CN202190220U

CN202190220U - Synchronous rectification circuit

Info

Publication number: CN202190220U
Application number: CN2011202954162U
Authority: CN
Inventors: 钟启豪; 李战伟; 刘绍辉; 朱红伟
Original assignee: SHENZHEN VAPEL POWER SUPPLY TECHNOLOGY Co Ltd
Current assignee: Shenzhen holdluck-zyt supply technology Limited by Share Ltd
Priority date: 2011-08-15
Filing date: 2011-08-15
Publication date: 2012-04-11
Anticipated expiration: 2021-08-15

Abstract

The utility model discloses a synchronous rectification circuit, comprising a rectification MOS tube and a follow current MOS tube, characterized by also comprising a current detection circuit for detecting the forward current flowing through the follow current tube, and a comparison control circuit, wherein the comparison control circuit comprises a comparator and a switch tube, the reverse input end of the comparator is connected with the output end of the current detection circuit, a reference voltage is input into the forward input end of the comparator, the switch tube is connected between a GND and the control end of the follow current MOS tube, and the output end of the comparator is connected with the control end of the switch tube. Compared with the prior art, the synchronous rectification circuit enables the reverse current control of a synchronous rectification circuit to be realized through a simple circuit, and has obvious beneficial effects.

Description

A kind of circuit of synchronous rectification

Technical field

The utility model relates to the DC-DC translation circuit, particularly relates to a kind of circuit of synchronous rectification.

Background technology

The effect of doing synchronous rectification with MOSFET is exactly to adopt the low MOSFET of on state resistance to replace the technology of rectifier diode with reduction rectifier loss, thereby improves the efficient of DC/DC converter, satisfies the needs of low-voltage, high-current rectifier; Because after the MOSFET conducting, electric current can pass through the MOSFET two-way flow, as flows through negative current, so just causes extra negative effect, as follows:

When 1, using circuit of synchronous rectification, because of the existence of negative current, the fully loaded duty ratio of sky is constant, and loss increases the efficient reduction when making zero load;

2, output is as being connected to storage battery, and the existence of negative current very easily makes the storage battery risk of short-circuits when unloaded.

Summary of the invention

The utility model technical problem to be solved is, a kind of circuit of synchronous rectification is provided, and can eliminate the negative effect of metal-oxide-semiconductor negative current to the DC-DC converter.

The technical problem of the utility model solves through following technical scheme:

A kind of circuit of synchronous rectification; Comprise rectification metal-oxide-semiconductor, afterflow metal-oxide-semiconductor; Also comprise the current detection circuit and the comparison control circuit that detect the forward current that flows through continued flow tube; Said comparison control circuit comprises comparator, switching tube; The reverse input end of said comparator is connected with the output of said current detection circuit, input input reference voltage in the same way, and said switching tube is connected between the control end of earth terminal and said afterflow metal-oxide-semiconductor, and the output of said comparator links to each other with said control end of switching tube.

Preferably, also comprise regulating circuit, said regulating circuit comprises first resistance, electric capacity, first diode and second resistance; First end of said second resistance is connected with the output of said current detection circuit, second end is connected with the reverse input end of said comparator; First end of said first resistance is connected with second end of said second resistance, second end is connected with the negative electrode of first diode; The anode of said first diode is connected with the signal input end of said rectifying tube, first end of said electric capacity and the negative electrode of said first diode, the second end ground connection.

Preferably, said switching tube is a triode, and its collector electrode is connected with the control end of afterflow metal-oxide-semiconductor, grounded emitter.

Said current detection circuit comprises current transformer, the 5th resistance, second diode, the 6th resistance; A winding TR1-B of said current transformer connects with said continued flow tube, first end of secondary winding TR1-A is connected with first end of said the 5th resistance; First end of said the 5th resistance also is connected with the anode of said second diode; The negative electrode of said second diode is connected with first end of said the 6th resistance; The equal ground connection of second end of second end of said the 5th resistance, second end of secondary winding TR1-A, the 6th resistance, the negative electrode of said second diode is the output of current detection circuit.

The utility model beneficial effect compared with prior art comprises: utilize current detection circuit and comparison control circuit that the afterflow metal-oxide-semiconductor is controlled; When the forward current that flows through the afterflow metal-oxide-semiconductor is lower than predetermined value; Close the intermittent current metal-oxide-semiconductor; Thereby the flow cycle of blocking-up negative current has the advantage that circuit is simple, power consumption is little, response is fast.

In the preferred version, can regulate the waveform of comparator reverse input end, thereby regulate the ON time when unloaded through regulating second electric capacity, first resistance.

Description of drawings

Fig. 1 is the main circuit diagram of the circuit of synchronous rectification of the utility model embodiment 1;

Fig. 2 is the circuit diagram of current detection circuit of the circuit of synchronous rectification of the utility model embodiment 1;

Fig. 3 is the circuit diagram of comparison control circuit of the circuit of synchronous rectification of the utility model embodiment 1;

The voltage oscillogram of the each point of the circuit of synchronous rectification of Fig. 4 the utility model embodiment 1;

Fig. 5 is the main circuit diagram of the circuit of synchronous rectification of the utility model embodiment 2.

Embodiment

Contrast accompanying drawing below and combine preferred specific embodiment that the utility model is carried out detailed elaboration.

Embodiment 1

As shown in Figure 1; The main circuit of present embodiment is common BUCK circuit of synchronous rectification; It adopts metal-oxide-semiconductor to substitute diode in the traditional B UCK circuit reducing rectifier loss, and this main circuit comprises power supply, rectification metal-oxide-semiconductor Q1, afterflow metal-oxide-semiconductor Q2 and forms lc circuit by inductance L, capacitor C 1.

The circuit of synchronous rectification of the utility model also comprises current detection circuit, comparison control circuit and regulating circuit; Current detection circuit is used to detect the forward current that flows through afterflow metal-oxide-semiconductor Q2; Comparison control circuit is used for according to the size of this forward current control signal of intermittent current metal-oxide-semiconductor Q2 optionally, and regulating circuit is used to regulate the ON time of BUCK circuit afterflow metal-oxide-semiconductor Q6 when unloaded.

Like Fig. 2, shown in 3, the current detection circuit of present embodiment comprises current transformer TR1, the 5th resistance R 5, the second diode D2, the 6th resistance R 6; A winding TR1-B of said current transformer connects with said continued flow tube Q2, first end of secondary winding TR1-A is connected with first end of said the 5th resistance R 5; First end of said the 5th resistance R 5 also is connected with the anode of the said second diode D2; The negative electrode of said second diode is connected with first end of said the 6th resistance R 6; The equal ground connection of second end of second end of said the 5th resistance R 5, second end of secondary winding TR1-A, the 6th resistance R 6, the negative electrode of the said second diode D2 are the output TP1 of current detection circuit.

Comparison control circuit comprises comparator U1, switching tube Q11, also comprises the 3rd resistance R 3, the 4th resistance R 4, the 7th resistance R 7, the 8th resistance R 8; Comparator U1 is input input reference voltage in the same way; This reference voltage is obtained through the 3rd resistance R 3, the 4th resistance R 4 dividing potential drops by input voltage VREF; Said switching tube Q11 is connected between the control end DRVBO of earth terminal and said afterflow metal-oxide-semiconductor, and the output signal of said comparator control signal as switching tube Q11 after the 7th resistance R 7, the 8th resistance R 8 dividing potential drops links to each other with the control end of switching tube Q11.

Regulating circuit comprises first resistance R 1, capacitor C 2, the first diode D1 and second resistance R 2; First end of second resistance R 2 is connected with the output TP1 of current detection circuit, second end is connected with the reverse input end of comparator U1; First end of first resistance R 1 is connected with second end of said second resistance R 2, second end is connected with the negative electrode of the first diode D1; The anode of the said first diode D1 is connected with the signal input end DRVAO of said rectifying tube Q1, first end of said capacitor C 2 and the negative electrode of the said first diode D1, the second end ground connection.

Below in conjunction with Fig. 4 the operation principle of the circuit of synchronous rectification of present embodiment is elaborated.

As shown in Figure 4, the drive waveforms of DRVA0, DRVB0-1 rectification metal-oxide-semiconductor Q1, afterflow metal-oxide-semiconductor Q6 when the negative current that flows through the afterflow metal-oxide-semiconductor is not controlled; Circuit of synchronous rectification flows through the current waveform I as shown in Figure 4 of afterflow metal-oxide-semiconductor Q6 this moment when zero load _Q6(middle horizontal line is 0 electric current), when the electric current that flows through Q6 is positive current Ib, TR1 will detect forward current Ib; The voltage that the voltage waveform that produce TP1 this moment inputs to comparator U1-2 pin (being the reverse input end of comparator U1) and U1-3 pin (being the input in the same way of comparator U1) compares, and when being higher than the U1-3 pin, output 1 pin of U1 will produce low level; Not conducting of switching tube Q11; The driving voltage DRVB0 of not middle intermittent current metal-oxide-semiconductor Q6 will be in case when flowing through the forward current Ib of afterflow metal-oxide-semiconductor Q6 and reducing that simultaneously negative current Ia increases, U1-2 pin level will be lower than U1-3 pin level; Output 1 pin of U1 will produce high level and make the Q11 conducting at this moment; The direct ground connection of signal DRVB0-1 that drives afterflow metal-oxide-semiconductor Q6 is not flowed into the drive end of afterflow metal-oxide-semiconductor Q6, thereby close intermittent current metal-oxide-semiconductor Q6, thereby break off the loop of reverse current Ia; This moment Q6 the DRVB0-2 of drive waveforms shown in figure five; Through regulating the level of U1-3 pin, i.e. R3, R4 resistance, the conducting pulsewidth size of Q6 when unloaded with regard to may command.

The ON time of afterflow metal-oxide-semiconductor Q6 when the effect of regulating circuit is to regulate zero load; The waveform waveform B as shown in Figure 5 of comparator U1-2 pin behind the adding regulating circuit; Size through control capacittance C2, first resistance R 1 can be controlled at waveform that the T1 time carves DVRA0 through C2, R1 time-delay; Make U1-2 pin waveform adjustable constantly at T2, thereby regulate the ON time of afterflow metal-oxide-semiconductor Q6 when unloaded.

Embodiment 2

The difference of present embodiment and embodiment 1 only is current detection circuit, and is as shown in Figure 5, and present embodiment adopts Hall element H to carry out current detecting, and an end ground connection, the other end of Hall element H are connected with the reverse input end of said comparator U1.Except that above-mentioned two embodiment, the current detection circuit of the utility model can also adopt well-known to those skilled in the art other that testing circuit of identical function is specifically arranged.

Above content is the further explain that combines concrete preferred implementation that the utility model is done, and can not assert that the practical implementation of the utility model is confined to these explanations.For the utility model person of ordinary skill in the field; Under the prerequisite that does not break away from the utility model design; Can also make some being equal to substitutes or obvious modification, and performance or purposes are identical, all should be regarded as belonging to the protection range of the utility model.

Claims

1. circuit of synchronous rectification; Comprise rectification metal-oxide-semiconductor (Q1), afterflow metal-oxide-semiconductor (Q2); It is characterized in that: also comprise the current detection circuit and the comparison control circuit that detect the forward current that flows through continued flow tube (Q2); Said comparison control circuit comprises comparator (U1), switching tube (Q11); The reverse input end of said comparator is connected with the output of said current detection circuit, input input reference voltage in the same way, and said switching tube (Q11) is connected between the control end of earth terminal and said afterflow metal-oxide-semiconductor, and the output of said comparator links to each other with the control end of said switching tube (Q11).

2. circuit of synchronous rectification according to claim 1 is characterized in that: also comprise regulating circuit, said regulating circuit comprises first resistance (R1), electric capacity (C2), first diode (D1) and second resistance (R2); First end of said second resistance (R2) is connected with the output of said current detection circuit, second end is connected with the reverse input end of said comparator; First end of said first resistance (R1) is connected with second end of said second resistance (R2), second end is connected with the negative electrode of first diode (D1); The anode of said first diode (D1) is connected with the signal input end of said rectifying tube (Q1), the negative electrode of first end of said electric capacity (C2) and said first diode (D1), the second end ground connection.

3. circuit of synchronous rectification according to claim 1 is characterized in that: said switching tube (Q11) is a triode, and its collector electrode is connected with the control end of afterflow metal-oxide-semiconductor, grounded emitter.

4. according to claim 1 or 2 said circuit of synchronous rectification, it is characterized in that: said current detection circuit comprises current transformer (TR1), the 5th resistance (R5), second diode (D2), the 6th resistance (R6); The series connection of a winding (TR1-B) of said current transformer and said continued flow tube (Q2)), first end of secondary winding (TR1-A) is connected with first end of said the 5th resistance (R5); First end of said the 5th resistance (R5) also is connected with the anode of said second diode (D2); The negative electrode of said second diode is connected with first end of said the 6th resistance (R6); The equal ground connection of second end of second end of second end of said the 5th resistance (R5), secondary winding (TR1-A), the 6th resistance (R6), the negative electrode of said second diode (D2) is the output of current detection circuit.

5. circuit of synchronous rectification according to claim 1 and 2 is characterized in that: said current detection circuit comprises Hall element (H), and an end ground connection of said Hall element (H), the other end are connected with the reverse input end of said comparator (U1).