JPS60121426A - Power supply circuit for camera - Google Patents

Abstract

PURPOSE:To prevent surely the malfunction of a camera just after power-on by holding the output of a drive circuit, which is controlled by a microcomputer, constant with a signal generated from a strobe circuit having a prescribed constitution. CONSTITUTION:When a power switch is turned on, a high-level strobe signal is generated quickly by a strobe circuit 23 consisting of a capacitor C1 and a resistance R1 connected in series and a diode D1 of a constant voltage element connected in parallel to them in a power supply circuit. A transistor TR Tr2 of a drive circuit 6 is turned on by this signal, and a TR Tr1 is turned off independently of the output of a microcomputer 3, and the output of the circuit 6 is kept constant. Consequently, the malfunction based on operation unstableness of the microcomputer just after power-on is prevented surely.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a power supply circuit for a camera that uses a microcomputer to quickly and reliably prevent the camera from operating immediately after the camera is powered on.

(B) Conventional technology The electronicization of cameras has been remarkable over the past few years, and many operations that previously relied on human experience and intuition, including exposure adjustment and even automatic focal length adjustment, are now automatically controlled by electronic control. It is supposed to be carried out in Recently, custom-designed circuit elements called custom ICs have been used in electronic circuits for performing such electronic control.

Custom ICs are advantageous in terms of operation and manufacturing, as there is no waste in the circuit configuration, reliable circuit operation, and no need for peripheral circuits, but the development time is relatively long.
Moreover, there is a problem in that the manufacturing cost is high.

Therefore, if a microcomputer (hereinafter referred to as "microcomputer") is used instead of a custom IC, costs can be reduced and the development period can be shortened, but the output state at reset is determined by the manufacturer's specifications. In order to ensure that the camera performs the necessary operations, it is necessary to add peripheral circuits or take other measures.

Incidentally, a microcomputer is generally set to an initial state by a reset signal, maintains that state constant during the reset period, and performs arithmetic processing according to a predetermined program after the reset is released. To avoid this, the microcomputer is given a necessary reset signal before it starts operating after power is turned on, but the output state of the microcomputer becomes undefined before the reset signal is given after power is supplied. In particular, if a CR circuit is used in the reset signal generation circuit, this undefined time becomes longer. As a result, for example autofocus? JM Adjustment Organization? If the output state of the microcomputer is opposite to the original output state when the power is turned on, the infrared light-emitting diode for self-Ia distance measurement may emit light, or the series of shots that start with lens movement may be interrupted. There may be problems such as the sequence starts, or cameras with a date imprinting mechanism may imprint the date multiple times on the same film, or various indicator lamps (for example, indicating that the self-timer is in operation). There is a risk that problems such as the display rung) being erroneously lit may occur.

(c) Purpose and structure of the invention The present invention has been made in view of the above points, and its purpose is to quickly and reliably prevent malfunctions of a camera using a microcomputer immediately after the power is turned on. A strobe circuit that generates a strobe signal is provided, and the strobe circuit is composed of a series circuit of a resistor and a capacitor connected in parallel with a constant voltage element, and the output state of the drive circuit, which is controlled by a microcomputer, is kept constant by the strobe signal. It is configured to hold.

) Example The present invention will be explained below based on the drawings.

FIG. 1 is a block diagram of an electric circuit of a camera using a power supply circuit according to the present invention, in which 1 is a battery as a power source, 2 is a power supply circuit according to the present invention, and 3 is a voltage once boosted by the power supply circuit 2. The microcomputer 3 is supplied with a power supply voltage stepped down by 4 Vl, and various controls are performed by the microcomputer 3 according to a predetermined program. The strobe unit built into the 4Vi camera, 5 is about 1 by the source circuit 2.
An autofocus circuit that is supplied with a high voltage boosted to 5V and automatically adjusts the focal length; 6 is a drive circuit that drives a load based on commands from the microcomputer 3; the load is an autofocus circuit that imprints the date on the film. Date unit 7 and film? There is an autowind unit 8 that automatically winds up the winder. This is a shutter unit that opens and closes the shutter based on commands from the microcomputer 3.

FIG. 2 shows an embodiment of the power supply circuit according to the present invention, which maintains the output state of the microcomputer in a constant state for a certain period of time after the power is turned on in the above-mentioned camera.

The power supply circuit 2 includes a step-up circuit 21 that steps up the power supply voltage of the battery supplied to the input terminal A, and a step-down circuit 2 that drops the output of the step-up circuit 21 to a voltage 1 suitable for the power supply voltage of the microcomputer 3.
2, a strobe circuit 23 for setting the output state P of the drive circuit 6, a reset circuit 24 for setting the microcomputer 3 in a reset state, a diode D for preventing reverse current when the power supply voltage drops, and a power supply voltage drop. It consists of a backup capacitor C. The driver circuit 6 includes an output transistor T as shown in the 31st part.
r + and an output setting transistor T r 2 are embedded, and the base of this output setting transistor T r 2 is connected to the strobe terminal STB.

Prior to shooting, the power switch (not shown) is turned on as shown in FIG.
When voltage ii is supplied, the output of the booster circuit 21 is stepped down by the step-down circuit 22 and supplied to the strobe circuit 23, the reset circuit 24, and the microcomputer 3. Reset circuit 2
4 is constituted by a series circuit of a capacitor C2 and a resistor R3, so the potential at point H changes as shown in FIG. 4(b). Now set the reset level of microcomputer 3 to LR.
Then, at the time ti when VH reaches LH, a reset signal is manually input to the reset terminal R of the microcomputer 3, so at this point the microcomputer 3il-j enters the reset state, but for the period T (approximately 1.5 ~7.0 mS), the output is in an undefined state.

However, strobe circuit 2311″i capacitor C.

A diode -1 is connected in parallel with the resistor R+ in a series circuit with the resistor R1 and the resistor R1.
When the power is turned on, the m-level V at point M is initially the voltage caused by diode D1 to charge capacitor CI through diode D1, as shown in Figure 4 (c). Descending ■ F-Tak It rises from a high level, not from 0. As a result, this potential V,
is applied as a strobe signal to the base of the output setting transistor T r 2 built into the drive circuit 6. In this example, the strobe level L8 is set to the base-emitter voltage vBE (approximately 0) of the transistor T r 2.
．． 6 V), at time point 12 when the level Ls of the strobe signal exceeds this VICE, the transistor Tr2 becomes conductive, and as a result, the output transistor Tr2 becomes conductive.
1 is constrained to a non-conducting state. Therefore, since the rear drive circuit 6 does not output any output after time 12 during the period T in which the operation of the microcomputer 3 is unstable, no malfunction of the camera occurs regardless of the output state of the microcomputer 3. After the power is turned on, the strobe signal 75E exceeds lobe level L8.
It is determined by the characteristics of the constant voltage element connected in series with the capacitor C7 of the strobe circuit 24, and in addition to the exemplified diode, a Zener diode may also be used.
before reaching strobe level L8 (R tick 0 to 1□)
Since the m source pressure to the microcomputer 3 is also low, the output transistors T and l of the drive circuit 6 cannot be operated with this level of output from the microcomputer 3, and the time is not long enough to cause the camera to malfunction. do not have.

In the above embodiment, the strobe circuit was constructed with a series circuit of a capacitor and a resistor, and a constant voltage element such as a diode was connected in parallel with the resistor. If the rise of the strobe signal is accelerated by selecting , there is no need to connect a constant voltage element.

(e) As described in detail, in the present invention, a strobe circuit is provided which generates a strobe signal when the power of the camera is turned on, and the strobe circuit is composed of a capacitor and a resistor, and a constant voltage is connected in parallel to the resistor. Since the elements are connected and the output state of the microcomputer drive circuit is quickly held constant using a strobe signal, it is possible to prevent the camera from malfunctioning due to an unstable state of the microcomputer output after power is turned on.

[Brief explanation of drawings]

Is Fig. 1 a power supply circuit according to the present invention? FIG. 2 is a block diagram of the electric circuit of the camera to be used. FIG. 2 is an embodiment of the power supply circuit according to the present invention. FIG. 3 is a circuit configuration diagram of the main part of the drive circuit.
The figure is a waveform diagram of a reset signal and a strobe signal output from the power supply circuit according to the present invention. 1...? M pond, 2... power supply circuit, 21... booster circuit, 22... step-down circuit, 23... strobe circuit,
24...Reset circuit, 3...Microcomputer, 6...
Drive circuit patent applicant Konishi Roku Photo Industry Co., Ltd. Agent Patent attorney Hiroshi Suzuki

Claims (1)

[Claims] The strobe circuit consists of a capacitor and a resistor connected in series and a constant voltage element connected in parallel with the resistor, and generates a strobe signal when the power is turned on, and the output state of a drive circuit controlled by a microcomputer is determined by the strobe signal. 1. A power supply circuit for a camera, comprising a holding circuit that maintains the power at a constant level.