickness of the input signal.
0” is output.

The output of the operational amplifier OP1 provides a midpoint potential to the operational amplifier OP2 of the photometric circuit (2), and also provides a voltage for comparison to one input terminal of the comparator OP5.

Vref is a reference power supply that provides a reference voltage Vr for a DA converter, which will be described later, and also connects a resistor R to the transistor Tr1.
15 and R16 to control the output of the transistor.

GC is gate control logic and comparator OP mentioned above
The output of comparator OP5 transmits a control signal to storage register SR and shift register R, and the output of comparator OP5 becomes 1.
At this time, a reset signal is transmitted to the storage register SR.

The storage register-SR has bits FF1 to FF4, and stores the contents of each bit.

Sw1 to Sw4 are switching circuits made of semiconductor elements, and switching is controlled by the storage register SR.

The resistance value of RN is determined by a circuit network such as a ladder circuit in conjunction with the switching circuit, converts the reference voltage Vr into a value corresponding to the resistance value, and transmits it to the input terminal of the operational amplifier OP4.

FIG. 2 is an explanatory diagram of the operation of the A-D conversion system, and shows the operation when the subject light information voltage Vs is 11V.

In the figure, Eo indicates the voltage applied to the input terminal of the comparator OP5 shown in the second figure, and Vs-Vd indicates the voltage to be compared applied to the other input terminal of the comparator OP5.

FIG. 3 is an explanatory diagram for explaining the midpoint potential supply method of the power supply circuit according to the present invention, where EA is the power supply voltage, Es is the saturation region voltage of the operational amplifier, Eo is the midpoint potential, and vh is the operating range of the operational amplifier. There is.

The operation of the embodiment of the power supply circuit according to the present invention will be described.

When the power switch Swa is turned on, a resistor R1 is connected to the input terminal of the operational amplifier OP1 forming a voltage floor circuit.
, R2, and the divided voltage Eo is applied, and Eo is transmitted to the output terminal thereof.

The voltage Eo is transmitted to one input terminal of the operational amplifier OP2 of the photometric circuit (2) and the comparator OP5.
A midpoint potential is applied to OP2 to put the operational amplifier OP2 into operation.

Since the midpoint potential applied to the operational amplifier OP2 is applied from the power supply EA via the voltage floor circuit, the midpoint potential Eo varies at a constant rate with respect to fluctuations in the power supply voltage EA, and the operating range of the operational amplifier OP2 varies. Even if the power supply voltage EA changes from the state shown in FIG. 3a to the state shown in FIG. 3b, vh can always maintain a constant ratio to the power supply voltage.

Next, by pressing a shutter button (not shown), the switch Swb is turned on in the second step of the operation, and voltage is supplied to the subsequent circuit.

When the object light is received by the light receiving element D1 of the photometry circuit (■), an object light information voltage Vs corresponding to the object light is generated between the input terminals of the operational amplifier OP2, and this voltage Vs is logarithmically compressed by the photometry circuit (■) and then sent to the operational amplifier. The signal is transmitted to the negative input terminal of OP3, amplified by the operational amplifier OP3, and transmitted to the negative input terminal of the operational amplifier OP4.

On the other hand, the first bit FF1 of storage register SR
When the switch Swb is turned on, the logical value becomes “1”.
” is set, the switching circuit Sw1 corresponding to the bit FF1 is turned on, and the reference voltage Vr output from the reference power supply Vref is connected to the circuit network RN via Sw1.
The output -Vd corresponding to the resistance value of the circuit network RN determined by the switching circuit Sw1 is applied to the negative input terminal of the operational amplifier OP4.

The output -Vd is added together with the object optical information voltage Vs by the operational amplifier OP4 and is transmitted to the negative input terminal of the comparator OP5.

Assume now that the object light information voltage Vs is 11V, and when bit FF1 of the storage register SR is set to 1, the output -Vd of the circuit network RN is generated at -23V by the operation of a known ladder circuit.

This -Vd and the subject light information voltage Vs are calculated by the operational amplifier OP.
4, and the added value and the bias voltage Eo are compared by a comparator OP5.

Since Vs is 11V and -Vd is -23V, the added value is 3V.

On the other hand, since Eo is at ground potential, Vs-Vd>E
o, comparator OP5 generates an output of "0", which is transmitted to gate control logic GC to hold the contents of bit FF1 of storage register SR, and FF1=1 is determined.

At the same time, the control signal is transferred from FF11 to FF22 of shift register R by the output of gate control logic GC, the theoretical value "1" is set to bit FF2 of storage register SR, and the circuit network RN is changed by the same operation as described above. The output -Vd becomes -(23+22)V, which is added to Vs by the operational amplifier OP4 and compared with the voltage Eo.

As a result, Vs-Vd<Eo, the output of comparator OP3 becomes "1" and transmits the output to gate control logic GC, which controls gate control logic GC, and transmits a reset signal to bit FF2 of storage register SR. The content of the bit FF2 is determined to be "0".

Thereafter, FF3=1 and FF4=1 are determined in the same manner, and the contents of the storage register SR are set to 1, 0, 1, and I.

The above-described operation converts analog subject information into digital values.

As described above, in the power supply circuit according to the present invention, the output impedance is infinitely small, the current consumption is extremely low, and the output voltage is always applied at a constant ratio to the power supply voltage in response to fluctuations in the power supply voltage. Even if a circuit is used, the power consumption is extremely low because it applies a potential, and the operating range of the amplifying circuit can be maximized regardless of fluctuations in the power supply voltage, so it is suitable for low-power applications such as cameras. This has great effects in power supply circuits used in portable equipment powered by

Furthermore, since a voltage follower circuit is used as the midpoint potential generation source, the midpoint potential input terminal of the amplifier circuit is connected to the reference potential input terminal of a circuit other than the amplifier circuit, and voltage fluctuations occur in the other circuits. Even in such a case, the midpoint potential of the amplifier circuit is not affected thereby, and an operating range of a constant ratio can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment in which the voltage circuit according to the present invention is used in a photometric A-D converter, Fig. 2 is an operation explanatory diagram illustrating the operation of the embodiment shown in Fig. 1, and Fig. 3 is FIG. 3 is an explanatory diagram illustrating a midpoint potential supply method of the power supply circuit according to the present invention. OP1... operational amplifier, OP4... operational amplifier, OP5... comparator, GC...
・Gate control logic, SR...Storage register, RN...Circuit network, I...
...Photometering circuit.

Claims (1)

[Claims] 1. A differential amplifier circuit that amplifies the quantity of electricity to be measured and a voltage follower circuit that generates an output corresponding to fluctuations in the power supply voltage for the amplifier circuit are provided, and the output voltage of the voltage follower circuit is adjusted to match the output voltage of the amplifier circuit. A power supply circuit characterized by having a midpoint potential.