A soft-start circuit for a switched-capacitor power converter and a soft-start operation method based thereon.

Abstract

This invention discloses a soft-start circuit and its operation method for a switched-capacitor power converter. The soft-start circuit includes a first and second switching transistor disposed between the input terminal and the ground terminal of the switched-capacitor power converter, a normally-on switching transistor disposed between the input terminal and the ground terminal of the switched-capacitor power converter, a diode, a resistor, and an output capacitor. The cathode of the diode is located near the normally-on switching transistor. One end of the output inductor is connected between the first and second switching transistors via a wire, and the other end is connected between the resistor and the output capacitor. A bootstrap capacitor, a bootstrap power supply diode, and a drive power supply capacitor are connected via wires. The other end of the bootstrap capacitor is connected between the normally-on switching transistor and the diode via a wire. The cathode of the bootstrap power supply diode is located near the normally-on switching transistor. The other end of the drive power supply capacitor is connected to the source of the highest-voltage-side switching transistor of the switched-capacitor power converter via a wire.

Description

Technical Field

[0001] This invention relates to the field of power conversion technology, specifically to a soft-start or hot-swap circuit for a switched capacitor power converter. Background Technology

[0002] Switched-capacitor power converters offer advantages such as fewer or no magnetic components, small size, high power density, high efficiency, low EMI, and low noise. However, due to the large number of capacitors in a switched-capacitor power converter, a near-AC short circuit occurs across the capacitors during startup, generating a large inrush current that significantly increases the risk of capacitor damage. Since switched-capacitor power converters also use a large number of low-voltage switching transistors, the inrush current during startup also increases the risk of transistor damage. During startup, the switching transistors operate in a switching state, and the large turn-off current can induce a large inrush voltage on the low-voltage switching transistors, easily leading to overvoltage breakdown and damage. The same problem exists during hot-swapping of the circuit, causing damage to the switched-capacitor power converter. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a soft-start circuit that is simple in structure, small in size and low in cost, which can be applied to switched capacitor power converters to reduce the voltage / current stress of switched capacitor power converters at the moment of startup and improve the reliability of the circuit.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] The soft-start circuit structure of the switched capacitor power converter includes a first switch Q1 and a second switch Q2 connected by a wire between the input terminal and the ground terminal of the switched capacitor power converter, a normally-on switch Q3 connected by a wire between the input terminal and the ground terminal of the switched capacitor power converter, a diode D1, a resistor R1, and an output capacitor Co. The cathode of the diode D1 is located on the side closer to the normally-on switch Q3. The output inductor Lo is connected at one end between the first switch Q1 and the second switch Q2 and at the other end between the resistor R1 and the output capacitor Co through a wire.

[0006] It also includes a bootstrap capacitor Cbst2, a bootstrap power supply diode D2, and a drive power supply capacitor Cbst1 connected in sequence by wires; the other end of the bootstrap capacitor Cbst2 is connected between the normally-on switching transistor Q3 and the diode D1 by wires; the negative terminal of the bootstrap power supply diode D2 is located on the side closer to the normally-on switching transistor Q3, and the other end of the drive power supply capacitor Cbst1 is connected to the source of the highest voltage side switching transistor of the switched capacitor power converter by wires.

[0007] As a preferred embodiment, the normally-on switch Q3 is a switch with low on-resistance.

[0008] The technical problem to be solved by the present invention is to provide a soft-start operation method for a switched capacitor power converter with a turns ratio of K under ideal conditions, including the soft-start circuit of the switched capacitor power converter as described above.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a soft-start operation method for a switched capacitor power converter with an ideal turns ratio of K, including the soft-start circuit of the switched capacitor power converter as described above, specifically as follows:

[0010] (1) From t0 to t1:

[0011] Starting at time t0, the power converter begins its slow-start process, increasing the duty cycle of the first switch Q1 from 0% and decreasing the duty cycle of the second switch Q2 from 100%. The conduction times of the first switch Q1 and the second switch Q2 are complementary. During the circuit's slow-start process, Vin' and Vout are continuously monitored to determine whether the rise of Vin' satisfies formula (A) or the rise of Vout satisfies formula (B).

[0012] Vin'>a*M*t*Vin-b(A)

[0013] Vout>K*(a*M*t*Vin-b)(B)

[0014] In the formula, the turns ratio is K, the duty cycle increase rate is M, the input voltage is Vin, and the time is t;

[0015] In the formula, the range of values ​​for coefficients a and b is:

[0016] 1≥a>0 (C)

[0017] V BR >b≥0 (D)

[0018] In the above formula, V BR The maximum allowable voltage stress of the high-voltage side switching transistor in a switched-capacitor power converter;

[0019] If formula (A) or formula (B) holds true, the duty cycle of the first switch Q1 increases to 100%, and the duty cycle of the second switch Q2 decreases to 0%, i.e., until time t1; during the process from t0 to t1, the voltage V across the output capacitor Co in the soft-start circuit... Co The voltage increases linearly from 0V to the power input voltage Vin.

[0020] If neither formula (A) nor formula (B) holds true, it is necessary to stop increasing the duty cycle D of the first switch Q1, or restore the duty cycle D of the first switch Q1 to 0%, restart the next round of the start-up process, and the time t starts increasing again from 0, thus achieving hiccup-style start-up; after hiccuping several times, the duty cycle D of the first switch Q1 reaches 100%, and the duty cycle of the second switch Q2 decreases to 0%, that is, at time t1;

[0021] If neither formula (A) nor formula (B) holds true, the soft-start circuit will enter a continuous hiccup mode, meaning the Vin' level will never approach Vin, causing the normally-on switch Q3 to fail to meet the closing condition: Vin - Vin' <V BR -Vin'*K; thus, the normally open switch Q3 cannot be closed, and the soft-start circuit achieves self-protection.

[0022] (2) t1 to t2:

[0023] At time t1, due to the effect of the current-limiting resistor R1, the output voltage Vout of the switched capacitor power converter is less than K times Vin. Vout continues to increase for a period of time until Vout is approximately equal to K times Vin.

[0024] If Vin' satisfies formula (A) or Vout satisfies formula (B), and the difference between Vin and Vin' does not exceed the voltage stress margin of the high-voltage side switching transistor of the switched capacitor power converter, that is:

[0025] Vin-Vin' <V BR -Vin'*K;

[0026] In the above formula, V BR K represents the maximum allowable voltage stress of the high-voltage side switching transistor in the switched capacitor power converter, and K is the turns ratio of the switched capacitor power converter under ideal conditions.

[0027] This moment is recorded as time t2. The normally open switch Q3 is closed, and the first switch Q1, diode D1, resistor R1, and output inductor Lo are bypassed. The slow start process ends, and the system enters the steady-state operation stage.

[0028] As a preferred embodiment, during the process from t0 to t1, when the duty cycle of the first switching transistor Q1 in the slow-start circuit increases to no more than 10%, the voltage Vout is checked to see if it is greater than 0V, which can determine whether the circuit is in a load short-circuit state. When the voltage Vout is 0V, and it is determined to be in a load short-circuit state, the slow-start circuit restarts, thereby achieving self-protection.

[0029] The beneficial effects of this invention are:

[0030] (1) The function of this soft-start circuit is to reduce the voltage V across the output capacitor Co in the soft-start circuit during the soft-start process. Co The voltage is increased to Vin at a certain slope. During startup, the duty cycle of the first switch Q1 in the soft-start circuit increases from 0% to 100%, therefore the voltage V across the output capacitor Co in the soft-start circuit increases. Co The voltage increases from 0V to Vin.

[0031] (2) The series resistor R1 and diode D1 form a current limiting and reverse current protection circuit. The resistor R1 serves to limit the current, preventing the switched capacitor converter from being suddenly short-circuited during startup or from generating excessive inrush current due to a short circuit before startup, which could burn out the soft-start circuit. In addition, when a large capacitive load is connected to the downstream of the switched capacitor converter, the resistor R1 can also provide current limiting protection.

[0032] The function of diode D1 is to prevent reverse current flow during the startup of the switched-capacitor converter. When a large capacitive load is connected to the downstream of the switched-capacitor converter, the soft-start circuit will adopt a hiccup-type startup method. During the hiccup-type startup process, the duty cycle of the first switch Q1 in the soft-start circuit increases from 0% to a certain value, and then starts increasing from 0% to a certain value again, repeating this cycle until the Vin' voltage approaches Vin, and then the normally closed switch Q3 closes.

[0033] (3) The normally-on switching transistor Q3, its bootstrap capacitor Cbst2, and its bootstrap diode D2. Q3 closes after the soft-start process, thus preventing excessive input current loss in the soft-start circuit during normal load operation of the switched-capacitor converter. Q3 is powered by the bootstrap capacitor Cbst2, whose energy is supplemented by the drive capacitor Cbst1 of the highest-voltage-side switching transistor of the switched-capacitor converter and the bootstrap diode D2. In each switching cycle of the switched-capacitor converter, the highest-voltage-side switching transistor closes, connecting the bootstrap capacitor Cbst2 in parallel with the drive capacitor Cbst1 through the bootstrap diode D2. The charge stored in the drive capacitor Cbst1 is released to the bootstrap capacitor Cbst2 through the bootstrap diode D2, i.e., the drive capacitor Cbst1 charges the bootstrap capacitor Cbst2. In addition, the normally-on switching transistor Q3 can also be powered by a fly-buck or fly-back power supply, but this would be less efficient in terms of size. By using the drive power supply capacitor of the high-voltage switching transistor of the switched capacitor converter, the bootstrap power supply capacitor Cbst2, and the bootstrap power supply diode D2 to power the normally-on switching transistor Q3, the number of components can be reduced, and the characteristics of small size and high power density of the switched capacitor converter can be brought into play. Attached Figure Description

[0034] Figure 1Block diagram of a switched capacitor power converter with soft-start circuit.

[0035] Figure 2 Example 1: Soft-start circuit and 1 / 2 switched capacitor power converter

[0036] Figure 3 Example 2: Soft-start circuit and 1 / 4 switched capacitor power converter

[0037] Figure 4 Voltage and current waveforms during the soft-start process of a 1 / 4 switched capacitor power converter. Detailed Implementation

[0038] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0039] like Figure 1 , 2 As shown, this is a switched capacitor power converter with an ideal turns ratio of 1 / 2, including a soft-start circuit for the switched capacitor power converter.

[0040] The soft-start circuit of the switched capacitor power converter includes a first switch Q1 and a second switch Q2 connected by a wire between the input terminal and the ground terminal of the switched capacitor power converter, a normally-on switch Q3 connected by a wire between the input terminal and the ground terminal of the switched capacitor power converter, a diode D1, a resistor R1, and an output capacitor Co. The normally-on switch Q3 is a switch with low on-resistance. The cathode of the diode D1 is located near the normally-on switch Q3. The output inductor Lo is connected at one end between the first switch Q1 and the second switch Q2 and at the other end between the resistor R1 and the output capacitor Co via a wire.

[0041] It also includes a bootstrap capacitor Cbst2, a bootstrap power supply diode D2, and a drive power supply capacitor Cbst1 connected in sequence by wires; the other end of the bootstrap capacitor Cbst2 is connected between the normally-on switch Q3 and the diode D1 by wires; the negative terminal of the bootstrap power supply diode D2 is located on the side closer to the normally-on switch Q3, and the other end of the drive power supply capacitor Cbst1 is connected to the source of the highest voltage side switch S4 of the switched capacitor power converter by wires.

[0042] The switching transistor Q2 can also be replaced by a diode, with the connection direction being the same as that of the body diode of Q2.

[0043] like Figure 3 As shown, this is a switched capacitor power converter with an ideal turns ratio of 1 / 4, including a soft-start circuit for the switched capacitor power converter.

[0044] A soft-start operation method for a switched capacitor power converter with an ideal turns ratio of K, including the soft-start circuit of the switched capacitor power converter as described above, is as follows:

[0045] (1) From t0 to t1:

[0046] Starting at time t0, the power converter begins the slow start process, causing the duty cycle of the first switch Q1 to increase from 0% and the duty cycle of the second switch Q2 to decrease from 100%. The conduction times of the first switch Q1 and the second switch Q2 are complementary.

[0047] In the soft-start circuit, when the duty cycle of the first switching transistor Q1 increases to no more than 10%, the voltage Vout is checked to see if it is greater than 0V, which can determine whether the circuit is in a load short-circuit state. When the voltage Vout is not greater than 0V, it is determined to be in a load short-circuit state. The soft-start circuit restarts at intervals to achieve self-protection.

[0048] When the Vout voltage is greater than 0V, the circuit soft start-up proceeds normally.

[0049] During the circuit soft start-up process, Vin' and Vout are continuously monitored to determine whether the rise of Vin' satisfies formula (A) or the rise of Vout satisfies formula (B):

[0050] Vin'>a*M*t*Vin-b(A)

[0051] Vout>K*(a*M*t*Vin-b)(B)

[0052] In the formula, the turns ratio is K, the duty cycle increase rate is M, the input voltage is Vin, and the time is t;

[0053] In the formula, the range of values ​​for coefficients a and b is:

[0054] 1≥a>0 (C)

[0055] V BR >b≥0 (D)

[0056] In the above formula, V BR The maximum allowable voltage stress of the high-voltage side switching transistor in a switched-capacitor power converter;

[0057] If formula (A) or formula (B) holds true, the duty cycle of the first switch Q1 increases to 100%, and the duty cycle of the second switch Q2 decreases to 0%, i.e., until time t1; during the process from t0 to t1, the voltage V across the output capacitor Co in the soft-start circuit... Co The voltage increases linearly from 0V to the power input voltage Vin.

[0058] If neither formula (A) nor formula (B) holds true, it is necessary to stop increasing the duty cycle D of the first switch Q1, or restore the duty cycle D of the first switch Q1 to 0%, restart the next round of the start-up process, and the time t starts increasing again from 0, thus achieving hiccup-style start-up; after hiccuping several times, the duty cycle D of the first switch Q1 reaches 100%, and the duty cycle of the second switch Q2 decreases to 0%, that is, at time t1;

[0059] If neither formula (A) nor formula (B) holds true, the soft-start circuit will enter a continuous hiccup mode, meaning the Vin' level will never approach Vin, causing the normally-on switch Q3 to fail to meet the closing condition: Vin - Vin' <V BR -Vin'*K; thus, the normally open switch Q3 cannot be closed, and the soft-start circuit achieves self-protection.

[0060] (2) t1 to t2:

[0061] At time t1, due to the effect of the current-limiting resistor R1, the output voltage Vout of the switched capacitor power converter is less than K times Vin. Vout continues to increase for a period of time until Vout is approximately equal to K times Vin.

[0062] If Vin' satisfies formula (A) or Vout satisfies formula (B), and the difference between Vin and Vin' does not exceed the voltage stress margin of the high-voltage side switching transistor of the switched capacitor power converter, that is:

[0063] Vin-Vin' <V BR -Vin'*K;

[0064] In the above formula, V BR K represents the maximum allowable voltage stress of the high-voltage side switching transistor in the switched capacitor power converter, and K is the turns ratio of the switched capacitor power converter under ideal conditions.

[0065] This moment is recorded as time t2. The normally open switch Q3 is closed, and the first switch Q1, diode D1, resistor R1, and output inductor Lo are bypassed. The slow start process ends, and the system enters the steady-state operation stage.

[0066] The above-mentioned slow-start operation method can be applied to the slow-start operation of switched capacitor power converters under different circumstances.

[0067] like Figure 4 The image shows the voltage and current waveform changes during the normal soft-start process of a 1 / 4 switched capacitor power converter, as detailed below:

[0068] (1) From t0 to t1:

[0069] Starting at time t0, the power converter begins the slow start process. The duty cycle of the first switch Q1 increases from 0%, and the duty cycle of the second switch Q2 decreases from 100%. The conduction times of the first switch Q1 and the second switch Q2 are complementary.

[0070] In the soft-start circuit, when the duty cycle of the first switching transistor Q1 increases to no more than 10%, the Vout voltage is detected; if the Vout voltage is greater than 0V, the soft-start circuit proceeds normally.

[0071] During the circuit soft start-up process, Vin' and Vout are continuously monitored to determine whether the rise of Vin' satisfies the above formula (A) or whether the rise of Vout satisfies formula (B).

[0072] If formula (A) or formula (B) holds true, the duty cycle of the first switch Q1 increases to 100%, and the duty cycle of the second switch Q2 decreases to 0%, i.e., until time t1; during the process from t0 to t1, the voltage V across the output capacitor Co in the soft-start circuit... Co The voltage increases linearly from 0V to the power input voltage Vin.

[0073] (2) t1 to t2:

[0074] At time t1, due to the effect of the current-limiting resistor R1, the output voltage Vout of the switched capacitor power converter is less than 1 / 4 of V. Co Vout continues to increase for a period of time, until Vout is approximately equal to 1 / 4 of V. Co If Vin' satisfies formula (A) or Vout satisfies formula (B), and the difference between Vin and Vin' does not exceed the voltage stress margin of the high-voltage side switching transistor of the switched capacitor power converter, that is:

[0075] Vin-Vin' <V BR -Vin'*K;

[0076] In the above formula, V BR The maximum allowable voltage stress of the high-voltage side switching transistor of the switched capacitor power converter is K, which is the turns ratio of the switched capacitor power converter under ideal conditions and is taken as 1 / 4 here.

[0077] This moment is recorded as t2. The normally-on switch Q3 is closed, and the first switch Q1, diode D1, resistor R1, and output inductor Lo are bypassed. The slow-start process ends, and the system enters the steady-state operation phase.

[0078] Switched capacitor power converters may encounter situations such as load short circuit and start-up with capacitive load. The following will describe the slow-start state using the above-mentioned slow-start operation method under the conditions of load short circuit or capacitive load:

[0079] When the load is in a short-circuit state, during the t0-t1 time range of the slow-start process, the Vout voltage will remain at 0V, and Vin' will also be approximately 0V. In the slow-start circuit, when the duty cycle of the first switching transistor Q1 increases to no more than 10%, the Vout voltage is detected as 0V. Due to the protective effect of the current-limiting resistor R1, excessive short-circuit current will not be generated in the slow-start circuit, thus protecting it from burnout. The slow-start circuit restarts at intervals; if the short-circuit problem is not resolved, the circuit will not enter normal operating condition, thus achieving self-protection.

[0080] When the load is capacitive and the capacitance value is small, the slow-start process using the above-mentioned slow-start operation method is as follows:

[0081] (1) From t0 to t1:

[0082] Starting at time t0, the power converter begins the slow start process, causing the duty cycle of the first switch Q1 to increase from 0% and the duty cycle of the second switch Q2 to decrease from 100%. The conduction times of the first switch Q1 and the second switch Q2 are complementary.

[0083] In the soft-start circuit, when the duty cycle of the first switching transistor Q1 increases to no more than 10%, the voltage Vout is checked to see if it is greater than 0V, which can determine whether the circuit is in a load short-circuit state. When the voltage Vout is not greater than 0V, it is determined to be in a load short-circuit state. The soft-start circuit restarts at intervals to achieve self-protection.

[0084] During the circuit soft start-up process, Vin' and Vout are continuously monitored to determine whether the rise of Vin' satisfies formula (A) or the rise of Vout satisfies formula (B):

[0085] If formula (A) or formula (B) holds true, the duty cycle of the first switch Q1 increases to 100%, and the duty cycle of the second switch Q2 decreases to 0%, i.e., until time t1; during the process from t0 to t1, the voltage across the output capacitor Co in the soft-start circuit increases linearly from 0V to the power input voltage Vin.

[0086] If neither formula (A) nor formula (B) holds true, it is necessary to stop increasing the duty cycle D of the first switch Q1, or restore the duty cycle D of the first switch Q1 to 0%, restart the next round of the start-up process, and the time t starts increasing again from 0, thus achieving hiccup-style start-up; after hiccuping several times, the duty cycle D of the first switch Q1 reaches 100%, and the duty cycle of the second switch Q2 decreases to 0%, that is, at time t1;

[0087] (2) t1 to t2:

[0088] At time t1, due to the effect of the current-limiting resistor R1, the output voltage Vout of the switched capacitor power converter is less than K times V. Co Vout continues to increase for a period of time, until Vout is approximately equal to K times V. Co If Vin' satisfies formula (A) or Vout satisfies formula (B), and the difference between Vin and Vin' does not exceed the voltage stress margin of the high-voltage side switching transistor of the switched capacitor power converter, that is:

[0089] Vin-Vin' <V BR -Vin'*K;

[0090] In the above formula, V BR K represents the maximum allowable voltage stress of the high-voltage side switching transistor in the switched capacitor power converter, and K is the turns ratio of the switched capacitor power converter under ideal conditions.

[0091] This moment is recorded as time t2. The normally open switch Q3 is closed, and the first switch Q1, diode D1, resistor R1, and output inductor Lo are bypassed. The slow start process ends, and the system enters the steady-state operation stage.

[0092] When a switched capacitor power converter is connected to a large capacitor load, during the circuit slow start process, Vin' and Vout are continuously detected to determine whether the rise of Vin' satisfies formula (A) or the rise of Vout satisfies formula (B). If formula (A) or (B) is always true within the time range of t0-t1 during the slow start process, then the slow start process will be successful in one go.

[0093] If neither formula (A) nor formula (B) is satisfied during the slow start process, it is necessary to stop increasing the duty cycle D of the first switch Q1, or restore the duty cycle D of the first switch Q1 to 0%, restart the next round of the start process, and the time t starts increasing again from 0..., that is, to achieve hiccup-style start;

[0094] After several hiccups, the duty cycle D of the first switching transistor Q1 reaches 100%. If Vin' satisfies formula (A) or Vout satisfies formula (B), and the difference between Vin and Vin' does not exceed the voltage stress margin of the high-voltage side switching transistor of the switched capacitor power converter, that is:

[0095] Vin-Vin' <V BR -Vin'*K;

[0096] In the above formula, V BR K represents the maximum allowable voltage stress of the high-voltage side switching transistor in the switched capacitor power converter, and K is the turns ratio of the switched capacitor power converter under ideal conditions.

[0097] Then, the normally open switch Q3 is closed, and the circuit enters steady-state operation.

[0098] When the switched capacitor power converter is connected to an excessively large capacitive load, neither formula (A) nor formula (B) can be satisfied. The soft-start circuit will enter a continuous hiccup mode, meaning that the Vin' level can never approach Vin, causing the normally-on switch Q3 to fail to meet the closing condition: Vin - Vin' <V BR -Vin'*K; thus, the normally open switch Q3 cannot close, and the soft-start circuit achieves self-protection.

[0099] When the switched capacitor power converter is connected to a resistive load with a large resistance value, formula (A) or formula (B) can be satisfied, and the soft start circuit can start normally.

[0100] When the switched capacitor power converter is connected to a resistive load with a small resistance value, neither formula (A) nor formula (B) is satisfied. It is necessary to stop increasing the duty cycle D of the first switching transistor Q1, or restore the duty cycle D of the first switching transistor Q1 to 0%, restart the next round of startup process, and the time t starts increasing from 0 again... that is, to achieve hiccup-style startup.

[0101] If neither formula (A) nor formula (B) holds true, the soft-start circuit will enter a continuous hiccup mode, meaning the Vin' level will never approach Vin, causing the normally-on switch Q3 to fail to meet the closing condition: Vin - Vin' <V BR -Vin'*K; thus, the normally open switch Q3 cannot be closed, and the soft-start circuit achieves self-protection, protecting the switch and other components from burning out due to excessive current stress.

[0102] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some examples of its application, and are not intended to limit the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A soft-start circuit for a switched capacitor power converter, characterized in that: The system includes a first switching transistor Q1 and a second switching transistor Q2 connected by a wire between the input terminal and the ground terminal of the switched capacitor power converter; a normally-on switching transistor Q3 connected by a wire between the input terminal and the ground terminal of the switched capacitor power converter; a diode D1; a resistor R1; and an output capacitor Co. The cathode of diode D1 is located near the normally-on switching transistor Q3. One end of the output inductor Lo is connected between the first switching transistor Q1 and the second switching transistor Q2, and the other end is connected between the resistor R1 and the output capacitor Co. The system also includes a bootstrap capacitor Cbst2, a bootstrap power supply diode D2, and a drive power supply capacitor Cbst1 connected by a wire. The other end of the bootstrap capacitor Cbst2 is connected between the normally-on switching transistor Q3 and the diode D1. The cathode of the bootstrap power supply diode D2 is located near the normally-on switching transistor Q3. The other end of the drive power supply capacitor Cbst1 is connected to the source of the highest voltage-side switching transistor of the switched capacitor power converter.

2. The soft-start circuit for a switched capacitor power converter as described in claim 1, characterized in that: The normally-on switch Q3 is a switch with low on-resistance.

3. A soft-start operation method for a switched capacitor power converter with an ideal turns ratio of K, including the soft-start circuit of the switched capacitor power converter as described in 1 or 2 above, is as follows: (1) From t0 to t1: Starting at time t0, the power converter begins its slow-start process, increasing the duty cycle of the first switch Q1 from 0% and decreasing the duty cycle of the second switch Q2 from 100%. The conduction times of the first switch Q1 and the second switch Q2 are complementary. During the slow-start process, Vin' and Vout are continuously monitored to determine whether the rise of Vin' satisfies formula (A) or the rise of Vout satisfies formula (B): Vin' > a * M * t * Vin - b (A) Vout>K*(a*M*t*Vin-b)(B) In the formula, the turns ratio is K, the duty cycle increase rate is M, the input voltage is Vin, and the time is t; In the formula, the range of values ​​for coefficients a and b is: 1 ≥ a > 0 (C) V BR >b≥0(D) In the above formula, V BR The maximum allowable voltage stress of the high-voltage side switching transistor in a switched capacitor power converter; If formula (A) or formula (B) holds true, the duty cycle of the first switch Q1 increases to 100%, and the duty cycle of the second switch Q2 decreases to 0%, i.e., until time t1; during the process from t0 to t1, the voltage V across the output capacitor Co in the soft-start circuit... Co The voltage increases linearly from 0V to the power input voltage Vin. If neither formula (A) nor formula (B) holds true, it is necessary to stop increasing the duty cycle D of the first switch Q1, or restore the duty cycle D of the first switch Q1 to 0%, restart the next round of the start-up process, and the time t starts increasing again from 0, thus achieving hiccup-style start-up; after hiccuping several times, the duty cycle D of the first switch Q1 reaches 100%, and the duty cycle of the second switch Q2 decreases to 0%, that is, at time t1; If neither formula (A) nor formula (B) holds true, the soft-start circuit will enter a continuous hiccup mode, meaning the Vin' level will never approach Vin, causing the normally-on switch Q3 to fail to meet the closing condition: Vin - Vin' <V BR -Vin'*K; thus, the normally open switch Q3 cannot close, and the soft-start circuit achieves self-protection. (2) t1 to t2: At time t1, due to the effect of the current-limiting resistor R1, the output voltage Vout of the switched capacitor power converter is less than K times Vin. Vout continues to increase for a period of time until Vout is approximately equal to K times Vin. If Vin' satisfies formula (A) or Vout satisfies formula (B), and the difference between Vin and Vin' does not exceed the voltage stress margin of the high-voltage side switching transistor of the switched capacitor power converter, that is: Wine-Wine' <V BR -Wave; In the above formula, V BR K represents the maximum allowable voltage stress of the high-voltage side switching transistor in the switched capacitor power converter, and K is the turns ratio of the switched capacitor power converter under ideal conditions. This moment is recorded as time t2. The normally open switch Q3 is closed, and the first switch Q1, diode D1, resistor R1, and output inductor Lo are bypassed. The slow start process ends, and the system enters the steady-state operation stage.

4. The soft-start operation method of a switched capacitor power converter with an ideal turns ratio of K, as described in claim 3, characterized in that: During the process from t0 to t1, when the duty cycle of the first switching transistor Q1 in the slow-start circuit increases to no more than 10%, the voltage Vout is checked to see if it is greater than 0V, which can determine whether the circuit is in a load short-circuit state. When the voltage Vout is 0V and it is determined to be in a load short-circuit state, the slow-start circuit restarts, thereby achieving self-protection.

Images