CN2812397Y

CN2812397Y - A pulse amplitude modulation switching power supply circuit

Info

Publication number: CN2812397Y
Application number: CN 200520132517
Authority: CN
Inventors: 戴科; 沈明; 马梁
Original assignee: Hangzhou Huawei 3Com Technology Co Ltd
Current assignee: Hangzhou H3C Technologies Co Ltd
Priority date: 2005-11-03
Filing date: 2005-11-09
Publication date: 2006-08-30
Anticipated expiration: 2015-11-09

Abstract

The utility model discloses a PWM switch power supply circuit. The PWM switch power supply circuit supplied by the utility model realizes the match between the impedance of a PWM output terminal and the impedance of a transmission line on the basis of adding low cost through adding resistors R1 and R2 on the TS output terminal and the BS output terminal of a PWM terminal, the value of the R1 is equal to the difference between the value of the impedance of a transmission line between the input terminal of an upper transistor and the TS output terminal of a PWM chip and the value of the inner resistance of the PWM chip, and the value of the R2 is equal to the difference between the value of the impedance of a transmission line between the input terminal of a lower transistor and the TS output terminal of the PWM chip and the value of the inner resistance of the PWM chip. Thus, oscillating signals on drive signals outputted by the PWM chip caused by the mismatch of impedance are eliminated, oscillating signals on signals of the output terminal of the PWM switch power supply circuit and input signals of the upper transistor and the lower transistor caused by the mismatch of impedance are eliminated, namely the periodic noise of the output terminal of the PWM switch power supply circuit caused by the mismatch of impedance is eliminated.

Description

A kind of pulse amplitude modulation switching power circuit

Technical field

The utility model relates to pulse amplitude modulation voltage signal control technology field, is specifically related to a kind of pulse amplitude modulation switching power circuit.

Background technology

Along with the development of chip manufacturing process, the chip that can be operated on low-voltage, the big electric current occurs in a large number, makes voltage-dropping type pulse amplitude modulation (PWM, Pulse Wide Modulation) voltage control chip obtain extensive use.PWM voltage control chip and mos field effect transistor (MOSFET, Metallic Oxide Semiconductor Field Effect Transistor), inductance, electric capacity etc. are formed the PWM switching power circuit together, so that, thereby make that electronic system can reliability service for chip provides its required various voltage signals.

Fig. 1 is the basic composition figure of PWM switching power circuit, and shown in figure l, PWM switch power supply route PWM chip, last MOSFET are Ml, MOSFET is compositions such as M2, inductance L, capacitor C down.Its operation principle is: the PWM chip is that TS output and following pipe output are the BS output by last pipe output respectively, alternately output upper tube drive signal Top_drive and pipe drive signal Bottom_drive down, driven M1 and M2 are with the alternate conduction of control M1 and M2.

The PWM switching power circuit is easy to produce periodically very noisy at output, and the reason that noise produces mainly contains two:

1, the driving force of PWM is strong excessively, make on the input voltage signal of M1 and M2 produce strong upper and lower towards signal or oscillator signal.Because drive signal Top_drive and Bottom_drive cycle are effective, directly cause the output voltage signal of PWM switching power circuit to produce periodic swinging.

2, Top_drive and Bottom_drive are bad in the control of printed circuit board (PCB) (PCB) upward wiring, cause the circuit stray inductance excessive.It is same because Top_drive and Bottom_drive cycle are effective, the parasitic capacitance of stray inductance and M1, M2 inside periodically acts on, on the input voltage signal of M1 and M2, produce vibration, cause the output voltage signal of PWM switching power circuit to produce periodic swinging.

Periodic swinging on the PWM switching power circuit output voltage signal has caused periodic noise at the output of PWM switching power circuit.When being subjected to electrical chip to the voltage signal sensitivity, this periodic noise can be subjected to electrical chip to bring various harmful effects, may cause when serious can't work by electrical chip, and then influence the operate as normal of late-class circuit.Therefore, the periodic noise that how effectively to reduce PWM switching power circuit output is a problem demanding prompt solution.

The general now periodic noise that adopts dual mode to reduce PWM switching power circuit output, respectively shown in Fig. 2-a and 2-b: a kind of is to increase the coupling inductance respectively at the TS of PWM chip output and BS output, and a kind of is to increase the low matching capacitance of effective series resistance (ESR) respectively at the TS of PWM chip output and BS output.Its basic principle is: because inductance and electric capacity all are energy-storage travelling wave tube, therefore utilize inductance or electric capacity absorb M1 and M2 input voltage signal up and down towards the portion of energy of signal or oscillator signal, make the amplitude of oscillator signal reduce, the result makes the amplitude of the oscillator signal on the output voltage signal reduce, thereby has reduced the noise of output.

No matter adopting inductance still is the periodic noise that electric capacity reduces PWM switching power circuit output, all has following shortcoming:

L, noise reduction efficacy are low.The PWM switching power circuit of above-mentioned increase coupling inductance or electric capacity can only passively slow down the noise of PWM switching power circuit, and can not fundamentally eliminate the noise source that makes the PWM switching power circuit produce periodic noise.

2, increase the device fabrication cost.No matter be to increase coupling inductance or the electric capacity of low ESR, all can increase the cost of PWM switching power circuit, and then increase the manufacturing cost of entire equipment.

The utility model content

In view of this, main purpose of the present utility model is to provide a kind of PWM switching power circuit, with the noise of effective inhibition PWM switching power circuit output.

For achieving the above object, the technical solution of the utility model is achieved in that

A kind of PWM switching power circuit, this circuit comprises: PWM chip, last transistor, following transistor, it is characterized in that, this circuit comprises: resistance R 1 and resistance R 2, wherein, the two ends of R1 link to each other with last transistorized input with the TS output of PWM chip respectively, and the two ends of R2 link to each other with following transistorized input with the BS output of PWM chip respectively.

The resistance of described R1 equals the poor of the resistance value of the TS output of PWM chip and the transmission line between the last transistorized input and PWM chip internal resistance value, and the resistance of described R2 equals the BS output of PWM chip and the resistance value of the transmission line between the transistorized input and PWM chip internal resistance value poor down.

Described transistor is MOSFET.

The resistance of described resistance R l is less than 10 ohm.

The resistance of described resistance R 2 is less than 10 ohm.

Compared with prior art, PWM switching power circuit provided by the utility model, increase resistance R 1 and R2 respectively by TS output and BS output at the PWM end, and the value of R1 equals the TS output of PWM chip and goes up the resistance value of the transmission line between transistorized input and the internal resistance value of PWM chip poor, the value of R2 equals the BS output of PWM chip and following internal resistance value poor of the resistance value of the transmission line between transistorized input and PWM chip, on the basis that increases lower cost, realized the coupling of impedance of PWM chip output and transmission line impedance, thereby eliminated owing to do not match oscillator signal on the PWM chip output drive signal that causes of impedance, and then eliminated owing to do not match oscillator signal on the last transistor that causes and following transistor input signal and the PWM switching power circuit output end signal of impedance, promptly eliminated owing to the do not match periodic noise of the PWM switching power circuit output that causes of impedance.

Description of drawings

Fig. 1 is the basic composition figure of PWM switching power circuit;

Fig. 2-a utilizes the coupling inductance to reduce the schematic diagram of PWM switching power circuit output noise in the prior art;

Fig. 2-b utilizes matching capacitance to reduce the schematic diagram of PWM switching power circuit output noise in the prior art;

Fig. 3 is the schematic diagram of the PWM switching power circuit that the utility model proposes;

Fig. 4-a is M1 and the waveform voltage signal figure of M2 input and the waveform voltage signal figure of PWM switching power circuit output shown in Figure 1 when not increasing build-out resistor;

After the increase build-out resistor that Fig. 4-b provides for the utility model is M1 and the waveform voltage signal figure of M2 input and the waveform voltage signal figure of PWM switching power circuit output shown in Figure 3.

Embodiment

The oscillator signal that produces on the output end voltage signal of PWM switching power circuit mainly causes owing to impedance is discontinuous, be that the impedance of PWM chip output and the impedance of transmission line do not match, thereby the drive signal that has caused the output of PWM chip is to M1 or M2 transmission the time, on transmission line, produce reflection, the output of result's part voltage signal reflected back PWM chip, the voltage signal of this reflected back is superimposed upon on the original drive signal, thereby caused the vibration of drive signal, and then caused the vibration of M1 and M2 input signal, and then caused the vibration of PWM switching power circuit output voltage signal.The intensity of reflected voltage signal is that the amplitude of oscillator signal can be weighed by reflection coefficient, reflection coefficient equals the difference of impedance of PWM chip output and transmission line impedance divided by impedance of PWM chip output and transmission line impedance sum, reflection coefficient is big more, and the oscillation amplitude of the drive signal of PWM chip output output is big more.Therefore, core concept of the present utility model is: two outputs at the PWM chip increase build-out resistor respectively, make the impedance of two outputs of PWM chip equate respectively with the impedance of transmission line separately.Like this, reflection coefficient is zero, thereby eliminated owing to the do not match vibration of drive signal of the PWM chip output that causes of impedance, and then eliminated M1 and the input signal of M2 and the vibration on the PWM switching power circuit output voltage signal that does not match and cause owing to impedance, promptly eliminated owing to the do not match periodic noise of the PWM switching power circuit output that causes of impedance.

Below in conjunction with drawings and the specific embodiments the utility model is further described in more detail.

Fig. 3 is the schematic diagram of the PWM switching power circuit that provides of the utility model, and as shown in Figure 3, the main distinction of the PWM switching power circuit shown in this circuit and Fig. 1 or Fig. 2-a or Fig. 2-b is:

At two outputs of PWM chip, promptly TS output and BS output have increased build-out resistor R1 and R2 respectively.Particularly, the two ends of R1 link to each other with the TS output of PWM chip and the input of M1 respectively, and R1=RT1-R0, and wherein, RT1 is the resistance value of the transmission line between the input of the TS output of PWM chip and M1, and R0 is the internal resistance value of PWM chip; The two ends of R2 link to each other with the BS output of PWM chip and the input of M2 respectively, and R2=RT2-R0, and wherein, RT2 is the resistance value of the transmission line between the input of the BS output of PWM chip and M2, and R0 is the internal resistance value of PWM chip.

Here, the internal resistance of PWM chip can be learnt that RTl and RT2 can be learnt by the PCB layout analysis by the property parameters of PWM chip.

In concrete the application, M1 shown in Figure 3 and M2 also can be the transistors of other P type or N type except being the MOSFET.

Fig. 4-a has provided when not increasing build-out resistor, the waveform voltage signal figure of the waveform voltage signal figure of M1 or M2 input and PWM switching power circuit output, shown in Fig. 4-a, the oscillogram on the left side is the waveform voltage signal figure of M1 or M2 input, and the oscillogram on the right is the waveform voltage signal figure of PWM switching power circuit output; After Fig. 4-b has provided the increase build-out resistor that the utility model provides, the waveform voltage signal figure of the waveform voltage signal figure of M1 or M2 input and PWM switching power circuit output, shown in Fig. 4-b, the oscillogram on the left side is the waveform voltage signal figure of M1 or M2 input, and the oscillogram on the right is the waveform voltage signal figure of PWM switching power circuit output.As can be seen, compare with not increasing build-out resistor, after the increase build-out resistor, the oscillation amplitude of the voltage signal of the input of M1 and M2 obviously reduces, and the oscillation amplitude of PWM output end voltage signal also obviously reduces.Here, the vibration by a small margin that exists on the oscillogram shown in Fig. 4-b and upper and lower towards signal, mainly be because resistance R 1 and R2 can eliminate the vibration that does not match and cause owing to impedance fully, for the open and close because of the PWM chip cause upper and lower towards and the vibration that causes of circuit stray inductance and MOSFET endophyte electric capacity then can partly eliminate.

In actual applications, rule of thumb, the resistance of build-out resistor is preferably less than 10 ohm, and maximum is not above 50 ohm.

The above only is embodiment of the present utility model, in order to restriction the utility model, all any modifications of being made, is not equal to replacement, improvement etc. within spirit of the present utility model and principle, all should be included within the protection range of the present utility model.

Claims

1, a kind of pulse amplitude modulation switching power circuit, this circuit comprises: pulse amplitude modulation PWM chip, last transistor, following transistor, it is characterized in that, this circuit comprises: resistance R 1 and resistance R 2, wherein, the two ends of R1 link to each other with last transistorized input with the pipe TS output of going up of PWM chip respectively, and the two ends of R2 link to each other with following transistorized input with the following pipe BS output of PWM chip respectively.

2, circuit as claimed in claim 1, it is characterized in that, the resistance of described R1 equals the poor of the resistance value of the TS output of PWM chip and the transmission line between the last transistorized input and PWM chip internal resistance value, and the resistance of described R2 equals the BS output of PWM chip and the resistance value of the transmission line between the transistorized input and PWM chip internal resistance value poor down.

3, circuit as claimed in claim 1 is characterized in that, described transistor is mos field effect transistor MOSFET.

4, circuit as claimed in claim 1 is characterized in that, the resistance of described resistance R 1 is less than 10 ohm.

5, as claim 1 or 4 described circuit, it is characterized in that the resistance of described resistance R 2 is less than 10 ohm.