CN101778523A - Electronic ballast used for controlling load circuit of fluorescent lamp and control method thereof - Google Patents

Abstract

The invention relates to an electronic ballast used for controlling a load circuit of a fluorescent lamp and a control method thereof. The electronic ballast comprises a main control module, a first power switch tube, a second power switch tube and a follow current capacitor. The electronic ballast also comprises a sampling resistor connected between the source electrode of the second power switch tube and the ground in series; and the main control module comprises a comparator and a logic control unit which are connected in series. The invention detects whether a system enters the working state of a ZVS or not by adding one sampling resistor and feeding back the current or the voltage of the sampling resistor, also enhances the switch frequency of the power switch tubes at real time by the logic control unit inside the electronic ballast according to a detection result and ensures that the load circuit of the fluorescent lamp presents sensibility, thereby achieving the effect of the ZVS so as to enhance the safe reliability of the operation of the load circuit of the fluorescent lamp.

Description

A kind of electric ballast and control method thereof that is used to control load circuit of fluorescent lamp

Technical field

The present invention relates to integrated circuit, relate in particular to a kind of electric ballast and control method thereof that is used to control load circuit of fluorescent lamp.

Background technology

As everyone knows, electric ballast is a kind of equipment that is used to control normal startup of fluorescent lamp and steady operation, generally, the schematic diagram of electronic ballast control driving fluorescent lamp load circuit works can be as shown in Figure 1, electric ballast 10 ' comprises master control module 1 ' (being the electric ballast chip), the first power switch pipe M1, the second power switch pipe M2 and afterflow capacitor C 2, load circuit of fluorescent lamp 2 comprises inductance L, the first capacitance C1, the second capacitance C3 and fluorescent tube equivalent resistance Rlamp, master control module 1 ' output one a high control signal HO and a low control signal LO is with the controlling and driving first power switch pipe M1 and the second power switch pipe M2 alternate conduction; Electric ballast when work, the oscillogram of the voltage VA at the level VHO of high control signal HO, the level VLO of low control signal LO and A point place as shown in Figure 2:

(1) when level VHO be high level, when level VLO is low level, the first power switch pipe M1 conducting, the second power switch pipe M2 closes, this moment, power Vcc was powered to load circuit of fluorescent lamp 2 by the first power switch pipe M1, and the voltage at afterflow capacitor C 2 two ends is high level;

(2) when level VHO by high step-down, when level VLO does not also uprise, the first power switch pipe M1 and the second power switch pipe M2 all close, and afterflow capacitor C 2 is by the loop discharge of the second capacitance C3-inductance L-(the first capacitance C1, fluorescent tube equivalent resistance Rlamp), and VLO uprises until level;

(3) when level VHO be low level, when level VLO was high level, the first power switch pipe M1 closed, the second power switch pipe M2 conducting, this moment, the flow direction of electric current was that earth terminal charges to the second capacitance C3 via load circuit of fluorescent lamp 2, and the voltage at afterflow capacitor C 2 two ends is low level;

(4) when level VLO by high step-down, when level VHO does not also uprise, the first power switch pipe M1 and the second power switch pipe M2 all close, electric current gives the afterflow capacitor C 2 chargings by the loop of (the first capacitance C1, fluorescent tube equivalent resistance Rlamp)-inductance L-second capacitance C3, and VHO uprises until level.

When level VHO and level VLO are low level simultaneously; this section period is called Dead Time (Tdeadtime); the effect of Dead Time is to guarantee that level VHO and level VLO can not be high level simultaneously; because if such situation occurs; the first power switch pipe M1 and second power switch pipe M2 conducting simultaneously; have huge current flow by the first power switch pipe M1 and the second power switch pipe M2; cause the heating of the first power switch pipe M1 and the second power switch pipe M2; thereby influence its useful life; even burn out; therefore, obviously, Dead Time is a kind of necessary means of protective circuit.

Usually the size of Dead Time is by the decision of master control module 1 ' internal circuit, and under the situation of fixing Dead Time, the electric speed of afterflow capacitor C 2 different putting (filling) can produce different influences to circuit.Fig. 3 is the each point change in voltage schematic diagram under the different velocity of discharge situations of afterflow capacitor C 2:

(1) velocity of discharge is slower: voltage VA changes along the track of curve A, and high level appears in VLO when level, and during the second power switch pipe M2 conducting, voltage VA is non-vanishing, at this moment, has bigger electric current to flow through the second power switch pipe M2;

(2) velocity of discharge is moderate: voltage VA changes along the track of curve B, and high level appears in VLO when level, during the second power switch pipe M2 conducting, the lucky vanishing of voltage VA, be ZVS (zero voltage switch) state, at this moment, do not have electric current to flow through the second power switch pipe M2 in theory;

(3) velocity of discharge is very fast: voltage VA changes along the track of curve C, and high level appears in VLO when level, during the second power switch pipe M2 conducting, voltage VA before be zero sometime, also be the ZVS state, at this moment, also do not have electric current to flow through the second power switch pipe M2 in theory;

(4) similar process of Chong Dian process and discharge is so no longer repeat.

Obviously, in the above-mentioned situation (1), because in one-period, big electric current be will occur and the first power switch pipe M1 or the second power switch pipe M2 flow through, this moment, the first power switch pipe M1, the second power switch pipe M2 were very easy to the heating damage, therefore, did not wish to occur this situation.In actual applications, the size of afterflow capacitor C 2, inductance L, the first capacitance C1, the second capacitance C3 and fluorescent tube equivalent resistance Rlamp all can exert an influence to (filling) the electric speed of putting of afterflow capacitor C 2, therefore, suppose that the parameter of choosing these elements is a desired value.

As shown in Figure 1, through the second capacitance C3, B point place forms alternating voltage, can know from classical Circuit theory, by inductance L, the first capacitance C1, the AC power of 2 pairs of certain frequencies of load circuit of fluorescent lamp that fluorescent tube equivalent resistance Rlamp constitutes has reactance of different nature, can be divided into induction reactance, three types of capacitive reactance and impedances, this reactance characteristic is by inductance L, the first capacitance C1, the size of fluorescent tube equivalent resistance Rlamp and the frequency of AC power determine jointly, the reactance characteristic difference of load circuit of fluorescent lamp 2, then also different to the influence of putting (filling) electric speed of afterflow capacitor C 2, Fig. 4 is the phase diagram of the each point voltage and current under the different reactance characteristic of load circuit of fluorescent lamp 2:

Presenting perception with load circuit of fluorescent lamp 2 is example, can know by classical Circuit theory, the electric current I B and the B point voltage VB of place that are flowed into load circuit of fluorescent lamp 2 by B point place among Fig. 1 incite somebody to action not homophase, its current phase will lag behind voltage-phase, promptly in Tdeadtime, electric current I B will be later than voltage VB and descend; Because level VHO, VLO are low level simultaneously at this moment, the first power switch pipe M1, the second power switch pipe M2 close simultaneously, and the alternating current that actual flow is crossed B point place is provided by afterflow capacitor C 2.

According to formula: ${\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">i</figure-callout>}}_2={\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">C</figure-callout>}}_2\frac{{\mathrm{dV}}_A}{\mathrm{dt}}$ (1), as can be known,

The current value i that afterflow capacitor C 2 provides ₂Big more, variation (decline) speed of afterflow capacitor C 2 both end voltage

Also fast more, promptly voltage change ratio is big more;

Again according to formula: Q=C ₂Δ V _A(2), as can be known,

It is big more that holding circuit is stablized required electric weight Q, variation (decline) the amount Δ V of afterflow capacitor C 2 both end voltage _AAlso big more.

In like manner can get, in the moment that Tdeadtime begins, electric current I B perception＞IB is resistive＞the IB capacitive; According to formula (1) as can be known, under the different imaginary loading states, the velocity magnitude ordering that afterflow capacitor C 2 both end voltage descend is at this moment:

Be that afterflow capacitor C 2 both end voltage under the inductive load state descend the fastest.

By classical Circuit theory as can be known, electric current is electric weight to the integration of time, is expressed as the area that shade covers in Fig. 4, therefore as can be known, at Tdeadtime in the time period, the required electric weight of the required electric weight＞capacitive load of the required electric weight＞resistive load of inductive load; According to formula (2) as can be known, the variation delta V of afterflow capacitor C 2 both end voltage _{The A perception}＞Δ V _{A is resistive}＞Δ V _{The A capacitive}

In view of the foregoing, can draw to draw a conclusion at different reactance characteristic loads:

(1) when load circuit of fluorescent lamp 2 presents induction reactance character, B point place current waveform lags behind voltage waveform, and promptly electric current I B will be later than voltage VB decline; The A point voltage VA of place decrease speed is the fastest, and variable quantity is also maximum;

(2) when load circuit of fluorescent lamp 2 presents resistance, B point place voltage and current homophase; The A point voltage VA of place decrease speed is slower, and variable quantity is also less;

(3) when load circuit of fluorescent lamp 2 presents capacitive reactance, B point place current waveform is ahead of voltage waveform, and promptly electric current I B will descend early than voltage VB; A point place voltage decrease speed is the slowest, and variable quantity is also minimum.

In sum, when load circuit of fluorescent lamp 2 presented the induction reactance characteristic, the voltage decrease speed at the mid point A place of the first power switch pipe M1 and the second power switch pipe M2 was the fastest.Therefore, how to strengthen load circuit of fluorescent lamp induction reactance characteristic, to guarantee that the first power switch pipe M1 and the second power switch pipe M2 (being the half-bridge drive circuit power switch pipe) work in the ZVS state in Dead Time, thereby avoid the first power switch pipe M1 and second power switch pipe M2 heating to damage, become the problem of insider's primary study.

Summary of the invention

In order to address the above problem, the present invention aims to provide a kind of electric ballast and control method thereof that is used to control load circuit of fluorescent lamp, when avoiding in the electric ballast power tube switch, there is high-tension problem in the two ends of power tube, thereby make the loss of power switch pipe drop to minimum, and then effectively improve the security reliability of load circuit of fluorescent lamp work, and prolong its useful life.

The described a kind of electric ballast that is used to control load circuit of fluorescent lamp of one of the present invention, it comprises the master control module, first power switch pipe, second power switch pipe and afterflow electric capacity, wherein, the output of described master control module is connected with the grid of described first power switch pipe and the grid of second power switch pipe respectively, and the source electrode of this first power switch pipe is connected with the drain electrode of second power switch pipe, described afterflow electric capacity is connected between the drain electrode and ground of second power switch pipe

Described electric ballast comprises that also one is connected on the source electrode of described second power switch pipe and the sampling resistor between the ground;

Described master control module comprises comparator and the logic control element that is connected in series, and the input of described comparator is connected with the input of described sampling resistor, and accepts the predeterminated voltage signal of an outside; Described logic control element is controlled the frequency of described master control module output signal according to the comparison signal of comparator output.

The control method of two described a kind of load circuit of fluorescent lamp of the present invention, it comprises the following steps:

Step 1, sampling step, the detection voltage VRtest when the described load circuit of fluorescent lamp of sampling is operated in the T0 sometime behind the Dead Time;

Step 2, comparison step compares a detection voltage VRtest described in the step 1 and a predeterminated voltage Vr, and exports a control signal according to comparative result;

Step 3, controlled step according to the control signal described in the step 2, is adjusted the driving frequency of described load circuit of fluorescent lamp, makes this load circuit of fluorescent lamp be operated in induction reactance characteristic district.

In the control method of above-mentioned load circuit of fluorescent lamp, in step 2 and step 3, as described detection voltage VRtest during less than predeterminated voltage Vr, keep the driving frequency of described load circuit of fluorescent lamp, as described detection voltage VRtest during, improve the driving frequency of described load circuit of fluorescent lamp greater than predeterminated voltage Vr.

Owing to adopted above-mentioned technical solution, the present invention is by setting up a sampling resistor, and the curtage that feeds back this sampling resistor comes detection system whether to enter the operating state of ZVS, improve the switching frequency of power switch pipe simultaneously in real time according to testing result by the logic control element of electric ballast inside, guarantee that load circuit of fluorescent lamp presents perception, thereby reach the effect of ZVS, to improve the security reliability of load circuit of fluorescent lamp work.

Description of drawings

Fig. 1 is the work schematic diagram of electronic ballast control driving fluorescent lamp load circuit in the prior art;

When Fig. 2 is the electric ballast work of Fig. 1, the oscillogram of the voltage VA at the level VHO of high control signal HO, the level VLO of low control signal LO and A point place;

Fig. 3 is the each point change in voltage schematic diagram under the different velocity of discharge situations of the afterflow electric capacity of Fig. 1;

Fig. 4 is the phase diagram of the each point voltage and current under the different reactance characteristic of the load circuit of fluorescent lamp of Fig. 1;

Fig. 5 is a kind of work schematic diagram that is used to control the electronic ballast control driving fluorescent lamp load circuit of load circuit of fluorescent lamp of the present invention;

Fig. 6 is electric ballast when work each point change in voltage schematic diagram of Fig. 5.

Embodiment

Below in conjunction with accompanying drawing, specific embodiments of the invention are elaborated.

As shown in Figure 5, one of the present invention's the electric ballast that is used to control load circuit of fluorescent lamp, load circuit of fluorescent lamp 2 comprises inductance L, the first capacitance C1, the second capacitance C3 and fluorescent tube equivalent resistance Rlamp, electric ballast 10 comprises master control module 1, the first power switch pipe M1, the second power switch pipe M2, sampling resistor Rtest and afterflow capacitor C 2, wherein

The first power switch pipe M1, the second power switch pipe M2 and sampling resistor Rtest connect successively, and the drain electrode of the first power switch pipe M1 is connected the output head grounding of sampling resistor Rtest with power Vcc; Afterflow capacitor C 2 is connected between the drain electrode and ground of the second power switch pipe M2, and the input of afterflow capacitor C 2 also is connected with the input of the second capacitance C3;

Master control module 1 comprises comparator 11 and the logic control element 12 that is connected in series, and wherein, the input of comparator 11 is connected with the input of sampling resistor Rtest, and accepts the predeterminated voltage signal Vr of an outside; Logic control element 12 is according to the comparison signal of comparator 11 output, and control is respectively to the high control signal HO of the grid output of the grid of the first power switch pipe M1 and the second power switch pipe M2 and the frequency of low control signal LO.

The expression formula that can be got the impedance Z of load circuit of fluorescent lamp 2 by the structure of load circuit of fluorescent lamp 2 is:

$Z=\frac{R}{{\left(\mathrm{Rwc}\right)}^2+1}+[\mathrm{wL}-\frac{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">R</figure-callout>}}^2\mathrm{<figure-callout\; id="1"\; label="wc"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">wc</figure-callout>}}{1+{\left(\mathrm{Rwc}\right)}^2}]j,$

In the formula, R is the value of fluorescent tube equivalent resistance Rlamp; The value of getting the first capacitance C1 and the second capacitance C3 is C; W=2 π f, f are the driving frequency of load circuit of fluorescent lamp 2;

By following formula as can be known,

When $\mathrm{wL}-\frac{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">R</figure-callout>}}^2\mathrm{<figure-callout\; id="1"\; label="wc"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">wc</figure-callout>}}{1+{\left(\mathrm{Rwc}\right)}^2}>0$ The time, load circuit of fluorescent lamp 2 shows as induction reactance, promptly $f>\frac{1}{2\mathrm{\&pi;RC}}\sqrt{\frac{R^{2}C}{L}-1}$ The time, load shows as induction reactance;

When $\mathrm{wL}-\frac{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">R</figure-callout>}}^2\mathrm{<figure-callout\; id="1"\; label="wc"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">wc</figure-callout>}}{1+{\left(\mathrm{Rwc}\right)}^2}=0$ The time, load circuit of fluorescent lamp 2 shows as impedance;

When $\mathrm{wL}-\frac{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">R</figure-callout>}}^2\mathrm{<figure-callout\; id="1"\; label="wc"\; filenames="H2009102655952E00031.png,H2009102655952E00041.png"\; state="\{\{state\}\}">wc</figure-callout>}}{1+{\left(\mathrm{Rwc}\right)}^2}<0$ The time, load circuit of fluorescent lamp 2 shows as capacitive reactance.

Therefore, in certain frequency range, increase driving frequency f, load circuit of fluorescent lamp 2 perception will strengthen, the decrease speed of A point place voltage also can be accelerated among Fig. 5, this shows, in the application of reality, as long as utilize the method that changes driving frequency f, just can avoid load circuit of fluorescent lamp 2 to enter the capacitive state.

Seeing also Fig. 5, Fig. 6, in the present embodiment, is example with the electric ballast of said structure, and the control method of a kind of load circuit of fluorescent lamp of two of the present invention is elaborated, and this control method comprises the following steps,

Step 1, sampling step, sampling when load circuit of fluorescent lamp 2 is operated in Dead Time after, i.e. behind the level VLO rising edge of master control module 1 output low control signal LO a certain blink, T0 was interior the time the detection voltage VRtest at sampling resistor Rtest two ends;

Step 2, comparison step passes to comparator 11 with detecting voltage VRtest in the step 1, and should detect voltage VRtest and a predeterminated voltage Vr compares by comparator 11, and logic control element 12 is exported a control signal according to this comparative result;

Step 3, controlled step according to control signal in the step 2, is adjusted the driving frequency f of load circuit of fluorescent lamp 2, and promptly the switching frequency of the first power switch pipe M1 and the second power switch pipe M2 makes this load circuit of fluorescent lamp 2 always work in induction reactance characteristic district.

Specifically:

When detecting voltage VRtest less than predeterminated voltage Vr, the electric current I Rtest that promptly flows through sampling resistor Rtest slowly increases by 0, accordingly, detecting voltage VRtest slowly increases by 0, at this moment, the level VLO of low control signal LO is a high level, the second power switch pipe M2 opens, the A point voltage VA of place is 0, and load circuit of fluorescent lamp 2 is perception, and voltage VA curve changes along track B, C, promptly satisfies the ZVS state, then comparator 11 is failure to actuate, and the control signal of logic control element 12 outputs is used to keep the driving frequency f of load circuit of fluorescent lamp 2;

When detecting voltage VRtest greater than predeterminated voltage Vr, the electric current I Rtest that promptly flows through sampling resistor Rtest can produce a transient pulse earlier, and then slowly increase, accordingly, detect voltage VRtest and produce transient pulse, at this moment, the level VLO of low control signal LO is a high level, the second power switch pipe M2 opens, the A point voltage VA of place is not 0, and voltage VA curve changes along track A, does not promptly satisfy the ZVS state, therefore, when this transient pulse occurring, be about to enter the capacitive state or entered the capacitive state with regard to the operating state that shows circuit, then comparator 11 upsets this moment, the control signal of logic control element 12 outputs is used to improve the frequency of high control signal HO and low control signal LO, thereby improves the switching frequency of the first power switch pipe M1 and the second power switch pipe M2.

Switching frequency along with the first power switch pipe M1 and the second power switch pipe M2, it is the raising of the driving frequency f of load circuit of fluorescent lamp 2, load circuit of fluorescent lamp 2 can present perception gradually and constantly strengthen, the charge and discharge speed of afterflow capacitor C 2 can be accelerated gradually in Dead Time, till detecting voltage VRtest and not having pulse (or have only very by a small margin pulse) to occur in time T 0.

In sum, the present invention can very fastly and reliable must guarantee that whole system enters the operating state of (or approaching) ZVS, and then guarantees that load circuit of fluorescent lamp is operated in perception district, and makes the loss of power switch pipe drop to the end.

Below embodiment has been described in detail the present invention in conjunction with the accompanying drawings, and those skilled in the art can make the many variations example to the present invention according to the above description.Thereby some details among the embodiment should not constitute limitation of the invention, and the scope that the present invention will define with appended claims is as protection scope of the present invention.

Claims (3)

1. electric ballast that is used to control load circuit of fluorescent lamp, it comprises master control module, first power switch pipe, second power switch pipe and afterflow electric capacity, wherein, the output of described master control module is connected with the grid of described first power switch pipe and the grid of second power switch pipe respectively, and the source electrode of this first power switch pipe is connected with the drain electrode of second power switch pipe, described afterflow electric capacity is connected between the drain electrode and ground of second power switch pipe, it is characterized in that

Described electric ballast comprises that also one is connected on the source electrode of described second power switch pipe and the sampling resistor between the ground;

Described master control module comprises comparator and the logic control element that is connected in series, and the input of described comparator is connected with the input of described sampling resistor, and accepts the predeterminated voltage signal of an outside; Described logic control element is controlled the frequency of described master control module output signal according to the comparison signal of comparator output.

2. the control method of a load circuit of fluorescent lamp is characterized in that, described control method comprises the following steps:

Step 1, sampling step, the detection voltage VRtest when the described load circuit of fluorescent lamp of sampling is operated in the T0 sometime behind the Dead Time;

Step 2, comparison step compares a detection voltage VRtest described in the step 1 and a predeterminated voltage Vr, and exports a control signal according to comparative result;

Step 3, controlled step according to the control signal described in the step 2, is adjusted the driving frequency of described load circuit of fluorescent lamp, makes this load circuit of fluorescent lamp be operated in induction reactance characteristic district.

3. the control method of load circuit of fluorescent lamp according to claim 2, it is characterized in that, in step 2 and step 3, as described detection voltage VRtest during less than predeterminated voltage Vr, keep the driving frequency of described load circuit of fluorescent lamp, as described detection voltage VRtest during, improve the driving frequency of described load circuit of fluorescent lamp greater than predeterminated voltage Vr.

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