TW202002480A - Short-circuit protection system for current detection terminal in switching power supply - Google Patents

Abstract

The invention relates to a short-circuit protection system for a current detection terminal in a switching power supply, and provides a power supply control system used in a switching power supply. The short-circuit protection system comprises a current detection terminal, an integrating and sampling assembly, a power tube, a modulation assembly, a logic control assembly and a driving assembly, wherein the power tube has second resistance and is connected with a sampling resistor in series; when the switching power supply is in normal operation, the switching pin-to-ground resistance Rsw1 of the power tube when being turned on is the sum of first resistance Rcs and second resistance Ron, and the ratio of the second resistance Ron and the first resistance Rcs is k1 (0 < k1 < 1); when the current detection terminal is short circuited, the on-resistance of the power tube is equal to the sum of the second resistance and the short-circuit resistance, and the ratio of the second resistance and the short-circuit resistance is K3 (k3 > 1); the logic control assembly is configured to receive a modulation signal and generate a driving signal based on the modulation signal; and the driving assemblyis configured to turn off a gate based on the driving signal.

Description

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

The present disclosure relates to integrated circuits. More specifically, some embodiments of the present invention relate to short-circuit protection methods for current sensing terminals in switching power supplies.

Figure 1 shows a simplified application diagram of a conventional 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 PIN) is an important interface between the controller and the system. The controller converts the current flowing through the sampling resistor into a resistor through the system from the current sensing terminal to the ground (generally called the sampling resistor). Voltage, thereby indirectly sensing the exciting current in the switching power supply coil by detecting the voltage at the current sensing terminal (CS PIN), and turning off the exciting current when the preset value is reached.

When the current sensing terminal (CS PIN) is short-circuited, the controller cannot detect the excitation current in the coil and turns off when the preset value is reached, resulting in current in the excitation coil until the coil is saturated. Saturation of the excitation coil has a great safety risk, because after the excitation coil is saturated, the coil is equivalent to a short circuit, and the excitation current will rise linearly. The power switch connected to the excitation coil is prone to be subjected to high voltage and large current stress at the same time. Excessive power causes damage due to overheating. At present, some technologies prevent the occurrence of disasters by controlling the maximum on-time of the excitation coil, but as the requirements of the switching power supply increase, this method will conflict with other system indicators. In the application of switching power supply, the short-circuit protection function of the current sensing terminal that takes into account various indicators is more difficult to achieve.

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

Some 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 present 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 can be applied to PFC controllers of Buck, Boost, Buck-Boost, and flyback architectures.

Provided is a power supply control system used in a switching power supply, including: a current sensing terminal, the current sensing terminal is connected to a power control system and a switching power supply; an integrating and sampling component 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, where the sampling voltage is obtained at least in part from the first impedance Rcs of the grounded sampling resistor, the power tube has a second impedance and the sampling resistance Series connection; wherein when the switching power supply is working normally, the impedance of the switching pin to ground when the power tube is on is Rsw1 is the sum of the first impedance Rcs and the second impedance Ron, wherein the second impedance Ron The ratio 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 ratio of the second impedance to the short-circuit impedance is k3 (k3>>1), the modulation element is configured to receive the first voltage and the ramp voltage based on the first signal, and based on the first voltage and the ramp Voltage to generate a modulation signal; a logic control element configured to receive the modulation signal and generate a drive signal based on the modulation signal; and a drive element configured to turn off the gate based on the drive signal.

According to embodiments, one or more beneficial effects may be achieved. With reference to the following detailed description and accompanying drawings, these beneficial effects of the present invention, as well as various additional objects, features, and advantages will be fully understood.

M1, M2‧‧‧Power tube

RT‧‧‧External over-temperature protection terminal

Ipk‧‧‧current

FB‧‧‧sensing feedback signal of power control system

Rcs‧‧‧ First impedance

VDD‧‧‧Power supply terminal

Vline‧‧‧Input voltage

GATE‧‧‧Gate

Inductance of Lm‧‧‧excitation coil

SW‧‧‧Source start

VDDH‧‧‧Controller power supply

CS‧‧‧Current sensing terminal

t‧‧‧ time of current

GND‧‧‧Quality status

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

R‧‧‧ is the on-resistance Ron or 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 shows a startup circuit diagram of a switching power supply controller according to an embodiment of the present disclosure.

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

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

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

The features and exemplary embodiments of the various aspects of the invention will be described in detail below. In the following detailed description, many specific details are presented in order to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by showing examples of the present invention. The present invention is by no means limited to any specific configurations and algorithms proposed below, but covers any modification, replacement, and improvement of elements, components, and algorithms without departing from the spirit of the present 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 diagram is only an example, and it 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 a startup and reference voltage generation module, a demagnetization signal generation module, a sampling module, an error amplifier module, a core control module, a peak current detection module, a logic control module, a drive module and a protection module Etc.

The power supply system includes an electromagnetic interference (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 rectifier filter circuit can add π-type filter circuit or common-mode filter circuit to improve the filtering effect. A person skilled in the art may set different connection methods for the diode according to needs to achieve different ripple requirements. The rectifier diode can be combined with an RC absorption circuit. The RC absorption circuit can be adjusted or not according to need.

FIG. 3 shows a startup circuit diagram of a switching power supply controller according to an embodiment of the present disclosure. The figure shows a startup circuit driven by a power MOS tube, 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 level before starting, M2 is not turned on, PG is high after starting, and M2 is turned on, which is equivalent to a switch. After the system starts, the current Ipk in the inductor flows through M2 and then through the sampling resistor Rcs. 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 wafer area and cost when actually designing the controller, according to a preferred embodiment, the on-resistance of M2 at normal temperature can be designed to be around 150 milliohms. The sampling resistor Rcs resistance value on the system is determined by the system output voltage and current requirements, generally a few hundred milliohms to a few ohms. Therefore, during normal operation, the on-resistance of M2 is less than Rcs. When the CS pin is shorted (usually zero ohm or a few milliohm contact resistance), the impedance of M2 is greater than Rcs. With this feature, the invention realizes the CS PIN 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 junction transistor (IGBT). Preferably, the power transistor is a field effect transistor (for example, a metal oxide semiconductor field effect transistor (Metal-Oxide-Semiconductor Field-Effect TransistoMOSFET)).

FIG. 4 shows another startup circuit diagram of the switching power supply controller according to the embodiment of the present disclosure. The voltage drop across the power tube M2 or sampling resistor Rcs 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 excitation coil, R is the on-resistance Ron or Rcs of the power tube M2, and t is the time for the current to flow. V is the voltage drop across the power tube M2 or Rcs. The change of the above formula voltage V with time t is shown in Figure 5 below.

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

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

CS PIN 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 PIN is short-circuited: SW PIN to ground impedance: M2 on-resistance Ron+Rshort (Rshort is the impedance after CS PIN short-circuited to ground), denoted as Rsw2, then Rsw2=Ron+Rshort, Rshort<<Ron; Note Ron=k3*Rshort(k3>>1); Rsw2=(k3+1)*Rshort; CS PIN to ground impedance: Rshort, there is Rsw2>>Rshort; note k2* Rsw2=k2*(k3+1)* Rshort If k2* Rsw2>Rshort, then k2>(1/(1+k3).

In summary, the value of k2 needs to meet the condition: (1/(1+k3)<k2<(1/(1+k1)). The value of k2 is appropriate, which can make k2*Rsw and Rcs in the above two cases. k2*Rsw and Rshort have sufficient margin.

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

FIG. 6 shows 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 resistance from CS PIN to ground (sampling resistance Rcs), and the on-resistance of M2 when the CS PIN is short-circuited is greater than the resistance from CS PIN to ground ( Is zero or a few milliohms short-circuit contact impedance). Because the resistance of the power tube M2 and CS PIN to the ground is connected in series, and directly comparing the size of the resistance will be more complicated in the circuit implementation, so the normal working state and the CS PIN short-circuit state of the power tube M2 on-resistance and CS PIN to the ground resistance The change in the relationship of the resistance value is converted into the change in the relationship between the voltage across the power tube M2 and the voltage of the CS PIN.

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

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

In the circuit implementation, the switch M3 is added to transfer the voltage of the SW PIN to the voltage of the node SW_cs. The sum of the resistance values of R10 and R11 in Figure 6 is much larger than that of R9. The role of R9 is only to protect the comparator in the controller, so that the SW_cs voltage is close to the SW PIN 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 the 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 PIN voltage. In normal operation, the voltage of the node SW_k is less than the voltage of the CS PIN. When the CS PIN is short-circuited, the voltage of the node SW_k is greater than the voltage of the CS PIN. The voltage of the node SW_k is R10/(R10+R11)*VSW, and R10/(R10+R11) is the aforementioned k2. When it is detected that the voltage of the node SW_k is higher than the CS PIN voltage for several consecutive switching cycles, it is considered that the CS PIN has a short circuit failure and the controller is turned off until the controller power supply VDDH is restarted or the system is re-powered (Vline is re-powered). This can be 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 needs to not affect the normal operation, but also needs to ensure that the current IPK in the coil will not damage M1, M2 and the transformer winding when the CS PIN 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 terminal, the current sensing terminal is connected to a power control system and a switching power supply; an integrating and sampling element, the integrating and sampling element is configured To receive the sampling voltage and the reference voltage, and generate a first signal based at least in part on the sampling voltage and the reference voltage, where the sampling voltage is obtained at least in part from the first impedance Rcs of the grounded sampling resistor, the power tube has a Two impedances are connected in series with the sampling resistor; when the switching power supply is working normally, the impedance of the switching pin to ground when the power tube is on is Rsw1 which is the sum of the first 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 on-resistance of the power tube is equal to the second impedance and The sum of short-circuit impedances, wherein the ratio of the second impedance to the short-circuit impedance is k3 (k3>>1), the modulation element, the modulation element is configured to receive the first voltage based on the first signal and the ramp voltage, and A modulation signal is generated based on the first voltage and the ramp voltage; a logic control element configured to receive the modulation signal and generate a drive signal based on the modulation signal; and a drive element configured to be based on the drive signal To turn off the gate.

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

According to an embodiment of the present disclosure, the power supply control system further includes a peak current sensing module. The peak current sensing module is used to sense the peak current of the switching power supply and adjust the reference voltage based at least in part on the peak current.

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 drive element is further configured to: Trigger signal to turn off the gate.

According to an embodiment of the present disclosure, the power control system further includes a switch tube, which is connected in parallel with the power tube and in series with the first resistor and the second resistor. The resistance values of the first resistor and the second resistor need to be large enough to flow through the first The current of 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 relationship between the on-resistance of the power tube M2 in the startup circuit and the resistance value of the sampling resistor on the system in normal mode and failure mode changes, and this feature is used to implement the short-circuit protection function of the current sensing port. At the same time, it does not affect other system performance.

According to an embodiment of the present disclosure, the short-circuit protection circuit of the current sensing port described herein is for reference only as an example, 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 switching power supply circuits, including but not limited to current intermittent mode, current continuous mode and critical current mode.

The short-circuit protection of the current sensing port described in this article is suitable for the start-up circuit described in this article. 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 elements of various embodiments of the present invention are used with one or more software elements, one or more hardware elements, and/or one or more combinations of software and hardware elements, individually and/or At least combined with another component. In another example, some or all elements of the various embodiments of the present invention are implemented individually and/or at least in combination with another element in one or more circuits, such as one or more analog circuits and/or 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 present 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 shown embodiments, but only by the scope of the appended claims.

RT‧‧‧External over-temperature protection terminal

FB‧‧‧sensing feedback signal of power control system

VDD‧‧‧Power supply terminal

GATE‧‧‧Gate

SW‧‧‧Source start

CS‧‧‧Current sensing terminal

GND‧‧‧Quality status

Claims (8)

A power supply control system used in a switching power supply includes: a current sensing end, the current sensing end connecting the power supply 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 the first impedance Rcs of the grounded sampling resistor, A power tube, the power tube has a second impedance connected in series with the sampling resistor; wherein when the switching power supply is working normally, the impedance of the switching pin to ground when the power tube is on is Rsw1 being the first impedance The sum of 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 power tube’s The on-impedance 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), the modulation element, the modulation element is configured to receive based on A first voltage and a ramp voltage of the first signal, and a modulation signal is generated based on the first voltage and the ramp voltage; a logic control element, the logic control element is configured to receive the modulation signal, And a driving signal is generated based on the modulation signal; and a driving element configured to turn off the gate based on the driving signal. The power control system as described in item 1 of the patent application scope, 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 control system according to item 1 of the patent application scope further includes a peak current sensing module, the peak current sensing module is used to sense the peak current of the switching power supply, and is 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 patent application scope, further includes a demagnetization sensing element configured to sense a feedback signal of the power supply control system and generate a trigger signal based on the feedback signal ; Wherein the driving element is further configured to: turn on the gate based on the trigger signal. A switching power supply including a controller as described in items 1-4 of the patent application. A power supply control system used in a switching power supply includes: a current sensing end, the current sensing end connecting the power supply 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 the first impedance Rcs of the grounded sampling resistor, A power tube, the power tube has a second impedance connected in series with the sampling resistor; wherein when the switching power supply is working normally, the impedance of the switching pin to ground when the power tube is on is Rsw1 being the first impedance The sum of 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 power tube’s The on-impedance 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), the modulation element, the modulation element is configured to receive based on A first voltage and a ramp voltage of the first signal, and a modulation signal is generated based on the first voltage and the ramp voltage; a logic control element, the logic control element is configured to receive the modulation signal, And generating a driving signal based on the modulation signal; a driving element configured to turn off the gate based on the driving signal; and a switching tube, the switching tube is connected in parallel with the power tube and A resistor and a second resistor are connected in series, and the sum of the resistance values of the first resistor and the second resistor needs to be large enough so that the current flowing through the first resistor and the second resistor is much smaller than the current flowing through the power tube . The power control system as described in item 6 of the patent application scope further includes a diode and a third resistor, wherein the third resistor is connected to the gate of the switch; the anode of the diode is connected to the The drain of the switch is connected, and the negative electrode is connected to the gate of the switch. The power supply control system as described in item 6 of the patent application scope, wherein a body diode is connected between the drain and the source of the switch tube.

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