JPH077313B2 - DC power switch circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a DC power supply switching circuit formed including a stabilizing circuit of a transistor control system.

[Prior Art] A transistor control type stabilizing circuit formed including a first resistor for supplying a base current connected to a DC input power source, and a stabilizing current voltage generated by this stabilizing circuit is a reference voltage. A signal generator that emits a signal when
A DC power supply switching circuit including a switching-type secondary power supply circuit that generates a secondary power supply from a stabilized power supply is known.

The general structure of such a conventional DC power supply switching circuit is as shown in FIG. In FIG. 2, the DC power supply switching circuit includes a stabilizing circuit 10 and a current limiting circuit 20, and generates a stabilized power source 3 and a signal generator 30 and a secondary power source circuit 40 connected to the stabilized power source 3. It is configured to include and.

The stabilizing circuit 10 is a transistor TR as a series control element.
1. A first resistor R1 as a collector resistor for negative feedback and a Zener diode ZD, which form a so-called emitter follower type stabilized power supply.

The first resistor R1 is connected to the high-potential-side electric circuit of the DC input power supply (unregulated power supply) 1 when the switch SW is turned ON, and supplies a base current. A capacitor C for ripple settling is provided.

The current limiting circuit 20 controls the rush power when the power is turned on, and is composed of resistors R3, R5, R6 and transistors TR3, TR4 to detect the load current (stabilized power supply current) and suppress the current rush.

Further, the signal generator 30 connected to the stabilized power supply 3 outputs a reset release signal to the device side when the normal and stable operation conditions of the connected device are established. V1N by comparing the generated reference voltage Vref
The reset release signal is output when it becomes Vref.

The secondary power supply circuit 40 generates a new secondary power supply (for example, + 5V) to be used inside the device and is a switching control system.

Therefore, when the switch SW is turned on to the DC input power source 1 to supply power to the device, current is supplied to the base via the resistor R1 and the collector current IC flows. The VCE and IC when the power is turned on are shown in FIG. That is, the transistor TR1
Since the emitter voltage of is almost the same as the low side voltage of the DC input power supply 1, VCE becomes the DC input power supply voltage and gradually decreases as the capacitor C is charged, and the voltage with the voltage determined by the Zener diode ZD. It becomes constant according to the difference. On the other hand, the IC increases rapidly and the resistance R3
It is cut by the current value limited by and decreases as the capacitor C is charged.

In this way, the stabilized power supply 3 rises while limiting the rush power supply when the power is turned on. And stabilized power supply voltage V1N
Is equal to the reference voltage Vref, the signal generation circuit 30 outputs a reset release signal (high level). Here, assuming that the time from when the power is turned on to when the secondary power supply stabilizes in the specified state is T1, the reset release signal should be output after the time T1 has elapsed.

[Problems to be Solved by the Invention] However, in the conventional DC power supply switching circuit described above, it is not possible to select the rising characteristics when the power is turned on and the tracking characteristics when a sudden load change occurs during operation of the equipment, to ideal states. It had a reciprocal two-dimensional defect.

That is, the loss of the transistor TR1 of the stabilizing circuit 10 is VCE
Since it is represented by the product of IC and IC, the resistance of resistors R1 and R3 should be increased to limit the rush current. On the other hand, in the signal generation circuit 30, the reset release signal is output earlier if the rising speed of the stabilized power supply voltage V1N is faster.
On the other hand, the secondary power supply circuit 40 has a large time constant in the circuit due to the switching method, and the time T1 is determined from the output characteristics. Therefore, the secondary power supply circuit 40 is proportional to the rising speed of the stabilized power supply voltage V1N. It doesn't rise faster.

Therefore, when the stabilized power supply voltage V1N rapidly rises as shown by the dotted line in FIG. 4 (A) due to the resistance value of the resistor R3 and the rising characteristics of the DC input power supply, the reset release signal is the same. As shown in (C), the rise time of the secondary power supply
There is a problem in that the device is output before T1 [see (B)] elapses and the device malfunctions. Therefore, in order to protect the transistor TR1 when the power is turned on and to ensure the generation of the reset release signal after the secondary power supply is established, it is desirable to make the resistance values of the resistors R1 and R3 relatively large to delay the rising characteristic. I can say.

However, if the resistance values of the resistors R1 and R3 are increased, the responsiveness decreases. Therefore, during steady operation, if there is a rapid and large load change such as driving a cash drawer of a cash register, it cannot follow up, and the stabilized power supply 3 The situation is that the prescribed value cannot be maintained.

Therefore, in the conventional DC power supply switching circuit, after considering the rise characteristic at power-on and the follow-up characteristic to abrupt load change during steady operation, we find a compromise that is a step back from each ideal state and operate it. I had no choice but to do it.

The present invention has been made in view of the above circumstances. An object of the present invention is to limit a current rush at power-on and to issue a reset release signal in a timely manner.
It is an object of the present invention to provide a DC power supply switching circuit that can generate a reliable and reliable stabilized power supply that can sufficiently follow a sudden load change during steady operation.

[Means for Solving the Problems] The present invention provides a transistor-controlled stabilizing circuit including a first resistor for supplying a base current connected to a DC input power supply, and a stabilizing circuit formed by this stabilizing circuit. In a DC power supply switching circuit comprising a signal generator that issues a reset release signal when a stabilized power supply voltage becomes equal to a reference voltage, and a switching type secondary power supply circuit that generates a secondary power supply from a stabilized power supply. Selecting a resistance value of the first resistor so that a rush current at power-on can be limited and a reset release signal is generated from the signal generator after the secondary power supply circuit is stabilized, A second resistor connectable in parallel with the resistor and a characteristic switching circuit for connecting the second resistor in parallel with the first resistor on condition that a reset release signal is output from the signal generator are provided. Configuration and to achieve the object was.

[Operation] When the power is turned on, the first resistor having a large resistance value determines the rising characteristic of the stabilizing circuit to limit the rush current, and the secondary power supply circuit generates the reset release signal from the signal generator after stabilizing. After the reset release signal is output, the second resistor is connected in parallel to reduce the overall resistance value and enhance the follow-up characteristic to the load fluctuation of the stabilizing circuit.

[Embodiment] An embodiment of a DC power supply switching circuit according to the present invention will be described with reference to FIG.

In this embodiment, a stabilizing circuit 10, a characteristic switching circuit 20, a signal generating circuit 30, and a secondary power supply circuit 40 constitute a DC power supply switching circuit.

The stabilizing circuit 10 is a transistor TR as a series control element.
1, a first resistor R1 serving as a collector resistor for negative feedback, and a Zener diode ZD, and a ripple-setting capacitor C is provided.

The first resistor R1 is supposed to supply a base current when the switch SW is connected to the high potential side electric circuit of the DC input power supply 1, and its resistance value is sufficient to protect the transistor TR1 at the time of power-on rush current. Secondary power supply circuit
The value is selected so that the reset release signal is generated from the signal generating circuit 30 after the secondary power source 40 is stabilized. Therefore, the conventional current limiting circuit is omitted. The configurations of the signal generation circuit 30 and the secondary power supply circuit 40 are the same as those of the conventional configuration described above, and thus the description thereof is omitted.

Now, the characteristic improvement of the stabilizing circuit 10 which is a technical feature of the present invention is performed by the second resistor R2 and the characteristic switching circuit 20. The second resistor R2 in this embodiment is smaller than the resistance value of the first resistor R1 and can be connected in parallel with the first resistor R1.

The characteristic switching circuit 20 includes a transistor TR4 having a base connected between the voltage dividing resistors R5 and R6, and voltage dividing resistors R7 and R8 connected in series between the collector of the transistor TR4 and the switch SW.
And a second resistor R whose base is connected between voltage dividing resistors R7 and R8.
And a switching transistor TR2 for connecting 2 in parallel with the first resistor R1. Each of the constituent elements has the characteristic switching circuit 20 which is the second when the stabilized power supply is turned on and the reset release signal is output from the signal generation circuit 30.
Resistor R2 is connected in parallel with the first resistor R1.

Next, the operation of this embodiment will be described.

(At power-on) When the switch SW is turned on and the stabilizing circuit 10 is driven, VCE of the transistor TR1 gradually decreases with the charging of the capacitor C, and the IC rapidly rises and gradually stabilizes (see FIG. 3). . Here, since the rush current is small in the IC due to the first resistor R1 having a large resistance value, the transistor TR1 can be fully protected. Further, since its rising characteristic is relatively slow depending on the characteristic of the secondary power supply circuit 40, the reset release signal from the signal generating circuit 30 is generated by the secondary power supply as shown by the solid line in FIG. It is output after surely starting up.

(During steady operation) When the secondary power supply, which is the output of the secondary power supply circuit 40, reaches the specified voltage, the characteristic switching circuit 20 causes the second resistance value R2 having a small resistance value to be parallel to the first resistance R1. Connecting. That is, the parallel connection reduces the overall resistance value. Since the collector resistance for the negative feedback of the stabilizing circuit 10 is switched to a small one, its response is remarkably improved. The value of the second resistor R is determined in consideration of the load characteristics connected to the stabilized power supply 3 and the secondary power supply. Therefore, even if there is a sudden load change during steady operation, the stabilizing circuit 10 can follow so that a sufficient stabilizing power supply can be supplied.

Therefore, according to this embodiment, the resistance value of the first resistor R1 can limit the rush current when the power is turned on, and the reset release signal is generated from the signal generator after the secondary power supply circuit 40 is stabilized. And the second resistor R2 that can be connected in parallel with the first resistor R1 and the second resistor R2 is connected to the first resistor R1 on condition that the reset release signal is output from the signal generator.
Since the characteristic switching circuit 20 for parallel connection to the circuit is provided, the current rush at power-on can be limited and the reset release signal can be issued in a timely manner. It is possible to supply a reliable stabilized power supply that can sufficiently follow a sudden load change during operation.

Further, the characteristic of the stabilizing circuit 10 is that it is configured by connecting the second resistor R2 in parallel to the first resistor R1,
It is possible to easily select the optimum tracking characteristic for the connected load characteristic.

In the above embodiments, the stabilizing circuit 10 is activated by operating the switch SW, but this switch SW may be omitted. Also, the second resistor R2
The resistance value of 1 does not have to be smaller than the value of the first resistance value R1.

[Effects of the Invention] As is clear from the above description, the resistance value of the first resistor is
It is possible to limit the rush current when the power is turned on, and select so that the reset release signal is generated from the signal generator after the secondary power supply circuit stabilizes, and the second resistor that can be connected in parallel to the first resistor and the signal generation. Since the configuration is provided with a characteristic switching circuit for connecting the second resistor in parallel with the first resistor on condition that the reset release signal is output from the device, the current rush at power-on is limited to timely. It is possible to generate a reset release signal at the same time, and to have an excellent effect that a stabilized power supply can be generated which is sufficiently secured even against a sudden load change during steady operation.

[Brief description of drawings]

FIG. 1 is an overall circuit diagram showing an embodiment of a DC power supply switching circuit according to the present invention, FIGS. 2, 3, and 4 are conventional DC power supply switching circuits, and FIG. 2 is an overall circuit diagram, FIG. 3 is a diagram showing voltage and current when the power is turned on, and FIG. 4 is a timing chart between signals. 1 ... DC input power supply, 3 ... Stabilized power supply, 10 ... Stabilization circuit, 20 ... Characteristic switching circuit, 30 ... Signal generation circuit, 40 ... Secondary power supply circuit, R1 ... First resistor , R2 …… Second resistance.

Claims (2)

[Claims] 1. A stabilizing circuit of a transistor control system formed including a first resistor for supplying a base current connected to a DC input power supply, and a stabilizing power supply voltage generated by this stabilizing circuit is a reference voltage. In the DC power source switching circuit, which includes a signal generator that issues a reset release signal when it becomes equal to, and a switching type secondary power supply circuit that generates a secondary power supply from a stabilized power supply, a resistance of the first resistor. The value is selected so that the rush current at power-on can be limited and the reset release signal is generated from the signal generator after the secondary power supply circuit is stabilized, and the second resistance can be connected in parallel to the first resistor. And a characteristic switching circuit for connecting the second resistor in parallel with the first resistor on condition that a reset release signal is output from the signal generator. Source close circuit. 2. The direct current switching circuit according to claim 1, wherein the resistance value of the second resistor is smaller than the resistance value of the first resistor.