JPH0424653Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a power supply circuit, and more specifically, for example, supplying +/- power to an A/D converter installed in a digital multimeter. The present invention also relates to a power supply circuit that can apply a data hold signal when a power switch is off.

[Technical background of the invention] Generally, this type of power supply circuit has a DC power supply section E formed by connecting two DC power supplies E ₁ and E ₂ in series, for example, as shown in FIG. The positive and negative terminals are connected to the A/D via power switch _SW1 .
Negative L + power input terminal consisting of converter, etc.
Vdd and the - power input terminal Vss, and connect the neutral point of the DC power supply section E to the common terminal of the negative pole L.
I am trying to connect to COM. Also, that
A hold switch _SW2 is connected between the HOLD terminal and the negative electrode side of the DC power supply section E, and the HOLD terminal is connected to the DC power supply section E through a resistor R.
By turning on the switch _SW2 , the potential of the HOLD terminal is changed from, for example, +V to -V to operate the hold function. In this case, the power switch _SW1 is
Since it is necessary to turn on and off the positive and negative sides of the DC power supply section E at the same time, a dual slide switch or a push switch with a lock mechanism is used.

However, this type of switch is relatively complex and expensive, and requires additional man-hours to install. Furthermore, there is a high possibility that forgetting to turn off the power switch SW ₁ may lead to unnecessary consumption of battery power. Furthermore, to hold the data, press the hold switch SW ₂ each time.
It is necessary to press , and the operation is troublesome.

[Purpose of the invention] This invention was devised in view of the above-mentioned conventional circumstances.The purpose of this invention is to use a single open/close switch with a simple structure as a power switch, and when the switch is turned off, the A/D An object of the present invention is to provide a power supply circuit that automatically supplies a data hold signal to a load such as a converter.

[Example] Hereinafter, this invention will be explained in detail with reference to an example shown in FIG.

This power supply circuit is applied to a load L consisting of, for example, an A/D converter installed in a digital meter, and the load L includes a + power input terminal Vdd, a - power input terminal Vss, a common terminal COM, and a A HOLD terminal is provided for data hold function.

This power supply circuit includes, for example, a DC power supply part E formed by connecting two DC power supplies E ₁ and E ₂ in series, as in the conventional example described above, and the positive and negative poles of this DC power supply part E are connected to the load L. Corresponding Vdd terminal and Vss
According to this embodiment, a series circuit including a resistor R ₁ , an on/off switch SW and a capacitor C is connected to the DC power supply section E, and its neutral point is connected to the COM terminal. are connected in parallel. In this case, the open/close switch SW may be a normally open type with a simple structure, preferably having an ON contact a, an OFF contact b, and a movable contact c that can be switched to either of them, and the above-mentioned resistor R ₁ is connected to the ON contact a. The movable contact c is connected to the capacitor C side. The bases of NPN transistors Q ₂ and Q ₃ are connected between the capacitor C and the movable contact c via resistors R ₃ and R ₄ , respectively. The emitter of the transistor _Q2 is connected to the negative electrode side of the DC power supply section E, and the base of the PNP type transistor _Q1 is connected to the collector of the transistor Q2 via a resistor _R2 . On the other hand, the emitter-collector of transistor _Q3 is connected between the emitter of transistor _Q2 and the Vss terminal. The emitter-collector of the transistor _Q1 is connected between the positive electrode side of the DC power supply section E and the Vdd terminal. Further, the base of an NPN transistor _Q4 is connected to the above OFF contact b via a resistor _R5 , the emitter of this transistor _Q4 is connected to the above Vss terminal, and its collector is
The HOLD terminal is connected to the above Vdd terminal via a resistor _R6 .

In the above configuration, when the movable contact c of the switch SW is turned to the ON contact a side, base current is supplied to the bases of the transistors Q ₂ and Q ₃ via the resistors R ₃ and R ₄ , and the base current is supplied to the bases of the transistors Q ₂ and When Q ₃ is turned on, transistor Q ₁ is also turned on due to conduction in transistor Q ₂ , thereby applying predetermined +V voltage and −V voltage to the Vdd and Vss terminals, respectively. At this time, the capacitor C is charged by the DC power supply section E. Furthermore, since the HOLD terminal is held at +V potential via the resistor _R6 , the A/D converter, which is the load L, is in a free-run state.

Therefore, if you move the movable contact c to the OFF contact b side,
The charge stored in the capacitor C is discharged through the resistors R ₃ , R ₄ and R ₅ , which keeps the transistors Q ₁ , Q ₂ and Q ₃ conductive, thus turning off the on/off switch SW. However, the battery voltage is supplied to the load L (A/D converter), and transistor _Q4 is turned on.
Since the HOLD terminal becomes the -V potential of the Vss terminal, the final data of the A/D converter L is latched based on this signal. This state lasts for a predetermined time (for example, 5 seconds) determined by the discharge time constant determined by the capacitance of capacitor C and the resistance values of each resistor R ₃ and R ₄ .
The process continues and ends when transistors Q ₂ and Q ₃ are turned off.

[Effects] As is clear from the description of the embodiments described above, according to this invention, the positive and negative sides of the DC power supply section can be turned on and off at the same time with a single open/close switch with a simple structure. In this case, the opening/closing switch may be a normally open type switch without a locking mechanism, such as a push button switch, which reliably prevents wasteful consumption of battery power due to forgetting to turn off the switch. In addition, according to this invention, when the switch is turned off, a hold signal is automatically output, so there is no need to press the hold switch each time as in the conventional case. There isn't.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit according to this invention, and FIG. 2 is a circuit diagram showing a conventional example. In the figure, E is a DC power supply section, C is a capacitor, SW
are open/close switches, R ₁ to R ₆ are resistors, Q ₁ to _{Q 4} are transistors, and L is a load.

Claims (1)

[Claims for Utility Model Registration] A power supply circuit that supplies power to a load, including a + power input terminal, a - power input terminal, a common terminal, and a hold terminal for a data hold function, which has a DC power supply section, The positive and negative poles of the DC power supply section are connected to the corresponding + power input terminal and - power input terminal, respectively, and the neutral point is connected to the common terminal, where the positive and negative poles of the DC power supply section are It is connected through an on/off switch between it and charges when it is turned on.
Between the capacitor that is discharged when off and the positive and + power supply input terminals of the above DC power supply section, and between its negative and -
two switching transistors connected to each of the power supply input terminals, which are made conductive when the on-off switch is turned on, and when turned off, are held in a conductive state for a predetermined time by the discharge current of the capacitor, and then become non-conductive; A power supply characterized by comprising switching means for switching the potential of the hold terminal to either the + power input terminal or the - power input terminal by the discharge current of the capacitor as the on/off switch is turned off. circuit.