JPS625687Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an inrush current control circuit used in a capacitor input type stabilized power supply circuit.

Conventionally, an inrush current control circuit connects a current limiting resistor and a control element such as a thyristor or transistor in parallel, and when the charging voltage of the capacitor rises to a certain extent, these control elements become conductive, and the capacitor is connected through a low impedance. There are many circuits in use that are configured to charge the battery. However, in such a circuit, the inrush current that flows when the power is turned on is suppressed to a small level by the action of the current limiting resistor, but when the control element becomes conductive, the capacitor is charged through a low impedance, so a relatively large secondary current is generated. Inrush current may flow. Moreover, this secondary inrush current is often larger than the inrush current when the power is turned on.

FIG. 1 is a configuration diagram showing an example of a conventional inrush current control circuit. In the figure, IN is an input terminal for the power supply voltage Vcc, R ₁ and R ₂ are resistors, Dz is a Zener diodes, Tr is a transistor, A ₁ is a comparator, and C is an input capacitor of the power supply circuit. Resistor R ₁ is an inrush current limiting resistor, and a transistor is connected in parallel with it.
Tr is connected. Comparator _A1 compares the constant voltage Vz generated by the zener diode Dz with the terminal voltage v _c at the terminal of the capacitor C, and calculates the terminal voltage v _c
When the voltage reaches a constant voltage Vz, the transistor Tr becomes conductive.

The operation of the inrush current control circuit configured as above will be explained using the waveform diagram of FIG. 2. In FIG. 2, a indicates the power supply voltage Vcc, b indicates the inflow current i _c of the capacitor C, and c indicates the terminal voltage v _c . Now, if power supply voltage Vcc is applied at time t ₀ , current i _c flows through capacitor C via resistor R ₁ . At this time, since the initial value of the terminal voltage v _c of the capacitor C is zero, the transistor Tr is kept in an off state, and the peak value i _cp1 of the flowing current i _c is determined by the value of the resistor R ₁ . The current i _c and the terminal voltage v _c change according to a logarithmic function as shown in the figure, and when the terminal voltage v _c reaches a constant voltage Vz at time t ₁ , the transistor Tr is turned on, and the current i _c mainly flows through the transistor Tr. will flow through. When the transistor Tr is turned on, the voltage drop at this portion becomes very small, so the capacitor C is charged to approximately the power supply voltage Vcc. However, when the transistor Tr is turned on, the resistor _R1 , which has a relatively large value, is approximately short-circuited by the transistor Tr, so that an inrush current i _cp2 flows through the capacitor C again, and this current returns to the initial value i _cp1 This is not a desirable phenomenon as it often becomes larger.

Here, in order to limit the magnitude of the secondary inrush current i _cp2 , the value of the terminal voltage v _c when turning on the transistor Tr may be set higher;
In this way, the transistor Tr will be connected from power on.
The time T ₁ until the switch is turned on, that is, the input time becomes longer. In this way, the magnitude of the inrush current and secondary inrush current when the power is turned on, and the power-on time are contradictory elements, and generally in a power supply circuit, the magnitude of the rush current and the power-on time are the power-on characteristics of the power supply circuit. be evaluated.

The object of the present invention is to eliminate the drawbacks of the conventional device as described above and to realize a rush current control circuit with a simple configuration that can provide a power supply circuit with excellent power-on characteristics.

The inrush current control circuit of the present invention charges the capacitor with a constant current by operating the transistor, which was conventionally connected in parallel with the inrush current limiting resistor and operated as a switch, as an analog continuously variable element. This realizes a power supply circuit with no secondary inrush current and short turn-on time.

FIG. 3 is a configuration diagram showing an embodiment of the inrush current control circuit of the present invention. In the figure, parts similar to those in FIG. 1 are designated by the same reference numerals. R ₃ and R ₄ are resistors, C ₁ is a capacitor, and A ₂ is a differential amplifier.
The output of the differential amplifier A ₂ is applied to the base of the transistor Tr, and the output voltage v _A of the first-order lag circuit consisting of the resistor R ₂ and _{the capacitor C 1 and} the resistor R ₃ are applied to the input of the differential amplifier A 2. , _R4 , and the terminal voltage _vc of the capacitor C is applied thereto.

The operation of the inrush current control circuit of the present invention configured as described above will be explained using the waveform diagram of FIG. 4.
In FIG. 4, a represents the power supply voltage Vcc, b represents the output voltage v _A of the first-order lag circuit, c represents the inflow current i _c of the capacitor C, d represents the terminal voltage v _c , and e represents the relationship between the above voltages. . Now, at time t ₀ , the power supply voltage
When Vcc is applied, the initial value of the output voltage v _A of the first-order lag circuit at this time is zero, and the output voltage v _A rises as shown in FIG. 4b. Here, the differential amplifier A ₂ makes the transistor Tr conductive and controls the magnitude of the current i _c so that v _A =R ₄ /R ₃ +R ₄ v _c (1). Therefore, the terminal voltage v _c increases with the relationship v _c = 1/βv _A (2), as shown in Figure 4 d and e, if the voltage dividing ratio of resistors R ₃ and R ₄ is β. , reaches the power supply voltage Vcc.

This situation can be expressed as follows. first,
The output voltage v _A of the first-order lag circuit is Also, the terminal voltage v _c is The current i _c flowing through the capacitor C is becomes.

Here, the terminal voltage v _c rises 1/β times faster than v _A and reaches the power supply voltage Vcc, so if the voltage division ratio β is β << 1, the terminal voltage v _c becomes equal to the power supply voltage Vcc. The time T ₂ it takes for the transistor Tr to become saturated is very small compared to the time constant R ₂ C ₁ of the output voltage v _A , and the above equation is in the range O≦t≦T ₂ ≪R ₂ C ₁ This can be considered. For this reason, Using the relational expressions (4) and (5), v _c = 1/βVcct/R ₂ C ₁ = Vcct/βR ₂ C ₁ (6) i _c = C/βR ₂ C ₁ Vcc ( 7) Therefore, the rise in the terminal voltage v _c can be regarded as almost a straight line, as shown in Figure 4d. Further, from this, the capacitor C is charged with a substantially constant current as shown in FIG. 4c. As shown in FIGS. 4c and 4d, when the terminal voltage v _c reaches the power supply voltage Vcc at time t ₂ , the current i _c stops flowing. Then the transistor Tr
As the output voltage of the first-order lag circuit increases, it becomes saturated and turns on like a switch. Also,
The input time T ₂ at this time is T ₂ =βR ₂ C ₁ (8). In this way, in the inrush current control circuit of the present invention, since the capacitor C is charged with a constant current,
The turn-on time is short and no secondary inrush current is generated.

In addition, in the circuit of FIG. 3, the resistors R ₃ and R ₄
The voltage division ratio β of is selected to be small, the transistor Tr is controlled using a minute section that can be regarded as a straight line of the output voltage v _A of the first-order lag circuit, and the capacitor C is charged with a constant current. ,
By replacing resistor _R3 with a capacitor and matching the time constant with the first-order delay circuit, capacitor C can be charged with a completely constant current.

FIG. 5 is a block diagram showing another embodiment of the inrush current control circuit of the present invention. The circuit shown in the figure is a differential amplifier in the inrush current control circuit of FIG.
A ₂ is realized by one transistor Tr ₁ .

As explained above, in the inrush current control circuit of the present invention, a current control transistor is inserted in series with the input capacitor, and a first-order lag circuit is used to generate a reference voltage that increases linearly with time. Since the conduction of the transistor is controlled so that the terminal voltage increases in accordance with this reference voltage, the capacitor can be charged with a constant current, there is no secondary inrush current, and the charging time is short. An inrush current control circuit that can provide a high power supply circuit can be realized with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a conventional inrush current control circuit, and FIG. 2 is a waveform diagram illustrating its operation. 3 and 5 are block diagrams showing embodiments of the inrush current control circuit of the present invention, and FIG. 4 is a waveform diagram illustrating its operation. A ₁ ... Comparator, A ₂ ... Differential amplifier.

Claims (1)

[Scope of utility model registration request] In an inrush current control circuit inserted on the input side of a capacitor input type stabilized power supply circuit, a transistor inserted before the input capacitor of the stabilized power supply circuit controls the magnitude of the charging current of the input capacitor, and a transistor that controls the magnitude of the charging current of the input capacitor; A first-order lag circuit generates a reference voltage that increases with time; a voltage divider circuit divides the terminal voltage of the input capacitor; and the output of this voltage divider circuit is compared with the reference voltage to calculate the magnitude of the output. and a differential amplifier that controls conduction of the transistor so as to follow the magnitude of a reference voltage, and controls to bring the transistor into a saturated state after the charging voltage of the input capacitor becomes equal to the power supply voltage. Features an inrush current control circuit.