CN102938612A

CN102938612A - Digital control method of DC (direct current) converter meeting wide input-output voltage requirements

Info

Publication number: CN102938612A
Application number: CN2012104837694A
Authority: CN
Inventors: 王新辉; 吴艳玲; 陈威兵
Original assignee: Changsha University
Current assignee: Changsha University
Priority date: 2012-11-26
Filing date: 2012-11-26
Publication date: 2013-02-20

Abstract

The invention discloses a digital control method of a DC (direct current) converter meeting wide input-output voltage requirements. In order to realize the method, a BUCK circuit comprising an FAN2108 chip and peripheral circuit devices, an output voltage setting circuit, a PWM (pulse-width modulation) waveform generation circuit, a PWM waveform driving and separating circuit, an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) tube resistance value adjusting circuit are adopted, and a connecting method of the circuits, a circuit starting method, and a principle and a method for controlling output voltage are also adopted. According to the method, the range of input direct current voltage VIN is 3-24V, so that when circuit hardware and connection of the circuit hardware are not changed, the continuous and wide-range adjustment on output voltage VOUT from 0.8V to 80% of the VIN can be realized by input data set according to user demands, so that the DC converter is suitable for different loads needing different direct current voltages, and particularly suitable for the condition that batteries are used for power generation in the open so as to supply power for mobile devices needing different direct current power voltages.

Description

A kind of DC converter digital control method that adapts to wide input and output voltage requirement

Technical field

The invention belongs to the Power Electronic Circuit engineering field, relate to a kind of DC converter control method that adapts to wide input and output voltage requirement.

Technical background

Direct current DC-DC converter with the FAN2108 formation; has output voltage feedback regulation function; input voltage can both adapt at 3V to 24V; output voltage can be by suitably selecting the feedback resistance of circuit and the ratio of biasing resistor; between 0.8V to 0.8VIN, select arbitrarily; efficient is very high, and the load current of output can be crossed 8A, and the defencive function of circuit is complete.The DC-DC translation circuit DC power supply of general employing FAN2108, the resistance R 1 that is fed back to 19 pin by output voltage and the voltage ratio of biasing resistor RBIAS decide the size of output voltage, after in case each parameter of these two resistance values and circuit is determined, output dc voltage can only be some magnitudes of voltage, can not realize that output voltage is adjustable in a big way.Therefore its functional characteristics can not all be excavated out, uses to have larger limitation.

Summary of the invention

Utilize FAN2108 can adapt to very wide input voltage range in order to overcome the problem of above-mentioned existence, to the invention provides, can be useful in again than wide output voltage range adjustable working a kind of and adapt to the DC converter digital control method that wide input and output voltage requires.

Technical scheme of the present invention is: by in the FAN2108 peripheral circuit, feed back to 19 pin at output voltage and incorporate MOSFET tube resistor resistance adjuster into to the biasing resistor RBIAS two ends of ground wire, change feedback factor, come the size of regulation output voltage.It may further comprise the steps:

1) consists of as shown in Figure 1 the electric circuit constitute;

2) method of start-up circuit: the PWM waveform duty cycle that the PWM waveform generator is sent is made as 0 start-up circuit, makes MOSFET pipe Q1 close the circuit output voltage minimum fully;

3) set output voltage, by the input voltage initialization circuit set required output voltage corresponding digital control amount;

4) circuit output dc voltage control method: PWM waveform generator, according to the suitable PWM waveform of the digital output of inputting, the conducting ratio of control MOSFET pipe Q1, export certain equivalent resistance size, change 19 pin of FAN2108 to the parallel resistance resistance of ground wire, change the feedback factor of FAN2108 feedback loop, make circuit export desired output voltage values;

Described step 1) resistance R in _BIAS, R1 the resistance choosing method be: at first select a suitable R _BIASResistance can be chosen by the typical application circuit of FAN2108; Then on request minimum output voltage calculates the resistance choose resistance R 1, and other FAN2108 chip periphery component parameters can be chosen by the typical application circuit of FAN2108.The MOSFET pipe should select NMOS pipe, by the PWM frequency select the operating frequency of MOSFET pipe, cut-in voltage select 4V and in.Resistance R 1, capacitor C 11, C12 mainly strobe, the alternating current component of filtering MOSFET pipe switch, and capacitance can be selected according to the switching frequency of PWM.The PWM waveform generator is preferably selected single-chip microcomputer, can simplify better the output voltage initialization circuit, if select single-chip microcomputer, then can use simple key-press input.

Described step 2) output minimum voltage computational methods in:

0.8V/R _BIAS＝(V _OUT-0.8V)/R1+650nA (1)

Described step 3) the digital control amount of set point of input is N in.

Described step 4) the output voltage computing formula is in:

0.8V/(R _BIAS//R _N)＝(V _OUT-0.8V)/R1+650nA (2)

In the formula, R _NThe equivalent resistance (R of MOSFET tube resistor resistance adjuster output _NSize relevant with N).Calculate for simplifying, the 650nA in (1), (2) formula can ignore.

The operation principle of described circuit: connect based on circuit of the present invention, by in the feedback loop of FAN2108,19 pin of FAN2108 to ground wire branch road RBIAS two ends a resistance R that available PWM ripple is controlled in parallel _N, by changing the PWM duty ratio, change MOSFET tube resistor resistance adjuster output equivalent resistance value, realize the adjusting to feedback factor, thereby in the situation that does not change the circuit hardware parameter, regulate on request the output voltage size that changes circuit.

Use the present invention, not only can adapt to the very wide input voltage of input voltage range (input voltage V _INScope is at 3-24V), can make simultaneously output voltage in wider scope (at 0.8V-0.8V _IN) regulate, adapt to the desired voltage of load.It is applied widely, is particluarly suitable for the situation that the field powers with solar cell without civil power.

Description of drawings

Fig. 1 is circuit composition diagram of the present invention.

FAN2108 has used concrete circuit connection diagram to represent among the figure, and other circuit have adopted block diagram to represent.

Fig. 2 is the connection line figure of a specific embodiment of the present invention.

Embodiment

With specific embodiment technical scheme of the present invention and the course of work are further described by reference to the accompanying drawings with following, but protection scope of the present invention is not limited to this:

1, one input voltage of embodiment is 12V, output voltage at 1.8V to the embodiment that can regulate arbitrarily between the 9.6V.

With reference to Fig. 1, step 1) a kind of DC converter control method that adapts to wide input and output voltage requirement, it is characterized in that, by by FAN2108 chip and peripheral circuit element BUCK circuit thereof, output voltage input circuit, PWM wave generator circuit, PWM drive waveform and buffer circuit are set, MOSFET tube resistor resistance Circuit tuning forms;

Step 2) with reference to Fig. 2, to the selection of FAN2108 peripheral circuits parameter, its operating frequency is by R ₁Determine, get 31K Ω, operating frequency=500KHz, the inductance value is 2.2 μ H.

Step 3) with reference to Fig. 2, selects resistance R _BIAS=2K.

Step 4) with reference to Fig. 2, calculate the R1 resistance, when the PWM duty ratio is 0, R _x=∞, this moment, output voltage was 1.8V, by 0.8V/R _BIAS=(V _OUT-0.8V)/R1+650nA can calculate R1=2.49K.As PWM Waveform switch frequency selection purposes 4KHz, filter capacitor C11 gets 3.3nF, and C12 chooses the electrochemical capacitor of 3 4.7 μ F, filtering flutter component.

Step 5), as long as control set point digital quantity N makes the PWM pulsewidth regulate by digital quantity N, just can control output voltage VO UT is 1.8V in minimum value, to adjustable between maximum 0.8VIN=0.8 * 12V=9.6V.

Step 6) with reference to Fig. 2, the PWM wave generator circuit adopts ATMEGA 16 single-chip microcomputers, and the output voltage initialization circuit adopts 2 free-standing buttons, and output is adopted the photoisolator circuit with buffer circuit, and MOSFET requires its cut-in voltage less than or equal to 4V, conducting resistance R _DSLittle, other parameters such as On current are without special requirement.

During the permission maximum of set point digital quantity N, should calculate according to the maximum of requirement output voltage voltage, only otherwise make on FAN2108 and 19 pin too little because of feedback factor, cause that voltage VFB is too little on 19 pin, be VFB＜795mV, cause without feedback to get final product, to avoid making circuit working undesired.

Use the present invention, input voltage VIN can adapt between 3～24V wider on a large scale in variation, output can be adjustable between 0.8V～0.8VIN, so can adapt to the supply voltage of different DC load needs.It is particluarly suitable for the generating of field use solar-energy photo-voltaic cell, the mobile electronic device work of multiple DC power supply voltage request.

Claims

1. one kind adapts to the DC converter digital control method that wide input and output voltage requires, it is characterized in that, by FAN2108 chip and peripheral circuit element BUCK circuit thereof, output voltage input circuit, PWM wave generator circuit, PWM drive waveform and buffer circuit are set, MOSFET tube resistor resistance Circuit tuning forms;

2. the DC converter control method of the wide input and output voltage requirement of adaptation according to claim 1 is characterized in that, described BUCK circuit adopts FAN2108 and peripheral circuit thereof to form; The PWM waveform generator can be that single-chip microcomputer consists of, and perhaps the PWM of other circuit formation produces circuit; MOSFET tube resistor resistance adjuster is comprised of NMOS pipe Q1 and resistance R 10, filter capacitor C11, C12; The RBIAS that 19 pin of MOSFET tube resistor adjuster and FAN2108 connect is connected in parallel.

3. the DC converter control method that requires with the wide input and output voltage of 2 described adaptations according to claim 1, it is characterized in that, adopt right 1 and 2 described circuit, its control method is: the digital control amount of inputting according to the output voltage initialization circuit, change the PWM ripple duty ratio of PWM waveform generator output, thereby change the conducting ratio of MOSFET pipe Q1, change the equivalent resistance resistance size of MOSFET tube resistor adjuster output, thereby change the parallel resistance resistance to ground wire that connects on 19 pin of FAN2108, change the Voltage Feedback coefficient of FAN, reach the size of regulating FAN2108 output voltage VO UT.

4. the DC converter control method that requires with the wide input and output voltage of 2 described adaptations according to claim 1, it is characterized in that, starting method is: during circuit start, should make PWM ripple duty ratio is 0 start-up circuit, the MOSFET pipe is closed fully, the parallel resistance resistance to ground that connects on 19 pin of FAN2108 is maximum, and making output voltage is the minimum that circuit can reach.