CN207720021U - 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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- CN207720021U CN207720021U CN201721696202.XU CN201721696202U CN207720021U CN 207720021 U CN207720021 U CN 207720021U CN 201721696202 U CN201721696202 U CN 201721696202U CN 207720021 U CN207720021 U CN 207720021U
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Abstract
The utility model 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, feedback circuit to add optocoupler to control by TL431.The utility model at the sampled voltage of UC3842 by accessing an emitter follower, and to increase an artificial slope synchronous with pulsewidth modulation clock on control voltage, △ I disturbances can be reduced to zero by it within the subsequent period.Therefore, even if system is operated in duty ratio more than 50% or under the conditions of continuous inductive current, unstable situation will not occur in system.
Description
Technical field
The utility model is related to electronic technology field of power supplies more particularly to a kind of Switching Power Supply based on UC3842 to protect electricity
Road.
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 disadvantages for this circuit：(1) defect of overload protection；When power overload situation or output short-circuit,
The protection circuit operation of UC3842 makes the duty ratio of output pulse reduce, and output voltage reduces, the supply voltage of UC3842 also with
Reduction, when that cannot work as low as UC3842, entire 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.Due to transformer is there are leakage inductance etc., some Switching Power Supplies are in each switch
There is very high switch spike voltage in period, even if in the case of duty ratio very little, auxiliary power supply voltage can not drop to foot
It is enough low, so can not achieve ideal defencive function.(2) defect 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
It closes, 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 induct certain perceptual voltage.Impedance that this inductive component is presented in high frequency can be very big, thus it will consume it is prodigious
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 cause the maloperation of UC3842 in this way, or even can cause aircraft bombing.Therefore,
This overcurrent protection function of UC3842 is difficult to play a very good protection sometimes, and there is certain defects.
Utility model content
This practical purpose is：To solve the existing protective circuit of switch power source based on UC3842, there is overloads
It cannot play a very good protection when protection and overcurrent protection, there is certain defects.
The technical solution of the utility model 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 chip TL431.
Specifically, the circuit is specially：220V exchanges are electrically accessed the rectification circuit D1, the outlet of rectification circuit D1
The anode of capacitance C8, one end of resistance R6, one end of resistance R9, one end of capacitance C6 and just are separately connected after connection resistance R5 again
One end of grade winding N1, the cathode ground connection of capacitance C8, the Vi interfaces of the other end connection chip UC3842 of capacitance R6, capacitance C6's
The cathode with the other end of resistance R9 and diode D3, the other end of armature winding N1 connect the sun of diode D3 to the other end respectively
Pole；From one end of the drain electrode and capacitance C7 of the anode, metal-oxide-semiconductor of 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 being separately connected resistance R12 in parallel and diode N2, and the source electrode of metal-oxide-semiconductor connects
One end of one end and resistance R8 of connecting resistance R11, resistance R8 are connected with one end of resistance R11, and the grid of MOS pipes is separately connected
One end of one end and resistance R10 of resistance R7, 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 of capacitance C5, the other end of resistance R10 jointly
And the other end of resistance R11 is grounded；It is total with one end of capacitance C9 again behind one end of the cathode connection capacitance C4 of diode D2
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
One end of one end and resistance R2 for holding C11 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 are separately connected chip
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, the other end of diode D5 connect one end of one end and resistance R13 of the anode of capacitance C10, resistance R15, secondary windings
The other end of N3 and the cathode of capacitance C10 are grounded, and are separately connected again after the other end connection optocoupler OP1 output ends 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 of resistance R3 connect core
One end of the reference pole and resistance R14 of piece TL431, the other end of the other end connection resistance R15 of resistance R14 and resistance R16's
One end, the anode of chip TL431 and the other end of resistance R16 are grounded.
After adopting the above scheme, the beneficial effects of the utility model are as follows：
(1) by accessing an emitter follower at the sampled voltage of UC3842, to be increased on control voltage
One artificial slope synchronous with pulsewidth modulation clock, △ I disturbances can be reduced to zero by it within the subsequent period.Therefore,
Even if system is operated in duty ratio more than 50% or under the conditions of continuous inductive current, unstable feelings will not occur in system
Condition.
(2) after using noninductive resistance, 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.Itself is a the errors of high-gain to put by chip TL431
Big device is directly done using foot 1 and is fed back, and has drawn a resistance to foot l from the foot 8 (reference voltage foot) of UC3842, foot 2 passes through R18
Ground connection, has thus skipped the internal amplifier of UC3842, to which the transmission time of feedback signal is shortened half, makes power supply
Dynamic response become faster.
(4) the problems such as foot l for directly controlling UC3842 can also simplify the frequency compensation and small output power of system.
Description of the drawings
Fig. 1 is the structural schematic diagram of the utility model；
Fig. 2 is the structural schematic diagram of the prior art of the utility model.
Specific implementation mode
The following will be combined with the drawings in the embodiments of the present invention, the technical solution in the present embodiment is carried out it is clear, complete
Site preparation describes, it is clear that described embodiment is only a part of the embodiment of the utility model, rather than whole implementation
Example.Based on the embodiments of the present invention, those of ordinary skill in the art are obtained without making creative work
The every other embodiment obtained, shall fall within the protection scope of the present 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 chip TL431.
Specifically, the circuit is specially：220V exchanges are electrically accessed the rectification circuit D1, the outlet of rectification circuit D1
The anode of capacitance C8, one end of resistance R6, one end of resistance R9, one end of capacitance C6 and just are separately connected after connection resistance R5 again
One end of grade winding N1, the cathode ground connection of capacitance C8, the Vi interfaces of the other end connection chip UC3842 of capacitance R6, capacitance C6's
The cathode with the other end of resistance R9 and diode D3, the other end of armature winding N1 connect the sun of diode D3 to the other end respectively
Pole；From one end of the drain electrode and capacitance C7 of the anode, metal-oxide-semiconductor of 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 being separately connected resistance R12 in parallel and diode N2, and the source electrode of metal-oxide-semiconductor connects
One end of one end and resistance R8 of connecting resistance R11, resistance R8 are connected with one end of resistance R11, and the grid of MOS pipes is separately connected
One end of one end and resistance R10 of resistance R7, 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 of capacitance C5, the other end of resistance R10 jointly
And the other end of resistance R11 is grounded；It is total with one end of capacitance C9 again behind one end of the cathode connection capacitance C4 of diode D2
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
One end of one end and resistance R2 for holding C11 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 are separately connected chip
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, the other end of diode D5 connect one end of one end and resistance R13 of the anode of capacitance C10, resistance R15, secondary windings
The other end of N3 and the cathode of capacitance C10 are grounded, and are separately connected again after the other end connection optocoupler OP1 output ends 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 of resistance R3 connect core
One end of the reference pole and resistance R14 of piece TL431, the other end of the other end connection resistance R15 of resistance R14 and resistance R16's
One end, the anode of chip TL431 and the other end of resistance R16 are grounded.
The principles of the present invention are：By accessing an emitter follower at the sampled voltage of UC3842, thus
An artificial slope synchronous with pulsewidth modulation clock is increased on control voltage, it can disturb △ I within the subsequent period
It is dynamic to be reduced to zero.Therefore, even if system is operated in duty ratio more than 50% or under the conditions of continuous inductive current, system will not
There is unstable situation.Noninductive resistance is a kind of wire resistor of Double-wire parallel wound, and precision is high and is easily able to high-power.It adopts
After noninductive resistance, impedance will not increase with the increase of frequency.In this way, even if sample resistance is disappeared at high frequencies
The power of consumption is not more than its nominal power, therefore aircraft bombing phenomenon would not also occurs.It is known that amplifier is used as
It is required for transmission time when signal transmission, is not that output is established simultaneously with input.If feedback signal is connected to UC3842's
Pressure feedback port, then feedback signal need to continue through two high-gain error amplifiers, transmission time increases.Due to chip
Itself is a the error amplifiers of high-gain by TL431, therefore, are directly done and are fed back using foot 1, from the 8 (base of foot of UC3842
Quasi- voltage foot) draw a resistance to foot l, foot 2 is grounded by R18, has thus skipped the internal amplifier of UC3842, from
And the transmission time of feedback signal is shortened half, so that the dynamic response of power supply is become faster；Meanwhile directly controlling the foot of UC3842
L can also simplify the problems such as frequency compensation and small output power of system.
It is obvious to a person skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and
And without departing substantially from the spirit or essential attributes of the utility model, it can realize that this practicality is new in other specific forms
Type.Therefore, in all respects, the present embodiments are to be considered as illustrative and not restrictive, this practicality is new
The range of type is indicated by the appended claims rather than the foregoing description, it is intended that containing in the equivalent requirements of the claims will be fallen
All changes in justice and range are embraced therein.Any reference numeral in claim should not be considered as limitation
Involved claim.
In addition, it should be understood that although this specification is described in terms of embodiments, but not each embodiment is only wrapped
Containing an independent technical solution, this description of the specification is merely for the sake of clarity, and those skilled in the art should
It considers the specification as a whole, the technical solutions in the various embodiments may also be suitably combined, forms those skilled in the art
The other embodiment being appreciated that.
Claims (2)
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, which is characterized in that an emitter follower is accessed at the sampled voltage of chip UC3842,
Sample resistance uses noninductive resistance, feedback circuit to add optocoupler to control by microarray biochip TL431；The circuit is specially：220V is handed over
Galvanic electricity accesses the rectification circuit D1, is separately connected anode, the electricity of capacitance C8 after the outlet connection resistance R5 of rectification circuit D1 again
Hinder one end of R6, one end of resistance R9, capacitance C6 one end and armature winding N1 one end, capacitance C8 cathode ground connection, capacitance
The Vi interfaces of the other end connection chip UC3842 of R6, the other end of capacitance C6 respectively with the other end of resistance R9 and diode D3
Cathode, the anode of the other end connection diode D3 of armature winding N1；From the sun of one end connection diode D2 of feedback winding N2
Pole, the drain electrode of metal-oxide-semiconductor and capacitance C7 one end, from the other end ground connection for presenting winding N2, the other end of capacitance C7 is separately connected simultaneously
It is grounded after the resistance R12 and diode N2 of connection, one end of one end and resistance R8 of the source electrode connection resistance R11 of metal-oxide-semiconductor, resistance R8
It is connected with one end of resistance R11, the grid of metal-oxide-semiconductor is separately connected one end of one end and resistance R10 of resistance R7, and resistance R7's is another
One end connects the Vo interfaces of chip UC3842, and the other end of resistance R8 and one end of capacitance C5 connect chip UC3842's jointly
The other end of Ics interfaces, the other end of capacitance C5, the other end of resistance R10 and resistance R11 is grounded；The moon of diode D2
It connect the Vi interfaces of chip UC3842, capacitance C9 and capacitance C4 behind one end of pole connection capacitance C4 jointly with one end of capacitance C9 again
The other end be grounded；One end of collector connection capacitance C11 and one end of resistance R2 of optocoupler OP1 connects chip jointly
The Vcomp interfaces of UC3842, one end of the emitter connection resistance R18 of optocoupler OP1 input terminals, the other end and electricity of resistance R18
One end of resistance R17 connects the Vfb interfaces of chip UC3842 jointly, the other end of resistance R2 and the other end of resistance R17 respectively with
And the collector of the common connecting triode V1 of Vref interfaces of chip UC3842, the Vref interfaces of chip UC3842 are sequentially connected electricity
It is grounded after resistance R4 and capacitance C3；The base stage of the Rt/Ct interface connecting triodes V1 of chip UC3842, one end connection three of resistance R1
The transmitter of pole pipe V1, the other end are separately connected Ics interfaces and the ground of chip UC3842.
2. a kind of protective circuit of switch power source based on UC3842 according to claim 1, which is characterized 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
The anode of capacitance C10, one end and resistance R13 of resistance R15 one end, the cathode of the other end and capacitance C10 of secondary windings N3
It is grounded, one end of capacitance C1 and the cathode of TL43 is separately connected again after the other end connection optocoupler OP1 output ends of resistance R13,
One end of the other end connection resistance R3 of capacitance C1, the reference pole of the other end connection chip TL431 of resistance R3 and resistance R14's
One end, one end of the other end and resistance R16 of the other end connection resistance R15 of resistance R14, the anode and resistance of chip TL431
The other end of R16 is grounded.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201721696202.XU CN207720021U (en) | 2017-12-07 | 2017-12-07 | A kind of protective circuit of switch power source based on UC3842 |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201721696202.XU CN207720021U (en) | 2017-12-07 | 2017-12-07 | A kind of protective circuit of switch power source based on UC3842 |
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| CN207720021U true CN207720021U (en) | 2018-08-10 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107947549A (en) * | 2017-12-07 | 2018-04-20 | 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 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107947549A (en) * | 2017-12-07 | 2018-04-20 | 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 |
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Address after: 621000 Yongxing Town Industrial Park, Mianyang High-tech Zone, Sichuan Province Patentee after: Sichuan Jingweida Science and Technology Group Co., Ltd. Address before: 621000 Yongxing Town Industrial Park, Mianyang High-tech Zone, Sichuan Province Patentee before: MIANYANG HIGHLY-TECH JINGWEIDA SCIENTIFIC CO., LTD. |