TWI382660B - Soft-start circuit - Google Patents

Description

Soft start circuit

This invention relates to a soft start circuit and, more particularly, to a soft start circuit for generating a successively varying output voltage having a positive or negative value.

When the electronic device is started, in order to avoid the influence of the surge current caused by the power source on the electronic device, the time for starting the power of the electronic device is often extended in design. If there is no soft start mechanism to extend the start-up time, a large amount of surge current will easily cause damage to the connection interface or internal components of the electronic device. Therefore, by controlling the ramp-up rate of the supply voltage, the effect of the soft start mechanism can be achieved to protect the electronic device. The soft start circuit is a circuit for providing the above soft start mechanism. However, in the rising process, controlling the accuracy and rising rate of each voltage level determines the sound of the soft start circuit. A conventional soft-start circuit uses a plurality of resistors to achieve a soft-starting mechanism in which the voltage is stepped up. Such a method is less than ideal when the resistance is susceptible to temperature, so the accuracy will not be accurate enough.

Therefore, how to design a soft-start circuit can maintain high accuracy when generating a continuously varying output voltage with positive or negative values, which is an urgent problem to be solved in the industry.

Accordingly, one aspect of the present invention is to provide a soft start circuit comprising: an input stage, a pump stage, a second resistor, and a capacitor. The input stage is configured to receive an input voltage to provide a reference current at the first terminal, wherein the input stage includes a first resistor, and the reference current is a ratio of the input voltage to the first resistance; the pump stage includes N parallels and each includes a current a current branch of the source and the switch, the current source is connected to the first end point, and the switch is connected to the second end point, so that the current is transmitted from the current source to the second end point when the switch operates in the connected state, and the switch operates to be disconnected In the state, the current is stopped from the current source, wherein the N switches have 2 ^N sequential connection modes to generate a successively varying output current at the second end to generate 2 ^N current levels; and a second resistor And the capacitor is connected in parallel between the second end point and the ground potential, the output current is received, and the output voltage with successive changes is generated at the second end point to generate 2 ^N voltage levels according to the product of the output current and the second resistance.

The advantage of applying the present invention is that the above-mentioned purpose is easily achieved by sequentially and stably raising the output voltage by a soft start circuit having switches of different connection modes.

Please refer to FIG. 1 , which is a schematic diagram of a soft start circuit 1 according to a first embodiment of the present invention. The soft start circuit 1 includes an input stage 10, a pump stage 12, a second resistor 14, and a capacitor 16. The input stage 10 is configured to receive the input voltage Vi to provide a reference current 101 at the first terminal 11 . Wherein a first input stage 10 comprises a resistor 100 to enabling 101 the current value of reference current input voltage Vi and the ratio of the first resistor R _1. That is, if the current value of the reference current 101 is Ir, the relationship between the reference current 101, the input voltage Vi, and the first resistor R ₁ can be expressed as Ir=Vi/R ₁ . In the present embodiment, the input stage 10 further includes an operational amplifier 102 and an N-type MOS transistor 104. The operational amplifier 102 substantially receives the input voltage Vi to control the N-type MOS transistor 104, thereby generating a reference current 101. In other embodiments, other circuits may be employed to generate the reference current 101.

The pump stage 12 of the present embodiment includes seven current branches 120 that are connected in parallel and each including a current source 120a and a switch 120b. Current source 120a in each current branch 120 is coupled to a first terminal 11 and switch 120b is coupled to a second terminal 13. Current branch 120 transfers current from current source 120a to second terminal 13 when switch 120b is operating in the connected state. When the switch 120b is operating in the off state, the current branch 120 stops transmitting current from the current source 120a. The seven current branches 120 have a total of seven switches 120b, so the seven switches 120b have ²⁷ connection modes. After the ²⁷ connection modes are sequentially executed, an output current 121 having a successive change is generated at the second terminal 13 to generate an output current 121 of ²⁷ , that is, 128 current levels. If the seven switches 120b are operating in a connected mode in which all of the seven switches 120b are in the off state, the pump stage 12 will not generate any output current 121. If, among the seven switches 120b, only the switch 120b corresponding to the current source 120a having the smallest current value is in the connected state, the pump stage 12 will generate the minimum output current 121. If the seven switches 120b are operating in a connected mode in which all of the seven switches 120b are in the connected state, the pump stage 12 will produce a maximum output current 121. In one embodiment, when the current value of the reference current 101 is Ir, the current values of the current sources 120a of the seven current branches 120 are Ir/2 ¹ , Ir/2 ² , Ir/2 ³ , ... , Ir/2 ⁷ . Then, the maximum value of the output current 121 is (1/2 ¹ + 1/2 ² + 1/2 ³ + ... + 1/2 ⁷ ) * Ir, which is a value equal to the reference current 101. It should be noted that in other embodiments, the ratio between the current branches 120 may vary depending on the needs. Therefore, as described above, when the connection mode sequentially switches from the first connection mode in which no current is generated to the last connection mode in which the maximum output current 121 is generated, it will be successively changed at the second end point 13. Output current 121. Moreover, the rate of increase of the output current 121 can be accurately adjusted by the switching speed between the connection modes. In this embodiment, the successive changes are a positive value, and the output current 121 is sequentially increased in the positive direction. However, in other embodiments, if the generated output current 121 is a negative value, the successive changes are performed. It is a negative value, and the output current 121 is successively increased in the negative direction. The connection mode will switch from the first connection mode in which no current is generated to the last connection mode in which the most negative output current 121 is generated, and generate an output current having a negative direction successively change at the second terminal 13 121.

The second resistor 14 and the capacitor 16 are connected in parallel between the second terminal 13 and the ground potential GND, and receive the output current 121 to generate a successively varying output voltage Vo at the second terminal 13 to be based on the output current 121 and the second The product of resistors 14 produces ²⁷ voltage levels. If the value of the output voltage is Vo, the resistance value of the second resistor 14 is R _{2 ,} and the value of the output current is Io, the relationship between the output voltage, the second resistance, and the output current is Vo=R ₂ ^* Io. When the output current 121 reaches the maximum value as described above, the output voltage is Vo=R ₂ ^* Io=R ₂ ^* (1/2 ¹ +1/2 ² +1/2 ³ +...+1/2 ^{7 *} Ir = R ₂ ^* (1/2 ¹ + 1/2 ² + 1/2 ³ + ... + 1/2 ⁷ ) ^* Vi / R ₁ . It should be noted that 1/2 ¹ +1/2 ² +1/2 ³ +...+1/2 ⁷ is a value close to 1, so the above relationship can be simplified to Vo=Vi ^* R ₂ /R ₁ . When the first and second resistors 100 and 14 have the same resistance, the maximum value of the output voltage Vo is an approximation of the input voltage Vi. In other embodiments, when the second resistor 14 has a resistance greater than the resistance of the first resistor 100, the maximum value of the generated output voltage Vo is greater than the input voltage Vi. Therefore, the output voltage Vo can be accurately adjusted through the design of the resistance ratios of the first and second resistors 100 and 14. The output voltage Vo and the output current 121 generated by switching between different connection modes provide an accurate soft start mechanism, so that an external circuit 18 connected to the second terminal 13 for receiving the output voltage Vo is protected from suffering Damage to the surge current. It should be noted that in the embodiment of the negative output current described above, the corresponding output voltage is also a negative value, so that an output voltage Vo having a negative successive change will be generated. The connection mode will sequentially switch from the first connection mode in which no voltage is generated to the last connection mode in which the most negative output voltage Vo is generated, and generate an output voltage Vo having a negative direction successively change at the second terminal 13 .

The soft start circuit in this embodiment switches to the last connection mode that generates the maximum output current by the first connection mode from which no current is generated, and generates the output current and the output voltage with successive changes, and reaches the soft state. The effect of the startup mechanism. The current sources contained in each current branch of the pump stage are much more stable than those susceptible to temperature. Therefore, the soft start circuit in this embodiment provides a soft start mechanism with a more accurate voltage, current level, and more accurate voltage and current rise rates.

Please refer to FIG. 2, which is a schematic diagram of the soft start circuit 2 in the second embodiment of the present invention. The soft start circuit 2 in this embodiment is similar to the soft start circuit in the first embodiment. However, the soft start circuit 2 further includes a lower limit voltage module 20 substantially connected between the second resistor 14 and the ground potential GND. The lower limit voltage module 20 is configured to transmit the lower limit voltage Vb to the second end point 13 such that the voltage of the second end point 13 is the sum of the output voltage Vo and the lower limit voltage Vb. It should be noted that the lower limit voltage module 20 in this embodiment includes a resistor 200, an operational amplifier 202, and an N-type MOS transistor 204. The operational amplifier 202 receives the lower limit voltage Vb to control the N-type MOS transistor 204 to deliver the lower limit voltage Vb to the second terminal 13. In other embodiments, other types of circuitry may be employed to achieve the effect of delivering a lower voltage limit. The lower limit voltage Vb provides an additional voltage that causes the external circuit 18 to receive an output voltage greater than the input voltage Vo when the output voltage reaches a maximum value. The voltage value of the lower limit voltage Vb can be adjusted in different embodiments depending on the situation.

Please refer to FIG. 3, which is a schematic diagram of the soft start circuit 3 in the third embodiment of the present invention. The soft start circuit 3 in this embodiment is similar to the soft start circuit in the first embodiment. However, the soft start circuit 3 further includes a direct output module 30, wherein the external circuit 18 is connected to the direct output module 30. The direct output module 30 receives the output voltage Vo from the second terminal 13 . When the switch 120b of the pump stage 12 is in the connected state and the output voltage Vo reaches the maximum value, the direct output module 30 directly inputs the input voltage Vi. Transfer to external circuit 18. It should be noted that the output voltage Vo in the first embodiment is only an approximation of the input voltage Vi. Therefore, if the external circuit 18 requires an accurate voltage level, the direct output module 30 can be after the soft start process. An accurate voltage level is provided to the external circuit 18. Furthermore, the present embodiment can also be applied to the second embodiment, so that when the switch 120b of the pump stage 12 is in the connected state and the output voltage Vo reaches the maximum value, the direct output module 30 directly inputs the input voltage. The sum of Vi and the lower limit voltage Vb is transferred to the external circuit 18.

The soft start circuit of the present invention can generate a successively varying output voltage by a current source and a switch to achieve a soft start mechanism with high accuracy and high stability. Furthermore, the maximum value of the output voltage can be adjusted by the ratio between the first and second resistors or the design of the lower voltage. Moreover, the design of the direct output module can maintain the accuracy of the maximum output voltage.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and modified without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

1. . . Soft start circuit

10. . . Input stage

100. . . First resistance

101. . . Reference current

102. . . Operational amplifier

104. . . N-type gold oxide semi-transistor

11. . . First endpoint

12. . . Pump stage

120. . . Current branch

120a. . . Battery

120b. . . switch

121. . . Output current

13. . . Second endpoint

14. . . Second resistance

16. . . capacitance

18. . . External circuit

20. . . Lower limit voltage module

200. . . resistance

202. . . Operational amplifier

204. . . N-type gold oxide semi-transistor

30. . . Direct output module

The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood.

1 is a schematic diagram of a soft start circuit of a first embodiment of the present invention;

2 is a schematic diagram of a soft start circuit of a second embodiment of the present invention;

Figure 3 is a schematic diagram of a soft start circuit of a third embodiment of the present invention.

1. . . Soft start circuit

10. . . Input stage

100. . . First resistance

101. . . Reference current

102. . . Operational amplifier

104. . . N-type gold oxide semi-transistor

11. . . First endpoint

12. . . Pump stage

120. . . Current branch

120a. . . Battery

120b. . . switch

121. . . Output current

13. . . Second endpoint

14. . . Second resistance

16. . . capacitance

18. . . External circuit

Claims (10)

A soft-start circuit includes: an input stage for receiving an input voltage to provide a reference current at a first terminal, wherein the input stage includes a first resistor to cause the reference current a ratio of the input voltage to the first resistor; a pump stage comprising N parallel current branches each including a current source and a switch, the current source being coupled to the first terminal, The switch is coupled to a second terminal to transmit a current from the current source to the second terminal when the switch operates in a connected state, and to stop transmitting from the current source when the switch operates in an open state The current, wherein the N switches have 2 ^N sequential connection modes, so that the second terminal generates one output current with one successive change to generate 2 ^N current levels; a second resistance and a a capacitor connected in parallel between the second terminal and a ground potential, receiving the output current, generating an output voltage having a successive change at the second end, according to the output current and the second resistor product generating 2 ^N a voltage level; and a direct output module, wherein an external circuit is connected to the direct output module, the direct output module receives the output voltage from the second terminal, and when the switches are all operating in the connection state And the output voltage reaches a maximum value, and the direct output module directly transmits the input voltage to the external circuit. The soft start circuit of claim 1, wherein the current value of the reference current is Ir, and the current values of the current sources of the N current branches are Ir/2 ¹ , Ir/2 ² , Ir/2 ^{3 respectively.} ,..., Ir/2 ^N . The soft start circuit of claim 2, wherein the first and second resistors have the same one of resistance values, and the maximum value of the output voltage is approximate to the input voltage. The soft start circuit of claim 3, wherein an external circuit is connected to the second terminal for receiving the output voltage. The soft start circuit of claim 2, wherein the second resistor has a resistance greater than a resistance of the first resistor, and a maximum value of the output voltage is greater than the input voltage. The soft start circuit of claim 1, further comprising a lower bound voltage module substantially connected between the second resistor and the ground potential, wherein the lower voltage module is configured to transmit a lower limit voltage to the The second end point is such that the voltage of the second end point is the sum of the output voltage and the lower limit voltage. The soft start circuit of claim 6, wherein an external circuit is connected to the second terminal for receiving the sum of the output voltage and the lower limit voltage. The soft start circuit as claimed in claim 6 further includes a direct input a module, wherein an external circuit is connected to the direct output module, the direct output module receives the output voltage from the second terminal, and the output voltage is reached when the switches are all in the connected state A maximum value, the direct output module directly transmits the sum of the input voltage and the lower limit voltage to the external circuit. The soft start circuit of claim 1, wherein the successive change is a positive value. The soft start circuit of claim 1, wherein the successive change is a negative value.