JPH04128051U - power circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a power supply circuit that has hysteresis characteristics at the start and stop of operation by making the voltage detection level when the input voltage increases higher than the detection level when it decreases. [Structure] When the input voltage VDD reaches the level V2, the regulator B starts operating, and the potential of the control terminal 11 of the regulator B is self-maintained by the output voltage Vo, even if the input voltage VDD falls below the level V2. The operation continues even if When the input voltage V _DD falls below the level V1, which is lower than the level V2, the self-holding is released, the potential of the control terminal 11 changes, and the operation of the regulator B is stopped. This causes the regulator to operate with hysteresis between levels V1 and V2.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to a power supply circuit that inputs an external voltage and outputs a predetermined constant voltage. Regarding a power supply circuit that controls operation/non-operation according to the level of external voltage It is something.

0002

[Conventional technology]

A normal power supply circuit has an external voltage detection circuit built in, and one Detection level is set and the external input voltage is higher or lower than that detection level. It was designed to detect whether the power supply circuit is operating or not and control the operation/non-operation of the power supply circuit. Therefore, external Since the rise and fall of the input voltage are detected at the same detection level, external input Operation mode in which it operates if the power voltage is higher than the above level, and does not operate if it is lower. becomes.

0003

[Problem that the idea aims to solve]

By the way, in devices that use batteries as an external power source, avoid using exhausted batteries. In order to ensure that the battery voltage is higher than a certain level, It is desirable that the battery voltage decreases due to consumption during use. It is desirable to allow equipment to continue operating even when pressure reaches low levels.

0004 To meet such demands, it is impossible to use conventional circuits with a single voltage detection level. Therefore, it is desirable to have a circuit that detects voltage at different levels when the voltage rises and when the voltage falls. be caught.

[0005] The purpose of this invention is to detect the voltage at a high level and start operation when the input voltage increases. , when the input voltage drops, the voltage is detected at a low level and the operation is stopped. By providing a power supply circuit that can satisfy such demands, be.

[0006]

[Means to solve the problem]

Therefore, in the present invention, the connection is made when the input voltage applied to the input terminal reaches the first level. a first switch that outputs the earth potential and outputs the input voltage when the voltage falls below the first level; a second switching element whose voltage applied to the input terminal is higher than the first level; When the level is reached, the ground potential is output, and when it falls below the second level, the above input voltage is output. The second switching element that outputs and the control terminal that inputs the above input voltage are connected to ground potential. A regulator that operates when the voltage reaches a certain level and stops operating when the voltage reaches a certain level; When the second switching element is inactive, the potential outputted by the second switching element is applied to the control terminal. The third switching element does not provide power when the regulator is in operation, and the When the potential output by the first switching element is applied to the control terminal, the first switching element becomes inactive. The fourth switching element is not provided in the fourth switching element.

[0007]

【Example】

Examples of the present invention will be described below. Figure 1 shows the circuit diagram of a power supply circuit in one embodiment. It is a road map. The block A part is the voltage detection part, and the block B part is the voltage detection part. This is a regulator whose operation/non-operation is controlled by the detection output of section A. i.e. , this regulator B operates when the output of voltage detection section A is at ground potential, and when the power supply voltage is It becomes inoperable when pressure is applied.

[0008] In the voltage detection section A, 1 is the input terminal of the external power supply, and 2 is the detection voltage V1 set. 3 is the second comparator set to the detection voltage V2 (>V1). The drain of the terminal 4 is connected to the input terminal 1, and the gate is connected to the ground, so that it is always on. PMOS, 5 and 6 as pull-up resistors are connected directly between PMOS4 and ground. It is a column-connected NMOS. One NMOS 6 is connected to the first comparator 2. When the output voltage Va rises, the other NMOS 7 turns on and the second comparator 3 It turns on when the output voltage Vb rises. 7 is the output voltage of the first comparator 2. PMOS turns on when falling, 8 acts as a pull-down resistor that is always on. These MOSs 7 and 8 are connected in series between the power supply and ground. 9 is PMOS, 10 is NMOS, and the common connection point of MOS4 and 5 and MOS7, They are connected in series between 8 common connection points. And this MOS9 and 10 common The voltage at the connection point is input to regulator B as the detection voltage Vc of voltage detection section A. . Moreover, the output voltage Vo of the regulator B is applied to the gates of MOS9 and 10. When the voltage Vo is ground potential 0v, one MOS9 turns on and rises. When the voltage is turned on, the other MOS 10 is turned on.

[0009] In the regulator B, 11 is a control terminal that receives the detection voltage Vc of the voltage detection section A. 12 is a power input terminal to which the voltage of input terminal 1 is applied, 13 is an output terminal, When the voltage at the power input terminal 12 exceeds a predetermined value, the voltage Vc at the control terminal 11 When it is at ground potential, a constant voltage Vo is output (operated) to the output terminal 13, and it starts up. In this case, the output voltage is set to ground potential (non-operating).

Now, in the above, when the external power is turned on (the power supply voltage V _DD of the input terminal 1 = 0v), the output voltages Va and Vb of both the comparators 2 and 3 are 0v. Further, the output of regulator B is also 0V. Therefore, MOS5, 6, 8, and 10 are in the off state, and MOS7 and 9 are in the on state. Therefore, the voltage (V _DD ) of the input terminal 1 is applied to the control terminal 11 of the regulator B via the route from MOS4 to MOS9 as a pull-up resistor, and its output voltage remains at 0V.

[0011] After that, when the voltage at the input terminal 1 increases, first when V _DD =V1 is reached, the first comparator 2 is turned on and the voltage Va rises. At this time, MOS5 is turned on and MOS7 is turned off. However, at this point, the on/off states of MOSs 9 and 10 do not change yet, and the voltage at the control terminal 11 of regulator B is VDD.

Next, when V _DD =V2 is reached, the output voltage Vb of the second comparator 3 rises. As a result, the common connection point between MOS4 and MOS5 becomes 0V, so that voltage is applied to the control terminal 11 of regulator B via the route of MOS9. As a result, regulator B starts operating, and a constant voltage Vo is generated at its output terminal 13.

[0013] Therefore, MOS9 whose gate receives this voltage Vo is turned off, and MOS10 is turned on. Turn on. At this time, MOS7 is in an off state. Therefore, regulator B's The control terminal 11 connects the turned-on MOS 10 and the MOS 8 which acts as a pull-down resistor. The operation of regulator B is self-protected through this route. It will be held.

After this, when the voltage at the input terminal 1 decreases and becomes V1<V _DD <V2, the output voltage Vb of the second comparator 3 falls and the MOS 6 is turned off, but the control terminal 11 of the regulator B is As described above, since there is no change from the state where the ground potential is applied on the route from MOS10 to MOS8, the constant voltage Vo continues to be output to the output terminal 13 of regulator B.

[0015] When the voltage at the input terminal 1 further decreases to V _DD <V1, the output voltage Va of the first comparator 2 falls, MOS 5 is turned off, and MOS 7 is turned on. As a result, the voltage VDD at the input terminal 1 is applied to the control terminal 11 of the regulator B via the route of the MOSs 7 and 10, and the regulator B stops operating. Therefore, the voltage Vo at the output terminal 13 falls to 0V, MOS9 is turned on, MO10 is turned off, and the voltage V _DD at the input terminal 1 is applied to the control terminal 11 via the route from MOS4 to MOS9, and from then on MOS7 This state continues regardless of whether it is turned off.

As described above, when the power supply voltage V DD of the input terminal 1 rises, the regulator B starts operating when the output of the second comparator 3, which has a high detection level, rises, and the power supply voltage V _DD rises. When falling, a hysteresis operation is performed in which the operation is stopped when the output voltage of the first comparator 2, which has a low detection level, falls. A timing chart of the above operation is shown in FIG. Note that the MOSs 4 and 8 can be replaced with ordinary resistance elements.

[0017]

[Effect of the idea]

From the above, according to the present invention, the detection level at the falling edge of the input voltage is higher than the detection level at the rising edge of the input voltage. It is possible to provide a hysteresis characteristic that lowers the detection level. this Therefore, when the input voltage source is battery voltage, the battery voltage will reach the high detection level mentioned above. The voltage will not be detected unless the voltage reaches the specified voltage, thus preventing the use of exhausted batteries. This eliminates the risk of causing unexpected situations. Also, the battery voltage may drop during use. In some cases, the circuit is not detected until it reaches a low detection level, so the circuit may stop inadvertently. This can be prevented.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a voltage detection circuit according to an embodiment of the present invention.

FIG. 2 is a timing chart of the operation of the circuit of the same embodiment.

[Explanation of symbols]

A: Voltage detection section, B: Regulator, 1: Input terminal,
2. First comparator, 3: Second comparator, 4: P
MOS, 5, 6: NMOS, 7: PMOS, 8: NMO
S, 9: PMOS, 10: NMOS, 11: Control terminal,
12: Power input terminal, 13: Output terminal.

Claims (1)

[Scope of utility model registration request] 1. A first switching element that outputs a ground potential when an input voltage applied to an input terminal reaches a first level, and outputs the input voltage when the input voltage falls below the first level; and the input terminal. When the voltage applied to the second level reaches a second level higher than the first level, the ground potential is output, and the second level is higher than the first level.
a second switching element that outputs the input voltage when the input voltage falls below the level of the second switching element; a regulator that inputs the input voltage and operates when the control terminal reaches a ground potential and becomes inoperable when the control terminal reaches a predetermined potential; When the third switching element applies the potential output by the second switching element to the control terminal and does not apply it during operation, and the potential output from the first switching element when the regulator is in operation is applied to the control terminal. A power supply circuit comprising: a fourth switching element that supplies power to the current state and does not provide power when inactive.