JPH077312B2 - DC power switch circuit - Google Patents

Description

The present invention relates to a DC power supply switching circuit formed including a transistor control type stabilizing circuit.

[Prior Art] A transistor control type stabilization circuit formed including a first resistor for supplying a base current connected to a DC input power supply, and a stabilization power supply voltage generated by this stabilization 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 DC limiting circuit 20 to generate a stabilized power supply 3 and is also connected to the stabilized power supply 3.
30 and a secondary power supply circuit 40.

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

The current limiting circuit 20 controls the rush power supply when the power is turned on, and includes resistors R3, R5, R6 and transistors TR3, TR4, and detects the load current (stabilized power supply current) to 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
When Vret is reached, a reset release signal is output. 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, if the switch SW is turned on to the DC input power source 1 to supply power to the equipment, current is supplied to the base via the resistor R1 and the collector current IC flows. VCE and I at power up
C is shown in FIG.

That is, since the emitter voltage of the transistor TR1 is almost the same as the low side voltage of the DC input power source 1, VCE becomes the DC input power source voltage, which gradually decreases as the capacitor C is charged, and is determined by the Zener diode ZD. It becomes constant according to the voltage difference from the voltage. On the other hand, the IC rapidly increases, is cut by the current value limited by the resistor R3 of the current limiting circuit 20, and decreases as the capacitor C is charged.

In this way, the stabilized power supply 3 starts up while limiting the rush power supply when the power is turned on. And stabilized power supply voltage V1
When N becomes equal to the reference voltage Vref, the signal generation circuit 3
The reset release signal (high level) is output from 0.
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, so that it is proportional to the rising speed of the stabilized power supply voltage V1N. It doesn't mean that it will 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.

In view of the above circumstances, an object of the present invention is to reliably limit the current rush at power-on, issue a reset release signal in a timely manner, and sufficiently follow a sudden load change during steady operation. Another object of the present invention is to provide a DC power supply switching circuit capable of generating a reliable stabilized power supply.

[Means for Solving the Problem] The present invention focuses on the configuration of a conventional current limiting circuit, and switches the characteristics of the stabilizing circuit between the time of power-on and the steady operation based on a configuration similar to this. Then, the above problem is solved.

That is, a transistor control type stabilization circuit formed including a first resistor for supplying a base current, which is connected to a DC input power supply, and a stabilization power supply voltage generated by this stabilization circuit are equal to a reference voltage. In a direct current power supply switching circuit including a signal generator that outputs a reset release signal when the power is turned on, and a switching type secondary power supply circuit that generates a secondary power supply from a stabilized power supply, the first resistance can be connected in parallel. A second resistance, a current detection circuit for detecting the current of the stabilized power supply, and the second resistance in parallel with the first resistance provided that the detection signal of the current detection circuit has reached a predetermined value. A characteristic switching circuit for connection is provided, and the resistance value of the first resistor can cooperate with the resistor of the current detection circuit to limit the rush current when the power is turned on and after the secondary power supply circuit stabilizes, Signal The above object is achieved by a configuration selected so that the reset release signal is generated from the genital organ.

[Operation] When the power is turned on, the rising characteristic of the stabilizing circuit is determined by the first resistance having a large resistance value and the resistance of the current detecting circuit to limit the rush current, and at the time of steady operation, the current detecting circuit and the characteristic switching circuit. The second resistor is connected in parallel to the first resistor in cooperation with the above 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 DC power supply switching circuit is composed of the stabilization circuit 10, the current detection circuit 20-1, the characteristic switching circuit 20-2, the signal generation circuit 30, and the secondary power supply circuit 40.

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, 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 path of the DC input power source 1, and its resistance value is used to protect the transistor TR1 in cooperation with the resistor R3 described later. The value is selected so that the rush current at the time of power-on can be sufficiently limited and the reset release signal is generated from the signal generation circuit 30 after the secondary power supply of the secondary power supply circuit 40 is stabilized. Therefore, the conventional current limiting circuit (20) 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 stabilization circuit 10 which is a technical feature of the present invention is performed by the second resistor R2, the current detection circuit 20-1 and the characteristic switching circuit 20-2. 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 current detection circuit 20-1 is composed of a resistor R3, a transistor TR3, and voltage dividing resistors R5, R6 connected to the high-potential side electric circuit of the stabilized power supply 3. The characteristic switching circuit 20-2 is a voltage dividing resistor.
A transistor TR4 having a base connected between R5 and R6, a voltage dividing resistor R7, R8 connected in series between the collector of the transistor TR4 and the switch SW, and a base connected between the voltage dividing resistors R7 and R8 It comprises a switching transistor TR2 for connecting the second resistor R2 in parallel with the first resistor R1. Each component is selected such that the characteristic switching circuit 20-2 connects the second resistor R2 in parallel with the first resistor R1 after the stabilized power supply rises and the secondary power supply voltage reaches the specified voltage. There is.

Next, the operation will be described.

(At power-on) If the switch SW is turned on and the stabilizing circuit 10 is driven, VCE of the transistor TR1 gradually decreases as the capacitor C charges, and the IC rapidly rises and gradually stabilizes (see FIG. 3). ). Since the IC has a small rush current due to the first resistor R1 and the resistor R3 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 sure to be the secondary power supply as shown by the solid line in FIG. It is output after rising to.

(During steady operation) When the stabilized power supply 3 enters steady operation at the specified voltage V1N,
By the action of the current detection circuit 20-1 and the characteristic switching circuit 20-2,
A second resistance value R2 having a small resistance value is connected in parallel with the first resistance value R1. 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 2 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, a stabilizing circuit can be provided so that sufficient stabilizing power can be supplied.
10 can follow.

Therefore, according to this embodiment, the second resistor R2 that can be connected in parallel with the first resistor R1, the current detection circuit 20-1 for detecting the current of the stabilized power supply 3, and the current detection circuit 20-1. A characteristic switching circuit for connecting the second resistor 2 in parallel with the first resistor R1 on condition that the detection signal of 20-1 has reached a predetermined value.
-2 is provided, and the resistance value of the first resistor R1 is set to the current detection circuit 20.
-It is configured so that the rush current at power-on can be limited in cooperation with the resistance of -1 and the secondary power supply circuit 40 is selected so that the reset release signal is generated from the signal generator after the power supply is stabilized. It is possible to supply a reliable stabilized power supply that can control a rush at the time of turning on and can issue a reset release signal in a timely manner and can sufficiently follow a rapid load change during steady 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
May have a resistance value smaller than that of the first resistor R1.

[Effects of the Invention] As is clear from the above description, the second resistor connectable in parallel with the first resistor, the current detection circuit for detecting the current of the stabilized power supply, and the detection signal of this current detection circuit And a characteristic switching circuit for connecting the second resistor in parallel with the first resistor on condition that the resistance value of the first resistor is in parallel with the resistance of the current detection circuit. 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 has stabilized. Therefore, the power-rush at power-on is limited and reset is performed in a timely manner. It has the excellent effect that it can generate a release signal and can generate a reliable and reliable stabilized power supply that can sufficiently follow 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, 20-1 ... Current detection circuit, 20-2 ... Characteristic switching circuit, 30 ... Signal generation circuit, 40 ... 2 Next power supply circuit, R1 ... first resistance, 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 supply 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, The connectable second resistor, a current detection circuit for detecting the current of the stabilized power supply, and the second resistor with the first resistance provided that the detection signal of the current detection circuit has reached a predetermined value. A characteristic switching circuit for parallel connection to the resistor is provided, and the resistance value of the first resistor can cooperate with the resistor of the current detection circuit to limit the rush current at power-on and the secondary power supply circuit can Signal after stabilization A DC power supply switching circuit characterized in that a reset release signal is generated from a generator. 2. A DC power supply switching circuit according to claim 1, wherein the second resistance value is smaller than the resistance value of the first resistance.