CN1332513A

CN1332513A - Positively exciting circuit unit

Info

Publication number: CN1332513A
Application number: CN 00125625
Authority: CN
Inventors: 丁贤后; 王士民
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2000-09-28
Filing date: 2000-09-28
Publication date: 2002-01-23
Anticipated expiration: 2020-09-28
Also published as: CN1115762C

Abstract

The positively exciting circuit unit has a clamping circuit comprising a clamping switch and a clamping capacitor connected serially across the subsidiary side of the transformer. When the main switching transistor Q1 is on, the clamping switch Q2 is off and the transformer outputs energy to the subsidiary side; when the main switching transistor Q1 if off, the subsidiary side of the transformer has raised reverse voltage, the clamping switch Q2 is on and the voltage across the clamping capacitor C1 is raised; after the voltage across the clamping capacitor C1 raises the certain value, discharge begins, the exciting current in the transformer reverses and the transformer is reset.

Description

A kind of Positively exciting circuit unit

The present invention relates to high frequency switch power, relate in particular to a kind of Positively exciting circuit unit that is used for small-power switching power-supply.

Positively exciting circuit unit generally is made up of transformer, main switch and secondary output rectifier and filter, is characterized in that former limit, the secondary of transformer worked simultaneously.Because what the former limit of circuit winding passed through is unidirectional pulsating current,, has in the prior art and take clamp circuit to realize so its transformer must take measures to make the magnetic core of transformer to reset.With U.S. Pat 05781420 is that example is carried out brief description, and this patent is to realize that with an output rectifying tube clamp circuit in parallel the magnetic core of transformer resets at the secondary of Positively exciting circuit unit, and this clamp circuit is made up of a switch and electric capacity.This patent has solved the problem that the magnetic core of transformer resets, but this patent also has shortcoming, exports on the rectifying tube because its clamp circuit is connected in parallel on, so the due to voltage spikes of its secondary can be higher, the spike that is refracted to former limit equally is also just higher, thereby causes the peak voltage of main switch can be bigger.

The purpose of this invention is to provide a kind of Positively exciting circuit unit, this circuit can solve the magnetic core reset issues of transformer, can not cause the main switch peak voltage too high owing to resetting again.

A kind of Positively exciting circuit unit that the present invention proposes comprises transformer T, is positioned at the main switch Q1 and the secondary straightening and filtering unit on former limit, and described straightening and filtering unit comprises output rectifying tube CR1, output continued flow tube CR2, filter inductance L1 and filter capacitor C2; The positive pole of described output rectifying tube CR1 links to each other with the secondary in-phase end, and its negative pole is connected in series mutually with described filter inductance L1; The negative pole of described output continued flow tube CR2 links to each other with node between described output rectifying tube CR1 and the described filter inductance L1, and the positive pole of described output continued flow tube CR2 links to each other with the end of oppisite phase of transformer T secondary; The end of described filter capacitor C2 links to each other with the other end of described filter inductance L1, the end of oppisite phase of its another termination transformer T secondary; In addition, the secondary of transformer T also in parallel a clamp circuit that is composed in series by clamp switch Q1 and clamping capacitance C1, the conducting of described main switch Q1 and described clamp switch Q2 is anti-phase each other.

Described Positively exciting circuit unit, the control mode of its clamp switch Q2 can be self-driven, also can be that separate excitation drives.

Do detailed explanation below in conjunction with drawings and Examples.

Fig. 1 is the schematic diagram of U.S. Pat 05781420.

Fig. 2 is the Positively exciting circuit unit that the present invention proposes.

Fig. 3 is the sequential chart of Primary Component main switch Q1, clamp switch Q2 among Fig. 2 and the voltage oscillogram of main switch Q1, clamping capacitance C1.

Fig. 4 is one embodiment of the present of invention.

Fig. 5 is an alternative embodiment of the invention.

Fig. 1 is the principle assumption diagram of U.S. Pat 05781420, and wherein Q is a main switch, and Qq is a clamp switch, and Cq is a clamping capacitance, and CR, CR ' are respectively output rectification, output continued flow tube, and L is an output inductor, and C is an output filter capacitor.The operation principle of this circuit is as follows: have no progeny when main switch Q closes, the dump energy of transformer is passed through output continued flow tube CR ' from the secondary of transformer, clamp switch Qq discharges to clamping capacitance Cq, voltage on the clamping capacitance Cq raises, when discharging, dump energy finishes, energy on the clamping capacitance Cq passes through L, load, return transformer, make exciting current reverse, thereby magnetic core of transformer is resetted, voltage on the main switch Q descends simultaneously, the voltage swing of main switch Q is by the decision of clamping capacitance Cq voltage and the transformer turn ratio, and is suitable as long as the value of clamping capacitance Cq is chosen, and the voltage during conducting will be lower once more for main switch Q.

The solution that the present invention proposes as shown in Figure 2, wherein Q1 is a main switch, Q2 is a clamp switch, C1 is a clamping capacitance, CR1, CR2 are respectively output rectifying tube, output continued flow tube, L1 is a filter inductance, C2 is a filter capacitor, T is a transformer.Its operation principle is: when main switch Q1 opened, transformer T exported energy to secondary, and secondary current flows through output rectifying tube CR1, filter inductance L1 and load, and the voltage on the clamping capacitance C1 is negative for just going up down at this moment, and clamp switch Q2 is in off state.Have no progeny when main switch Q1 closes, the voltage on the main switch Q1 rises, accordingly, the voltage of transformer T secondary drops to zero gradually, until oppositely uprising, simultaneously, output rectifying tube CR1 turn-offs, output continued flow tube CR2 conducting, and output current is by output continued flow tube CR2 afterflow; When transformer T secondary voltage oppositely is elevated to after the voltage of clamping capacitance C1 equates, clamp circuit is started working, clamp switch Q2 conducting, and the dump energy of transformer T is given clamping capacitance C1 charging by clamp switch Q2, and the voltage of clamping capacitance C1 rises; After the voltage on the clamping capacitance C1 rises to certain value, the dump energy of transformer T discharges and finishes, and clamping capacitance C1 discharges to transformer T secondary by clamp switch Q2, and the exciting current of transformer T is reverse, T resets to transformer, and the voltage on the clamping capacitance C1 descends; After the voltage on the clamping capacitance C1 drops to a certain value, main switch Q1 conducting, clamp switch Q2 turn-offs, and Positively exciting circuit unit begins to enter the next work period.

Since the secondary of transformer T main switch Q1 close have no progeny be equivalent in parallel with clamping capacitance C1, make the former and deputy limit of transformer T can not produce the sudden change of voltage, thereby limited the shutoff peak voltage of main switch Q1 and the peak voltage of output rectifying tube CR1, output continued flow tube CR2; Because clamp circuit has been placed on secondary, the withstand voltage of clamp switch and clamping capacitance all can be obtained lower.In the prior art, the turning-on voltage of main switch Q1 is the twice input voltage, and in this device, the turning-on voltage of main switch Q1 is subjected to the voltage control on the clamping capacitance C1, by optimization to clamping capacitance C1 value, the turning-on voltage that can make main switch Q1 is much smaller than the twice input voltage, when half LC harmonic period of clamping capacitance C1 and transformer T secondary inductance L is less than or equal to the turn-off time of main switch Q1, the turning-on voltage of main switch Q1 only is an input voltage, clamping capacitance C1 value is optimum when equating, this moment, turning-on voltage and the peak voltage of main switch Q1 were all minimum.

Fig. 3 is the sequential chart of Primary Component main switch Q1, clamp switch Q2 of Fig. 2 and the voltage oscillogram of main switch Q1, clamping capacitance C1, and transverse axis is the time among the figure, and the longitudinal axis is a voltage.As can be seen from Figure 3, the conducting of main switch Q1, clamp switch Q2 is anti-phase.Main switch Q1 closes and has no progeny, and main switch Q1 voltage is subjected to the clamp of clamping capacitance C1, and variation tendency and clamping capacitance C1 are identical.

Fig. 4 is one embodiment of the present of invention, and wherein Q11 is a main switch, and T is a transformer, and Q3, Q4 are respectively output synchronous rectifier, output synchronous freewheeling pipe, and L11 is a filter inductance, and C21 is a filter capacitor, and C11 is a clamping capacitance, and Q21 is the clamp switch pipe.The clamp switch of present embodiment N-channel MOS pipe, the drain electrode of described clamp switch pipe Q21 links to each other with the in-phase end of described transformer T secondary, and source electrode links to each other with described clamping capacitance C1, and the end of oppisite phase of grid and described transformer T secondary joins.The control mode of described N-channel MOS pipe is self-driven.This circuit is when being used for DC-dc power module, and specified input voltage is 48V, and rated output voltage is 5V, and output-current rating is 20A.In the present embodiment, main switch Q11 closes and has no progeny, and the drain electrode of clamp switch pipe Q21, source voltage rise, after rising to certain value, begin to descend, the decline process is the process that resets of transformer T magnetic core just, when dropping to the 64V left and right sides, main switch Q11 begins to open, and the magnitude of voltage when it is opened is much smaller than the 96V of prior art, so its turn-on consumption will reduce greatly, efficient greatly improves, full load, overall efficiency has reached 89～90%, and the efficient of prior art only is 83%.

Fig. 5 is the another kind of embodiment of this patent, and wherein Q12 is a main switch, and T is a transformer, Q3, Q4 are respectively output synchronous rectifier, output synchronous freewheeling pipe, and L12 is a filter inductance, and C22 is an output filter capacitor, C12 is a clamping capacitance, and Q22 is the clamp switch pipe.Different with Fig. 4 is that what the clamp switch Q22 of present embodiment used is the P channel MOS tube.The drain electrode of described clamp switch Q22 links to each other with described clamping capacitance C12, and the end of oppisite phase of its source electrode and described transformer T secondary joins, and the in-phase end of its grid and described transformer T secondary joins.When this device was used for same DC-dc power module, efficient also can accomplish 89～90%.

The Positively exciting circuit unit that the present invention proposes adopts side edge clamp, has solved the reset issues to magnetic core of transformer.Simultaneously, owing to adopt side edge clamp, for general DC-DC supply convertor, its secondary voltage will be much smaller than original edge voltage, so the former limit clamp of the relative prior art of withstand voltage of its clamp switch and clamping capacitance is much lower.The Positively exciting circuit unit that the present invention proposes carries out clamp to main switch, has reduced the turn-on consumption of main switch, and the efficient of power supply has brought up to 89～90% from prior art 83%.Clamp switch among the present invention can be made self-driven, so circuit structure can be done very simply, need not to add more device; Because this clamp circuit is connected in parallel on the transformer secondary, so the peak voltage on its winding is less, makes the peak voltage of main switch also less.

Claims

1, a kind of Positively exciting circuit unit comprises transformer T, is positioned at the main switch Q1 and the secondary straightening and filtering unit on former limit, and described straightening and filtering unit comprises output rectifying tube CR1, output continued flow tube CR2, filter inductance L1 and filter capacitor C2; The positive pole of described output rectifying tube CR1 links to each other with the secondary in-phase end, and its negative pole is connected in series with described filter inductance L1; The negative pole of described output continued flow tube CR2 links to each other with node between described output rectifying tube CR1 and the described filter inductance L1, and the positive pole of described output continued flow tube CR2 links to each other with the end of oppisite phase of transformer T secondary; The end of described filter capacitor C2 links to each other with the other end of described filter inductance L1, the end of oppisite phase of its another termination transformer T secondary, it is characterized in that: transformer T secondary also in parallel be composed in series a clamp circuit by clamp switch and clamping capacitance C1, the conducting of described main switch Q1 and described clamp switch is anti-phase each other.

2, Positively exciting circuit unit as claimed in claim 2, it is characterized in that: described clamp switch can be the N-channel MOS pipe, the drain electrode of described N-channel MOS pipe links to each other with the in-phase end of described transformer T secondary, source electrode links to each other with described clamping capacitance C11, and the end of oppisite phase of grid and described transformer T secondary joins.

3, Positively exciting circuit unit as claimed in claim 2, it is characterized in that: described clamp switch can also be the P channel MOS tube, the drain electrode of described P channel MOS tube links to each other with described clamping capacitance C12, the end of oppisite phase of source electrode and described transformer T secondary joins, and the in-phase end of grid and described transformer T secondary joins.

4, as claim 2,3, one of 4 described Positively exciting circuit units, it is characterized in that: described clamp switch can be to adopt self-driven or its swashs the control mode that drives.

5, as claim 2,3, one of 4 described Positively exciting circuit units, it is characterized in that: the best value condition of described clamping capacitance C1 satisfies: half LC1 harmonic period of clamping capacitance C1 and transformer T secondary inductance L equals the turn-off time of main switch Q1.