JPS6310653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit using a battery as an energy source.

Due to the characteristics of batteries, the terminal voltage changes depending on the amount of discharge, temperature, and load, so it is difficult to use them as a power source for electronic circuits, and a certain degree of stabilization circuit is required. A conventional configuration of such a stabilizing circuit will be described below.

FIG. 1 shows a conventional example of a power supply circuit using a battery as an input. It consists of a battery 1, a transistor 2, a resistor 3, a Zener diode 4, and a capacitor 5. resistance 3
is provided to allow current to flow through the base resistor of the transistor 2 and the Zener diode 4. A constant voltage determined by a Zener diode appears at the base of the transistor, and a value obtained by subtracting the base-emitter voltage from the Zener voltage appears at the emitter of the transistor, which is the circuit output. The capacitor 5 serves as a bypass capacitor and also as circuit protection when the battery voltage drops for some reason. This is a printing device that uses a battery as a power source, and the large current loads such as motors and electromagnets are taken from the battery, and the circuit voltage that requires a relatively constant voltage is supplied from the circuit shown in Figure 1. This can occur when a momentary large current flows through an electromagnet, etc. 1st
In the circuit shown in the figure, an unstable output always flows through the circuit even when the battery voltage drops, and the battery will fail if you forget to turn off the power switch. This has a very large impact, since expensive batteries will become permanently unusable, especially when rechargeable secondary batteries are used. Therefore, a power supply circuit is required that stops the supply of power when the battery is discharged and the voltage drops to such an extent that the battery performance can be recovered by charging.

An object of the present invention is to provide a power supply circuit that solves the problems of the conventional art, and which suddenly turns off the output when the battery voltage drops below a predetermined value, and once the output is turned off, The present invention provides a power supply circuit that reliably prevents overdischarge by having a configuration that turns on when the voltage is restored to a voltage considerably higher than the power supply voltage.

FIG. 2 shows a power supply circuit according to an embodiment of the present invention, including a battery 1, transistors 6, 12, 15, resistors 7, 9,
10, 14, a Zener diode 8, diodes 11, 16, and a capacitor 13. Normally, transistors 6 and 15 are turned on, and Zener diode 8 and diode 11 are turned on, and transistor 12 is turned on.
The base voltage of the transistor 12 is stabilized, and the emitter voltage of the transistor 12, which is the output, is stabilized. The output voltage is (Zener voltage + diode forward voltage -
It appears as the base-emitter voltage of transistor 12). The diode 11 raises the output voltage by the forward voltage of the diode and has a temperature coefficient almost equal to that of the transistor 12, so that (the forward voltage of the diode - the base-emitter voltage of the transistor 12) almost cancels out. As the battery voltage gradually decreases and approaches the Zener voltage of the Zener diode 8, the voltage across the resistor 7 decreases, and when it falls below the base-emitter voltage of the transistor 6, the transistor 6 is turned off.

Then, the base current of the transistor 12 stops flowing, and the output voltage is abruptly cut off. Base resistor 14, transistor 15, diode 16
When the battery voltage is restored by replacing the battery or charging the battery, the transistor 15 is turned off and the diode 16 is inserted into the Zener diode loop.
The forward voltage is increased by 6, increasing the return voltage. This means that once the output is turned off, the terminal voltage of the battery rises again and the output is immediately turned on again, preventing an oscillation state in which the output is repeatedly turned off and on again, and provides reliable over-discharge protection for the battery. Further, the transistor 15 is set to be cut off abruptly when the output voltage of the transistor 12 drops below a predetermined value, and the diode 16 is inserted into the Zener diode loop, so the Zener voltage appears to be high as described above. So, transistor 6
speed up the off. This sharpens the transition of the transistor 12 from on to off. In addition, the diode 16 has the effect of apparently increasing the Zener voltage after the output is turned off and reducing leakage current due to the Zener diode. In the circuit shown in Figure 2, the Zener diode 8 also serves as the reference voltage for detecting and stabilizing the battery voltage drop, so the number of parts around the Zener diode can be reduced, reducing costs and improving reliability. The number of adjustment points such as variations in Zener diodes has also been reduced.

In recent years, low-power devices such as CMOS with a wide voltage range have been developed, and the permissible range for power supply voltage fluctuations has become wider. Therefore, there are cases where a stabilized output is not required, and in this case diode 1
1 may be omitted. By doing so, the output voltage can be further increased.

FIG. 3 shows the characteristic diagram of FIG. 2, which is an embodiment of the present invention. The relationship between the input voltage VI, which is the battery voltage, and the output voltage VO of the voltage circuit has steep rise and fall characteristics as well as hysteresis characteristics, so once it is turned off, it will not return to a voltage considerably higher than the voltage at which it was turned off. and does not return to the on state.

As described above, the present invention detects the voltage of the power supply and, depending on the detected voltage, connects it to the power supply via the resistor 7 in order to control the circuit disconnection transistor 12 connected between the power supply and the load circuit. A Zener diode 8 that generates a constant voltage is connected between the power supply and the base of the circuit interrupting transistor 12, and the end of the resistor 7 on the power supply side is connected to the emitter, and the end of the Zener diode side is connected to the base. a first control transistor 6 connected in series in the forward direction between the other end of the Zener diode and the power supply; 2 control transistors 15 are provided, and when the voltage of the power supply falls below a predetermined value, the first control transistor 6 is turned off, thereby turning off the circuit disconnection transistor 12,
Furthermore, since the second control transistor 15 is turned off when the circuit disconnection transistor 12 is turned off, and the diode 16 is inserted into the Zener diode loop, the following effects are produced. That is, when the output voltage of the circuit interrupting transistor falls below a predetermined value, the load direction diode 16 is inserted in series with the Zener diode due to the action of the transistor 15, thereby apparently raising the Zener voltage by the forward direction voltage of the diode 16. Thus, the first control transistor 6 is turned off earlier, and the cut-off of the circuit disconnection transistor 12 is sharpened. Also, since the return voltage increases by the amount of the Zener diode 16, once the output is cut off, it has a hysteresis characteristic such that it will not return to the on state unless it returns to a voltage considerably higher than the voltage when it was cut off. , which avoids oscillation and stabilizes the off-state to reliably prevent over-discharge. At the same time, the apparent increase in Zener voltage also reduces the leakage current of the Zener diode. Furthermore, the function of the Zener diode and the diode 16 is used to both detect and stabilize the battery voltage drop, and the number of parts is small, resulting in low cost and high reliability, as well as fewer adjustment points such as variations in the Zener diode. Provided power supply circuit.

[Brief explanation of the drawing]

FIG. 1 is a power supply circuit of a conventional example, FIG. 2 is a power supply circuit of an embodiment of the present invention, and FIG. 3 is a characteristic diagram of the circuit of FIG. 2.

Claims (1)

[Claims] 1 A Zener diode 8 which is connected to the power supply through a resistor 7 and generates a constant voltage, and a Zener diode which is connected between the power supply and the base of the circuit interrupting transistor 12 and whose end on the power supply side of the resistor 7 is connected to the emitter. A first control transistor 6 whose side end is connected to the base, a diode 16 which is connected in series in the forward direction between the other end of the Zener diode and the power supply, and a circuit interrupting transistor which is connected in parallel to the diode. A second control transistor 15 which inputs the output of 12 to its base is provided, and when the voltage of the power supply becomes lower than a predetermined value, the first control transistor 6 is turned off to turn off the circuit interrupting transistor 12. 1. A power supply circuit characterized in that the second control transistor 15 is turned off when the circuit disconnection transistor 12 is turned off, and the diode 16 is inserted into a Zener diode loop.