CN107947549A - A kind of protective circuit of switch power source based on UC3842 - Google Patents
A kind of protective circuit of switch power source based on UC3842 Download PDFInfo
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- CN107947549A CN107947549A CN201711286642.2A CN201711286642A CN107947549A CN 107947549 A CN107947549 A CN 107947549A CN 201711286642 A CN201711286642 A CN 201711286642A CN 107947549 A CN107947549 A CN 107947549A
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- 230000001681 protective effect Effects 0.000 title claims abstract description 10
- 238000004804 winding Methods 0.000 claims description 21
- 239000004065 semiconductor Substances 0.000 claims description 7
- 230000005611 electricity Effects 0.000 claims description 4
- 230000001939 inductive effect Effects 0.000 abstract description 6
- 238000005516 engineering process Methods 0.000 abstract description 3
- 230000001360 synchronised effect Effects 0.000 abstract description 3
- 230000007547 defect Effects 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 230000008054 signal transmission Effects 0.000 description 2
- 206010016322 Feeling abnormal Diseases 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
Abstract
The present invention discloses a kind of protective circuit of switch power source based on UC3842; it is related to electronic technology field of power supplies; including rectification circuit, high frequency transformer, MOS power tubes and current source PWM chip UC3842; an emitter follower is accessed at the sampled voltage of chip UC3842; sample resistance uses noninductive resistance, and feedback circuit adds optocoupler to control by TL431.The present invention at the sampled voltage of UC3842 by accessing an emitter follower, so as to add an artificial slope synchronous with pulsewidth modulation clock on control voltage, △ I disturbances can be reduced to zero by it within the follow-up cycle.Therefore, even if system is operated in duty cycle more than 50% or under the conditions of continuous inductive current, unstable situation will not occur in system.
Description
Technical field
The present invention relates to electronic technology field of power supplies, more particularly to a kind of protective circuit of switch power source based on UC3842.
Background technology
UC3842 is a kind of current-control type pulse width modulating chip of function admirable of Unltmde companies of U.S. production, it
It is few with number of pin, the features such as peripheral circuit is simple, thus be widely used.But with UC3842 switching frequencies
Raising, also there are many problems in the protection circuit for the Switching Power Supply being made of it.The typical application circuits of UC3842 are such as
Shown in Fig. 1, there are this some shortcoming for this circuit：(1) the defects of overload protection；When power overload situation or output short-circuit,
The protection circuit operation of UC3842, reduces the duty cycle of output pulse, and output voltage reduces, the supply voltage of UC3842 also with
Reduction, when it is low cannot work to UC3842 when, whole circuit is closed, and is then begun start-up course next time by R6 skewers.At this
Under kind guard mode, its mean power is very low.Since transformer is there are reasons such as leakage inductances, some Switching Power Supplies are in each switch
There is very high switch spike voltage in cycle, and in the case of duty cycle very little, auxiliary power supply voltage can not drop to foot
It is enough low, so can not achieve preferable defencive function.(2) the defects of overcurrent protection；Since detection resistance can induce peak value electricity
Inducing current, so self-assembling formation pulse current-limiting circuit one by one, as long as the level in detection resistance reaches lV, pulse width modulator is immediately
Close, therefore this peak inductive current detection technique can precisely limit the maximum current of output so that in Switching Power Supply
Magnetic element and power device need not design larger surplus, it is ensured that the reliable operation of regulated power supply.But usually we
The sampling resistor of use is all metal film or oxidation film resistance, and this resistance is thoughts, when electric current flows through sample resistance, just
Can be inducted certain perceptual voltage.Impedance that this inductive component is presented in high frequency can be very big, thus it will consumption it is very big
Power.With the increase of frequency, the electric current for flowing through sample resistance is possible to not discharge also before next cycle of oscillation arrives,
The electric current that sample resistance is born will be increasing, will so cause the maloperation of UC3842, or even can cause aircraft bombing.Therefore,
This overcurrent protection function of UC3842 is difficult to play a very good protection sometimes, there is it is certain the defects of.
The content of the invention
This practical purpose is：To solve the existing protective circuit of switch power source based on UC3842, there is overload
Protection and overcurrent protection when, cannot play a very good protection, there is it is certain the defects of.
Technical scheme is as follows：
A kind of protective circuit of switch power source based on UC3842, including rectification circuit, high frequency transformer, MOS power tubes with
And current source PWM chip UC3842, an emitter follower, sample resistance are accessed at the sampled voltage of chip UC3842
Using noninductive resistance, feedback circuit adds optocoupler to control by TL431.
Specifically, the circuit is specially：220V exchanges are electrically accessed the rectification circuit D1, the outlet of rectification circuit D1
Connect the cathode for connecting capacitance C8 after resistance R5 respectively again, one end of resistance R6, one end of resistance R9, one end of capacitance C6 and just
One end of level winding N1, the anode ground connection of capacitance C8, the Vi interfaces of the other end connection chip UC3842 of capacitance R6, capacitance C6's
The other end connects the sun of diode D3 with the other end of resistance R9 and the cathode of diode D3, the other end of armature winding N1 respectively
Pole；The drain electrode of anode, metal-oxide-semiconductor and one end of capacitance C7 from one end connection diode D2 of feedback winding N2, from feedback winding N2's
The other end is grounded, and the other end of capacitance C7 is grounded after connecting the resistance R12 and diode N2 of parallel connection respectively, and the source electrode of metal-oxide-semiconductor connects
One end of connecting resistance R11 and one end of resistance R8, resistance R8 are connected with one end of resistance R11, and the grid of MOS pipes connects respectively
One end of resistance R7 and one end of resistance R10, the Vo interfaces of the other end connection chip UC3842 of resistance R7, resistance R8's is another
One end and one end of capacitance C5 connect the Ics interfaces of chip UC3842, the other end, the other end of resistance R10 of capacitance C5 jointly
And the other end of resistance R11 is grounded；One end behind one end of the cathode connection capacitance C4 of diode D2 again with capacitance C9 is total to
With the Vi interfaces of connection chip UC3842, the other end of capacitance C9 and capacitance C4 are grounded；The collector connection electricity of optocoupler OP1
Hold one end of C11 and one end of resistance R2 connects the Vcomp interfaces of chip UC3842, the emitter of optocoupler OP1 input terminals jointly
One end of resistance R18 is connected, the other end of resistance R18 and one end of resistance R17 connect the Vfb interfaces of chip UC3842 jointly,
The other end and the other end difference of resistance R17 and the common connecting triode V1 of Vref interfaces of chip UC3842 of resistance R2
Collector, the Vref interfaces of chip UC3842 are grounded after being sequentially connected resistance R4 and capacitance C3；The Rt/Ct of chip UC3842 connects
The base stage of mouth connecting triode V1, the transmitter of one end connecting triode V1 of resistance R1, the other end connect chip respectively
The Ics interfaces of UC3842 and ground.
Further, the connection of secondary windings side is in the circuit：One end connection diode D5's of secondary windings N3
Anode, anode, one end of resistance R15 and one end of resistance R13 of the other end connection capacitance C10 of diode D5, secondary windings
The other end of N3 and the cathode of capacitance C10 are grounded, and are connected respectively again after the other end connection optocoupler OP1 output terminals of resistance R13
One end of capacitance C1 and the cathode of TL43, one end of the other end connection resistance R3 of capacitance C1, the other end connection of resistance R3
The reference pole of TL431 and one end of resistance R14, the other end of the other end connection resistance R15 of resistance R14 and the one of resistance R16
End, the anode of TL431 and the other end of resistance R16 are grounded.
After using the above scheme, beneficial effects of the present invention are as follows：
(1) by accessing an emitter follower at the sampled voltage of UC3842, so as to be added on control voltage
One artificial slope synchronous with pulsewidth modulation clock, △ I disturbances can be reduced to zero by it within the follow-up cycle.Therefore,
Even if system is operated in duty cycle more than 50% or under the conditions of continuous inductive current, unstable feelings will not occur in system
Condition.
(2) after using noninductive resistance, its impedance will not increase with the increase of frequency, even if sampling at high frequencies
The power that resistance is consumed is not more than its nominal power, therefore aircraft bombing phenomenon would not also occurs.
(3) feedback circuit uses TL43l instead and adds optocoupler to control.The error amplifier of inherently one high-gain of TL431,
Directly done and fed back using foot 1, drawn a resistance to be grounded to foot l, foot 2 by R18 from the foot 8 (reference voltage foot) of UC3842,
The internal amplifier of UC3842 has thus been skipped, so that the transmission time of feedback signal is shortened half, has made the dynamic of power supply
State response accelerates
(4) the problems such as frequency compensation and small output power of system can also be simplified by directly controlling the foot l of UC3842.
Brief description of the drawings
Fig. 1 is the structure diagram of the present invention；
Fig. 2 is the structure diagram of the prior art of the present invention.
Embodiment
Below in conjunction with the attached drawing in the embodiment of the present invention, the technical solution in the present embodiment is carried out clearly and completely
Description, it is clear that described embodiment is only the part of the embodiment of the present invention, instead of all the embodiments.Based on this
Embodiment in invention, the every other reality that those of ordinary skill in the art are obtained without making creative work
Example is applied, belongs to the scope of protection of the invention.
A kind of protective circuit of switch power source based on UC3842, including rectification circuit, high frequency transformer, MOS power tubes with
And current source PWM chip UC3842, an emitter follower, sample resistance are accessed at the sampled voltage of chip UC3842
Using noninductive resistance, feedback circuit adds optocoupler to control by TL431.
Specifically, the circuit is specially：220V exchanges are electrically accessed the rectification circuit D1, the outlet of rectification circuit D1
Connect the cathode for connecting capacitance C8 after resistance R5 respectively again, one end of resistance R6, one end of resistance R9, one end of capacitance C6 and just
One end of level winding N1, the anode ground connection of capacitance C8, the Vi interfaces of the other end connection chip UC3842 of capacitance R6, capacitance C6's
The other end connects the sun of diode D3 with the other end of resistance R9 and the cathode of diode D3, the other end of armature winding N1 respectively
Pole；The drain electrode of anode, metal-oxide-semiconductor and one end of capacitance C7 from one end connection diode D2 of feedback winding N2, from feedback winding N2's
The other end is grounded, and the other end of capacitance C7 is grounded after connecting the resistance R12 and diode N2 of parallel connection respectively, and the source electrode of metal-oxide-semiconductor connects
One end of connecting resistance R11 and one end of resistance R8, resistance R8 are connected with one end of resistance R11, and the grid of MOS pipes connects respectively
One end of resistance R7 and one end of resistance R10, the Vo interfaces of the other end connection chip UC3842 of resistance R7, resistance R8's is another
One end and one end of capacitance C5 connect the Ics interfaces of chip UC3842, the other end, the other end of resistance R10 of capacitance C5 jointly
And the other end of resistance R11 is grounded；One end behind one end of the cathode connection capacitance C4 of diode D2 again with capacitance C9 is total to
With the Vi interfaces of connection chip UC3842, the other end of capacitance C9 and capacitance C4 are grounded；The collector connection electricity of optocoupler OP1
Hold one end of C11 and one end of resistance R2 connects the Vcomp interfaces of chip UC3842, the emitter of optocoupler OP1 input terminals jointly
One end of resistance R18 is connected, the other end of resistance R18 and one end of resistance R17 connect the Vfb interfaces of chip UC3842 jointly,
The other end and the other end difference of resistance R17 and the common connecting triode V1 of Vref interfaces of chip UC3842 of resistance R2
Collector, the Vref interfaces of chip UC3842 are grounded after being sequentially connected resistance R4 and capacitance C3；The Rt/Ct of chip UC3842 connects
The base stage of mouth connecting triode V1, the transmitter of one end connecting triode V1 of resistance R1, the other end connect chip respectively
The Ics interfaces of UC3842 and ground.
Further, the connection of secondary windings side is in the circuit：One end connection diode D5's of secondary windings N3
Anode, anode, one end of resistance R15 and one end of resistance R13 of the other end connection capacitance C10 of diode D5, secondary windings
The other end of N3 and the cathode of capacitance C10 are grounded, and are connected respectively again after the other end connection optocoupler OP1 output terminals of resistance R13
One end of capacitance C1 and the cathode of TL43, one end of the other end connection resistance R3 of capacitance C1, the other end connection of resistance R3
The reference pole of TL431 and one end of resistance R14, the other end of the other end connection resistance R15 of resistance R14 and the one of resistance R16
End, the anode of TL431 and the other end of resistance R16 are grounded.
The principle of the present invention is：By accessing an emitter follower at the sampled voltage of UC3842, so as to control
An artificial slope synchronous with pulsewidth modulation clock is added on voltage, it can subtract △ I disturbances within the follow-up cycle
It is small to zero.Therefore, even if system is operated in duty cycle more than 50% or under the conditions of continuous inductive current, system will not occur
Unstable situation.Noninductive resistance is a kind of wire resistor of Double-wire parallel wound, its precision is high and is easily able to high-power.Using nothing
After sensing resistor, its impedance will not increase with the increase of frequency.In this way, even if sample resistance is consumed at high frequencies
Power is not more than its nominal power, therefore aircraft bombing phenomenon would not also occurs.It is known that amplifier is used as signal
Transmission time is required for during transmission, is not to export with inputting while establishing.If feedback signal is connected to the voltage of UC3842
Feedback end, then feedback signal need to continue through two high-gain error amplifiers, transmission time increases.Due to TL431 inherently
It is the error amplifier of a high-gain, therefore, is directly done and fed back using foot 1, is drawn from the foot 8 (reference voltage foot) of UC3842
One resistance is grounded to foot l, foot 2 by R18, has thus skipped the internal amplifier of UC3842, so that feedback signal
Transmission time shortens half, the dynamic response of power supply is accelerated；Meanwhile the foot l for directly controlling UC3842 can also simplify system
Frequency compensation and the problems such as small output power.
It is obvious to a person skilled in the art that the invention is not restricted to the details of above-mentioned one exemplary embodiment, Er Qie
In the case of without departing substantially from spirit or essential attributes of the invention, the present invention can be realized in other specific forms.Therefore, no matter
From the point of view of which point, the present embodiments are to be considered as illustrative and not restrictive, and the scope of the present invention is by appended power
Profit requires rather than described above limits, it is intended that all in the implication and scope of the equivalency of claim by falling
Change is included in the present invention.Any reference numeral in claim should not be considered as to the involved claim of limitation.
Moreover, it will be appreciated that although the present specification is described in terms of embodiments, not each embodiment is only wrapped
Containing an independent technical solution, this narrating mode of specification is only that those skilled in the art should for clarity
Using specification as an entirety, the technical solutions in the various embodiments may also be suitably combined, forms those skilled in the art
It is appreciated that other embodiment.
Claims (3)
1. a kind of protective circuit of switch power source based on UC3842, including rectification circuit, high frequency transformer, MOS power tubes and
Current source PWM chip UC3842, it is characterised in that an emitter follower is accessed at the sampled voltage of chip UC3842,
Sample resistance uses noninductive resistance, and feedback circuit adds optocoupler to control by TL431.
A kind of 2. protective circuit of switch power source based on UC3842 according to claim 1, it is characterised in that the circuit
Specially：220V exchanges are electrically accessed the rectification circuit D1, and electricity is connected respectively again after the outlet connection resistance R5 of rectification circuit D1
Hold one end of the cathode of C8, one end of resistance R6, one end of resistance R9, one end of capacitance C6 and armature winding N1, capacitance C8's
Anode is grounded, the Vi interfaces of the other end connection chip UC3842 of capacitance R6, and the other end of capacitance C6 is another with resistance R9 respectively
One end and the cathode of diode D3, the anode of the other end connection diode D3 of armature winding N1；Connect from one end of feedback winding N2
The drain electrode of the anode, metal-oxide-semiconductor of diode D2 and one end of capacitance C7 are connect, from the other end ground connection for presenting winding N2, capacitance C7's is another
One end is grounded after connecting the resistance R12 and diode N2 of parallel connection respectively, one end of the source electrode connection resistance R11 of metal-oxide-semiconductor and resistance
One end of R8, resistance R8 are connected with one end of resistance R11, and the grid of metal-oxide-semiconductor connects one end and the resistance R10 of resistance R7 respectively
One end, the Vo interfaces of the other end connection chip UC3842 of resistance R7, the other end of resistance R8 and one end of capacitance C5 connect jointly
The Ics interfaces of chip UC3842 are connect, the other end of the other end of capacitance C5, the other end of resistance R10 and resistance R11 connects
Ground；The Vi for being connected chip UC3842 behind one end of the cathode connection capacitance C4 of diode D2 jointly with one end of capacitance C9 again connects
Mouthful, the other end of capacitance C9 and capacitance C4 are grounded；One end of the collector connection capacitance C11 of optocoupler OP1 and the one of resistance R2
The Vcomp interfaces of the common connection chip UC3842 in end, one end of the emitter connection resistance R18 of optocoupler OP1 input terminals, resistance
The other end of R18 and one end of resistance R17 connect the Vfb interfaces of chip UC3842, the other end and resistance R17 of resistance R2 jointly
The other end respectively and chip UC3842 the common connecting triode V1 of Vref interfaces collector, the Vref of chip UC3842
Interface is grounded after being sequentially connected resistance R4 and capacitance C3；The base stage of the Rt/Ct interface connecting triodes V1 of chip UC3842, resistance
The transmitter of one end connecting triode V1 of R1, the other end connect Ics interfaces and the ground of chip UC3842 respectively.
A kind of 3. protective circuit of switch power source based on UC3842 according to claim 2, it is characterised in that the circuit
The connection of middle secondary windings side is：The anode of one end connection diode D5 of secondary windings N3, the other end connection of diode D5
One end of the anode of capacitance C10, one end of resistance R15 and resistance R13, the other end of secondary windings N3 and the cathode of capacitance C10
It is grounded, one end of capacitance C1 and the cathode of TL43 is connected respectively again after the other end connection optocoupler OP1 output terminals of resistance R13,
One end of the other end connection resistance R3 of capacitance C1, the reference pole of the other end connection TL431 of resistance R3 and the one of resistance R14
End, the other end of other end connection resistance R15 of resistance R14 and one end of resistance R16, the anode of TL431 and resistance R16's
The other end is grounded.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201711286642.2A CN107947549A (en) | 2017-12-07 | 2017-12-07 | A kind of protective circuit of switch power source based on UC3842 |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201711286642.2A CN107947549A (en) | 2017-12-07 | 2017-12-07 | A kind of protective circuit of switch power source based on UC3842 |
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| CN107947549A true CN107947549A (en) | 2018-04-20 |
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| CN201711286642.2A Pending CN107947549A (en) | 2017-12-07 | 2017-12-07 | A kind of protective circuit of switch power source based on UC3842 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108712061A (en) * | 2018-04-24 | 2018-10-26 | 广州金升阳科技有限公司 | A kind of current-mode power driving circuit |
| CN110739665A (en) * | 2019-09-10 | 2020-01-31 | 科华恒盛股份有限公司 | Protection circuit and switching power supply |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103199686A (en) * | 2013-03-29 | 2013-07-10 | 朱汝庆 | Switching power supply protective circuit |
| CN207720021U (en) * | 2017-12-07 | 2018-08-10 | 绵阳高新区经纬达科技有限公司 | A kind of protective circuit of switch power source based on UC3842 |
-
2017
- 2017-12-07 CN CN201711286642.2A patent/CN107947549A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103199686A (en) * | 2013-03-29 | 2013-07-10 | 朱汝庆 | Switching power supply protective circuit |
| CN207720021U (en) * | 2017-12-07 | 2018-08-10 | 绵阳高新区经纬达科技有限公司 | A kind of protective circuit of switch power source based on UC3842 |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108712061A (en) * | 2018-04-24 | 2018-10-26 | 广州金升阳科技有限公司 | A kind of current-mode power driving circuit |
| CN110739665A (en) * | 2019-09-10 | 2020-01-31 | 科华恒盛股份有限公司 | Protection circuit and switching power supply |
| CN110739665B (en) * | 2019-09-10 | 2022-03-11 | 科华恒盛股份有限公司 | Protection circuit and switching power supply |
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Address after: 621000 Yongxing Town Industrial Park, Mianyang High-tech Zone, Sichuan Province Applicant after: Sichuan Jingweida Science and Technology Group Co., Ltd. Address before: 621000 Yongxing Town Industrial Park, Mianyang High-tech Zone, Sichuan Province Applicant before: MIANYANG HIGHLY-TECH JINGWEIDA SCIENTIFIC CO., LTD. |