JP2013101447A - Start circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a start circuit capable of securing stable operation with low current consumption without reference to the state of a supply voltage.SOLUTION: The start circuit includes a P-channel transistor MP1 which is arranged in parallel to a current source (supply voltage VE) of a bias circuit operating based upon a low power supply potential, a first switch S1 arranged between a gate of the P-channel transistor MP1 and a high-potential power source, and a resistance R3 and a second switch S2 arranged in series between the gate of the P-channel transistor MP1 and a low-potential power source. The first switch S1 turns ON/OFF with a bias voltage of a constant-current source, and the second switch S2 turns ON/OFF with a power supply start signal associated with the start of a system power source.

Description

  The present invention relates to a starting circuit for starting a bias circuit, which operates stably with low current consumption.

  In general, in order to operate an electronic circuit, a bias circuit represented by a reference voltage circuit, a reference current circuit, or the like is required.

  Since the operating current is zero and the bias circuit has a stable point, the bias circuit does not start when the power is turned on. For this reason, a dedicated starting circuit is required (for example, refer to Patent Document 1).

  FIG. 4 is a circuit diagram of a bandgap reference voltage circuit as an example of a bias circuit. The reference voltage circuit unit 10 shown in FIG. 4 includes three constant current sources I1, I2, and I3 in parallel with the power source V that outputs the voltage VE. A transistor Q1 is connected in series to the output side of the constant current source I1, a resistor R1 and a transistor Q2 are connected in series to the output side of the constant current source I2, and a resistor is connected to the output side of the constant current source I3. R2 and transistor Q3 are connected in series.

  The input side of the operational amplifier 11 is connected between the output side of the constant current source I1 and the transistor Q1 and between the output side of the constant current source I2 and the resistor R1, and the output (bias voltage) of the operational amplifier 11 is Feedback is made to the constant current sources I1, I2, and I3. A reference voltage signal Vref is output between the constant current source I3 and the resistor R2.

  In such a band gap reference voltage circuit (reference voltage circuit unit 10), since the output current I = 0A of the power supply V is one of the stable points, even if the power supply V shown in FIG. Do not output Vref. For this reason, the circuit is activated by forcibly flowing the output current I through the constant current sources I1, I2, and I3 at the time of activation. For this reason, in the start-up circuit, there is a problem that even when the start-up of the target circuit is completed, current always flows and the current consumption increases while the power supply voltage VE is applied.

  With respect to this problem, in Patent Document 1, a switch (switching element) is provided in a circuit, and when this switch is turned on at the time of activation to output an output current I, a capacitor connected to the gate of the switch is charged. There has been proposed a technique in which the gate-source potential of the switch is lowered to turn off the switch.

  According to this startup circuit, the startup current can be stopped because the switch is turned off after startup. Further, since the gate drive of the switch is performed by charging the capacitor, there is an advantage that when the charging is completed, no more current flows.

Japanese Patent Laid-Open No. 09-081252

  However, in the above-described startup circuit of Patent Document 1, when the charging voltage of the capacitor and the power supply voltage are maintained in substantially the same state, the switch is always in the OFF state, so that the startup current does not flow. .

  For this reason, there has been a problem that the start-up circuit may not start depending on the rising speed of the power supply voltage. In addition, since the gate voltage of the switch is held by a capacitor, the switch gate voltage does not follow the fluctuation of the power supply voltage when the power supply voltage changes transiently. There was a problem that the operation might become unstable.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a start-up circuit that can secure a stable operation regardless of the state of a power supply voltage with low current consumption.

  In order to solve the above problems, a start circuit of the present invention includes a transistor arranged in parallel with a current source of a bias circuit that operates with a low power supply potential as a reference, and a start current flowing therethrough, a gate of the transistor, and a high potential power supply And a resistor and a second switch arranged in series between the gate of the transistor and a low potential power source, the first switch being a constant current source The second switch is turned on / off by a power supply start signal relating to the start of the system power supply.

  At this time, the transistor can be a P-channel transistor, the first switch can be a P-channel transistor, the second switch can be an N-channel transistor, and the N-channel transistor as the second switch is: It is turned on / off by the output signal from the low voltage detection circuit.

  According to such a configuration, a stable operation can be ensured with low current consumption regardless of the state of the power supply voltage.

  In addition, the start-up circuit of the present invention is arranged in parallel with a current source of a bias circuit that operates with a high power supply potential as a reference, and between the gate of the transistor and the low-potential power supply to flow the start-up current. A first switch, a resistor arranged in series between the gate of the transistor and a high-potential power source, and a second switch, and the first switch is turned on by a bias voltage of a constant current source The second switch is turned on / off by a power activation signal related to activation of the system power.

  Also in this case, the transistor can be an N-channel transistor, the first switch can be an N-channel transistor, and the second switch can be a P-channel transistor.

  The starter circuit of the present invention can ensure a stable operation with low current consumption regardless of the state of the power supply voltage.

It is explanatory drawing of the starting circuit which concerns on one Embodiment of this invention (when operate | moving on the basis of the low power supply potential side). It is explanatory drawing of the other starting circuit which concerns on one Embodiment of this invention (when operate | moving on the basis of the low power supply potential side). FIG. 3 is a circuit diagram corresponding to FIG. 2, and is a circuit diagram in the case of operating with a high power supply potential side as a reference. It is a circuit diagram of the conventional reference voltage circuit.

  Next, a starting circuit according to an embodiment of the present invention will be described with reference to the drawings. In addition, although the Example shown below is a suitable specific example in the starting circuit of this invention, and there may be a technically preferable various limitation, the technical scope of this invention limits this invention especially. Unless otherwise stated, the present invention is not limited to these embodiments. In addition, the constituent elements in the embodiments shown below can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the description of the embodiment described below does not limit the contents of the invention described in the claims.

(Embodiment 1)
FIG. 1 is an explanatory diagram when a starting circuit according to an embodiment of the present invention is used in a band gap reference voltage circuit. Since the configuration of the reference voltage circuit unit 10 is the same as that of the above prior art (FIG. 4), the same reference numerals are given and the description thereof is omitted.

  In FIG. 1, the startup circuit unit 20 is connected in parallel between the power supply V and the reference voltage circuit unit 10. The starter circuit unit 20 includes a first switch S1, a resistor R3, and a second switch S2 connected in series, and a P-channel transistor MP1 for flowing a starter current connected in parallel.

  The drain of the P-channel transistor MP1 is connected between the output terminal of the constant current source I1 of the reference voltage circuit unit 10 and the input terminal of the operational amplifier 11, and the gate of the P-channel transistor MP1 is connected to the first switch S1 and the resistor R3. Connected between. Thus, the first switch S1 is connected between the gate of the P-channel transistor MP1 and the high potential power source. A resistor R3 and a switch S2 are connected in series between the gate of the P-channel transistor MP1 and the low potential power source.

  The first switch S <b> 1 is turned on / off by the constant current source bias voltage output from the operational amplifier 11 of the reference voltage circuit unit 10. The second switch S2 is turned on / off by a power activation signal EN related to power activation including a system on / off signal, a power on reset signal, and the like, as well as a system reset signal and a low voltage detection circuit signal.

  In such a configuration, before the activation, the second switch S2 is turned on by a power activation signal EN such as a logic signal for notifying activation of the system or the power supply or a system reset signal. The first switch S1 is turned off in a state where the bias voltage of the constant current source is not activated.

  When the power supply V rises, the voltage between the gate and the source of the P-channel transistor MP1 is applied through the second switch S2 and the resistor R3, a starting current flows through the P-channel transistor MP1, and the reference voltage circuit unit 10 is forced. Is supplied with a current to output a reference voltage Vref.

  Further, when the reference voltage circuit unit 10 outputs the reference voltage Vref and the bias voltage of the constant current source is activated, the first switch S1 is turned on, the gate-source voltage of the P-channel transistor MP1 becomes zero, and the activation current No longer flows.

  Furthermore, when the system and power supply start-up is completed or when the system is set, the second switch S2 is turned off to cut off the current flowing through the resistor R3, thereby suppressing an increase in current consumption.

(Embodiment 2)
FIG. 2 is an explanatory diagram of another activation circuit according to an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure same as the said Embodiment 1 (FIG. 1), and the description is abbreviate | omitted.

  As shown in FIG. 2, in parallel with the power supply V, an activation circuit unit 30, a reference voltage circuit unit 40, and a low voltage detection circuit unit 50 are connected in parallel.

  The reference voltage circuit unit 40 is connected to P-channel transistors MP2, MP3, and MP4 in place of the constant current sources I1, I2, and I3 of the reference voltage circuit unit 10 shown in the first embodiment. Channel transistors MN1 and MN2 are connected.

  N-channel transistors MN1 and MN2 have their drains connected to the drains of P-channel transistors MP2 and MP3, the source of MN1 is connected to the emitter of transistor Q1, and the source of MN2 is connected to the emitter of Q2 through resistor R1. Has been.

  The gates of the N channel transistors MN1 and MN2 are connected between the drains of the P channel transistor MP2 and the N channel transistor MN1 and the drain of the P channel transistor MP1. Further, the gates of the P-channel transistors MP2 and MP3 are connected between the drain of the P-channel transistor MP3 and the drain of the N-channel transistor MN2, and the reference voltage signal Vref is connected between the drain of the P-channel transistor MP4 and the resistor R2. Is output to the low voltage detection circuit unit 50.

  The starter circuit unit 30 is connected to a P-channel transistor MP5 (first switch) in place of the first switch S1 of the starter circuit unit 20 of the first embodiment, and the gate voltage is driven by the bias voltage of the P-channel transistor MP3. Is used. Further, an N-channel transistor MN3 (second switch) is connected instead of the second switch S2, and the ON / OFF operation is performed by the output from the low voltage detection circuit unit 50 that monitors the power supply voltage VE.

  In the low voltage detection circuit unit 50, a third switch S3, a resistor R5, and a resistor R4 are connected in series, and a comparator COMP1 is connected in parallel.

  The comparator COMP1 receives a reference voltage signal Vref output from between the drain of the P-channel transistor MP4 and the resistor R2, and a signal output from between the resistor R5 and the resistor R4. An output signal is output to the gate of the N-channel transistor MN3.

  In such a configuration, when the power supply voltage VE is less than a predetermined value (for example, 3 V), the N-channel transistor MN3 is turned on by the output from the low voltage detection circuit unit 50. This predetermined value is arbitrarily determined according to the specification. The P-channel transistor MP5 is turned off in a state where the bias voltage of the P-channel transistor MP3 is not activated.

  When the power supply voltage VE rises, the gate-source voltage of the P-channel transistor MP1 is applied through the N-channel transistor MN3 and the resistor R3, so that a starting current flows through the P-channel transistor MP1 and the reference voltage circuit unit 40 Force a current to start the reference voltage.

  When the reference voltage circuit unit 40 is activated and the bias voltage of the P channel transistor MP3 is activated, the P channel transistor MP5 is turned on, the gate-source voltage of the P channel transistor MP1 becomes zero, and the activation current does not flow.

  Further, when the power supply voltage VE becomes equal to or higher than a predetermined value and the low voltage detection circuit unit 50 outputs a start-up completion signal of the power supply voltage VE, the N-channel transistor MN3 is turned off and the current flowing through the resistor R3 is cut off. Suppress.

  As described above, the starting circuit according to the present invention does not employ a configuration in which a voltage is held using a capacitor, so that a starting failure when the starting of the power supply voltage VE is slow or the power supply voltage VE varies transiently. The occurrence of unstable operation can be suppressed.

  By the way, in each of the above-described embodiments, the case where the constituent circuit operates with the low power supply potential side as a reference has been described. In this case, the polarity of the power supply voltage VE is reversed, the P-channel transistors (MP1 to MP5) and the N-channel transistors (MN1 to MN3) are interchanged, and the PNP transistors (Q1 to Q3) are changed to NPN transistors. By exchanging, the same effect can be produced. FIG. 3 shows a circuit example in the case of operating with the high power supply potential side as a reference. The startup circuit unit 31, the reference voltage circuit unit 41, and the low voltage detection circuit unit 51 of FIG. 3 correspond to the startup circuit unit 30, the reference voltage circuit unit 40, and the low voltage detection circuit unit 50 of FIG. In FIG. 3, the N-channel transistor MN15 corresponds to a first switch, and the P-channel transistor MP13 corresponds to a second switch.

DESCRIPTION OF SYMBOLS 10, 40, 41 ... Reference voltage circuit part 11 ... Operational amplifier 20, 30, 31 ... Start-up circuit part 50, 51 ... Low voltage detection circuit part MN1-MN3, MN11-MN15 ... N channel transistor MP1-MP5, MP11-MP13 ... P-channel transistors COMP1, COMP11 ... Comparator (comparator)
Q1-Q3, Q11-Q13 ... Transistors R1-R5, R11-R15 ... Resistors S1-S3, S13 ... Switches

Claims (5)

  A transistor that is arranged in parallel with a current source of a bias circuit that operates on the basis of a low power supply potential and allows a starting current to flow; a first switch connected between the gate of the transistor and a high potential power supply; A resistor and a second switch connected in series between the gate of the transistor and a low-potential power supply, wherein the first switch is turned on / off by a bias voltage of a constant current source, and the second switch Is a start circuit which is turned on / off by a power start signal related to the start of the system power.   2. The starter circuit according to claim 1, wherein the transistor is a P-channel transistor, the first switch is a P-channel transistor, and the second switch is an N-channel transistor.   The startup circuit according to claim 2, wherein the N-channel transistor as the second switch is turned on / off by an output signal from a low voltage detection circuit.   A transistor connected in parallel with a current source of a bias circuit that operates on the basis of a high power supply potential to flow a starting current, a first switch connected between the gate of the transistor and a low potential power supply, A resistor and a second switch connected in series between the gate of the transistor and a high-potential power supply, wherein the first switch is turned on / off by a bias voltage of a constant current source, and the second switch Is a start circuit which is turned on / off by a power start signal related to the start of the system power.   5. The activation circuit according to claim 4, wherein the transistor is an N-channel transistor, the first switch is an N-channel transistor, and the second switch is a P-channel transistor.

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