JPH07334256A - Power source circuit - Google Patents

Abstract

PURPOSE:To provide the power source circuit which reduces current consumption by holding an input voltage even when respective transfer gates are turned off. CONSTITUTION:Concerning the power source circuit provided with a current source 2 connected to a power source 10, reference voltage generating means 3 and reference voltage output means 7 connected on the output side of the reference voltage generating means 3, this circuit is equipped with a transfer gate 5 between the current source 2 and the reference voltage generating means 3, transfer gate 6 between the reference voltage generating means 3 and the reference voltage output means 7 and means for turning on/off the respective transfer gates, and the reference voltage output means 7 is constituted to hold the input voltage even when its input is a high impedance and the respective transfer gates are turned off. Since a current is intermittently supplied to the reference voltage generating means 3, the current consumption is decreased. Further, even when the transfer gates are turned off, the output voltage of the power source is kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit, and more particularly to a power supply circuit capable of maintaining an output voltage at an accurate constant voltage.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional power supply circuit. In the circuit of FIG. 3, a current source 2 and a reference voltage generating circuit 3 are connected to a battery 1 as a power source, and an operational amplifier 4 is connected to the output side of the reference voltage generating circuit 3. Then, the output voltage of the power supply circuit is taken out from the output side of the operational amplifier 4.

The reference voltage generating circuit 3 is composed of a bandgap circuit or the like, and is supplied with a constant current from the current source 2 to accurately generate a constant voltage. Since such a reference voltage generating circuit 3 cannot obtain a large output current, the operational amplifier 4 is connected to the output of the reference voltage generating circuit 3.
The operational amplifier 4 outputs a voltage having the same value as the output voltage of the reference voltage generating circuit 3 and can supply a large current to an external circuit.

[0004]

Such a power supply circuit has a drawback that the current consumption of the entire circuit is large because the reference voltage generating means 3 consumes a considerable amount of constant current. When such a power supply circuit is used for a power supply circuit such as a memory backup of a computer,
Since it is necessary to constantly supply a constant current to the reference voltage generating means, there is a problem that when a power source such as a battery having a limited power source capacity is used, the consumption of the power source becomes faster.

On the other hand, even in a power supply circuit using a power supply with a limited power supply capacity, the life of the power supply can be extended by reducing the current consumption of the reference voltage circuit. An object of the present invention is to obtain a power supply circuit that consumes less current.

[0006]

In order to achieve the above object, the present invention provides a current source connected to a power source and a reference voltage generating means, and a reference voltage output means connected to the output side of the reference voltage generating means. In a power supply circuit including: a transfer gate provided between the current source and the reference voltage generating means, a transfer gate provided between the reference voltage generating means and the reference voltage outputting means, and each of the transfer gates being turned on. The reference voltage output means is configured to hold the input voltage even when the input has a high impedance and the transfer gates are turned off.

[0007]

When the power supply circuit operates, each transfer gate repeatedly turns on and off. When the transfer gate is turned on, a constant current is supplied to the reference voltage generation means, the reference voltage generation means generates an accurate and constant reference voltage, and this reference voltage is output to the reference voltage output means. The reference voltage output means outputs an accurate and constant output voltage to the external circuit based on the reference voltage, and at the same time, enables a large current to be output to the external circuit.

When the transfer gate is off, the reference voltage generating means is not supplied with current and does not generate the reference voltage. At the same time, the connection between the reference voltage generation means and the reference voltage output means is cut off, but the reference voltage output means continues to hold the reference voltage input when the transfer gate is turned on. Therefore, the output voltage of the same value as when the transfer gate is turned on is continuously supplied from the power supply circuit to the external circuit. The input voltage held by the reference voltage output means decreases with the elapse of time, but the transfer gate is turned on again until the reference voltage decreases to a predetermined value, and the reference voltage generation means outputs a constant voltage to the reference voltage output means. Output.
After that, the same operation is repeated.

Since the reference voltage generating means does not consume current when the transfer gate is turned off, the current consumption of the power supply circuit can be reduced as compared with the case where the reference voltage generating means constantly keeps flowing current.

[0010]

FIG. 1 shows an embodiment of the present invention. Power supply circuit 10
In, the current source 2, the transfer gate 5, and the reference voltage generating circuit 3 are connected in series, and these are connected to the battery 1 which is a power source. The output side of the reference voltage generation circuit 3 is connected to the reference voltage output circuit 7 through the transfer gate 6, and the output voltage of the power supply circuit is obtained from the output side of the reference voltage output circuit 7. Further, a control signal generation circuit 8 for supplying a control signal to each transfer gate 5, 6 is provided.

Here, as the reference voltage generation circuit 3, any circuit can be used as long as it is a circuit that generates an accurate constant voltage, and for example, a bandgap circuit is used. The reference voltage output circuit 7 has a high impedance input impedance and has a function of holding the input voltage.
It is composed of an SFET input operational amplifier 4 and a capacitor 9 connected to one of its input terminals.

The above power supply circuit 10 can be built in an LSI or can be formed as a single power supply circuit. During operation of the power supply circuit 10, the control signal generating circuit 8 transfers two transfer gates 5,
The switch control signal shown in FIG. The switch control signal is a signal that repeatedly turns on and off at a constant cycle. In the example shown, the switch control signal has a cycle of 0.25 mS and an on period of 0.025 mS. However, this cycle and the on period are set to arbitrary values. can do.

When the transfer gates 5 and 6 are turned on, a constant current is supplied to the reference voltage generating circuit 3, and an accurate constant reference voltage is output from the output side thereof. This reference voltage is applied to the capacitor 9 of the reference voltage output circuit 7 through the transfer gate 6 which is turned on, and charges the capacitor 9. The operational amplifier 4 of the reference voltage output circuit 7 outputs the same voltage as the charging voltage of the capacitor 9 as the output of the power supply circuit 10.

In this embodiment, the amplification factor of the operational amplifier is set to 1, and a voltage having the same value as the reference voltage is output. However, by adjusting the amplification factor of the operational amplifier, a constant voltage different from the reference voltage can be obtained. It can also be output. Next, when the transfer gates 5 and 6 are turned off,
The reference voltage generation circuit 3 stops the generation of the reference voltage because the current supply is cut off. This transfer gate 5
The current of the battery 1 is not consumed in the reference voltage generating circuit 3 during the off state of.

Regarding the charging voltage of the capacitor 9, since the transfer gate 6 is turned off and the input impedance of the MOSFET input operational amplifier 4 is high impedance, it holds a substantially constant voltage. The input part of the operational amplifier 4 is a MOSFE
If a bipolar transistor is used instead of T, the input impedance becomes low, and even when the transfer gates 5 and 6 are turned off, the capacitor 9 to D
A C-like minute current continues to flow to the operational amplifier 4. For this reason, the charging voltage of the capacitor 9 decreases with the passage of time, and the accuracy of the output voltage cannot be maintained.

However, in this embodiment, since the operational amplifier 4 has a high input impedance, the charged voltage of the capacitor 9 is not discharged to either the reference voltage generating circuit 3 or the operational amplifier 4. Even when the transfer gates 5 and 6 are off, a substantially constant voltage is maintained. Therefore, the operational amplifier 4 is
Even while the transfer gates 5 and 6 are off, a voltage having substantially the same value as the charging voltage of the capacitor 9, that is, a voltage substantially the same as the reference voltage generated by the reference voltage generating circuit 3 is output to the external circuit.

As a practical matter, the charging voltage of the capacitor 9 drops slightly with the passage of time, but after a lapse of a predetermined time from the transfer gates 5 and 6 being turned off, the transfer gates 5 and 6 are turned on again, and the reference The voltage generating means 3 generates a reference voltage and outputs it to the reference voltage output means 7. After that, the same operation is repeated, and the power supply circuit 10 outputs an exactly constant voltage.

The period for turning on / off the transfer gate and the on / off time are selected so that the value of the input voltage of the reference voltage output means 7 can be kept within a required range in view of the operation described above. It As described above, the power supply circuit 10 shown in FIG. 1 continues to output a voltage equal to the reference voltage generated by the reference voltage generation circuit 3 regardless of whether the transfer gates 5 and 6 are on or off. Further, neither the reference voltage generating circuit 3 nor the capacitor 9 can output a large current value, but by using the operational amplifier 4, a required amount of current can be drawn as the output of the power supply circuit.

Further, when the transfer gates 5 and 6 are turned off, no current is supplied to the reference voltage generating circuit 3 and the current of the battery 1 is not consumed. Therefore, even if the battery 1 is used as the power supply, The current consumption can be reduced and the battery life can be extended. In this embodiment, since the ratio of the on time of the transfer gates 5 and 6 to the on / off cycle is 1:10, the current consumption of 600 μA is 60 μA (average ) Can be done.

[0020]

According to the present invention, it is possible to obtain a power supply circuit with low current consumption.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a power supply circuit of the present invention.

FIG. 2 is a diagram showing a waveform of a control signal of the transfer gate of FIG.

FIG. 3 is a block diagram showing a conventional power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Current source 3 ... Reference voltage generation circuit 4 ... Operational amplifier 5, 6 ... Transfer gate 7 ... Reference voltage output circuit 8 ... Control signal generation circuit 9 ... Capacitor 10 ... Power supply circuit

Claims (3)

[Claims] 1. A power supply circuit comprising a current source connected to a power supply and a reference voltage generation means, and a reference voltage output means connected to the output side of the reference voltage generation means, wherein the current source and the reference voltage generation are provided. A transfer gate provided between the means, a transfer gate provided between the reference voltage generation means and the reference voltage output means, and means for turning on and off each of the transfer gates, the reference voltage output means, A power supply circuit characterized in that its input has a high impedance, and is configured to hold an input voltage even when each of the transfer gates is off. 2. The reference voltage output means is a MOSFET
The power supply circuit according to claim 1, wherein the power supply circuit comprises an input operational amplifier and a capacitor whose one end is connected to the input of the operational amplifier. 3. The means for turning on / off the transfer gate outputs a signal for turning on / off the transfer gate at a constant cycle.
The power supply circuit described.