CN2785248Y

CN2785248Y - Switch power supply for stabilizing maximum output power limitation

Info

Publication number: CN2785248Y
Application number: CN 200520056602
Authority: CN
Inventors: 毛灿豪
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-31
Filing date: 2005-03-31
Publication date: 2006-05-31
Anticipated expiration: 2015-03-31

Abstract

The utility model discloses a switch power supply for stabilizing maximum output power limitation. The utility model comprises a transformer, a self excitation oscillator and a maximum power output limitation circuit; besides, the utility model is additionally provided with a temperature compensation circuit which can conduct temperature compensation for an on-state voltage of a switch tube in the maximum power output limitation circuit so as to enhance the stability of the entire switch power supply so that the maximum output power can not be influenced by the working temperature, and the maximum capacity of the circuit can be fully displayed.

Description

A kind of Switching Power Supply of stable peak power output restriction

Technical field

The utility model relates to a kind of Switching Power Supply; Be used for DC-DC (DC/DC) converter, ac/dc (AC/DC) converter, battery charger and light-emitting diode charger etc.

Background technology

General Switching Power Supply all is with special-purpose pulsewidth integrated manipulator, as " novel switched power supply practical technique " the 62nd, 63 page of Switching Power Supply of being introduced in the Electronic Industry Press---use pulsewidth integrated manipulator UC3842, it is the integrated circuit of applied current control (Current Mode Control) PWM.Its weak point is: 1, need special-purpose pulsewidth integrated manipulator, cost of manufacture height; 2, need bigger start and ongoing operation electric current; 3, the peripheral components requirement is more, is unfavorable for microminiaturization.

For this reason, it is that ZL02249259.3, denomination of invention are the utility model patent of " a kind of Switching Power Supply " that the present inventor has proposed a kind of patent No., this patent has solved the deficiency that above-mentioned prior art exists, and does not need special-purpose pulsewidth integrated manipulator, start and the ongoing operation electric current is little, circuit is simple; Can realize constant current, constant voltage output and have short-circuit protection function.

The inventor is in R﹠D process subsequently, find above-mentioned improved Switching Power Supply again, its peak power output restriction point can change along with the variation of working temperature, when working temperature is higher, corresponding the diminishing of its peak power output of allowing meeting, so when this type of Switching Power Supply of design, need to consider under maximum operating temperature, whole power supply can also keep enough power outputs, the output of allowing under the normal temperature operating state is artificially improved, to guarantee that Switching Power Supply output has bigger surplus, the peak power output that causes diminishes because working temperature raises with compensation.Though this way can be dealt with problems, thing followed problem is: the capacity of Switching Power Supply output just can not be fully, bring into play efficiently.

Summary of the invention

The purpose of this utility model is exactly in order to overcome above-mentioned the deficiencies in the prior art, proposes a kind of peak power output and is not subjected to working temperature to influence, can bring into play fully the Switching Power Supply of the heap(ed) capacity of circuit.

The utility model realizes that the above-mentioned purpose scheme is: a kind of Switching Power Supply of stable peak power output restriction comprises transformer and self-excited oscillator, maximum power output limiting circuit; Transformer comprises elementary winding T1-A and elementary winding T1-B; Self-excited oscillator comprises by resistance R 2, the charging circuit that capacitor C 3 is composed in series, the current transformation voltage feedback circuit that mainly comprises resistance R 6, primary winding T1-B and switching transistor Q1, via resistance R 2, the charging circuit input that capacitor C 3 is composed in series connects the positive pole of input voltage, output is coupled in the in-phase end of elementary winding T1-B, the input of switching transistor Q1 and resistance R 2, capacitor C 3 also connects, the output stage of the end of oppisite phase serial connection switching transistor Q1 of elementary winding T1-A, another output stage of switching transistor Q1 connects the end of oppisite phase of elementary winding T1-B and the negative pole of input voltage by resistance R 6;

The maximum power output limiting circuit comprises divider resistance R4, divider resistance R5 and transistor Q2, divider resistance R4, divider resistance R5 one end is connected to transistor Q2 base stage altogether, the in-phase end of the elementary winding T1-B of another termination of divider resistance R4 or the in-phase end of elementary winding T1-A, another output stage of the other end of divider resistance R5 and switching transistor Q1, the one end coupling of resistance R 6, the collector electrode of transistor Q2 also connects the control utmost point of switching transistor Q1, the emitter of transistor Q2 also connects the end of oppisite phase of elementary winding T1-B and the other end of resistance R 6, and elementary winding T1-A or elementary winding T1-B two ends are the output voltage signal end;

Also set up temperature-compensation circuit, described temperature-compensation circuit comprises resistance R 7 and diode D7, the in-phase end of the elementary winding T1-B of resistance R 7 one terminations or the in-phase end of elementary winding T1-A, resistance R 7 other ends also meet divider resistance R5 and the anode of diode D7, and the output stage of the negative electrode of diode D7 and switching transistor Q1, resistance R 6 also connect.

Above-mentioned Switching Power Supply also comprises the input rectifying filter circuit, and the voltage output cathode of input rectifying filter circuit connects the in-phase end of elementary winding T1-A, and the voltage output negative pole of input rectifying filter circuit connects the end of oppisite phase of elementary winding T1-B.

Above-mentioned Switching Power Supply, described transformer also comprises secondary winding T1-C, through secondary winding T1-C two ends output voltage signal.

Above-mentioned Switching Power Supply, also set up delay circuit, described delay circuit comprises resistance R 13, transistor Q4 and diode D10, described resistance R 13 1 ends link to each other with the negative pole end of input voltage, the base stage coupling of the other end of resistance R 13 and transistor Q4, the emitter of transistor Q4 connects diode D10 anode, the in-phase end of diode D10 negative electrode and elementary winding T1-B, the coupling of an end of capacitor C 3, the other end coupling of the collector electrode of transistor Q4 and capacitor C 3.Also set up the accelerated charging circuit, described accelerated charging circuit comprises diode D11, capacitor C 9 and resistance R 14, capacitor C 9 and resistance R 14 series connection, one end of another termination capacitor C 3 of capacitor C 9, the other end of another termination capacitor C 3 of resistance R 14, the negative electrode of diode D11 also connects capacitor C 9, resistance R 14, and the anode of diode D11 connects the negative pole end of input voltage.

Preferred field effect transistor MOSFET of above-mentioned switching transistor Q1 or bipolar transistor.

Above-mentioned Switching Power Supply, also set up high frequency noise and reduce circuit, be arranged at the end of oppisite phase of described primary winding T1-A, described high frequency noise reduces circuit and comprises capacitor C 11, the end of oppisite phase of the elementary winding T1-A of one termination of capacitor C 11, the other end of capacitor C 11 and the coupling of the negative pole of input voltage.

Above-mentioned Switching Power Supply is also set up output rectifier and filter, and cross-over connection is between elementary or secondary winding output; Described current rectifying and wave filtering circuit comprises diode D6, capacitor C 5, and described diode D6 anode is connected on the end of oppisite phase of transformer, and negative electrode is connected on the positive pole of capacitor C 5, and the negative pole of capacitor C 5 is connected on the in-phase end of transformer; Or diode D6 negative electrode is connected to the transformer in-phase end, and anode connects the negative terminal of capacitor C 5, the end of oppisite phase of the positive termination transformer of capacitor C 5; The anode of capacitor C 5 is a positive output end, and negative terminal is a negative output terminal.

Above-mentioned Switching Power Supply is also set up feedback control circuit, and described feedback control circuit comprises photoelectrical coupler U1-A and U1-B, resistance R 16, exports constant voltage circuit; Described output constant voltage circuit comprises resistance R 17, resistance R 19, resistance R 20, capacitor C 12, resistance R 18 and voltage-stabiliser tube U2, resistance R 16 and photoelectrical coupler U1A polyphone, the other end of resistance R 16 connects the positive output end of output rectifier and filter, and the negative electrode of photoelectrical coupler U1A connects voltage-stabiliser tube U2 negative electrode; Photoelectrical coupler U1-B input is connected with the negative electrode of diode D8, the in-phase end coupling of diode D8 anode and elementary winding T1-B, photoelectrical coupler U1-B output and the coupling of transistor Q2 base stage, resistance R 17, one end of resistance R 19 is connected to the output of described output rectifier and filter altogether, the other end of resistance R 17 connects voltage-stabiliser tube U2 negative electrode, one end of the other end of resistance R 19 and resistance R 18, the control of voltage-stabiliser tube U2 connects extremely altogether, the other end of resistance R 18 connects the anode of voltage-stabiliser tube U2, the resistance R 20 of series connection and C12 branch road are connected across between the voltage-stabiliser tube U2 negative electrode and the control utmost point, and the anode of voltage-stabiliser tube U2 is connected to the negative terminal of output.

Above-mentioned Switching Power Supply is also set up constant current output circuit, and described constant current output circuit comprises triode Q3, current-limiting resistance R21, resistance R 22, capacitor C 14; The collector electrode of triode Q3 connects the negative electrode of voltage-stabiliser tube U2, base stage connects resistance R 22 1 ends, resistance R 22 other ends connect the anode of voltage-stabiliser tube U2, capacitor C 14 is attempted by between triode Q3 base stage and the emitter-base bandgap grading, resistance R 21 is attempted by between the negative terminal of triode Q3 emitter-base bandgap grading and output, and triode Q3 emitter-base bandgap grading connects the in-phase end of transformer T1 output winding.

Adopt the beneficial effect of above scheme: 1, owing to set up temperature-compensation circuit, can do temperature-compensating to the conducting voltage of transistor Q2, improve the stability of whole Switching Power Supply, make peak power output not be subjected to working temperature to influence, can bring into play fully the heap(ed) capacity of circuit; 2, owing to be provided with delay circuit, when Switching Power Supply is imported very high voltage, increase the needed time cycle of whole self-oscillation, lower frequency of oscillation, thereby reduce the master switch loss, reduce the working temperature of switching tube Q1, increase the working life of switching tube Q1; 3, accelerated charging circuit and delay circuit are set and work together, thereby reach the purpose of output short circuit protection; 4, the high-frequency noise that current rectifying and wave filtering circuit can the elimination Switching Power Supply makes it unlikely and passes back in the input circuit; Piezo-resistance VDR1 wherein is as the input voltage clamper, and the high pressure that prevents from the power supply to be responded to breaks entire circuit; 5, high frequency noise is set and reduces circuit, reducing to external world, electromagnetic high-frequency disturbs; 6, because feedback control circuit and output constant voltage circuit are set, guarantee that output services voltage is stabilized in the set point; 7, set up the output constant-current circuit, guarantee that the output services current stabilization is in steady state value.

Description of drawings

Accompanying drawing is the utility model circuit theory diagrams.

Embodiment

Also in conjunction with the accompanying drawings the utility model is described in further detail below by specific embodiment.

Embodiment one: as shown in the figure, a kind of Switching Power Supply of stable peak power output restriction comprises input rectifying filter circuit, transformer, output rectifier and filter, self-excited oscillator, maximum power output limiting circuit, temperature-compensation circuit, surge voltage absorbing circuit and feedback control circuit, output constant voltage circuit and output constant-current circuit.

Wherein, transformer is made up of elementary winding T1-A, elementary winding T1-B and secondary winding T1-C, when the input voltage of Switching Power Supply is lower, for example is less than 48 volts, and output does not simultaneously need again to isolate with input, and then secondary winding T1-C can.

The input rectifying filter circuit comprises fuse F1, piezo-resistance VDR1, resistance R 1, diode D1, D2, D3, D4, capacitor C 1, C2 and inductance L 1.Diode D1, D2, D3, D4 constitute bridge rectifier, and capacitor C 1, C2 and inductance L 1 are formed pi type filter, with the high-frequency noise elimination of Switching Power Supply, and the unlikely input circuit of passing back.The output of input rectifying filter circuit meets elementary winding T1-A.Piezo-resistance VDR1 is as the input voltage clamper, and the high pressure that prevents from the power supply to be responded to breaks entire circuit.Direct current when input, diode D1, D2, D3, D4 can, just can as long as D1 and D4 replace with wiring.Resistance R 1 can, promptly resistance equals 0.Piezo-resistance VDR1 can.When the direct input DC power of Switching Power Supply, as when being used on the automobile, can not need the input rectifying filter circuit.

Self-excited oscillator comprises resistance R 2, capacitor C 3, resistance R 3, R6, primary winding T1-A, T1-B and switching transistor Q1.The charging circuit that the voltage output of input rectifying filter circuit is composed in series via resistance R 2, capacitor C 3, resistance R 3 connects the in-phase end of elementary winding T1-B, the input of switching transistor Q1 and resistance R 2, capacitor C 3 also connect, elementary winding T1-A end of oppisite phase links to each other with the collector electrode of switching transistor Q1, the emitter of switching transistor Q1 and the negative terminal that connects input after resistance R 6 is connected in series.The series position of resistance R 3 and capacitor C 3 can exchange.Resistance R 3 can not exist, and promptly resistance equals 0.Switching tube Q1 can be bipolar transistor or MOS transistor.

The maximum power output limiting circuit comprises resistance R 4, R5, capacitor C 8 and transistor Q2.The in-phase end of one end of resistance R 4 and connecting resistance R3 and elementary winding T1-B or elementary winding T1-A in-phase end, the other end of resistance R 4 also connects an end of base stage and the resistance R 5 of transistor Q2, the other end of resistance R 5 also connects the emitter of switching transistor Q1 and an end of resistance R 6, the base stage of the collector electrode of transistor Q2 and connecting resistance R2 and capacitor C 3 and transistor Q1, the emitter of transistor Q2 also connects elementary winding T1-B and resistance R 6, one end of capacitor C 8 also connects an end of base stage and the resistance R 5 of transistor Q2, the emitter-base bandgap grading of another termination transistor Q2 of capacitor C 8.Capacitor C 8 can not exist, and promptly capacitance equals 0.

Temperature-compensation circuit comprises resistance R 7 and diode D7, divider resistance R5 links to each other with the emitter of switching transistor Q1 by diode D7, the in-phase end of the elementary winding T1-B of resistance R 7 one terminations or elementary winding T1-A in-phase end, resistance R 7 other ends also meet divider resistance R5 and the anode of diode D7.The negative electrode of diode D7 connects the contact of switching tube Q1 and resistance R 6.

Output rectifier and filter comprises rectifier diode D6, capacitor C 4, C5.The positive pole of rectifier diode D6 connects the end of oppisite phase of secondary winding T1-C, and the negative pole of rectifier diode D6 links to each other with the in-phase end of secondary winding T1-C by capacitor C 5.The positive pole of load connects the positive pole of rectifier diode D6, and the negative pole of load connects the in-phase end of secondary winding T1-C.Filter capacitor C7 one end links to each other with the in-phase end of secondary winding T1-C, and the end of filter capacitor C7 also connects elementary winding T1-B and resistance R 6.Capacitor C 4, C5 can, promptly capacitance equals 0.When input voltage is lower, for example be less than 20 volts, filter capacitor C7 also can.When not needing input and output to isolate, output rectifier and filter can be connected on the elementary winding, be the end of oppisite phase that the positive pole of diode D6 meets elementary winding T1-A or T1-B, the negative pole of rectifier diode D6 links to each other by the in-phase end of capacitor C 5, elementary winding T1-A or T1-B; The positive pole of load connects the positive pole of rectifier diode D6, and the negative pole of load connects the in-phase end of elementary winding T1-A or T1-B.In addition, the serial connection position of the diode of output rectifier and filter and electric capacity is also interchangeable, it is the positive pole of the anti-phase termination capacitor C 5 of transformer T1, the negative pole of capacitor C 5 connects the anode of rectifier diode D6 again, the negative electrode of diode D6 links to each other with the in-phase end of transformer T1, the end of oppisite phase of the cathode connecting transformer T1 of load, the negative pole of load connects the negative pole of rectifier diode.

Constant voltage outputting circuit comprises resistance R 17, resistance R 19, resistance R 20, capacitor C 12, electric capacity R18 and voltage-stabiliser tube U2, one end of resistance R 17, resistance R 19 is connected to the output of described output rectifier and filter altogether, it is the positive pole of rectifier diode D6, the other end of resistance R 17 connects the voltage-stabiliser tube negative electrode, one end of the other end of resistance R 19 and resistance R 18, the control of voltage-stabiliser tube connect extremely altogether, the other end of resistance R 18 connects the anode of voltage-stabiliser tube, and the resistance R 20 of series connection and capacitor C 12 branch roads are connected across between the voltage-stabiliser tube negative electrode and the control utmost point.

Constant current output circuit comprises triode Q3, current-limiting resistance R21, resistance R 22, capacitor C 14; The collector electrode of triode Q3 connects the voltage-stabiliser tube negative electrode, base stage connects R22 one end, resistance R 22 other ends connect the anode of voltage-stabiliser tube, capacitor C 14 is attempted by between triode Q3 base stage and the emitter-base bandgap grading, resistance R 21 is attempted by between triode Q3 emitter-base bandgap grading and the voltage-stabiliser tube anode, and triode Q3 emitter-base bandgap grading connects the in-phase end of transformer T1 output winding.

Feedback control circuit comprises photoelectrical coupler U1-A and U1-B, resistance R 16, output constant voltage circuit, capacitor C 6, resistance R 9, resistance R 10 and diode D8; Resistance R 16 and photoelectrical coupler U1A polyphone, the other end of R16 connects the anode of rectifier diode D6, and the negative electrode of photoelectrical coupler U1A connects the voltage-stabiliser tube negative electrode; Capacitor C 6 one ends connect the end of oppisite phase of elementary winding T1-B, the other end is connected to diode D8 negative electrode, photoelectrical coupler U1-B input altogether, photoelectrical coupler U1-B output connects resistance R 10, the other end of resistance R 10 connects transistor Q2 base stage, and diode D8 anode connects the in-phase end of elementary winding T1-B by resistance R 9.In addition, resistance R 9, resistance R 10 also can be 0 to be R9, R10 short circuit; Resistance R 16 is connected in series the position with photoelectrical coupler U1A and also can exchanges.

Surge voltage absorbing circuit comprises diode D5, resistance R 8, capacitor C 10; Described resistance R 8, capacitor C 10 parallel connections, parallel branch one end connect diode D5 negative electrode, and the other end is connected with the in-phase end of elementary winding T1-A, and diode D5 anode links to each other with the end of oppisite phase of elementary winding T1-A.Resistance R 8 and capacitor C 10 can be replaced by a voltage-stabiliser tube, and the anode of voltage-stabiliser tube connects the in-phase end of elementary winding T1-A, and negative electrode is connected on the negative electrode of diode D5.Diode D5 and resistance R 8, the serial connection of capacitor C 10 or the serial connection of voltage-stabiliser tube are interchangeable in addition.Surge voltage absorbing circuit will be by the energy absorption of the leakage inductance of transformer T1-A, and is unlikely too high with the voltage at the two ends that guarantee T1-A, breakdown switch pipe Q1.When input voltage is lower, for example be less than 20 volts, surge voltage absorbing circuit can.

The course of work is as follows:

Switching transistor Q1 contains a connection stage and an off-phases during operation, and this Switching Power Supply is powered by elementary winding T1-B.Elementary winding T1-B or elementary winding T1-A or secondary winding T1-C, self-excited oscillator, maximum power output limiting circuit are realized the power supply of load jointly.

Self-oscillation: switching transistor Q1 connects via a high resistant resistance R 2, an elementary winding T1-B, capacitor C 3,3 continuous steps of low-resistance resistance R during connecting.At first, the DC power supply of capacitor C 2 outputs is charged to capacitor C 3 through resistance R 2, voltage on capacitor C 3 rises to switching transistor Q1 conducting voltage, switching transistor Q1 enters the deep layer conducting, the electric current of primary winding T1-A begins to rise, this electric current flow through simultaneously switching transistor Q1 and resistance R 6.Voltage rising when resistance R 6, and the resistance R 5 in the maximum power output limiting circuit is added to the voltage on the resistance R 6 on the base stage of transistor Q2, voltage on transistor Q2 base stage rises to and makes transistor Q2 conducting, voltage on the switching transistor Q1 base stage reduces and makes switching transistor Q1 end, and elementary winding T1-B produces a negative voltage makes switching transistor Q1 quicken to end.Simultaneously, be stored in energy among the transformer T and also begin to see through elementary winding or secondary winding T1-C, diode D6, capacitor C4 to capacitor C 5 and load discharge, finish until all energy releases of Switching Power Supply, switching transistor Q1 is conducting again more again, so just finishes a cycle of oscillation.

In the maximum power output limiting circuit, the base voltage of transistor Q2 is made of two voltage additions, and one is the voltage on the resistance R 6, receives the base stage of transistor Q2 through resistance R 5.Another is the voltage on the elementary winding T1-B, receives through resistance R 4 on the base stage of transistor Q2.By being directly proportional with voltage on being added to elementary winding T1-A through the forward voltage on the elementary winding T1-B, ratio is exactly the number of turns ratio of elementary winding T1-B and elementary winding T1-A.So as resistance R 4 is received on the contact of resistance R 2 and capacitor C 2, its effect is the same.When just input voltage was very high, the power consumption of resistance R 4 was bigger, so when low-voltage is imported, for example 48 volts below the DC, generally all can directly receive on the capacitor C 2 of direct current output point.Resistance R 4 is added to a voltage that is proportional to input on the base stage of transistor Q2, when input voltage big more, resistance R 4 is also big more at the bias voltage of transistor Q2 base stage, because the conducting voltage of transistor Q2 is constant under certain environment, so it is big more to work as input voltage, electric current required on the resistance R 6 is also more little, makes transistor Q2 conducting with regard to being enough to produce enough big voltage, and switching transistor Q1 ends.So it is high more to work as input voltage, the electric current of the primary of flowing through winding T1-A, switching transistor Q1, resistance R 6 is then few more.When load current is excessive, the corresponding increase of the electric current of the resistance R of flowing through 6, the voltage negative feedback effect of resistance R 6 make the base voltage of switching transistor Q1 reduce, thereby the conducting state of control switch transistor Q1 reduces electric current in the further conducting of transistor Q2.Just can make peak power output in quite broad input voltage range as long as suitably choose the numerical value of resistance R 4, R5, R6, keep stable, reach and stablize maximum power output control.

After setting up temperature-compensation circuit, when switching transistor Q1 conducting, the electric current resistance R 6 of flowing through, on resistance R 6, produce a voltage, meanwhile, the tie point of primary winding T1-B and diode D7 also produces a positive voltage, this voltage makes the electric current resistance R 7 of flowing through, diode D7, resistance R 6 flows back to power supply negative terminal again, because the resistance value of resistance R 7 is quite big, and the resistance value of resistance R 6 is very little, the voltage that the electric current of diode D7 is produced on resistance R 6 so flow through is very little, and this electric current is the bias current of diode, makes diode produce a forward conduction voltage V _F, the voltage addition on this voltage and the resistance R 6 is added the voltage that resistance R 4 and resistance R 5 produced and is added on the base stage of transistor Q2, when the base voltage Vbe of transistor Q2 arrives the conducting voltage of transistor Q2, and transistor Q2 conducting, switching tube Q1 closes.In addition, the end that resistance R 7 links to each other with the in-phase end of elementary winding T1-B also can be received the positive pole of power supply, promptly receives the in-phase end of elementary winding T1-A, so that the bias current of diode D7 to be provided.

When ambient temperature changes, the forward conduction voltage V of diode _FCan present negative temperature coefficientization, and the required conducting voltage of transistor Q2 also is the negative temperature coefficient variation, the chances are-2mv/ ℃, as long as suitably choose diode and its operating current, the conducting voltage of transistor Q2 can be done good temperature-compensating, makes variations in temperature very little with the variations in temperature of the conducting that makes transistor Q2 to the electric current of the required resistance R 6 of flowing through.

When input voltage is lower, for example be less than 20 volts, output does not simultaneously need again to isolate with input that then secondary winding T1-C can.Output can obtain from elementary winding T1-A or T1-B.Surge absorbing circuit also can, filter capacitor C7 also can.

In the output constant voltage circuit, when output voltage was higher than the partial pressure value that is set by R18 and R19, the U2 cathode voltage descended, and the electric current of U1-A and U1-B can increase.At this moment, the bias voltage that the electric current of U1B produces on resistance R 10 increases, and makes Q2 do sth. in advance conducting, and the ON time of switching transistor Q1 reduces thereupon, and final, output voltage can be adjusted on the predefined numerical value of the voltage divider of being made up of R18 and R19 automatically.

At the output constant-current circuit, when load current is very little, voltage can maintain this preset value, if load current constantly increases, the voltage of resistance R 21 can be followed rising, when the voltage on the resistance R 21 was raised to set point, Q3 is conducting immediately, and the electric current of photoelectrical coupler U1-A, U1-B increases, Q2 does sth. in advance conducting, the ON time of switching tube Q1 also reduces thereupon, and the energy that is stored in transformer also reduces, the output voltage of secondary winding T1-C thereby reduction.After output voltage reduced, therefore output current also reduced, and ultimate current can maintain near the preset value.At this moment, this Switching Power Supply is operated in constant current state, and constant current output is provided.

If the voltage control required precision is not high, the output constant voltage circuit in the secondary control circuit can be replaced by single voltage-stabiliser tube, and the negative electrode of voltage-stabiliser tube is connected on the collector electrode of Q3, and the anode of voltage-stabiliser tube is connected on the ground end of output, the i.e. negative pole of capacitor C 15.

Embodiment two, as shown in the figure, are provided with delay circuit at the two ends of capacitor C 3, and delay circuit comprises resistance R 13, transistor Q4, diode D10, resistance R 12.Described resistance R 13 1 ends link to each other with the negative terminal of input voltage, the other end of resistance R 13 links to each other with the base stage of transistor Q4, the emitter of transistor Q4 links to each other with the anode of diode D10, the negative electrode of diode D10 is linked on the contact of resistance R 3 and C3, link on the contact of elementary winding T1-B, the collector electrode of transistor Q4 is linked on the contact of capacitor C 3 and switching tube Q1 base stage by resistance R 12 again.

When transistor Q2 conducting, switching tube Q1 closes, and becomes negative voltage with the tie point of resistance R 3, electric current flow through resistance R 13, transistor Q4, diode D10, resistance R 3, elementary winding T1-B.This electric current makes transistor Q4 conducting, and capacitor C 3 is through resistance R 12, transistor Q4, diode D10 discharge.After the magnetic energy that is stored in transformer T1 discharges fully, the vanishing of elementary winding T1-B both end voltage, capacitor C 3 is through resistance R 2 chargings, voltage on capacitor C 3 is charged to the conducting voltage of switching tube Q1, switching tube Q1 conducting, electric current flow through primary winding T1-A, switching tube Q1, resistance R 6 flow back to power cathode again, at this moment produce a forward voltage and make switching tube Q1 enter the deep layer conducting on elementary winding T1-B.The electric current of primary winding T1-A rises, and the voltage of resistance R 6 rises until transistor Q2 conducting, and repeat whole cycle of oscillation once more.

In the above-mentioned delay circuit, the series position of diode D10 and transistor Q4 can exchange, and promptly receives the base stage of transistor Q4 after diode D10 and resistance R 13 series connection again, and the emitter-base bandgap grading of transistor Q4 is received on the contact of resistance R 3 and capacitor C 3.In addition because the value of general resistance R 3 is not very big, so the negative electrode of diode D10 can be received on the contact of resistance R 3 and elementary winding T1-B.The value of resistance R 12 can be zero, and promptly the collector electrode of transistor Q4 is directly received on the contact of capacitor C 3 and switching tube Q1 base stage.The serial connection position of resistance R 3 and capacitor C 3 can exchange.

In above-mentioned adjustment process, when making the output current minimizing of triode Q1 whenever the minimizing of the voltage on the Q1 base stage, elementary winding T1-B flyback immediately produces a negative voltage, and this negative voltage makes Q1 quicken to end on the one hand; On the other hand, under the negative voltage effect when elementary winding T1-B flyback, triode Q4 conducting, the discharge loop discharge that charging capacitor C4 connects formation through the collection utmost point and emitter-base bandgap grading, the diode D10 of resistance R 12, triode Q4, before taking place feasible next cycle of oscillation, C4 will charge to the conducting voltage of Q1 through R2, thereby produces a time of delay, when preventing underload and high voltage when input too fast switching frequency to infringement that switching transistor caused.

Embodiment three: on the basis of the foregoing description two, set up the accelerated charging circuit: in order to reach the purpose of output short circuit protection, be provided with accelerated charging circuit and delay circuit and work together.As shown in the figure, the accelerated charging circuit comprises diode D11, capacitor C 9 and resistance R 14, after capacitor C 9 and resistance R 14 series connection, one end of another termination capacitor C 3 of capacitor C 9, the other end of another termination capacitor C 3 of resistance R 14, the negative electrode of diode D11 also connects capacitor C 9, resistance R 14, and the anode of diode D11 connects the negative pole of input voltage.

In normal operating conditions, when switching transistor Q1 closed, the in-phase end of elementary winding T1-B was a negative voltage, and electric current flows through the in-phase end that diode D11, capacitor C 9 and resistance R 3 flow to elementary winding T1-B by power supply negative terminal.Capacitor C 9 is by this current charges.Finish when transformer energy discharges, elementary winding T1-B two ends are no-voltages, and transistor Q4 is no longer with capacitor C 3 discharges, and capacitor C 3 begins to see through resistance R 2 and resistance R 14 chargings.When output short-circuit, the voltage at elementary winding T1-B two ends seldom can not be to capacitor C 9 chargings, and therefore, capacitor C 9 can not see through resistance R 14 to capacitor C 3 accelerated chargings.Charging current is only by resistance R 2 chargings.

During design, resistance R 14 is provided than resistance R 2 big a lot of charging currents, make entire circuit very fast in the charging of capacitor C 3 just often, operating frequency is normal; When short circuit, 3 of capacitor C are by resistance R 2 chargings, and charging is slow a lot, and operating frequency is much lower, thereby the power during short-circuit condition is also very little, and the circuit of whole Switching Power Supply is protected.

Embodiment four: on the basis of above-mentioned arbitrary embodiment, set up high frequency noise and reduce circuit: comprise capacitor C 11 and resistance R 15, after capacitor C 11 and resistance R 15 series connection, the end of oppisite phase of the elementary winding T1-A of another termination of capacitor C 11, the negative pole of another termination input voltage of resistance R 15.When switching transistor Q1 closes, the inductance of elementary winding T1-B or leakage inductance and capacitor C 11 resonance, much lower when this frequency ratio does not have capacitor C 11, so high frequency noise is also few a lot.When switching transistor Q1 conducting, capacitor C 11 is through switching transistor Q1, resistance R 6, resistance R 15 discharges, makes capacitor C 11 at another cycle resonance once more.

Embodiment five: on the basis of the foregoing description; output in the output constant voltage circuit can also be provided with filter circuit; as shown in the figure; filter circuit constitutes a low pass LC filter by L2, C15; its resonance frequency is far below switching frequency; can reduce to the ripple of output current very lowly, voltage-stabiliser tube Z3 is as output over-voltage protection, to prevent too high output voltage.

In above-mentioned each example, wherein the value of resistance R 15 can be zero, promptly is equivalent to resistance R 15 short circuits.The serial connection position of resistance R 3 and capacitor C 3 all can exchange.

If in transformer T, increase winding and output rectification circuit, just can make the multi-output switching power supply, the maximum power of its output is limited by the peak power output restricting circuits.

Claims

1, a kind of Switching Power Supply of stable peak power output restriction comprises transformer and self-excited oscillator, maximum power output limiting circuit; Transformer comprises elementary winding T1-A and elementary winding T1-B; Self-excited oscillator comprises by resistance R 2, the charging circuit that capacitor C 3 is composed in series, the current transformation voltage feedback circuit that mainly comprises resistance R 6, primary winding T1-B and switching transistor Q1, via resistance R 2, the charging circuit input that capacitor C 3 is composed in series connects the positive pole of input voltage, output is coupled in the in-phase end of elementary winding T1-B, the input of switching transistor Q1 and resistance R 2, capacitor C 3 also connects, the output stage of the end of oppisite phase serial connection switching transistor Q1 of elementary winding T1-A, another output stage of switching transistor Q1 connects the end of oppisite phase of elementary winding T1-B and the negative pole of input voltage by resistance R 6;

It is characterized in that: also comprise temperature-compensation circuit, described temperature-compensation circuit comprises resistance R 7 and diode D7, the in-phase end of the elementary winding T1-B of resistance R 7 one terminations or the in-phase end of elementary winding T1-A, resistance R 7 other ends also meet divider resistance R5 and the anode of diode D7, and the output stage of the negative electrode of diode D7 and switching transistor Q1, resistance R 6 also connect.

2, Switching Power Supply according to claim 1, it is characterized in that: also comprise the input rectifying filter circuit, the voltage output cathode of input rectifying filter circuit connects the in-phase end of elementary winding T1-A, and the voltage output negative pole of input rectifying filter circuit connects the end of oppisite phase of elementary winding T1-B.

3, Switching Power Supply according to claim 1 is characterized in that: described transformer also comprises secondary winding T1-C, through secondary winding T1-C two ends output voltage signal.

4, Switching Power Supply according to claim 1, it is characterized in that: also comprise delay circuit, described delay circuit comprises resistance R 13, transistor Q4 and diode D10, described resistance R 13 1 ends link to each other with the negative pole of input voltage, the base stage coupling of the other end of resistance R 13 and transistor Q4, the emitter of transistor Q4 connects diode D10 anode, the one end coupling of the in-phase end of diode D10 negative electrode and elementary winding T1-B, capacitor C 3, the other end coupling of the collector electrode of transistor Q4 and capacitor C 3.

5, Switching Power Supply according to claim 4, it is characterized in that: also comprise the accelerated charging circuit, described accelerated charging circuit comprises diode D11, capacitor C 9 and resistance R 14, capacitor C 9 and resistance R 14 series connection, one end of another termination capacitor C 3 of capacitor C 9, the other end of another termination capacitor C 3 of resistance R 14, the negative electrode of diode D11 also connects capacitor C 9, resistance R 14, and the anode of diode D11 connects the negative pole of input voltage.

6, Switching Power Supply according to claim 1 is characterized in that: described switching transistor Q1 is field effect transistor MOSFET or bipolar transistor.

7, Switching Power Supply according to claim 1, it is characterized in that: comprise that also high frequency noise reduces circuit, be arranged at the end of oppisite phase of described primary winding T1-A, described high frequency noise reduces circuit and comprises capacitor C 11, the end of oppisite phase of the elementary winding T1-A of one termination of capacitor C 11, the other end of capacitor C 11 and the coupling of the negative pole of input voltage.

8, according to each described Switching Power Supply among the claim 1-7, it is characterized in that: also comprise output rectifier and filter, cross-over connection is between elementary or secondary winding output; Described current rectifying and wave filtering circuit comprises diode D6, capacitor C 5, and described diode D6 anode is connected on the end of oppisite phase of transformer, and negative electrode is connected on the positive pole of capacitor C 5, and the negative pole of capacitor C 5 is connected on the in-phase end of transformer; Or diode D6 negative electrode is connected to the transformer in-phase end, and anode connects the negative terminal of capacitor C 5, the end of oppisite phase of the positive termination transformer of capacitor C 5; The anode of capacitor C 5 is a positive output end, and negative terminal is a negative output terminal.

9, root Switching Power Supply according to claim 8 is characterized in that: also comprise feedback control circuit, described feedback control circuit comprises photoelectrical coupler U1-A and U1-B, resistance R 16, exports constant voltage circuit; Described output constant voltage circuit comprises resistance R 17, resistance R 19, resistance R 20, capacitor C 12, resistance R 18 and voltage-stabiliser tube U2, resistance R 16 and photoelectrical coupler U1A polyphone, the other end of resistance R 16 connects the positive output end of output rectifier and filter, and the negative electrode of photoelectrical coupler U1A connects the voltage-stabiliser tube negative electrode; Photoelectrical coupler U1-B input is connected with the negative electrode of diode D8, the in-phase end coupling of diode D8 anode and elementary winding T1-B, photoelectrical coupler U1-B output and the coupling of transistor Q2 base stage, resistance R 17, one end of resistance R 19 is connected to the positive output end of described output rectifier and filter altogether, the other end of resistance R 17 connects voltage-stabiliser tube U2 negative electrode, one end of the other end of resistance R 19 and resistance R 18, the control of voltage-stabiliser tube U2 connects extremely altogether, the other end of resistance R 18 connects the anode of voltage-stabiliser tube U2, the resistance R 20 of series connection and C12 branch road are connected across between the voltage-stabiliser tube U2 negative electrode and the control utmost point, and the anode of voltage-stabiliser tube U2 is connected to the negative terminal of output.

10, Switching Power Supply according to claim 9 is characterized in that: also comprise constant current output circuit, described constant current output circuit comprises triode Q3, current-limiting resistance R21, resistance R 22, capacitor C 14; The collector electrode of triode Q3 connects the negative electrode of voltage-stabiliser tube U2, base stage connects resistance R 22 1 ends, resistance R 22 other ends connect the anode of voltage-stabiliser tube U2, capacitor C 14 is attempted by between triode Q3 base stage and the emitter-base bandgap grading, resistance R 21 is attempted by between the negative terminal of triode Q3 emitter-base bandgap grading and output, and triode Q3 emitter-base bandgap grading connects the in-phase end of transformer T1 output winding.