CN112255451A - Overcurrent detection circuit, overcurrent protection circuit and switching power supply - Google Patents
Overcurrent detection circuit, overcurrent protection circuit and switching power supply Download PDFInfo
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- CN112255451A CN112255451A CN202011514089.5A CN202011514089A CN112255451A CN 112255451 A CN112255451 A CN 112255451A CN 202011514089 A CN202011514089 A CN 202011514089A CN 112255451 A CN112255451 A CN 112255451A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16533—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application
- G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16504—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the components employed
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
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Abstract
The invention discloses an overcurrent detection circuit which is applied to an overcurrent protection circuit in a switching power supply chip, wherein the overcurrent protection circuit comprises a current sampling module for generating sampling voltage, the overcurrent detection circuit comprises a current bias module, a current generation module and a current sink module, and the current generation module is respectively connected with the current bias module and the current sink module. The overcurrent detection circuit is applied to an overcurrent protection circuit in a switching power supply chip, and can judge whether the input is overcurrent or not based on the sampling voltage generated by a current sampling module of the overcurrent protection circuit. The overcurrent protection circuit is realized based on the integrated circuit manufacturing process of the transistor, is applied to the interior of a power supply chip, has wide detection current, can identify the output current burr when the power tube is opened to avoid circuit misoperation, and can accurately detect the output overcurrent of the chip power tube.
Description
Technical Field
The invention relates to the technical field of switching power supplies, in particular to an overcurrent detection circuit, an overcurrent protection circuit and a switching power supply.
Background
In the prior art, technical problems such as short circuit and overcurrent inevitably occur at the output end of a switching power supply chip in actual use, and the problems can cause damage to a power tube or a load of the chip.
At present, many techniques have also been disclosed or mentioned: when the switching power supply chip normally works, in order to limit the current in a certain safety range, the damage to a circuit and a load caused by the overlarge output current of the chip is avoided, an overcurrent detection protection circuit is integrated or arranged in the switching power supply chip, and then the function of limiting the output current in the safety range in time when the chip outputs overcurrent is played.
In the prior art, in a switching power supply management chip which takes a power triode as a switching tube, because the on-resistance of the triode and the switching current are not in a linear relation, the overcurrent cannot be judged by detecting the voltage on the on-resistance of the triode. Generally, a common overcurrent detection mode of a power transistor as a switching power management chip of a switching tube is to directly connect a detection resistor in series on the power tube, or connect a detection resistor in series at an output end of a system, so as to obtain a voltage across a sampling resistor to limit a maximum output current, thereby realizing an overcurrent protection function.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides an overcurrent detection circuit, an overcurrent protection circuit and a switching power supply.
In order to solve the technical problem, the invention is solved by the following technical scheme:
an overcurrent detection circuit is applied to an overcurrent protection circuit in a switching power supply chip, and comprises a current sampling module for generating sampling voltage, wherein the current sampling module is provided with a power tube and an output end, the voltage of the output end is marked as VN, the overcurrent detection circuit comprises a current bias module, a current generation module and a current sink module, the current generation module is respectively connected with the current bias module and the current sink module, the output voltage of the output end of the overcurrent detection circuit is marked as V0, and the second end of the current sink module is connected with the output end of the overcurrent detection circuit;
the current generating module comprises a first current module and a second current module connected with the first current module, the first current module comprises a first triode unit and a second triode unit, the first triode unit is respectively connected with the second triode unit, the output end of the current sampling module, the first end of the current bias module and the first end of the current sink module, and the second triode unit is connected with the output end of the current sampling module and the current bias module; the second current module comprises a third triode unit and a fourth triode unit, a voltage point is arranged at the input end of the second current module and is connected with the third triode unit and the fourth triode unit, the voltage point is recorded as VP, the fourth triode unit is respectively connected with the third triode unit, the second end of the current sink module and the current bias module, the third triode unit is respectively connected with the second triode unit and the current bias module, based on voltage VN, the current flowing out of the collector of the first triode unit is a first current, based on voltage VP, the current flowing out of the collector of the fourth triode unit is a second current, the current sink module draws the first current and the second current, the current bias module generates bias currents for the second triode unit and the third triode unit, the bias currents are constant values, and the bias currents are collector currents in the second triode unit and the third triode unit and triode sending currents in the current bias module The sum of the emitter currents;
when the current flowing through the power tube is smaller than the current of a preset overcurrent protection point of the power tube, the voltage VN is larger than the voltage VP, and as the bias current is a fixed value and is the sum of collector currents in the second triode unit and the third triode unit and the current of an emitter of a triode in the current bias module, the first current is larger than the second current, and further the first current drawn by the current sink module is larger than the second current drawn, the output voltage V0 at the output end of the overcurrent detection circuit is set to be low, namely the output voltage is output in a low level state; as the current flowing through the power tube is increased, the voltage VN is gradually reduced, and the current of the collector of the third triode unit is gradually increased based on the fact that the bias current is a fixed value; when the current flowing through the power tube is larger than the current of the preset overcurrent protection point, the voltage VN is smaller than the voltage VP, as the bias current is a fixed value and is the sum of the collector currents in the second triode unit and the third triode unit and the current of the triode emitter in the current bias module, the first current is smaller than the second current, the first current drawn by the current sink module is smaller than the second current drawn, the output voltage V0 at the output end of the overcurrent detection circuit is raised, and the output voltage is converted from a low level state to a high level state.
As an implementation manner, the over-current detection circuit includes a resistor R3, the current bias module includes a transistor Q7 and a resistor R4, a base of the transistor Q7 is connected to the reference signal terminal VREF, an emission set of the transistor Q7 is connected to a first end of a resistor R4, a second end of the resistor R4 is grounded, a collector of the transistor Q7 is connected to one end of the resistor R3, and the other end of the resistor R3 is connected to the second current module.
As an implementation, the first transistor unit includes a transistor Q3, the second transistor unit includes a transistor Q4, emitters of the transistors Q3 and Q4 are respectively connected to an output terminal of the sampling current module, a base of the transistor Q3 is respectively connected to a base of a transistor Q4 and a collector of a transistor Q7, a collector of the transistor Q3 is connected to a first terminal of the current sink module, and a collector of the transistor Q4 is respectively connected to an emitter of a transistor Q7 and a first terminal of a resistor R4;
the third triode unit includes triode Q5, the fourth triode unit includes triode Q6, the second current module still includes resistance R2, triode Q5, the projecting pole of Q6 and the one end of resistance R2 is connected respectively to the other end of resistance R3, mains voltage end VCC is connected to resistance R2's the other end, triode Q6's base and triode Q7's collecting electrode are connected respectively to triode Q5's base, the first end of resistance R4 and triode Q7's projecting pole are connected respectively to triode Q5's collecting electrode, the second end of current trap module and the output of overcurrent detection circuit are connected respectively to triode Q6's collecting electrode.
As an implementation, the current sink module includes transistors Q8 and Q9, a collector of the transistor Q8 is connected to a collector of the transistor Q3, bases of the transistor Q8 are respectively connected to a collector of the transistor Q8 and a base of the transistor Q9, emitters of the transistors Q8 and Q9 are respectively grounded, and a collector of the transistor Q9 is connected to a collector of the transistor Q6 and an output of the over-current detection circuit.
An overcurrent protection circuit is applied to a switching power supply and comprises a current sampling module, a pulse signal generating module, an overcurrent protection signal output module and the overcurrent detection circuit, wherein the pulse signal generating module is provided with a first output end and a second output end, the first output end is recorded as a third voltage point V3, the overcurrent protection signal output module is provided with a first input end and a second input end, the third voltage point V3 is connected with the second input end, and the second output end is connected with the first input end;
the current sampling module is used for generating sampling voltage and inputting the sampling voltage into the overcurrent detection circuit, the voltage output by the output end of the current sampling module is recorded as voltage VN, the overcurrent detection circuit outputs voltage V0 based on the voltage VN, the pulse signal generation module receives the output voltage V0 of the overcurrent detection circuit and carries out filtering processing, the second input end of the overcurrent protection signal output module receives the voltage of a third voltage point V3, and whether an overcurrent protection signal is generated or not is judged based on the size of the third voltage point V3.
As an implementation manner, the current sampling module includes transistors Q1, Q2 and a resistor R1, a collector of the transistor Q1 is connected to a power voltage terminal VCC, a base of the transistor Q1 is connected to the drive signal input terminal DRIVER and the base of the transistor Q2, a collector of the transistor Q2 is connected to one end of the resistor R1 and an emitter of the transistor Q3, the other end of the resistor R1 is connected to the power voltage terminal VCC, and emitters of the transistors Q1 and Q2 are connected to the signal output terminal SW.
As an implementation, the ratio of the current flowing through the transistor Q1 to the current flowing through the transistor Q2 is N: 1.
as an implementation manner, the pulse signal generating module includes transistors Q10, Q11, Q12, Q13, Q14, Q15, Q16, Q17, Q18, Q19 and Q19, a capacitor C19 and resistors R19, the bases of the transistors Q19, Q19 are sequentially connected, the base of the transistor Q19 is connected to a first input terminal of the over-current protection signal output module, the bases of the transistors Q19, Q19 are respectively connected to a power voltage terminal VCC, the collector of the transistor Q19 is connected to the collector of the transistor Q19, the base of the transistor Q19 is connected to a reference signal terminal VREF, the emitter of the transistor Q19 is connected to one end of the resistor R19, the collector of the resistor R19 is connected to a second collector of the transistor Q19, and the collector of the transistor Q19 is connected as a voltage point V of the collector of the transistor 19, and the collector of the transistor 19, the transistor Q19 is connected to a second collector of the transistor 19 and used as a voltage point of the transistor V19, a base of the transistor Q15 is connected to a collector of the transistor Q13, a collector of the transistor Q16 is connected to an emitter of the transistor Q17, a base of the transistor Q17 is connected to a base of the transistor Q15, an emitter of the transistor Q17 is connected to one end of a capacitor C1, the other end of the capacitor C1 is connected to a collector of the transistor Q18 and one end of a resistor R18, the other end of the resistor R18 is connected to a base of the transistor Q18, a collector of the transistor Q18 is connected to a collector of the transistor Q18, a collector of the transistor Q18 is connected to a base of the transistor Q18, a collector of the transistor Q18 is connected to a collector of the transistor Q18 and serves as a third voltage point V18, a voltage V18 of the third voltage point V18 serves as a second input terminal of the overcurrent protection signal output module, and emitters of the transistors Q18, the collector of transistor Q17 is connected to ground.
As an implementation manner, the over-current protection signal output module includes a transistor Q24 and a transistor Q25, a base of the transistor Q24 is connected to a base of the transistor Q22, an emitter of the transistor Q24 is connected to the power voltage terminal VCC, a collector of the transistor Q24 is connected to a collector of the transistor Q25 and outputs the signal OCP as a signal output terminal, an emitter of the transistor Q25 is grounded, and a base of the transistor Q25 is connected to a collector of the transistor Q23.
A switching power supply comprises the overcurrent protection circuit. Due to the adoption of the technical scheme, the invention has the remarkable technical effects that:
the overcurrent detection circuit is applied to an overcurrent protection circuit in a switching power supply chip, and can judge whether the current flowing through the power tube is overcurrent or not based on the sampling voltage generated by the current sampling module of the overcurrent protection circuit.
The overcurrent protection circuit is realized based on the integrated circuit manufacturing process of the transistor, is applied to the interior of a power supply chip, has wide detection current, can identify the output current burr when the power tube is opened to avoid circuit misoperation, can accurately detect the overcurrent of the current flowing through the power tube, and has the advantages of simple circuit structure, low production cost and low noise.
The switching power supply chip containing the overcurrent protection circuit can realize the functions of overcurrent detection and switch burr current identification by using fewer devices. In the process of the switching power supply chip, each device is isolated from each other, so that the circuit has good latch-up resistance and high interference resistance.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic block diagram of an overall overcurrent detection circuit according to the invention;
FIG. 2 is a functional schematic of the over-current detection circuit of the present invention;
FIG. 3 is a schematic circuit diagram of the over-current detection circuit of the present invention;
FIG. 4 is a schematic circuit diagram of the over-current protection circuit of the present invention;
FIG. 5 is a graph showing the variation of the current, VN voltage and VP voltage output by the signal output terminal OCP of the present patent with I1;
fig. 6 shows the waveforms of the current flowing through the power transistor Q1, the "P" pulse signal, and the signal output from the signal output terminal OCP during the simulation process using the power chip of this patent.
Detailed Description
The present invention will be described in further detail with reference to examples, which are illustrative of the present invention and are not to be construed as being limited thereto.
Example 1:
an overcurrent detection circuit, as shown in fig. 1 and 2, is applied to an overcurrent protection circuit in a switching power supply chip, the overcurrent protection circuit includes a current sampling module 100 for generating a sampling voltage, the current sampling module 100 is provided with a power tube and an output end, the output end voltage is denoted as VN, the overcurrent detection circuit 200 includes a current bias module 210, a current generation module 220 and a current sink module 230, the current generation module 220 is respectively connected with the current bias module 210 and the current sink module 230, the output voltage at the output end of the overcurrent detection circuit 200 is denoted as V0, and the second end of the current sink module 230 is connected with the output end of the overcurrent detection circuit 200;
the current generating module 220 includes a first current module 221 and a second current module 222 connected to the first current module 221, where the first current module 221 includes a first triode unit 2211 and a second triode unit 2212, the first triode unit 2211 is respectively connected to the second triode unit 2212, the output terminal of the current sampling module 100, the current bias module 210 and the first terminal of the current sink module, and the second triode unit 2212 is connected to the output terminal of the current sampling module 100 and the current bias module 210; the second current module 222 includes a third transistor unit 2221 and a fourth transistor unit 2222, the input end of the second current module 222 has a voltage point, which is denoted as VP, and is connected to the third transistor unit 2221 and the fourth transistor unit 2222, the fourth transistor unit 2222 is respectively connected to the third transistor unit 2221, the second end of the current sink module 230, and the current bias module 210, the third transistor unit 2221 is respectively connected to the second transistor unit 2212 and the current bias module 210, based on the voltage VN, the current flowing out of the collector of the first transistor unit 2211 is a first current, based on the voltage VP, the current flowing out of the collector of the fourth transistor unit 2222 is a second current, the current sink module 230 draws the first current and the second current, the current bias module 210 generates bias currents for the second transistor unit 2212 and the third transistor unit 2221, and the bias currents are constant values, the bias current is the sum of the collector currents in the second triode unit 2212 and the third triode unit 2221 and the current of the emitter of the triode in the current bias module 210, and the current of the emitter of the triode in the current bias module is basically unchanged;
when the current flowing through the power tube is smaller than the current of a preset overcurrent protection point of the power tube, the voltage VN is larger than the voltage VP, as the bias current is a fixed value and is the sum of collector currents in the second triode unit and the third triode unit and the current of an emitter of a triode in the current bias module, and the current of the emitter of the triode in the current bias module is basically unchanged, the first current is larger than the second current, and further the first current drawn by the current sink module is larger than the second current drawn, the output voltage V0 at the output end of the overcurrent detection circuit is set to be low, namely the output voltage is in a low level state; when the current flowing through the power tube is equal to the current of a preset overcurrent protection point, the voltage VN is equal to the voltage VP; when the current flowing through the power tube is larger than the current of a preset overcurrent protection point, the voltage VN is smaller than the voltage VP, as the bias current is a fixed value and is the sum of the collector currents in the second triode unit and the third triode unit and the current of the triode emitter in the current bias module, the current of the triode emitter in the current bias module is basically unchanged, the first current is smaller than the second current, the first current drawn by the current sink module is smaller than the second current drawn, the output voltage V0 at the output end of the overcurrent detection circuit is raised, and the output voltage is converted from a low level state to a high level state.
In this embodiment, the switching power supply includes a signal input terminal VREF, a signal input terminal DRIVER, a signal output terminal SW, a signal output terminal OCP, a power supply voltage terminal VCC, and a ground terminal gnd; the signal output end SW is the output end of a power tube in the switching power supply chip, the signal of the signal input end VREF is the reference voltage generated by an internal circuit of the switching power supply chip, and the signal of the signal input end DRIVER is the driving signal of an NPN type power switching tube; in addition, the internal circuit function module of the switching power supply chip mentioned above further includes: the device comprises a current sampling module, a pulse signal generating module and an overcurrent protection signal output module. In order to better realize the function of the over-current detection circuit, the current sampling module of the whole switching power supply chip comprises power tubes Q1 and Q2, Q2 is a sampling tube matched with Q1 according to the proportion of 1: N in the same way, R1 is a sampling resistor, the current sampling module is used for sampling output current, and when the current of the power tube Q1 is larger than the preset maximum output current, the output voltage V0 is turned from low level to high level; when the current of the power tube Q1 is smaller than the preset output maximum current, namely the current of the aforementioned overcurrent protection point, the output voltage V0 is set low.
In one embodiment, referring to fig. 3 more specifically, the over-current protection circuit includes a resistor R3, and the specific circuit of the current bias module 210 is: the current source circuit comprises a triode Q7 and a resistor R4, wherein the base electrode of a triode Q7 is connected with a reference signal end VREF, the emission set of the triode Q7 is connected with the first end of a resistor R4, the second end of a resistor R4 is grounded, the collector electrode of a triode Q7 is connected with one end of a resistor R3, and the other end of the resistor R3 is connected with a second current module;
the first triode unit 2211 comprises a triode Q3, the second triode unit 2212 comprises a triode Q4, emitting electrodes of the triodes Q3 and Q4 are respectively connected with an output end of the sampling current module, a base electrode of the triode Q3 is respectively connected with a base electrode of the triode Q4 and a collector electrode of the triode Q7, a collector electrode of the triode Q3 is connected with a first end of the current sink module, and a collector electrode of the triode Q4 is respectively connected with an emitting electrode of a triode Q7 and a first end of a resistor R4; the third triode unit 2221 comprises a triode Q5, the fourth triode unit 2222 comprises a triode Q6, the second current module 222 further comprises a resistor R2, the emitter electrodes of the triodes Q5 and Q6 and the other end of the resistor R3 are respectively connected with one end of a resistor R2, the other end of the resistor R2 is connected with a power supply voltage terminal VCC, the base electrode of the triode Q5 is respectively connected with the base electrode of the triode Q6 and the collector electrode of the triode Q7, the collector electrode of the triode Q5 is respectively connected with the first end of the resistor R4 and the emitter electrode of the triode Q7, and the collector electrode of the triode Q6 is respectively connected with the second end of the current sink module and the output end of the over-current detection circuit;
the current sink module 230 includes transistors Q8 and Q9, a collector of a transistor Q8 is connected to a collector of a transistor Q3, a base of a transistor Q8 is connected to a collector of a transistor Q8 and a base of a transistor Q9, emitters of the transistors Q8 and Q9 are grounded, and a collector of a transistor Q9 is connected to a collector of the transistor Q6 and an output of the over-current detection circuit.
The operating principle of the over-current detection circuit is as follows: the transistors Q2 and Q1 in the switching power supply chip are arranged according to the following steps of 1: when the proportion of N is matched, I0: i1= N: 1, wherein I0 is the collector current flowing through the transistor Q1, I1 is the current flowing through R1; the voltage VN = VCC-I1 × R1, where the voltage VN is the voltage output by the current sampling module in the switching power supply chip, and the voltage VP = VCC-I4 × R2; current I2= Veb/R3, Veb is the emitter-base junction voltage drop of the transistor Q5, and current I3= (VREF-VbeQ7)/R4 flowing through the resistor R4, wherein VbeQ7 is the base-emitter junction voltage drop of the transistor Q7, current I3 provides bias current for the transistors Q4 and Q5, and the magnitude of current I3 is the sum of collector currents IcQ4 and IcQ5 of the transistors Q4 and Q5 and the emitter current IeQ7 of the transistor Q7; since the reference signal terminal VREF is a reference voltage inside the switching power supply chip and is kept constant at a constant value, and the resistor R4 is constant, the current I3 is fixed. The current flowing through the power tube is denoted as I0, the current is set as Iocp for the overcurrent protection point of the power tube in advance, the collector current IcQ3 of the triode Q3 is the first current, the collector current IcQ6 of the triode Q6 is the second current, and as the current flowing through the power tube changes all the time, the working process of the overcurrent detection circuit can be described as follows: after the switching power supply is powered on, when the current I0< the current Iocp is in normal operation, namely when the current I0 flowing through the power tube is smaller than the current Iocp of a preset overcurrent protection point of the power tube, the voltage drop generated by the current I1 on the resistor R1 is relatively small, the voltage VN > the voltage VP, the current I3 is the sum of collector currents IcQ4 and IcQ5 of the transistors Q4 and Q5 and the emitter current IeQ7 of the transistor Q7, and the current IcQ4> the current IcQ5, since IcQ3= IcQ4 and IcQ5= IcQ6, IcQ3> IcQ6, since IcQ3= IcQ8= IcQ9 and IcQ3> IcQ6, the current flowing through the collector of the transistor Q9 is larger than the current flowing through the collector of the transistor Q6, so that the voltage VO is set to be low, namely the output voltage V0 is in a low level state; as the current I0 flowing through the power tube Q1 becomes larger and the voltage VN decreases gradually, the collector currents IcQ3 and IcQ4 of the transistors Q3 and Q4 become smaller and the collector currents IcQ5 and IcQ6 of the transistors Q5 and Q6 become larger and larger as the current I3 is fixed, when the current I0= the current Iocp, that is, when the current I0 flowing through the power tube is equal to the current Iocp at the preset overcurrent protection point of the power tube, the voltage VN = the voltage VP, the current IcQ4= the current IcQ5= the current IcQ3= the current IcQ6, and the current I4= the current IcQ5+ the current IcQ6+ the current IcQ 7; current I3= current IeQ4+ current IeQ5+ current IeQ7, and current I4= current I3 is derived from the fact that the collector current of the transistor is approximately equal to the emitter current; when current I0= current Iocp, voltage VN = voltage VP, voltage VP = VCC-I4 × R2, VN voltage VN = VCC-I1 × R1, I4 × R2= I1 × R1 can be derived; since currents I3= (VREF-VbeQ7)/R4 and I0: i1= N: 1, calculating the value of the current preset for the overcurrent protection point of the power tube as follows: iocp = I1 × N = I3 × R2 × N/R1= (VREF-VbeQ7) × R2 × N/(R4 × R1), and the value of Iocp is a preset current value of the overcurrent protection point of the power tube; when the current I0> the current Iocp, i.e. when the current I0 flowing through the power transistor is greater than the preset current Iocp at the overcurrent protection point of the power transistor, VN < VP can be IcQ4< IcQ5, and IcQ3< IcQ6, i.e. the current flowing through the collector of the transistor Q9 is smaller than the current flowing through the collector of the transistor Q6, so the voltage V0 is raised, i.e. the voltage V0 is changed from low to high; the whole process can be seen in fig. 5, which shows the signal output by the signal output terminal OCP and the variation curves of the voltages VN and VP with I1 in fig. 5.
Example 2:
an overcurrent protection circuit is applied to a switching power supply, as shown in fig. 4, and includes a current sampling module 100, a pulse signal generating module 300, an overcurrent protection signal output module 400 and the overcurrent detection circuit 200, where the pulse signal generating module 300 is provided with a first output end and a second output end, the first output end is recorded as a third voltage point V3, the overcurrent protection signal output module is provided with a first input end and a second input end, the third voltage point V3 is connected to the second input end, and the second output end is connected to the first input end;
the current sampling module 100 is configured to generate a sampling voltage and input the sampling voltage to the overcurrent detection circuit, the voltage output by the output end of the current sampling module 100 is denoted as a voltage VN, the overcurrent detection circuit outputs a voltage V0 based on the voltage VN, the pulse signal generation module 300 receives the output voltage V0 of the overcurrent detection circuit and performs filtering processing, the second input end of the overcurrent protection signal output module receives the voltage of a third voltage point V3, and whether an overcurrent protection signal is generated is determined based on the magnitude of the third voltage point V3.
In one embodiment, the current sampling module 100 includes transistors Q1, Q2 and a resistor R1, a collector of the transistor Q1 is connected to the power voltage terminal VCC, a base of the transistor Q1 is connected to the drive signal input terminal DRIVER and the base of the transistor Q2, a collector of the transistor Q2 is connected to one end of the resistor R1 and an emitter of the transistor Q3, the other end of the resistor R1 is connected to the power voltage terminal VCC, and emitters of the transistors Q1 and Q2 are connected to the signal output terminal SW. Specifically, the ratio of the current flowing through the transistor Q1 to the current flowing through the transistor Q2 is N: 1.
in a specific embodiment, the pulse signal generating module 300 includes transistors Q10, Q11, Q12, Q13, Q14, Q15, Q16, Q17, Q18, Q19, a capacitor C19, and resistors R19, the bases of the transistors Q19, Q19 are sequentially connected, the base of the transistor Q19 is connected to a first input terminal of the over-current protection signal output module, the emitters of the transistors Q19, Q19 are respectively connected to a power voltage VCC, the collector of the transistor Q19 is connected to the collector of the transistor Q19, the base of the transistor Q19 is connected to a reference signal terminal, the emitter of the transistor Q19 is connected to one end of the resistor R19, the other end of the resistor R19 is connected to the collector of the transistor Q19, the collector of the transistor Q19 is connected to a second voltage V, and the collector of the transistor 19 is connected as a second voltage V-point of the transistor 19, a base of the transistor Q15 is connected to a collector of the transistor Q13, a collector of the transistor Q16 is connected to an emitter of the transistor Q17, a base of the transistor Q17 is connected to a base of the transistor Q15, an emitter of the transistor Q17 is connected to one end of the capacitor C1, the other end of the capacitor C1 is connected to a collector of the transistor Q18 and one end of the resistor R6, the other end of the resistor R6 is connected to a base of the transistor Q20, a collector of the transistor Q20 is connected to a collector of the transistor Q20, a collector of the transistor Q20 is connected to a base of the transistor Q20, a collector of the transistor Q20 is connected to a collector of the transistor Q20, a third voltage point V20 is used as a second input terminal of the overcurrent protection signal output module, and emitters of the transistors Q20, Q20 and Q20 are grounded, the collector of transistor Q17 is connected to ground.
More specifically, the overcurrent protection signal output module 400 includes a transistor Q24 and a transistor Q25, a base of the transistor Q24 is connected to a base of the transistor Q22, an emitter of the transistor Q24 is connected to the power supply voltage terminal VCC, a collector of the transistor Q24 is connected to a collector of the transistor Q25 and serves as a signal output terminal to output the signal OCP, an emitter of the transistor Q25 is grounded, and a base of the transistor Q25 is connected to a collector of the transistor Q23.
The general working process of the overcurrent protection circuit of embodiment 2 is as follows:
the overcurrent protection circuit in this embodiment mainly includes four modules, namely a current sampling module 100, a pulse signal generating module 300, an overcurrent protection signal output module 400 and an overcurrent detection circuit 200, where the current sampling module 100 of the entire switching power supply chip includes power tubes Q1 and Q2, Q2 is a sampling tube matched with Q1 in a manner of 1: N ratio, R1 is a sampling resistor, the current sampling module 100 is configured to sample an output current, when a current of the power tube Q1 is greater than a preset maximum output current Iocp, an output voltage V0 is inverted from a low level to a high level, after the current is inverted to the high level, the pulse signal generating module 300 generates a pulse signal "P" and starts timing, if an overcurrent trigger signal is generated due to glitch or the like, that is, that a duration time of the output voltage V0 in a high level state is less than a pulse time t, the current overcurrent trigger is determined to be invalid, keeping the signal output by the signal output end OCP at a low level, and switching to the second judgment … … to circulate; if the duration time of the overcurrent trigger signal is longer than a pulse time t, judging that the trigger action of the overcurrent trigger is effective, converting the signal output by the signal output end OCP into a high level, and outputting an overcurrent protection signal; according to the process, the overcurrent protection circuit which can effectively judge whether the signal output end of the switching power supply chip is really overcurrent or not, filter interference burrs and achieve accurate detection and is simple in circuit can be formed.
Here, the functions of each module and the related parameter relationships are described in detail as follows:
in the current sampling module 100 and the overcurrent detection circuit 200, the sampling tube Q1 is a power tube inside a switching power supply chip, the power tube Q2 is a sampling tube matched with the power tube Q1 according to a ratio of 1: N, I0: i1= N: 1; voltage VN = VCC-I1 × R1, voltage VP = VCC-I4 × R2; the current I2 is the ratio of emitter-base junction voltage drop Veb of Q5 to R3, and the current I2= Veb/R3; i3= (VREF-Vbe)/R4, the voltage Vbe is the base-emitter junction voltage drop of the transistor Q7, the current I3 provides bias current for the transistors Q4 and Q5, when the current I0 flowing through the power tube Q1 is greater than the current Iocp of the preset power tube overcurrent protection point, the current I1 flowing through the transistor Q2 is Iocp/N and is converted into a voltage signal through the resistor R1, and the voltage = VN-I1 × R1.
In the pulse signal generating module 300, when the overcurrent detection circuit 200 does not generate an overcurrent protection signal, that is, does not trigger an overcurrent signal, the output voltage V0 is at a low level, at this time, the first voltage point V1 is at a high level, the transistor Q15 is turned on, the transistor Q17 is turned off, the second voltage point V2 is at a low level, the voltage of the left plate of the capacitor C1 is VCC, and the voltage of the right plate is Vbe; when the overcurrent detection circuit 200 generates an overcurrent protection signal, namely, a trigger overcurrent signal, the triode Q17 is turned on, the voltage of the left electrode plate of the capacitor C1 is changed from VCC to Vbe, the voltage of the right electrode plate of the capacitor C1 is changed into 2Vbe-VCC <0, at this time, the triode Q20 is turned off, the capacitor C1 is charged by the current I6 and timing is started, and the triode Q20 is turned on until the voltage of the right electrode plate of the capacitor C1 is changed into Vbe. During this period, the voltage of the collector of the transistor Q20 forms a pulse signal "P", the duration of the pulse signal "P" is equal to the charging time t of the capacitor C1, where the charging time t of the capacitor C1 is determined by the size of the capacitor C1 and the charging current I6, and during the charging time t, the voltage variation across the capacitor C1 is Vbe- (2 Vbe-VCC), and assuming that the capacitance value of the capacitor C1 is C1 and the charging current is I6, there is t = (Vbe- (2 Vbe-VCC)) = I6= (Vbe- (2 Vbe-VCC)) C1, and t = (Vbe- (2 Vbe-VCC)) × C1/I6= (VCC-Vbe) × C1/I6, where I6 is proportionally mirrored by the current source I5. When the overcurrent protection trigger signal is judged to be a glitch signal, the second voltage point V2 is at a low level, and the third voltage point V3 is at a high level; when the overcurrent trigger signal is active, the second voltage point V2 is at a high level, and the third voltage point V3 is at a low level;
in the overcurrent protection signal output module 400, when the third voltage point V3 is at a high level, the transistor Q25 is turned on, and a signal output by the signal output terminal OCP is at a low level; when the third voltage point V3 is at a low level, the transistor Q25 is turned off, the signal output from the signal output terminal OCP is at a high level, and an over-current protection signal is generated.
Based on the above functions of each module and the correlation between the modules, the operation principle of the whole overcurrent protection circuit is as follows:
the current flowing through the power tube is denoted as I0, the current is set to Iocp for the overcurrent protection point of the power tube in advance, and as the current flowing through the power tube changes all the time, the working process of the overcurrent detection circuit can be described as follows: after the switching power supply chip is powered on, when the switching power supply chip normally works, the input current is current I0< current Iocp, that is, when current I0 flowing through the power tube is smaller than current Iocp of a preset power tube overcurrent protection point, then, the voltage drop generated by current I1 on resistor R1 is relatively small, voltage VN > voltage VP exists, current I3 is the sum of collector currents IcQ4 and IcQ5 of transistors Q4 and Q5 and emitter current IeQ7 of transistor Q7, and IcQ4> IcQ5 (similarly, IcQ3> IcQ 6), since IcQ3= IcQ8= IcQ9, IcQ9 is the current flowing through the collector of transistor Q9, and IcQ3> IcQ6, that is, the current flowing through the collector of Q9 is greater than the current flowing through the collector of Q6, output voltage V0 is set to be low, that is a low level state; as the current I0 flowing through the power tube Q1 becomes larger and the voltage VN decreases gradually, the collector currents IcQ3 and IcQ4 of the transistors Q3 and Q4 become smaller and the collector currents IcQ5 and IcQ6 of the transistors Q5 and Q6 become larger and larger as the current I3 is fixed, when the current I0= the current Iocp, that is, when the current I0 flowing through the power tube is equal to the current Iocp at the preset overcurrent protection point of the power tube, the voltage VN = the voltage VP, the current IcQ4= the current IcQ5= the current IcQ3= the current IcQ6, and the current I4= the current IcQ5+ the current IcQ6+ the current IcQ 7; current I3= current IeQ4+ current IeQ5+ current IeQ7, and current I4= current I3 is derived from the fact that the collector current of the transistor is approximately equal to the emitter current; when current I0= current Iocp, voltage VN = voltage VP, voltage VP = VCC-I4 × R2, voltage VN = VCC-I1 × R1, I4 × R2= I1 × R1 can be derived; since currents I3= (VREF-VbeQ7)/R4 and I0: i1= N: 1, calculating the value of the current preset for the overcurrent protection point of the power tube as follows: iocp = I1 × N = I3 × R2 × N/R1= (VREF-VbeQ7) × R2 × N/(R4 × R1), and the value of Iocp is a preset current value of the overcurrent protection point of the power tube; when the current I0> the current Iocp, i.e., when the current I0 flowing through the power transistor is greater than the predetermined current Iocp at the overcurrent protection point of the power transistor, the voltage VN < the voltage VP, it can be obtained that the current IcQ4< the current IcQ5 and IcQ3< IcQ6, the current flowing through the collector of the transistor Q9 is smaller than the current flowing through the collector of the transistor Q6, so the output power V0 is raised, i.e., the output voltage V0 is changed from low to high.
After the output voltage V0 becomes high level, the triode Q13 is conducted, meanwhile, the triode Q15 is turned off, the voltage of a first voltage point V1 becomes low level, and the triode Q17 is conducted; before the triode Q17 is not conducted, the voltage of the left electrode plate of the capacitor C1 is VCC, the voltage of the right electrode plate is the voltage drop Vbe of the base electrode collector junction of the Q20, and the voltage of the two ends of the capacitor C1 is VCC-Vbe; after the triode Q17 is turned on, the voltage of the left electrode plate of the capacitor C1 is changed into the junction voltage drop Vbe between the base and the emitter of the triode Q17, and the voltage at the two ends of the capacitor cannot suddenly change, so that the voltage of the right electrode plate of the capacitor C1 is changed into Vbe- (VCC-Vbe) =2Vbe-VCC <0, and the voltage of the right electrode plate is negative, which causes the triode Q20 to be turned off, and the current I6 charges the capacitor C1, when the voltage of the right electrode plate of the capacitor C1 is less than the voltage Vbe, that is, before the triode Q20 is turned on, the collector of the triode Q20 generates a pulse signal "P", and the duration of the pulse signal. The triode Q21 is conducted in the lasting time t of the pulse signal P, the level of the second voltage point V2 is always in a low level state, and the state of the signal output by the output signal end OCP and the state of the second voltage point V2 are in the same level state; if the generated overcurrent trigger signal is generated by false action trigger such as burrs and the like, the duration time of the high level of the output voltage V0 is shorter than the time t, then the signal output by the output signal end OCP is low level within the time t, the overcurrent trigger signal is judged to be invalid overcurrent trigger, further the next overcurrent judgment … … is carried out, if the overcurrent trigger time is longer than t, the second voltage point V2 becomes high level due to the fact that the triode Q21 is turned off after the pulse signal passes, the signal output by the output signal end OCP is also high level, and an overcurrent protection signal is output, so that the function of filtering the current burrs at the output end is realized; after the effective overcurrent is triggered, the signal output by the output signal terminal OCP is at a high level, the above process is simulated, and a simulation diagram can refer to fig. 6.
Example 3:
the embodiment relates to a switching power supply, which comprises an overcurrent protection circuit in other embodiments.
In addition, it should be noted that the specific embodiments described in the present specification may differ in the shape of the components, the names of the components, and the like. All equivalent or simple changes of the structure, the characteristics and the principle of the invention which are described in the patent conception of the invention are included in the protection scope of the patent of the invention. Various modifications, additions and substitutions for the specific embodiments described may be made by those skilled in the art without departing from the scope of the invention as defined in the accompanying claims.
Claims (10)
1. An overcurrent detection circuit is applied to an overcurrent protection circuit in a switching power supply chip, and comprises a current sampling module for generating sampling voltage, wherein the current sampling module is provided with a power tube and an output end, and the voltage of the output end is marked as VN;
the current generating module comprises a first current module and a second current module connected with the first current module, the first current module comprises a first triode unit and a second triode unit, the first triode unit is respectively connected with the second triode unit, the output end of the current sampling module, the first end of the current bias module and the first end of the current sink module, and the second triode unit is connected with the output end of the current sampling module and the current bias module; the second current module comprises a third triode unit and a fourth triode unit, a voltage point is arranged at the input end of the second current module and is connected with the third triode unit and the fourth triode unit, the voltage point is recorded as VP, the fourth triode unit is respectively connected with the third triode unit, the second end of the current sink module and the current bias module, the third triode unit is respectively connected with the second triode unit and the current bias module, based on voltage VN, the current flowing out of the collector of the first triode unit is a first current, based on voltage VP, the current flowing out of the collector of the fourth triode unit is a second current, the current sink module draws the first current and the second current, the current bias module generates bias currents for the second triode unit and the third triode unit, the bias currents are constant values, and the bias currents are collector currents in the second triode unit and the third triode unit and triode sending currents in the current bias module The sum of the emitter currents;
when the current flowing through the power tube is smaller than the current of a preset overcurrent protection point of the power tube, the voltage VN is larger than the voltage VP, and as the bias current is a fixed value and is the sum of collector currents in the second triode unit and the third triode unit and the current of an emitter of a triode in the current bias module, the first current is larger than the second current, and further the first current drawn by the current sink module is larger than the second current drawn, the output voltage V0 at the output end of the overcurrent detection circuit is set to be low, namely the output voltage is output in a low level state; as the current flowing through the power tube is increased, the voltage VN is gradually reduced, and the current of the collector of the third triode unit is gradually increased based on the fact that the bias current is a fixed value; when the current flowing through the power tube is larger than the current of the preset overcurrent protection point, the voltage VN is smaller than the voltage VP, as the bias current is a fixed value and is the sum of the collector currents in the second triode unit and the third triode unit and the current of the triode emitter in the current bias module, the first current is smaller than the second current, the first current drawn by the current sink module is smaller than the second current drawn, the output voltage V0 at the output end of the overcurrent detection circuit is raised, and the output voltage is converted from a low level state to a high level state.
2. The over-current detection circuit of claim 1, wherein the over-current detection circuit comprises a resistor R3, the current bias module comprises a transistor Q7 and a resistor R4, a base of the transistor Q7 is connected to a reference signal terminal VREF, an emitter-collector of the transistor Q7 is connected to a first terminal of a resistor R4, a second terminal of the resistor R4 is grounded, a collector of the transistor Q7 is connected to one terminal of the resistor R3, and the other terminal of the resistor R3 is connected to the second current module.
3. The over-current detection circuit of claim 1, wherein the first transistor unit comprises a transistor Q3, the second transistor unit comprises a transistor Q4, emitters of the transistors Q3 and Q4 are respectively connected to an output terminal of the sampling current module, a base of the transistor Q3 is respectively connected to a base of a transistor Q4 and a collector of a transistor Q7, a collector of the transistor Q3 is connected to a first terminal of the current sink module, and a collector of the transistor Q4 is respectively connected to an emitter of a transistor Q7 and a first terminal of a resistor R4;
the third triode unit includes triode Q5, the fourth triode unit includes triode Q6, the second current module still includes resistance R2, triode Q5, the projecting pole of Q6 and the one end of resistance R2 is connected respectively to the other end of resistance R3, mains voltage end VCC is connected to resistance R2's the other end, triode Q6's base and triode Q7's collecting electrode are connected respectively to triode Q5's base, the first end of resistance R4 and triode Q7's projecting pole are connected respectively to triode Q5's collecting electrode, the second end of current trap module and the output of overcurrent detection circuit are connected respectively to triode Q6's collecting electrode.
4. The over-current detection circuit of claim 3, wherein the current sink module comprises transistors Q8 and Q9, a collector of the transistor Q8 is connected to a collector of the transistor Q3, bases of the transistor Q8 are respectively connected to a collector of the transistor Q8 and a base of the transistor Q9, emitters of the transistors Q8 and Q9 are respectively grounded, and a collector of the transistor Q9 is connected to a collector of the transistor Q6 and an output of the over-current detection circuit.
5. An overcurrent protection circuit, which is applied to a switching power supply and is characterized by comprising a current sampling module, a pulse signal generation module, an overcurrent protection signal output module and the overcurrent detection circuit of any one of claims 1 to 4, wherein the pulse signal generation module is provided with a first output end and a second output end, the first output end is recorded as a third voltage point V3, the overcurrent protection signal output module is provided with a first input end and a second input end, the third voltage point V3 is connected with the second input end, and the second output end is connected with the first input end;
the current sampling module is used for generating sampling voltage and inputting the sampling voltage into the overcurrent detection circuit, the voltage output by the output end of the current sampling module is recorded as voltage VN, the overcurrent detection circuit outputs voltage V0 based on the voltage VN, the pulse signal generation module receives the output voltage V0 of the overcurrent detection circuit and carries out filtering processing, the second input end of the overcurrent protection signal output module receives the voltage of a third voltage point V3, and whether an overcurrent protection signal is generated or not is judged based on the size of the third voltage point V3.
6. The overcurrent protection circuit of claim 5, wherein the current sampling module comprises transistors Q1, Q2 and a resistor R1, a collector of the transistor Q1 is connected to the power supply voltage terminal VCC, bases of the transistor Q1 are respectively connected to the driving signal input terminal DRIVER and bases of the transistor Q2, a collector of the transistor Q2 is respectively connected to one end of the resistor R1 and an emitter of the transistor Q3, the other end of the resistor R1 is connected to the power supply voltage terminal VCC, and emitters of the transistors Q1 and Q2 are respectively connected to the signal output terminal SW.
7. The over-current protection circuit of claim 6, wherein a ratio of current flowing through the transistor Q1 to current flowing through the transistor Q2 is N: 1.
8. the over-current protection circuit according to claim 5, wherein the pulse signal generating module comprises transistors Q10, Q11, Q12, Q13, Q14, Q15, Q16, Q17, Q18, Q19, Q20, Q21, Q22 and Q23, a capacitor C1 and resistors R5 and R5, bases of the transistors Q5, Q5 and Q5 are connected in sequence, a base of the transistor Q5 is connected to a first input terminal of the over-current protection signal output module, emitters of the transistors Q5, Q5 are respectively connected to a power supply voltage terminal VCC, a collector of the transistor Q5 is connected to a collector of the transistor Q5, a base of the transistor Q5 is connected to the reference signal terminal VREF, an emitter of the transistor Q5 is connected to one end of the resistor R5, a collector of the transistor Q5 is connected to a collector of the transistor Q5, and a collector of the transistor Q5 is connected to a ground point of the transistor Q5 and used as a first voltage detection circuit for detecting an over-current of the transistor Q5, a collector of the transistor Q14 is connected to a collector of the transistor Q15 and serves as a second voltage point V2, a base of the transistor Q15 is connected to a collector of the transistor Q13, a collector of the transistor Q16 is connected to an emitter of the transistor Q17, a base of the transistor Q17 is connected to a base of the transistor Q15, an emitter of the transistor Q17 is connected to one end of the capacitor C1, the other end of the capacitor C1 is connected to a collector of the transistor Q18 and one end of the resistor R6, the other end of the resistor R6 is connected to a base of the transistor Q20, a collector of the transistor Q20 is connected to a collector of the transistor Q20, a collector of the transistor Q20 is connected to a base of the transistor Q20 and serves as a third voltage point V20, and a voltage V20 of the third voltage point V20 serves as a second input terminal of the overcurrent protection signal output module, the emitters of the transistors Q13, Q15, Q20, Q21, and Q23 are grounded, respectively, and the collector of the transistor Q17 is grounded.
9. The foldback protection circuit of claim 6, wherein the foldback protection signal output module comprises a transistor Q24 and a transistor Q25, a base of the transistor Q24 is connected to a base of the transistor Q22, an emitter of the transistor Q24 is connected to the supply voltage terminal VCC, a collector of the transistor Q24 is connected to a collector of the transistor Q25 and serves as a signal output terminal to output the signal OCP, an emitter of the transistor Q25 is grounded, and a base of the transistor Q25 is connected to a collector of the transistor Q23.
10. A switching power supply comprising the overcurrent protection circuit as set forth in any one of claims 5 to 9.
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