TWI657647B - Short-circuit protection system for current sensing terminal in switching power supply - Google Patents

Abstract

The invention relates to a short-circuit protection system of a current sensing terminal in a switching power supply. A power supply control system for a switching power supply is provided, including: a current sensing end; an integrating and sampling element, a power tube, the power tube having a second impedance connected in series with the sampling resistor; and when the switching power supply is normal During operation, the switch-to-ground impedance Rsw1 when the power transistor is turned on is the sum of the first impedance Rcs and the second impedance Ron, where the ratio of the second impedance Ron to the first impedance Rcs is k1 (0 <k1 <1); when the current sensing terminal is short-circuited, the on-resistance of the power tube is equal to the sum of the second impedance and the short-circuit impedance, where the second impedance and the short-circuit impedance are The ratio is k3 (k3 >> 1), a modulation element; a logic control element, the logic control element is configured to receive a modulation signal and generate a driving signal based on the modulation signal; and a driving element, the driving element is configured to be based on a driving Signal to turn off the gate.

Description

Short-circuit protection system for current sensing terminal in switching power supply

The present disclosure relates to integrated circuits. More specifically, some embodiments of the present invention relate to a short circuit protection method for a current sensing terminal in a switching power supply.

Figure 1 shows a simplified application diagram of a traditional flyback switching power supply. Controllers in switching power supply applications generally have the following important ports: power supply terminal, ground terminal, voltage sensing terminal and current sensing terminal. Among them, the current sensing terminal (CS) is an important interface between the controller and the system. The controller converts the current flowing through the sampling resistor through the resistance of the current sensing terminal to ground (commonly called the sampling resistor) on the system. Is the voltage, so that the exciting current in the switching power supply coil is indirectly sensed by detecting the voltage at the current sensing terminal (CS), and the exciting current is turned off when the preset value is reached.

When the current sensing terminal (CS) is short-circuited, the controller cannot detect the exciting current in the coil and turns off when it reaches a preset value, resulting in the current in the exciting coil until the coil is saturated. The saturation of the exciting coil has a great safety hazard, because after the saturation of the exciting coil, the coil is equivalent to a short circuit, and the exciting current will rise linearly. The power switch tube connected to the exciting coil is prone to withstand high voltage and high current stress at the same time. Overpower causes damage due to overheating. At present, some technologies prevent the disaster by controlling the longest on-time of the exciting coil, but as the requirements of switching power supply increase, this method will conflict with other indicators of the system. In the application of switching power supply, the short-circuit protection function of the current sensing terminal that takes into account all the indicators is difficult to achieve.

Therefore, it is desirable to provide an improved short-circuit protection method for a current sensing terminal in a switching power supply.

Certain embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide an analog demagnetization sampling method and system for switching power supply output sampling. By way of example only, some embodiments of the invention have been applied to power conversion systems. However, it should be recognized that the present invention Has a wider range of applications. For example, the method according to the present disclosure may be applicable to PFC controllers of Buck, Boost, Buck-Boost, and flyback architectures.

Provided is a power supply control system for a switching power supply, including: a current sensing end, the current sensing end being connected to the power control system and the switching power supply; an integrating and sampling element, the integrating and sampling element being Configured to receive a sampling voltage and a reference voltage, and generate a first signal based at least in part on the sampling voltage and reference voltage, wherein the sampling voltage is obtained based at least in part on a first impedance Rcs of a grounded sampling resistor; A power tube having a second impedance connected in series with the sampling resistor; wherein when the switching power supply is operating normally, the switch-to-ground impedance Rsw1 when the power tube is turned on is the first impedance The sum of the impedance Rcs and the second impedance Ron, wherein the ratio of the second impedance Ron to the first impedance Rcs is k1 (0 <k1 <1); when the current sensing terminal is short-circuited, the The on-resistance of the power tube is equal to the sum of the second impedance and the short-circuit impedance, where the ratio of the second impedance to the short-circuit impedance is k3 (k3 >> 1); a modulation element, the modulation element is configured For pick Generating a modulation signal based on a first voltage and a ramp voltage of a first signal, and generating a modulation signal based on the first voltage and the ramp voltage; a logic control element configured to receive the modulation signal, and Generating a driving signal based on the modulation signal; and a driving element configured to turn off a gate based on the driving signal.

According to an embodiment, one or more beneficial effects can be achieved. These beneficial effects, as well as various additional objects, features, and advantages of the present invention will be fully understood with reference to the following detailed description and accompanying drawings.

M1, M2‧‧‧ Power tube

RT‧‧‧External over-temperature protection terminal

Ipk‧‧‧Current

FB‧‧‧Feedback signal from sensing power control system

Rcs‧‧‧First impedance

VDD‧‧‧ power supply

Vline‧‧‧Input voltage

GATE‧‧‧Gate

Lm‧‧‧ Sensitivity of Excitation Coil

SW‧‧‧Source Starter

VDDH‧‧‧Controller Power

CS‧‧‧Current sensing terminal

t‧‧‧ Time of current flowing

GND‧‧‧Standard

V‧‧‧ is the voltage drop across the power tube M2 or Rcs

R‧‧‧ is the second impedance Ron or the first impedance Rcs of the rate tube M2

M3‧‧‧ Switch tube

Ron‧‧‧Second Impedance

Figure 1 shows a simplified application diagram of a traditional flyback switching power supply.

FIG. 2 shows a functional block diagram of a flyback switching power supply according to an embodiment of the present disclosure.

FIG. 3 illustrates a startup circuit diagram of a switching power supply controller according to an embodiment of the present disclosure.

FIG. 4 illustrates another startup circuit diagram of a switching power supply controller according to an embodiment of the present disclosure.

FIG. 5 is a diagram illustrating a relationship between a current sensing terminal CS and a product of a voltage Vsw and a coefficient k in a normal mode and a failure mode according to an embodiment of the present disclosure.

FIG. 6 illustrates an exemplary implementation of the current sensing terminal short-circuit protection according to an embodiment of the present disclosure.

Features and exemplary embodiments of various aspects of the invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely for providing a better understanding of the present invention by showing examples of the present invention. The invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

FIG. 2 shows a functional block diagram of a flyback switching power supply according to an embodiment of the present disclosure. This figure is merely an example, which should not unduly limit the scope of the claims. Those of ordinary skill in the art should understand many variations, substitutions, and modifications. The controller is mainly composed of startup and reference voltage generation module, demagnetization signal generation module, sampling module, error amplifier module, core control module, peak current detection module, logic control module, drive module and protection module Etc composition.

The power supply system includes an electromagnetic interference (EMI) filter circuit and a rectifier filter circuit. Depending on the application, the EMI filter circuit can include one or two inductors. In the embodiment shown in FIG. 1, the output rectification filter circuit includes four output rectification diodes, and optionally includes a filter capacitor. For different output ripple requirements, the output rectification filter circuit can add a π-type filter circuit or a common mode filter circuit to improve the filtering effect. Those skilled in the art can set different connection methods for the diodes according to the needs to achieve different ripple requirements. The rectifier diode can be combined with an RC absorption circuit, and the RC absorption circuit can be adjusted or not used as required.

FIG. 3 illustrates a startup circuit diagram of a switching power supply controller according to an embodiment of the present disclosure. A starting circuit driven by a power MOS tube is illustrated, where M1 and M2 are power tubes. M2 is placed in the controller and M1 is placed on the system. The controller is controlled by the enable signal PG (power good) signal: PG is low before startup, M2 is not conductive, PG is high after startup, M2 is conductive, which is equivalent to a switch. After the system starts, the current Ipk in the inductor flows through M2 and then through The first impedance Rcs of the sampling resistor. In order not to affect the system efficiency and reduce the controller temperature, the on-resistance of M2 needs to be as small as possible.

Considering the chip area and cost when the controller is actually designed, according to a preferred embodiment, the on-resistance of M2 at room temperature can be designed around 150 milliohms. The first resistance Rcs of the sampling resistor on the system is determined by the system's output voltage and current requirements, and is generally in the range of several hundred milliohms to several ohms. Therefore, during normal operation, the on-resistance of M2 is less than Rcs. When CS is shorted (usually zero ohms or a few milliohms contact resistance), the impedance of M2 is greater than Rcs. With this feature, the present invention implements a CS short-circuit protection function.

In one example, a power transistor - type bipolar junction transistor (bipolar junction transistor, BJT). In yet another example, the power transistor is an Insulated Gate Bipolar Transistor (IGBT). Preferably, the power transistor is a field effect transistor (eg, a Metal-Oxide-Semiconductor Field-Effect TransistoMOSFET).

FIG. 4 illustrates another startup circuit diagram of a switching power supply controller according to an embodiment of the present disclosure. The voltage drop across the first impedance Rcs of the power tube M2 or the sampling resistor in Figure 3 or Figure 4 above can be expressed as follows:

Among them, Vline is the input voltage, Lm is the inductance of the exciting coil, R is the second impedance Ron or Rcs of the power tube M2, and t is the time when the current flows. V is the voltage drop across the power tube M2 or Rcs. The change of the above-mentioned formula voltage V with time t is shown in Fig. 5 below.

The specific impedance is calculated as follows: SW and CS to ground resistance are:

(1) When working normally: SW to ground impedance: M2's second impedance Ron + Rcs, recorded as Rsw1; where Ron <Rcs, recorded Ron = k1 * Rcs (0 <k1 <1), then Rsw1 = (1 + k1) * Rcs.

CS to ground impedance: Rcs

Remember k2 * Rsw1 = k2 * (1 + k1) * Rcs

If k2 * Rsw1 <Rcs, then 0 <k2 <(1 / (1 + k1)) <1. The smaller k1, the larger k2 can be.

(2) When CS is short-circuited: SW to ground impedance: M2's second impedance Ron + Rshort (Rshort is the impedance after CS shorted to ground), recorded as Rsw2, then Rsw2 = Ron + Rshort, Rshort << Ron; Ron = k3 * Rshort (k3 >> 1); Rsw2 = (k3 + 1) * Rshort; CS to ground impedance: Rshort, there is Rsw2 >> Rshort; remember k2 * Rsw2 = k2 * (k3 + 1) * Rshort

If k2 * Rsw2> Rshort, then k2> (1 / (1 + k3).

In summary, the value of k2 must meet the conditions: (1 / (1 + k3) <k2 <(1 / (1 + k1)). The value of k2 is appropriate, which can make k2 * Rsw and Rcs, k2 * Rsw and Rshort have sufficient margin.

FIG. 5 is a diagram illustrating a relationship between a current sensing terminal CS and a product of a voltage Vsw and a coefficient k in a normal mode and a failure mode according to an embodiment of the present disclosure.

FIG. 6 illustrates an exemplary implementation of the current sensing terminal short-circuit protection according to an embodiment of the present disclosure. Taking the driving power MOS tube as an example, the main principle is: during normal operation, the on-resistance of the power tube M2 is less than the CS to ground resistance (the first resistance Rcs of the sampling resistor), and the M2 on-resistance is greater than CS to ground when the CS is short Resistance (zero or a few milliohms short-circuit contact resistance). Because the resistance of the power tube M2 and CS is connected in series, and directly comparing the resistance will be more complicated in circuit implementation, so the normal working state and CS short-circuit state of the power tube M2 on-resistance and the resistance of the CS to ground resistance The relationship change is converted into a change in the relationship between the voltage across the power tube M2 and the CS voltage.

In Figure 6, the change in the resistance relationship between the power tube M2 and CS to ground resistance in normal operation mode and CS short circuit is converted into the change in the relationship between the voltage across the power tube M2 and the CS voltage. The voltage across the power tube M2 is the voltage difference between SW and CS, and is denoted as VSW-VCS. The voltage difference between CS and ground is the voltage of CS, which is recorded as VCS. VSW-VCS <VCS under normal operating conditions; VSW-VCS> VCS when CS is shorted.

According to the impedance calculation in the normal working mode and the CS short circuit state, if Ron = k1 * Rcs (0 <k1 <1) and Ron = k3 * Rshort (k3 >> 1), then k2 is in (1 / (1+ k3)) <k2 < The range of (1 / (1 + k1)) is satisfied: under normal operating conditions, k2 * VSW <VCS; k2 * VSW> VCS when CS is shorted. As an example, if k1 is 0.25, then 0 <k2 <0.8. We take k2 = 0.5, then: under normal working conditions, 0.5 * VSW <VCS; 0.5 * VSW> VCS when CS short circuit.

In the circuit implementation, a switch M3 is added to transfer the voltage of SW to the voltage of node SW_cs. The sum of the resistance values of R10 and R11 in Figure 6 is much larger than R9. The role of R9 is only to protect the comparator in the controller, so the SW_cs voltage is close to the SW voltage. The sum of the resistance values of R10 and R11 needs to be large enough so that the current flowing through R10 and R11 is much smaller than the current flowing through power tube M2.

When the voltage of the node SW_cs reaches the internally set vref value, it is sensed whether the voltage of the node SW_k is higher than the CS voltage. During normal operation, the voltage of node SW_k is less than the voltage of CS, and the voltage of node SW_k is greater than the voltage of CS when CS is shorted. The voltage of the node SW_k is R10 / (R10 + R11) * VSW, and R10 / (R10 + R11) is the aforementioned k2. When the node SW_k voltage is detected to be higher than the CS voltage for several consecutive switching cycles, the CS is considered to have a short-circuit failure and the controller is shut down until the controller power supply VDDH is powered off and restarted or the system is powered on again (Vline is powered on again). Set according to system requirements.

Similarly, the setting of vref can also be set according to the needs of the system. The selection of vref must not affect the normal work, but also ensure that the current IPK in the coil will not damage M1, M2 and the transformer winding when CS is shorted.

According to an embodiment of the present disclosure, there is provided a power supply control system for a switching power supply, including: a current sensing end, the current sensing end connecting the power control system and the switching power supply; an integrating and sampling element, the The integrating and sampling element is configured to receive a sampling voltage and a reference voltage and generate a first signal based at least in part on the sampling voltage and the reference voltage, wherein the sampling voltage is based at least in part on a grounded sampling resistor Obtained by a first impedance Rcs; a power tube having a second impedance connected in series with the sampling resistor; wherein when the switching power supply is operating normally, the switching pin of the power tube is turned on to ground The impedance Rsw1 is the sum of the first impedance Rcs and the second impedance Ron, where the ratio of the second impedance Ron to the first impedance Rcs is k1 (0 <k1 <1); when the current sense When the test terminal is short-circuited, the on-resistance of the power tube is equal to the sum of the second impedance and the short-circuit impedance, where the ratio of the second impedance to the short-circuit impedance is k3 (k3 >> 1); Modulating element Configured to receive a first voltage based on the first signal and a ramp voltage, and generate a modulation signal based on the first voltage and the ramp voltage; a logic control element, the logic control element is configured to receive all The modulation signal, and a driving signal is generated based on the modulation signal; and a driving element configured to turn off a gate based on the driving signal.

According to the embodiment of the present disclosure, assuming coefficient k2 * Rsw1 = k2 * (1 + k1) * Rcs, the value of coefficient k2 satisfies (1 / (1 + k3) <k2 <(1 / (1 + k1)) .

According to an embodiment of the present disclosure, the power control system further includes a peak current sensing module for sensing a peak current of the switching power supply, and is adjusted based at least in part on the peak current. Reference voltage.

According to an embodiment of the present disclosure, the power control system further includes a demagnetization sensing element configured to sense a feedback signal of the power control system and generate a trigger signal based on the feedback signal; wherein The driving element is further configured to turn off the gate based on the trigger signal.

According to an embodiment of the present disclosure, the power supply control system further includes a switch tube, which is connected in parallel with the power tube and in series with a first resistor and a second resistor, the first resistor and the second resistor The resistance value needs to be sufficiently large so that the current flowing through the first resistor and the second resistor is much smaller than the current flowing through the power tube.

According to the embodiment of the present disclosure, the on-resistance of the power tube M2 in the startup circuit and the resistance value of the sampling resistor on the system in the normal mode and the failure mode change, and this feature is used to implement the short-circuit protection function of the current sensing port. Without affecting other system performance.

According to an embodiment of the present disclosure, the short-circuit protection circuit of the current sensing port described herein is used as an example reference only, and is not limiting.

The short circuit protection method and circuit of the current sensing port described in this article are suitable for different modes of the switching power supply circuit, including but not limited to the current discontinuous mode, the current continuous mode, and the critical current mode.

The short-circuit protection of the current sensing port described in this article applies to the startup circuit described in the dry text. The short-circuit protection circuit of the current sensing port described in this article is also suitable for the case where the power transistor is used as the driving transistor.

For example, some or all of the elements of the various embodiments of the present invention use one or more software elements, one or more hardware elements, and / or one or more combinations of software and hardware elements, alone and / or At least in combination with another component. In another example, some or all of the elements of various embodiments of the present invention are implemented in one or more circuits alone and / or in combination with at least another element, such as one or more analog circuits and / Or one or more digital circuits. In yet another example, various embodiments and / or examples of the invention may be combined.

Although specific embodiments of the invention have been described, those skilled in the art will understand that other embodiments are equivalent to the described embodiments. Therefore, it will be understood that the invention is not limited to the specifically illustrated embodiments, but only by the scope of the appended claims.

Claims (7)

A power supply control system for a switching power supply includes: a current sensing terminal, the current sensing terminal is connected to the power control system and the switching power supply; an integrating and sampling element, the integrating and sampling element is configured as Receiving a sampling voltage and a reference voltage, and generating a first signal based at least in part on the sampling voltage and the reference voltage, wherein the sampling voltage is obtained based at least in part on a first impedance Rcs of a grounded sampling resistor, A power tube having a second impedance connected in series with the sampling resistor; wherein when the switching power supply is operating normally, the switch-to-ground impedance Rsw1 when the power tube is turned on is the first impedance The sum of the impedance Rcs and the second impedance Ron, wherein the ratio of the second impedance Ron to the first impedance Rcs is k1 (0 <k1 <1); when the current sensing terminal is short-circuited, the The on-resistance of the power tube is equal to the sum of the second impedance and the short-circuit impedance, where the ratio of the second impedance to the short-circuit impedance is k3 (k3 >> 1), a modulation element, and the modulation element is configured For receiving A modulation signal based on a first voltage and a ramp voltage of the first signal, and generating a modulation signal based on the first voltage and the ramp voltage; a logic control element configured to receive the modulation signal And generating a driving signal based on the modulation signal; and a driving element configured to turn off a gate based on the driving signal. For example, the power supply control system described in item 1 of the scope of the patent application, where the coefficient k2 * Rsw1 = k2 * (1 + k1) * Rcs is assumed, then the value of the coefficient k2 satisfies (1 / (1 + k3) <k2 <(1 / (1 + k1)). The power supply control system according to item 1 of the scope of patent application, further comprising a peak current sensing module for sensing the peak current of the switching power supply, and based at least in part on the Peak current to adjust the reference voltage. The power supply control system according to item 1 of the scope of patent application, further comprising a demagnetization sensing element configured to sense a feedback signal of the power control system, and generate a trigger signal based on the feedback signal ; Wherein the driving element is further configured to turn on the gate electrode based on the trigger signal. A power supply control system used in a switching power supply includes a current sensing terminal connected to the power control system and the switching power supply; an integrating and sampling element, the integrating and sampling element being configured as Receiving a sampling voltage and a reference voltage, and generating a first signal based at least in part on the sampling voltage and the reference voltage, wherein the sampling voltage is obtained based at least in part on a first impedance Rcs of a grounded sampling resistor, A power tube having a second impedance connected in series with the sampling resistor; wherein when the switching power supply is operating normally, the switch-to-ground impedance Rsw1 when the power tube is turned on is the first impedance The sum of the impedance Rcs and the second impedance Ron, wherein the ratio of the second impedance Ron to the first impedance Rcs is k1 (0 <k1 <1); when the current sensing terminal is short-circuited, the The on-resistance of the power tube is equal to the sum of the second impedance and the short-circuit impedance, where the ratio of the second impedance to the short-circuit impedance is k3 (k3 >> 1), a modulation element, and the modulation element is configured For receiving A modulation signal based on a first voltage and a ramp voltage of the first signal, and generating a modulation signal based on the first voltage and the ramp voltage; a logic control element configured to receive the modulation signal And generating a driving signal based on the modulation signal; a driving element configured to turn off a gate electrode based on the driving signal; and a switching tube connected in parallel with the power tube and connected with the power tube The first resistor and the second resistor are connected in series, and the sum of the resistance values of the first resistor and the second resistor needs to be sufficiently large so that the current flowing through the first resistor and the second resistor is much smaller than that flowing through the power tube. Current. The power supply control system according to item 5 of the scope of patent application, further comprising a diode and a third resistor, wherein the third resistor is connected to the gate of the switch tube; the anode of the diode is connected to the anode of the diode. The drain of the switching tube is connected, and the negative electrode is connected to the gate of the switching tube. The power supply control system according to item 5 of the scope of patent application, wherein a body diode is connected between the drain and the source of the switching tube.