CN117810921A - Short-circuit protection circuit and method for CS pin of switching power supply - Google Patents

Abstract

The invention relates to a short-circuit protection circuit and method for a CS pin of a switching power supply, wherein the method comprises the steps of setting a first time T ₁ And a first reference voltage V ₁ The method comprises the steps of carrying out a first treatment on the surface of the According to the first time T ₁ And a first reference voltage V ₁ Judging whether the CS pin is short-circuited; if the CS pin is judged to have short circuit, triggering the short circuit protection of the CS pin, and immediately closing the power tube; wherein T is ₁ Is a periodic signal and is synchronized with the switching period; it uses the power tube as starting point and delay time T ₁ The time is a trigger point; first time T ₁ According to the switching frequency setting of the switching power supply, the first time T ₁ The value range of the power supply is larger than or equal to the minimum conduction time allowed by the switching power supply and smaller than or equal to the maximum conduction time allowed by the switching power supply; the power tube is configured to, if at the first time T ₁ The internal conduction and the normal operation of the power tube can be realized. When the CS pin is short-circuited, the power tube can be turned off in the current switching period in time when the output is abnormal or the load jumps, so that the CS pin short-circuit protection is realized。

Description

Short-circuit protection circuit and method for CS pin of switching power supply

Technical Field

The invention relates to the technical field of power supplies, in particular to a short-circuit protection circuit and method for a CS pin of a switching power supply.

Background

With the increasing demand for switching power supplies, reducing production costs, increasing application functions, and optimizing performance have become fundamental requirements for the power supply portion of general consumer electronics.

As in the Flyback topology shown in fig. 1, the R0 resistor is connected in series with the power tube and the primary side of the transformer, and the current flowing through the transformer and the primary side of the power tube is detected by the voltage on R0.

As shown in the Boost topology of fig. 2, when the power tube is turned on, the inductor, the power tube and the resistor R1 are connected in series, and all the current flowing through the inductor and the power tube flows through the resistor R1.

When the power MOSFET is turned on, the inductor or one of the windings of the transformer is in series connection with the power tube and the resistor, and all or a proportion of the current flowing through the one of the windings of the transformer and the power tube flows through the resistor, in other words, when the power tube is turned on, the voltage on the resistor can represent the current flowing through the inductor and the power tube. In this application, CS is the Current Sense, also known as the Current Sense resistor.

In a current control mode, comparing CS voltage with an error amplification signal, and adjusting the on time of a power tube according to the input voltage and the output power so as to realize the purpose of voltage conversion; and at start-up and load jump, or output short circuit, the CS voltage needs to be compared with the internal peak voltage limit to determine the maximum current through the inductor, transformer, and power tube. In the voltage control mode, during normal operation, the internal sawtooth wave is compared with an error amplification signal, the on time of the power tube is adjusted according to the input voltage and the output power, and the purpose of voltage conversion is achieved, but when the voltage control mode is started and the load jumps or the output is short-circuited, the CS voltage needs to be compared with the internal peak voltage limit, and the maximum current flowing through the inductor, the transformer and the power tube is determined.

Therefore, in the two basic control modes, the CS voltage is directly used for controlling the switching-off of the switching tube so as to protect the switching tube and the transformer from damage caused by overcurrent.

During production or actual use, a CS short circuit may occur, i.e., the CS resistor is shorted to GND, as shown by the dotted line portion in fig. 3. Therefore, when the power tube is started, the voltage on the CS pin is zero, and under the two control modes, when the current on the power tube and the inductor is too large, the detection of the current cannot be completed, and the power tube is closed in time, so that the effect of protecting the power tube and the inductor is realized.

Disclosure of Invention

The invention aims to provide an improved short-circuit protection circuit and method for a CS pin of a switching power supply.

The technical scheme adopted for solving the technical problems is as follows: a short-circuit protection method for a CS pin of a switching power supply is constructed, which comprises the following steps:

setting a first time T ₁ And a first reference voltage V ₁ ；

According to the first time T ₁ And a first reference voltage V ₁ Judging whether the CS pin is short-circuited;

if the CS pin is judged to have short circuit, triggering the short circuit protection of the CS pin, and immediately closing the power tube;

wherein T is ₁ Is a periodic signal and is synchronized with the switching period; it uses the power tube as starting point and delay time T ₁ The time is a trigger point; first time T ₁ According to the switching frequency setting of the switching power supply, a first time T ₁ The value range of the power supply is larger than or equal to the minimum conduction time allowed by the switching power supply and smaller than or equal to the maximum conduction time allowed by the switching power supply; the power tube is configured to, if at the first time T ₁ The internal conduction and the normal operation of the power tube can be realized.

Preferably, said step is based on said first time T ₁ And a first reference voltage V ₁ Whether the CS pin is short-circuited specifically comprises:

at each switching cycle, using a first time T ₁ Detecting the voltage of the CS pin and the first reference voltage V ₁ Comparing the result and judging whether the CS pin is at T according to the comparing result ₁ Before the moment, or at T ₁ Time of day and T ₁ And if the CS pin is short-circuited, triggering the short-circuit protection of the CS pin, and immediately closing the power tube.

Preferably, the saidJudging whether the CS pin is at T according to the comparison result ₁ Before the moment, or at T ₁ The occurrence of short circuit after time T1 specifically includes:

in the current switching period, at T ₁ At the moment, judging whether the voltage of the CS pin is lower than the first reference voltage V ₁ If the voltage of the CS pin is not lower than the first reference voltage V ₁ Then determine the first time T ₁ The front CS pin is not short-circuited;

if the voltage of the CS pin is lower than the first reference voltage V ₁ Detecting whether a power current loop of the switching power supply is normal or not and whether current passes through a current detection resistor connected with a CS pin or not; if the power current loop is normal and passes through the current detection resistor connected with the CS pin, determining that the power current loop is at the first time T ₁ Short circuit occurs on the front CS pin; if the voltage of the CS pin is lower than the first reference voltage V ₁ At the same time, if the power current loop is normal and does not pass through the current detection resistor connected with the CS pin, the first time T is determined ₁ No short circuit occurs to the front CS pin.

Preferably, the step judges whether the CS pin is at T according to the result of the comparison ₁ Before the moment, or at T ₁ Time of day and T ₁ The short circuit after the moment further comprises:

in the current switching period, at T ₁ After the moment, if the power tube is still in an open state or the power current loop is normal and passes through a current detection resistor connected with a CS pin, comparing the voltage of the CS pin with the first reference voltage V ₁ If the voltage of the CS pin is lower than the first reference voltage V ₁ And immediately judging that the CS pin is short-circuited, and sending out a signal for closing the power tube.

Preferably, the step judges whether the CS pin is at T according to the result of the comparison ₁ Before the moment, or at T ₁ Time of day and T ₁ The short circuit after the moment further comprises:

in the current switching period, at T ₁ After the moment, if the power tube is in an on state, judging whether the instantaneous voltage of the CS pin is lower than that of the CS pin in the current switching periodT ₁ The peak value after the moment samples the voltage, if yes, judge at T ₁ After the moment, the CS pin is short-circuited.

Preferably, if the CS pin short circuit occurs at T ₁ After the moment, the short circuit happens and the short circuit protection of the CS pin is triggered, and the power tube is immediately closed.

Preferably, when the occurrence of short-circuit protection of the CS pin is detected in two or more continuous switching periods, the PWM signal driving the power tube is completely turned off, and the switching power supply is restarted or is in a latch state.

The invention also constructs a short-circuit protection circuit of a CS pin of a switching power supply, which is connected with a logic circuit for generating a PWM signal, wherein the PWM signal is used for controlling the switch of a power tube and comprises the following components:

a clock generation module for generating a first clock signal T ₁ The method comprises the steps of carrying out a first treatment on the surface of the Wherein T is ₁ Is a periodic signal, and T ₁ Synchronous with the switching period, it uses the power tube as starting point of timing, and delays T ₁ The time is a trigger point; first time T ₁ According to the switching frequency setting of the switching power supply, a first time T ₁ The minimum conduction time allowed by the switching power supply is greater than or equal to the minimum conduction time allowed by the switching power supply, and the maximum conduction time allowed by the switching power supply is less than or equal to the maximum conduction time allowed by the switching power supply; the power tube is configured to, if at the first time T ₁ Internal conduction, the power tube can work normally;

a comparison module for comparing the first time T ₁ And a first reference voltage V ₁ Whether the CS pin is short-circuited; and

and the control module is used for triggering the short-circuit protection of the CS pin and immediately closing the power tube when the CS pin is short-circuited.

Preferably, the clock generating module includes a first comparator, the input end of the first comparator inputs the second reference voltage and the SAW-wave signal SAW generated by the oscillator, and the output end of the first comparator outputs the first clock signal and is connected with the control module.

Preferably, the comparison module comprises a second comparator and/or a third comparator, the input end of the second comparator is respectively input with a first reference voltage and the voltage of the CS pin, and the output end of the second comparator is connected with the control module;

the input end of the third comparator is respectively input with a peak voltage limit value and the CS peak protection reference voltage, and the output end of the third comparator is connected with the control module.

The implementation of the invention has the following beneficial effects: when the CS pin is short-circuited, no matter in a current mode control mode or a voltage mode control mode, the power tube can be closed in the current switching period in time when the output is abnormal or the load jumps, so that the CS pin short-circuit protection is realized.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1 is a schematic diagram of a Flyback topology of a switching power supply in the related art;

FIG. 2 is a schematic diagram of a Boost topology of a switching power supply of the related art;

FIG. 3 is a schematic diagram of a related art switching power supply with a CS short circuit;

FIG. 4 is a schematic diagram of a method of short-circuit protection for a CS pin of a switching power supply of the present invention;

FIG. 5 is a partial circuit diagram of one embodiment of a switching power supply of the present invention;

FIG. 6 is a schematic diagram of one embodiment of a switching power supply CS pin short circuit protection circuit of the present invention;

FIG. 7 is a waveform diagram of the switching power supply of the present invention in operation;

FIG. 8 is a graph showing the waveform comparison effect of the switching power supply of the present invention when operated and when operated in the prior art;

FIG. 9 is a schematic diagram of one embodiment of a control module of the present invention.

Detailed Description

For a clearer understanding of technical features, objects and effects of the present invention, a detailed description of embodiments of the present invention will be made with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "rear", "upper", "lower", "left", "right", "longitudinal", "transverse", "vertical", "horizontal", "top", "bottom", "inner", "outer", "head", "tail", etc. are configured and operated in specific directions based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention, and do not indicate that the apparatus or element to be referred to must have specific directions, and thus should not be construed as limiting the present invention.

It should also be noted that unless explicitly stated or limited otherwise, terms such as "mounted," "connected," "secured," "disposed," and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. When an element is referred to as being "on" or "under" another element, it can be "directly" or "indirectly" on the other element or one or more intervening elements may also be present. The terms "first," "second," "third," and the like are used merely for convenience in describing the present invention and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated, whereby features defining "first," "second," "third," etc. may explicitly or implicitly include one or more such features. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

Fig. 4 shows a method for protecting a short circuit of a CS pin of a switching power supply according to an embodiment of the present invention, including the following steps:

step S1, setting a first time T ₁ And a first reference voltage V ₁ ；

Step S2, according to the first time T ₁ And a first reference voltage V ₁ Judging whether the CS pin is short-circuited;

and step S3, if the CS pin is judged to have short circuit, triggering the short circuit protection of the CS pin, and immediately closing the power tube.

Wherein T is ₁ Is a periodic signal and is synchronized with the switching period; it uses the power tube as starting point and delay time T ₁ The time is a trigger point; first time T ₁ According to the switching frequency setting of the switching power supply, the first time T ₁ The value range of (2) is larger than or equal to the minimum conduction time allowed by the switching power supply and smaller than or equal to the maximum conduction time allowed by the switching power supply, namely T _{ON_MIN} <T ₁ <T _{ON_MAX} . The power tube is configured to, if at the first time T ₁ Internal conduction, the power tube can work normally and safely, namely the power tube is in T ₁ Internal conduction does not cause damage to the power tube. T (T) ₁ The value of (2) is related to the switching frequency of the power tube, and can be generally selected to be 2ms, although the value can be selected according to the actual situation, and is not limited herein. First reference voltage V ₁ The voltage of the CS pin is compared with the voltage of the CS pin to determine whether the CS pin is short-circuited, and the value can be selected according to actual conditions without limitation.

Further, in step S2, according to the first time T ₁ And a first reference voltage V ₁ The method for judging whether the CS pin is short-circuited specifically comprises the following steps:

step S21, using the first time T in each switching period ₁ Detecting the voltage of the CS pin and a first reference voltage V ₁ The result of the comparison;

step S22, judging whether the CS pin is at T according to the comparison result ₁ Before the moment, or at T ₁ Time of day and T ₁ Short circuit occurs after the moment, ifAnd when the CS pin is short-circuited, triggering the short-circuit protection of the CS pin, and immediately closing the power tube.

In the present embodiment, "T ₁ The meaning of "after the moment" includes T ₁ The time point is included.

Further, in step S22, it is determined whether the CS pin is at T according to the comparison result ₁ Before the moment, or at T ₁ Time of day and T ₁ The occurrence of short circuit after the moment can be divided into two cases, the first is at T ₁ The judgment is carried out at the moment, and the purpose of the judgment is to confirm whether the CS pin is short-circuited before starting. The second case is at T ₁ After the moment, judging is carried out, and the purpose of judging is to confirm whether the CS pin is short-circuited in the working process.

At T ₁ The following judgment is made at the moment, and the specific content is as follows:

in the current switching period, at T ₁ At the moment, judging whether the voltage of the CS pin is lower than the first reference voltage V according to the comparison result ₁ 。

If the voltage of the CS pin is not lower than the first reference voltage V ₁ Then determine the first time T ₁ No short circuit occurs to the front CS pin.

If the voltage of the CS pin is lower than the first reference voltage V ₁ It is necessary to detect whether the power current loop of the switching power supply is normal or not and whether the current passes through the current detection resistor connected with the CS pin, so that detection errors caused by other loop currents flowing into the current detection resistor can be prevented, and further detection and judgment can improve detection accuracy. In this way, different topological structures can be dealt with, and aiming at Buck_boost topological application, current passes through a current detection resistor connected with a CS pin when the current is on, and current can also pass through the current detection resistor when the current is off. For the Flyback circuit, when the Flyback circuit is turned on, current passes through the current detection resistor connected with the CS pin, and when the Flyback circuit is turned off, the current does not pass through the current detection resistor, so that whether a power current loop of the switching power supply is normal or not and whether the current passes through the current detection resistor connected with the CS pin can be detected.

If the power current loop is normal and passes through the loop circuit and the CS leadA current detection resistor connected to the pin for determining at the first time T ₁ Short circuit occurs on the front CS pin; if the voltage of the CS pin is lower than the first reference voltage V ₁ At the same time, if the power current loop is normal and does not pass through the current detection resistor connected with the CS pin, the first time T is determined ₁ No short circuit occurs to the front CS pin.

Further, at T ₁ The following judgment is made after the moment, and two judgment modes exist, and the specific contents are as follows:

the first judgment mode is that in the current switching period, in T ₁ After the moment, if the power tube is still in an open state or the power current loop is normal and passes through a current detection resistor connected with the CS pin, comparing the voltage of the CS pin with a first reference voltage V ₁ If the voltage of the CS pin is lower than the first reference voltage V ₁ And immediately judging that the CS pin is short-circuited, and sending out a signal for closing the power tube.

The second judgment mode is that in the current switching period, in T ₁ After the moment, if the power tube is in an on state, judging whether the instantaneous voltage of the CS pin is lower than the T of the CS pin in the current switching period ₁ The peak value after the moment samples the voltage, if yes, judge at T ₁ After the moment, the CS pin is short-circuited.

Generally T ₁ In the time, the voltage of the CS pin is considered to be very small and is directly equal to the first reference voltage V ₁ Comparing; t (T) ₁ After the moment, if no short circuit occurs, the CS pin is normal, the peak sampled voltage of the CS pin is sampled, and the instantaneous voltage value of the CS pin is compared with the peak sampled voltage of the CS pin.

Step S3, if it is determined that the CS pin is shorted, triggering the CS pin to perform short-circuit protection, immediately turning off the power tube may be divided into two cases, specifically including:

step S31, if the short circuit of CS pin occurs at T ₁ Before the moment, then at T ₁ And triggering the short-circuit protection of the CS pin at the moment point, and immediately closing the power tube.

Step S32, if the short circuit of CS pin occurs at T ₁ After the moment, triggering the CS pin while short circuit occursAnd (5) short-circuit protection, and immediately closing the power tube.

Further, when the short-circuit protection of the CS pin is detected in two or more than two continuous switching periods, the complete protection is triggered, the PWM signal driving the power tube is completely turned off, and the switching power supply is restarted or is in a latch state.

Fig. 5 shows a partial circuit structure of a switching power supply 100 according to an embodiment of the present invention, which includes a CS pin short-circuit protection circuit 101, an oscillator 102, a logic circuit 103, a driving circuit 104, a power tube 105, a current measuring resistor 106 connected in series with the power tube 105, and a CS current control circuit 107 for adjusting the current of the power tube according to the sampling voltage of the measuring resistor and outputting the current to the logic circuit 103. The CS pin short-circuit protection circuit 101 is configured to close the power tube in the current switching cycle in time when the output is abnormal or the load jumps, so as to implement CS pin short-circuit protection, regardless of the current mode control mode or the voltage mode control mode, when the CS pin short-circuit occurs. It can be appreciated that, in addition to the circuit disclosed in the example of fig. 5, the switching power supply further includes other circuits of the switching power supply controller, which together form the switching power supply, and this part of the circuits may directly adopt the existing related circuits, which are not described herein.

Fig. 6 shows a CS pin short circuit protection circuit 101 according to an embodiment of the invention. As shown in fig. 5 and 6, the CS pin short circuit protection circuit 101 is connected to a logic circuit 103 for generating PWM signals; the PWM signal is used to control the switching of the power tube 105. The CS pin short circuit protection circuit 101 includes a clock generation module 11, a comparison module 12, and a control module 13.

Wherein the clock generation module is used for setting a first time T ₁ Generates a first clock signal T ₁ ，T ₁ After setting, a fixed time signal is provided. T (T) ₁ Is an internal fixed time associated with the driving signal, can be timed by the starting time of the external power tube 105, and delays T ₁ After a time, detection is performed at T ₁ At time, the power tube 105 is at T ₁ Closing before time or at T ₁ Closing after the moment, for T ₁ The moment has no effect.

In actual operation, as seen in FIG. 7, PWM signals and T ₁ There are three cases depending on the peripheral load and the input voltage: the first case is where the PWM pulse width is less than T ₁ Pulse width; the second case is where the PWM pulse width is greater than T ₁ Pulse width; third case, PWM pulse full sum T ₁ The pulse widths coincide. Based on the logic generated by the present embodiment, the third case is almost impossible to occur, so only the first case and the second case are shown.

Referring to fig. 8, the high start time of the first clock signal is the high start time of the PWM signal, and the high sustain time is smaller than the maximum on time T of the power transistor 105 _{ON_MAX} . The oscillator 102 generates the second clock signal CLK for controlling the power transistor 105 and also generates the SAW signal SAW, and a maximum on-time T is provided when generating the SAW signal SAW and the second clock signal CLK _{ON_MAX} The maximum time that the external power tube 105 can be turned on is determined. At maximum on time T _{ON_MAX} In, note that here is not the actual T _ON Time, using T ₁ Time, which can be selected to be 0<T ₁ <T _{ON_MAX} 。T ₁ The time is selected based on the power tube 105 at T ₁ The current flowing through the inductor and the power tube 105 is always on in the time, so that the inductor and the power tube 105 are not damaged.

Understandably, the first time T ₁ Is the sampling value V of CS pin _{cs sampling} Is greater than CS pin reference value V _{cs reference} The comparator output is then toggled high when the high duration is greater than the first time T ₁ Triggering short-circuit protection. T (T) ₁ There are several PWM switching periods in the time, and when a short circuit occurs, the on time in each PWM switching period must be the minimum on time, so that the power tube 105 will not be turned on for a long time.

Further, as shown in FIG. 6, the present embodiment includes a first reference voltage V ₁ . The first reference voltage V ₁ And related voltages, may or may not participate in limiting the minimum voltage during CS operationIn other words, the embodiment does not need to limit the minimum voltage of the CS operation in the detection process of implementing the CS protection.

Specifically, the present embodiment includes the second reference voltage signal V ₀ . Second reference voltage signal V ₀ For generating a delay time T ₁ The time is synchronized with the second clock signal CLK, the start of the time is PWM from low to high, i.e. the time when the external power tube 105 is turned off to on, and is delayed by a time T ₁ After that, a clock signal is issued.

The comparison module 12 is used for comparing the first time T ₁ And a first reference voltage V ₁ Whether the CS pin is short-circuited.

The control module 13 is configured to output a short-circuit protection signal to the logic circuit 103 when the CS pin is shorted, trigger the CS pin to be shorted, and immediately turn off the power tube.

Further, outputting a short-circuit protection signal to the logic circuit 103, triggering the short-circuit protection of the CS pin specifically includes outputting a shutdown signal P _{ro_cs} In the case of abnormality of several consecutive switching periods, the subsequent PWM signal is turned off, and the DRV driving signal is stopped.

In one embodiment, the operation of the CS pin short circuit protection circuit 101 includes:

(1) At T ₁ The following determination is made at the moment (the purpose of this determination is that before power-on, the CS pin has been shorted):

if PWM is logic high, the voltage of CS pin must be higher than a set first reference voltage V ₁ The method comprises the steps of carrying out a first treatment on the surface of the If PWM is logic low, the voltage at the CS pin can be any value.

If at T ₁ At this time, if the above condition is not satisfied, the CS pin short-circuit protection circuit 101 sends R _{st_cs} Zero clearing signal of the '1', setting the PWM signal from high to low, and closing the peripheral power tube.

After such a condition continues for several switching cycles, the CS pin short circuit protection circuit 101 sends out a closing signal P _{ro_cs} And closing the subsequent PWM pulse, and stopping wave generation by the controller.

If at T ₁ At this time, when the above condition is satisfied, R of the CS pin short-circuit protection circuit 101 _{st_cs} = '0', remaining intact, the PWM signal is still controlled by the loop or peak voltage signal.

(2) At T ₁ After this time, the following determination is made (the purpose of this determination is that a short circuit has occurred in the CS pin during operation):

if the PWM logic is low (the power tube has been turned off), then there is no operation; if the PWM logic is high (the power tube is still on), if the voltage of the CS pin is again lower than the set first reference voltage V ₁ The CS pin short-circuit protection module sends out R _{st_cs} Zero clearing signal of the '1', setting the PWM signal from high to low, and closing the peripheral power tube.

After such a condition continues for several switching cycles, the CS pin short circuit protection circuit 101 sends out a closing signal P _{ro_cs} And closing the subsequent PWM pulse, and stopping wave generation by the controller.

Alternatively, at T ₁ After the moment, the following determination can be made:

(3) If the PWM logic is low (the power tube has been turned off), then there is no operation; if the PWM logic is high (the power tube is still on), if the CS pin voltage is lower than the CS pin is at the slave T ₁ Time of day start (including T ₁ Time), the CS pin short-circuit protection module sends out rst_cs= '1' zero clearing signal, sets the PWM signal from high to low, and closes the peripheral power tube.

After such a situation lasts for several open periods, the CS short-circuit protection module sends out P _{ro_cs} And (3) a signal, closing the subsequent PWM pulse, and stopping wave generation by the controller.

Understandably, the comparison module 12 makes a determination at each switching cycle. If judge whether the short circuit occurs at T ₁ Before the moment, then at T ₁ At this point, if the PWM signal is still at logic high and the voltage at the CS pin is lower than the set first reference voltage V ₁ Then determine T ₁ Before, the CS pin is shorted.

If it is judged that the short circuit isWhether or not it occurs at T ₁ After the moment, there are two decision modes: the first mode of determination is that no control signal (including loop control signal and CS peak control signal) for closing PWM pulse is provided, and the voltage of CS pin is lower than the first reference voltage V again ₁ Then it is determined that the CS pin is shorted and the power tube 105 is immediately turned off. The second way of determining is that there is no control signal (including loop control signal and CS peak control signal) to turn off PWM pulse, and the voltage of CS pin is suddenly lower than the percentage of CS peak sampling voltage, for example 80% V _cspk Then it is determined that the CS pin is shorted and the power tube 105 is immediately turned off.

Optionally, outputting a short-circuit protection signal to the logic circuit 103, triggering the CS pin short-circuit protection may specifically include outputting a reset signal R to the logic circuit 103 _{st_cs} So that the power tube 105 is turned off in the current switching cycle. When the current switching period is abnormal, the rest switching time is closed, and the current flowing through the transformer and the power tube 105 in the current period is prevented from being too large, so that the purpose of protecting the transformer and the power tube 105 is achieved.

Optionally, outputting a short-circuit protection signal to the logic circuit 103, triggering the CS pin short-circuit protection may specifically include outputting an extension signal T to the logic circuit 103 _{off_ctr} To extend the off time of the power tube 105. When detecting that the current period is abnormal, CS short-circuit protection occurs, no matter T ₁ Before the moment or T ₁ After the moment, the turn-off time can be prolonged, so that the current discharge time is prolonged, and the inductance peak current at the turn-on time of the next period is reduced; the peak value of the current of the transformer is released to the lowest value as far as possible, so that the accumulated effect is avoided before the PWM pulse is completely stopped.

Optionally, outputting a short-circuit protection signal to the logic circuit 103, triggering the CS pin short-circuit protection may specifically include generating the CS pin short-circuit protection during a continuous preset switching period, and outputting a shutdown signal to turn off the power tube 105 for a preset number of periods. The CS short-circuit protection occurs in consecutive switching cycles, which will trigger a complete protection and the circuit will close the subsequent PWM pulse signal.

Further toThe clock generation module comprises a first comparator 111, wherein the input ends of the first comparator 111 respectively input a second reference voltage V ₀ And the sawtooth wave signal SAW generated by the oscillator 102, the output end of the first comparator 111 outputs a first clock signal, and is connected with the control module 13.

Optionally, the comparing module 12 includes a second comparator 121 and/or a third comparator 122, and the input ends of the second comparator 121 respectively input the first reference voltage V ₁ And the voltage of the CS pin, and the output end of the second comparator 121 is connected with the control module 13. The second comparator 121 compares the first reference voltage V ₁ And the voltage of the CS pin is compared, and a first comparison result Cs is output _data1 And compare the first comparison result Cs _data1 Into the control module 13.

The input end of the third comparator 122 inputs the peak voltage limit value Cspk and the CS peak protection reference voltage Cs respectively _{peak_ref} The output end of the third comparator 122 is connected to the control module 13. The third comparator 122 protects the input peak voltage limit Cspk and CS peak protection reference voltage Cs against _{peak_ref} Comparing and outputting a second comparison result Cs _data2 And comparing the second comparison result Cs _data2 Into the control module 13.

Optionally, as shown in fig. 6, the comparing module 12 further includes a peak sampling unit 123, and the input terminal of the peak sampling unit 123 inputs the voltage of the CS pin to obtain the peak voltage limit value. Specifically, the voltage at the CS pin is sampled by the peak sampling unit 123 to output a CS leading edge sampling voltage or an average sampling voltage, and the sampled voltage is fed to the third comparator 122 to be combined with the CS peak protection reference voltage CS _{peak_ref} A comparison is made.

Further, as shown in fig. 9, the control module 13 includes a first logic unit 131, a second logic unit 132, and a logic or gate 133. The first logic unit 131 is configured to determine whether the voltage of the CS pin is lower than the first reference voltage V ₁ . The input ends of the first logic unit 131 respectively input the first comparison result Cs _data1 A PWM signal and a first clock signal;

the second logic unit 132 is configured to determine whether the voltage of the CS pin is lowAt the peak voltage limit. The input ends of the second logic unit 132 respectively input the second comparison result Cs _data2 A PWM signal and a first clock signal;

the output end of the first logic unit 131 and the output end of the second logic unit 132 are respectively connected to the input end of the logic OR gate 133, and the logic OR gate 133 is used for judging that the voltage of the CS pin is lower than the first reference voltage V ₁ Or when the voltage of the CS pin is lower than the peak voltage limit value, outputting a reset signal R to the logic circuit 103 _{st_cs} So that the power tube 105 is turned off in the current switching cycle.

Optionally, the control module 13 further comprises a third logic unit 134. The input ends of the third logic unit 134 respectively input the first comparison result Cs _data1 Second comparison result Cs _data2 A PWM signal, and a first clock signal.

The third logic unit 134 is configured to determine that the voltage at the CS pin is lower than the first reference voltage V ₁ Or when the voltage of the CS pin is lower than the peak voltage limit value, outputting an extension signal T to the logic circuit 103 _{off_ctr} To extend the off time of the power tube 105; or outputting a closing signal P when CS pin short-circuit protection occurs in a continuous preset switching period _{ro_cs} So that the power tube 105 is turned off for a preset number of cycles.

Of course, this is only one embodiment, and it is also possible to do the inverse logic based on this embodiment, which is not described here in detail.

The implementation of the invention has the following beneficial effects:

when the resistor R0 or the CS pin is short-circuited, no matter in current mode control or voltage mode control, the power tube can be turned off in the current switching period in time when the output is abnormal or the load jumps.

When the resistor R0 or the CS pin is short-circuited, no matter current mode control or voltage mode control is performed, when the output is abnormal or the load jumps, the wave generation is automatically stopped after a few abnormal switching cycles, and the protection purpose is realized.

The resistor R0 or CS pin short circuit can occur before starting up or in the power supply working process, and the invention can realize effective protection.

It is to be understood that the above examples only represent preferred embodiments of the present invention, which are described in more detail and are not to be construed as limiting the scope of the invention; it should be noted that, for a person skilled in the art, the above technical features can be freely combined, and several variations and modifications can be made without departing from the scope of the invention; therefore, all changes and modifications that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (10)

1. The short-circuit protection method for the CS pin of the switching power supply is characterized by comprising the following steps of:

setting a first time T ₁ And a first reference voltage V ₁ ；

According to the first time T ₁ And a first reference voltage V ₁ Judging whether the CS pin is short-circuited;

if the CS pin is judged to have short circuit, triggering the short circuit protection of the CS pin, and immediately closing the power tube;

wherein T is ₁ Is a periodic signal and is synchronized with the switching period; it uses the power tube as starting point and delay time T ₁ The time is a trigger point; first time T ₁ According to the switching frequency setting of the switching power supply, a first time T ₁ The value range of the power supply is larger than or equal to the minimum conduction time allowed by the switching power supply and smaller than or equal to the maximum conduction time allowed by the switching power supply; the power tube is configured to, if at the first time T ₁ The internal conduction and the normal operation of the power tube can be realized.

2. The method for short-circuit protection of a CS pin of a switching power supply according to claim 1, wherein the step is performed according to the first time T ₁ And a first reference voltage V ₁ Whether the CS pin is short-circuited specifically comprises:

at each switching cycle, use is made ofFirst time T ₁ Detecting the voltage of the CS pin and the first reference voltage V ₁ Comparing result and judging whether CS pin is at T according to comparing result ₁ Before the moment, or at T ₁ Time of day and T ₁ And if the CS pin is short-circuited, triggering the short-circuit protection of the CS pin, and immediately closing the power tube.

3. The method for short-circuit protection of a CS pin of a switching power supply according to claim 2, wherein the step of determining whether the CS pin is at T is based on the result of the comparison ₁ Before the moment, or at T ₁ Time of day and T ₁ The short circuit generation after the moment specifically comprises the following steps:

in the current switching period, at T ₁ At the moment, judging whether the voltage of the CS pin is lower than the first reference voltage V ₁ If the voltage of the CS pin is not lower than the first reference voltage V ₁ Then determine the first time T ₁ The front CS pin is not short-circuited;

if the voltage of the CS pin is lower than the first reference voltage V ₁ Detecting whether a power current loop of the switching power supply is normal or not and whether current passes through a current detection resistor connected with a CS pin or not; if the power current loop is normal and passes through the current detection resistor connected with the CS pin, determining that the power current loop is at the first time T ₁ Short circuit occurs on the front CS pin; if the voltage of the CS pin is lower than the first reference voltage V ₁ At the same time, if the power current loop is normal and does not pass through the current detection resistor connected with the CS pin, the first time T is determined ₁ No short circuit occurs to the front CS pin.

4. The method for short-circuit protection of a CS pin of a switching power supply according to claim 3, wherein the step of determining whether the CS pin is T based on the result of the comparison ₁ Before the moment, or at T ₁ Time of day and T ₁ The short circuit after the moment further comprises:

in the current switching period, at T ₁ After the moment, if the power tube is still in an open state or the power current loop is normal and the power current loop is detected by the current connected with the CS pinMeasuring resistance, comparing the voltage of the CS pin with the first reference voltage V ₁ If the voltage of the CS pin is lower than the first reference voltage V ₁ And immediately judging that the CS pin is short-circuited, and sending out a signal for closing the power tube.

5. The method for short-circuit protection of a CS pin of a switching power supply according to claim 3, wherein the step of determining whether the CS pin is T based on the result of the comparison ₁ Before the moment, or at T ₁ Time of day and T ₁ The short circuit after the moment further comprises:

in the current switching period, at T ₁ After the moment, if the power tube is in an on state, judging whether the instantaneous voltage of the CS pin is lower than that of the CS pin in the current switching period in T ₁ The peak value after the moment samples the voltage, if yes, judge at T ₁ After the moment, the CS pin is short-circuited.

6. The method of claim 4 or 5, wherein if the CS pin short circuit occurs at T ₁ After the moment, the short circuit happens and the short circuit protection of the CS pin is triggered, and the power tube is immediately closed.

7. The method according to claim 1, wherein when CS pin short-circuit protection is detected in two or more consecutive switching cycles, the PWM signal driving the power transistor is completely turned off, and the switching power supply is restarted or is put in a latch state.

8. A switching power supply CS pin short circuit protection circuit connected to a logic circuit for generating a PWM signal for controlling switching of a power transistor, comprising:

a clock generation module for generating a first clock signal T ₁ The method comprises the steps of carrying out a first treatment on the surface of the Wherein T is ₁ Is a periodic signal, and T ₁ Synchronous with the switching period, it uses the power tube as starting point of timing, and delays T ₁ The time is a trigger point; first time T ₁ According to the switching frequency setting of the switching power supply, a first time T ₁ The minimum conduction time allowed by the switching power supply is greater than or equal to the minimum conduction time allowed by the switching power supply, and the maximum conduction time allowed by the switching power supply is less than or equal to the maximum conduction time allowed by the switching power supply; the power tube is configured to, if at the first time T ₁ Internal conduction, the power tube can work normally;

a comparison module for comparing the first time T ₁ And a first reference voltage V ₁ Whether the CS pin is short-circuited; and

and the control module is used for triggering the short-circuit protection of the CS pin and immediately closing the power tube when the CS pin is short-circuited.

9. The circuit of claim 8, wherein the clock generation module comprises a first comparator, the input end of the first comparator is respectively input with a second reference voltage and a SAW-tooth wave signal SAW generated by the oscillator, and the output end of the first comparator is output with the first clock signal and is connected with the control module.

10. The short-circuit protection circuit of the CS pin of the switching power supply according to claim 8, wherein the comparison module includes a second comparator and/or a third comparator, the input end of the second comparator inputs the first reference voltage and the voltage of the CS pin respectively, and the output end of the second comparator is connected with the control module;

the input end of the third comparator is respectively input with a peak voltage limit value and the CS peak protection reference voltage, and the output end of the third comparator is connected with the control module.