CN102065602A - Power supply circuit for led - Google Patents
Power supply circuit for led Download PDFInfo
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- CN102065602A CN102065602A CN2010102571659A CN201010257165A CN102065602A CN 102065602 A CN102065602 A CN 102065602A CN 2010102571659 A CN2010102571659 A CN 2010102571659A CN 201010257165 A CN201010257165 A CN 201010257165A CN 102065602 A CN102065602 A CN 102065602A
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- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention provides a power supply circuit for an LED, which can improve power factor through simple means and lower higher harmonic currents. Wherein, the power supply circuit (10) for an LED comprises a rectification circuit (16) and a drive circuit (22) for supplying power to the LED (14). The drive circuit (22) comprises a switch element (26), a current detection resistor (32) with one end connected with the second terminal (26b) of the switch element (26) and the other end connected with a zero-volt line (20), an integrating circuit (34) for outputting integral voltage (Vc) after receiving the current detection voltage (Vs) generated in the current detection resistor (32), and a PWM circuit (36) provided with a comparison circuit (42) for comparing the integral voltage (Vc) and a reference voltage (Vref). When the integral voltage (Vc) reaches the reference voltage (Vref), the PWM circuit outputs a resetting signal to a trigger (38) to turn on the switch element (26).
Description
Technical field
The present invention relates to receive from the commercial voltage of commercial AC power output and to the LED power circuit of LED feed point light current.
Background technology
Have with incandescent lamp bulb in the past and compare, the light-emitting diode of longer such advantage of lower and life-span of power consumption (below, be called " LED "), along with the raising of the person's of needs environmental consciousness, and as one of strategy of Saving Energy, the scope of application enlarges hastily.
But, LED is owing to than commercial voltage (for example pass through, 60Hz, 100V) low " direct current " voltage moves, so when using commercial voltage that LED is lighted, need carry out supplying power to after step-down/rectification (=be transformed into direct voltage) or the rectification/step-down LED power circuit of LED to this commercialization voltage.
As such LED power circuit, exploitation has following structure: at first the alternating voltage from commercial ac power source is carried out rectification and after transforming to direct voltage, by switching circuit this direct voltage is carried out step-down and supply to LED (for example, patent documentation 1).
In addition, except the circuit of patent documentation 1 record, also develop LED power circuit 1 as shown in Figure 7.This LED comprises with power circuit 1: the alternating voltage Vi (with reference to Fig. 8 (a)) from 2 outputs of commercial AC power is carried out rectification and forms the rectification circuit 3 of the direct voltage Vdc (with reference to Fig. 8 (c)) of pulsating current; And receive this direct voltage and supply with the constant-current circuit 5 decide electric current to LED4.
Constant-current circuit 5 comprises: high speed diode 5a; Reactor element 5b; Switch element 5c (in the drawings, having used MOSFET); The current sense resistor 5d that the electric current that flows to LED4 is detected; And have received current and detect the current detection voltage Vs that produces among the resistance 5d and the comparison circuit A that compares with reference voltage V ref, oscillator B, and the pwm circuit 5e (for example, the led driver IC " HV9910 " of Supertex company) of trigger C.
Trigger C is set (importing asserts signal to the set terminal S of trigger C from oscillator B) if oscillator B moves, and then imports connection signal and makes this switch element 5c become connection to the grid 5cg of switch element 5c.
Become the timing of connecting at switch element 5c, in Vdc (+), circulate in proper order according to this among LED4, reactor element 5b, switch element 5c, current sense resistor 5d and the Vdc (-), and shown in Fig. 9 (b), output current Io increases (" X " part in the drawings) linearly.
Because the output current Io that flows through among the current sense resistor 5d increases, so the current detection voltage Vs that produces among the current sense resistor 5d increases, if this current detection voltage Vs has reached reference voltage V ref, then import reset signal to the reseting terminal R of trigger C from comparison circuit A.Because to reseting terminal R input reset signal, this trigger C is reset, stop at the connection signal of the grid of switch element 5c and this switch element 5c becomes shutoff.Its result, the loop circuit (Fig. 7) of formation LED4, reactor element 5b and high speed diode 5a, the current value that supplies to the output current Io of LED4 reduces (" Y " part in Fig. 9 (b)) linearly.
From oscillator B action and switch element 5c becomes to connect and passed through official hour (operating frequency by oscillator B determines this time) afterwards, oscillator B moves once more, and switch element 5c becomes connection thereby trigger C is set, and repeats described action.
Herein, can use the resistance value Rs of reference voltage V ref and current sense resistor 5d as following (formula 1), to represent to flow to the peak I o (max) (comprising pulsation) of the output current Io of LED4, because Vref and Rs are constant, so shown in Fig. 8 (d), except the front and back of the magnitude of voltage vanishing of alternating voltage Vi, become and decide current waveform, should decide electric current by supplying with, LED4 lights.In addition, the light China ink part of Fig. 8 (d) means because the dither component that the operating frequency of oscillator B is brought.
Io (max)=Vref/Rs (formula 1)
Patent documentation 1: TOHKEMY 2004-296205 communique
Summary of the invention
But being input to such LED becomes (when with sinusoidal waveform in commercial ac voltage Vi comparing the difference of vpg connection bigger) waveform bigger as the distortion that has peak value in the initial and last timing in the half period of Fig. 8 (b) alternating voltage Vi that is shown in the input current Iin of power circuit 1.Its former because, the output current Io that flows through among the LED4 presents shown in Fig. 8 (d), rising sharp at first of its half period, keep constant current value afterwards, last such waveform that descends sharp in the half period, when output current Io rises sharp or when descending sharp, the value of input current Iin overshoot significantly (overshoot).
Like this, be input to LED (promptly with the distortion in the waveform of the input current Iin of power circuit 1, the waveform of the relative alternating voltage Vi of the waveform of input current Iin is in shape difference) be meant that more greatly the effective power ratio (=power factor) from the power (apparent power) of commercial AC power 2 outputs relatively is lower.If power factor is lower, then compare apparent power and become big with effective power, use the input current Iin of power circuit 1 to become big so be input to LED, and need surplus in the power supply capacity of commercial ac power source 2.
In addition, big if the distortion of the waveform of input current Iin becomes, then the higher harmonic current of input increases, if flow through higher harmonic current, then descend owing to the impedance that exists in the power circuit produces voltage, as a result of, supply voltage comprises high order harmonic component and produces distortion.
At such " reduction of power factor " and " increase of higher harmonic current ", implemented following such countermeasure in the past.
That is,, improve circuit and tackle by between commercial ac power source 2 and LED are with power circuit 1, appending PFC (Power Factor Correction, power factor correction) constant power factor at " reduction of power factor ".But; if such power factor correction circuit is appended to LED power circuit 1; then LED can become big with the circuit scale of power circuit 1; and can't corresponding at this LED with the requirement of the miniaturization of power circuit 1 (for example, power circuit and LED are encapsulated integratedly and constituted the such requirement of the one-piece type LED lamp of power circuit).In addition, also can't ignore the power loss that produces in the power factor correction circuit.
In addition, at " increase of higher harmonic current ",, suppress " peak value that before polarity just will be reversed, produces " in the input current Iin waveform and reduced higher harmonic current by the big smmothing capacitor of degree that appends the secondary side that is in rectification circuit 3.But, if append such smmothing capacitor, then when wishing that the dimmer that outlet side at commercial ac power source 2 sets phase control mode comes LED4 is carried out under the situation of light modulation, direct voltage from the pulsating current of rectification circuit 3 output has smoothly been crossed head and can't have been carried out phase control by dimmer, can't carry out the problem that light modulation action or light modulation action become unstable such so exist.
The present invention develops in view of the problem of such conventional art.Therefore, major subjects of the present invention is to provide a kind of LED power circuit, can by need not to append power factor correction circuit or smmothing capacitor etc., simple method improves power factor and reduces higher harmonic current, and then power loss also is lowered, thereby can raise the efficiency.
The invention of the 1st aspect provides a kind of LED power circuit 10, it is characterized in that possessing:
The zero volts line 20 of extending from the secondary side of described rectification circuit 16, with and the direct voltage supply lines 18 that is connected with the anode-side of LED14 of front end; With
Described drive circuit 22 possesses:
The invention of the 2nd aspect provides a kind of LED power circuit 10, it is characterized in that having:
The zero volts line 20 of extending from the secondary side of described rectification circuit 16, with and the direct voltage supply lines 18 that is connected with the anode-side of LED14 of front end; With
Described drive circuit 22 possesses:
Described pwm circuit 36 has:
Use Fig. 2～Fig. 4, the action effect when using LED of the present invention with power circuit 10 LED14 to be lighted describes.In Fig. 2, illustrate and supply to this LED with alternating voltage Vi (Fig. 2 (a)), the input current Iin (Fig. 2 (b)) of power circuit 10, from the direct voltage Vdc (Fig. 2 (c)) of rectification circuit 16 outputs and the waveform that outputs to the output current Io (Fig. 2 (d)) of LED14.
In addition, Fig. 3 and waveform shown in Figure 4 are that the magnitude of voltage at direct voltage Vdc is become the waveform that cuts during small under the lower timing (Fig. 4) of maximum timing (Fig. 3) or magnitude of voltage and amplify (in Fig. 2 on transverse axis (time) direction, 1 cycle is 1/50 second or 1/60 second (frequency 50,60Hz), is 1/ (50 * 10 in Fig. 3, Fig. 4 with respect to this
3) about (frequency 50kHz)), be respectively the current detection voltage Vs (Fig. 3 (c), Fig. 4 (c)) that produces in the voltage VL (Fig. 3 (a), Fig. 4 (a)) that is applied to reactor element 30, the output current Io (Fig. 3 (b), Fig. 4 (b)) that is input to LED14, the current sense resistor and from the integral voltage Vc (Fig. 3 (d), Fig. 4 (d)) of integrating circuit 34 outputs.
In addition, the light ink of Fig. 2 (d) partly means because the dither component that the operating frequency of oscillator 40 causes.
LED of the present invention possesses that received current detects the current detection voltage Vs that produces in the resistance 32 and the integrating circuit 34 of exporting integral voltage Vc with power circuit 10, comparison circuit 42 in the pwm circuit 36 is comparing on this point integral voltage Vc and reference voltage V ref from these integrating circuit 34 outputs, different (in addition with the LED of conventional art with power circuit 1, use under the situation of power circuit 1 at the LED of conventional art, as mentioned above, current detection voltage Vs and the reference voltage that produces among the current sense resistor 5d directly compared).
If from oscillator 40 to the set terminal S of trigger 38 input asserts signal and trigger 38 is set, then the lead-out terminal Q of slave flipflop 38 imports connection signal to the connection signal input terminal 26c of switch element 26, and switch element 26 becomes on-state (the 1st terminal 26a of=switch element 26 and the state of the 2nd terminal 26b mutual conduction).
If switch element 26 becomes on-state, then the direct voltage supply lines 18 and zero volts line 20 of extending from the secondary side of rectification circuit 16 is switched on via LED14, reactor element 30, switch element 26 and current sense resistor 32, and output current Io circulates in proper order according to this.At this moment, the voltage that produces in general switch element 26 and the current sense resistor 32 is small, so to reactor element 30, shown in Fig. 3 (a), Fig. 4 (a), when trigger 38 is set, apply [voltage between direct voltage supply lines 18 and zero volts line 20 (=Vdc)-be applied to LED14 voltage (=Vo)].
In addition, when trigger 38 is set, the electric current (=output current Io) that flows through in direct voltage supply lines 13-LED14-reactor element 30-switch element 26-current sense resistor 32-zero volts line 20 shown in Fig. 3 (b), Fig. 4 (b) with the gradient of regulation (in addition, the reactance of reactor element 30 is big more, and this gradient is slow more) and increase gradually linearly.
When having flow through output current Io, the current detection voltage Vs that produces in the current sense resistor 32 is Vs=Io * Rs (Rs is the resistance value of current sense resistor 32), so shown in Fig. 3 (c), Fig. 4 (c), rise linearly, afterwards, the increase gradually with output current Io increases accordingly linearly gradually.
At this moment, from the integral voltage Vc of integrating circuit 34 output that receives this current detection voltage Vs shown in Fig. 3 (d), Fig. 4 (d), do not rise linearly and during the increase gradually corresponding to current detection voltage Vs, increase gradually according to the timeconstant of integrating circuit 34.
, this integral voltage Vc reached reference voltage V ref if increasing gradually, then import reset signal to the reseting terminal R of trigger 38 from the comparison circuit 42 of pwm circuit 36, trigger 38 stops the connection signal input terminal 26c output connection signal at switch element 26, thereby switch element 26 becomes off state (the 1st terminal 26a and the 2nd terminal 26b of=switch element 26 are nonconducting states).
If switch element 26 becomes off state, then become non-conduction before direct voltage supply lines 18 and zero volts line 20 and form the such loop circuit of direct voltage supply lines 18-LED14-reactor element 30-high speed diode 28-direct voltage supply lines 18, the output current Io that flows through this loop circuit reduces shown in Fig. 3 (b), Fig. 4 (b) linearly.In addition, if switch element 26 becomes off state, be border and become nonconducting state between direct voltage supply lines 18 and zero volts line 20 as mentioned above then with the switch element 26 that becomes off state, so become zero (with reference to Fig. 3 (c), Fig. 4 (c)) when switch element 26 is observed, being in the current detection voltage Vs that produces the current sense resistor 32 of zero volts line 20 sides, also reduce (with reference to Fig. 3 (d), Fig. 4 (d)) gradually from the integral voltage Vc of integrating circuit 34 outputs thus according to the timeconstant of integrating circuit 34.
Afterwards, if sky is opened the period T (T is the inverse of the frequency of oscillation f of oscillator 40) of regulation and imported asserts signal from oscillator 40 to the set terminal S of trigger 38 once more, then from this trigger 38 to the connection signal input terminal 26c of switch element 26 output connection signal and switch element 26 becomes on-state, carry out described action repeatedly.
But, in the comparison circuit A of LED in the past with power circuit 1 (with reference to Fig. 7), current detection voltage Vs and reference voltage V ref are directly compared, no matter whether increase and decrease so supply to the direct voltage Vdc of constant-current circuit 5, switch element 5c becomes shutoff with certain current detection voltage Vs (=reference voltage V ref) all the time, its result, output current Io becomes constant substantially waveform (being square waveform), the step-down thereby power factor is had to as mentioned above.
For this point, use in the comparison circuit 42 of power circuit 10 at LED of the present invention, to comparing from the integral voltage Vc and the reference voltage V ref of integrating circuit 34 output according to current detection voltage Vs, integral voltage Vc as mentioned above, do not rise linearly and corresponding to the increase part gradually of current detection voltage Vs, increase gradually according to the timeconstant of integrating circuit 34, even current detection voltage Vs self has surpassed reference voltage V ref, himself also can not become the action reason of comparison circuit 42.In other words, by integral voltage Vc and reference voltage V ref are compared, and allowable current detects voltage Vs and surpasses reference voltage V ref.
Thus, direct voltage Vdc bigger (promptly, near the central authorities of the waveform in each half period under (=Fig. 3)) situation, switch element 26 does not become shutoff even current detection voltage Vs becomes above the size of reference voltage V ref, also flow through those many output current Io, on the contrary direct voltage Vdc less (promptly, near the two ends of the waveform in each half period, and under the part that direct voltage Vdc is bigger than the operation voltage of LED (=Fig. 4)) situation, current detection voltage Vs also correspondingly diminishes, so output current Io also tails off.Its result, the waveform of the output current Io of each half period is shown in Fig. 2 (d), and near the waveform (sine wave) of each half period of direct voltage Vdc, meanwhile power factor also improves.
The LED that the invention of the 3rd aspect record is put down in writing aspect the 2nd is with in the power circuit, it is characterized in that, also possessing between described rectification circuit 16 and described drive circuit 22 is connected in parallel with described rectification circuit 16, magnitude of voltage from the direct voltage Vdc of described rectification circuit 16 outputs is detected, be input to the voltage detecting circuit 50 of described oscillator 40
The described oscillator 40 of described pwm circuit 36 reduces frequency of oscillation f when the magnitude of voltage of the direct voltage Vdc that imports from described voltage detecting circuit 50 increases owing to power supply voltage variation, and frequency of oscillation f is increased.
Will from cycle of the set terminal S of 40 pairs of triggers 38 of oscillator input asserts signal (promptly, the inverse of the frequency of oscillation f of oscillator 40) when being made as T as mentioned above, shown in Fig. 3 (b), be set to the recruitment of the output current Io the time t1 till being reset from switch element 26, identical with the reduction of output current Io in time (T-t1) till the switch element 26 that is reset is set once more, so shown in Fig. 3 (a), time t1 and time (T-t1) separately in, in reactor element 30, flow through output current Io and the voltage V that produces
LWith long-pending equating of this time.
That is, if the voltage that produces among the LED14 is made as Vo, the direct voltage among the time t1 is made as Vdc1 (Vdc1 is near the maximum direct voltage of the direct voltage Vdc of pulsating current), then
(Vdc1-Vo) * t1=Vo * (T-t1) (formula 2)
If, then have with (formula 2) distortion
T1=T * (Vo/Vdc1) (formula 3).
That is, according to described (formula 3), T and Vo are constant, so if direct voltage Vdc1 changes owing to the alternating voltage Vi from commercial ac power source 12 changes (power supply voltage variation), then t1 also changes accordingly with it.
On the other hand, if the voltage that produces in the current sense resistor 32 is made as Vs1, the resistance value of current sense resistor 32 is made as Rs, reference voltage is made as Vref, the time constant of integrating circuit 34 is made as τ, then become
Vref=Vs1 * (1-ε
-(t1/ τ)) (formula 4),
Output current Io (max) 1=Vs1/Rs is so (formula 4) becomes
Io(max)1＝Vs/Rs＝Vref/(Rs×(1-ε
-(t1/τ)))
(formula 5).
Herein, because Rs, Vref and τ are constant, thus if the t1 change owing to the change of direct voltage Vdc1, then output current Io (max) 1 would also change accordingly with it, becomes the stable luminous reason that hinders LED14.
Therefore, use in the power circuit 10 at LED of the present invention, 50 couples of direct voltage Vdc1 that change according to commercial ac voltage Vi detect by voltage detecting circuit, oscillator 40 makes frequency of oscillation f reduce when the magnitude of voltage of detected direct voltage Vdc has increased, and frequency of oscillation f is increased.
Promptly, as described shown in (formula 3), t1=T * (Vo/Vdc1), so for example changed at Vdc1+10% situation under, making from the period T variation+10% of oscillator output asserts signal, in other words making the inverse of period T is that frequency of oscillation f changes-10%, thereby, can make the value of t1 become constant in the front and back of this variation.In addition, changed under-10% the situation, change+10% owing to same reason makes frequency of oscillation, thereby similarly, it is constant that t1 is become at Vdc1.
Like this, be adjusted into constant by value with t1, the change that does not rely on direct voltage Vdc1 (promptly, the vibration that causes from the power supply voltage variation of the alternating voltage Vi of commercial AC power 12 outputs), and that the mean value that can make the output current Io that flows through among the LED14 becomes is constant, can make LED14 stably luminous.
In addition, in described explanation, Fig. 3 that the direct voltage Vdc that use illustrates pulsating current becomes near each waveform the maximum (=Vdc1) timing (=become maximum timing with each half period from the alternating voltage Vi of commercial ac power source 12) with each half period is illustrated, but for example also can use as shown in Figure 4 from direct voltage Vdc lower (=Vdc2) regularly the time t2 that is set to till being reset of switch element 26 carry out identical explanation.
According to LED power circuit of the present invention, can improve power factor and reduce higher harmonic current by the simple method of not appending power factor correction circuit, smmothing capacitor etc., and then reduce power loss, thereby can raise the efficiency.
In addition, by at commercial ac power source and the LED of the present invention dimmer that phase control mode is installed between the power circuit, can use this dimmer to carry out agonic stable light modulation action.Its former because, the waveform of output current that supplies to LED by LED of the present invention with power circuit is near the waveform of the direct voltage of pulsating current, thereby the distortion of input current waveform is enhanced and power factor uprises (promptly, further near the state of ohmic load), thus can carry out phase control in each half period reliably.
Description of drawings
Fig. 1 illustrates the figure of the LED of the 1st embodiment of the present invention with power circuit.
Fig. 2 illustrates to supply to LED of the present invention figure with the waveform of the alternating voltage of power circuit etc.
Fig. 3 illustrates from the direct voltage of the rectification circuit output figure for each waveform under the maximum timing.
Fig. 4 is the figure that each waveform under the lower timing of the direct voltage of rectification circuit output is shown.
Fig. 5 illustrates the figure of the LED of the 2nd embodiment of the present invention with power circuit.
Fig. 6 is the figure that the circuit of the oscillator among the 2nd embodiment is shown.
Fig. 7 illustrates the figure of the LED of conventional art with power circuit.
Fig. 8 illustrates the LED that the supplies to conventional art figure with the waveform of the alternating voltage of power circuit etc.
Fig. 9 illustrates the figure of the LED of conventional art with the waveform of output current that flows through in the power circuit etc.
(symbol description)
The 10:LED power circuit; 12: commercial ac power source; 14:LED; 16: rectification circuit; 18: the direct voltage supply lines; 20: zero volts line; 22: drive circuit; 24a～24d: diode; 26: switch element; 28: high speed diode; 30: the reactor element; 32: current sense resistor; 34: integrating circuit; 36:PWM (pulse duration control) circuit; 38: trigger; 40: oscillator; 42: comparison circuit; 44: reference voltage generator; 50: voltage detecting circuit; 52a, 52b: resistance; 54: detect the voltage input line road; 56: smoothing capacitor; 58: detect voltage input end; 60: the asserts signal lead-out terminal; 62a, 62b, 62c: inverter; 64: the 1 resistance; 66: the 2 resistance; 68: the 3 resistance; 70: the 4 resistance; 72: capacitor.
Embodiment
Below, with reference to accompanying drawing, describe with power circuit 10 having used LED of the present invention.At first, use Fig. 1 that the LED of the 1st embodiment is described with power circuit 10, then, use Fig. 5 describes with power circuit 10 LED of the 2nd embodiment.In addition, in explanation during the 2nd embodiment,, quote the explanation among the 1st embodiment and omit its explanation, only the part different with the 1st embodiment described for the part common with the 1st embodiment.
The LED of the 1st embodiment is circuit that the alternating voltage Vi from commercial AC power 12 inputs is carried out rectification and powers to LED14 with power circuit 10, roughly comprises rectification circuit 16, direct voltage supply lines 18 and zero volts line 20 and drive circuit 22.In addition, forward is connected in series two LED and has constituted LED14 in the present embodiment, but kind and the number of the LED that uses are not particularly limited.
Direct voltage supply lines 18 and zero volts line 20 all are the electric wires that extends from this rectification circuit 16 in order to supply to drive circuit 22 from the direct voltage Vdc of the pulsating current of rectification circuit 16 outputs, and the front end of direct voltage supply lines 18 is connected with the anode-side of LED14.
Drive circuit 22 be between direct voltage supply lines 18 in the secondary side of rectification circuit 16 and zero volts line 20 relatively rectification circuit 16 settle in parallel, and receive from the direct voltage Vdc of rectification circuit 16 outputs via direct voltage supply lines 18 and, to comprise switch element 26, high speed diode 28, reactor element 30, current sense resistor 32, integrating circuit 34 and PWM (pulse duration control) circuit 36 circuit that LED14 powers.
Integrating circuit 34 is that received current detects the current detection voltage Vs that produces in the resistance 32 and exports the circuit of integral voltage Vc, in the present embodiment, has used the RC time constant circuit that comprises resistance 34a and capacitor 34b.
This resistance 34a is the one end and distolateral a connection of current sense resistor 32, the resistance that the other end is connected with the integral voltage output 34c of integrating circuit 34.In addition, capacitor 34b is that the one end is connected with described integral voltage output 34c, the capacitor that the other end is connected with zero volts line 20.In addition, the resistance that uses among resistance 34a and the capacitor 34b and the form of capacitor are not particularly limited.
Oscillator (OSC) the 40th, to the set terminal S of trigger 38 device with the cycle output asserts signal of regulation, its output 40a is connected with the set terminal S of trigger 38.Though the kind of this oscillator 40 is not particularly limited, as the 2nd embodiment (aftermentioned),, make under the situation of its frequency of oscillation variation according to the magnitude of voltage of the direct voltage Vdc that exports from rectification circuit 16, use voltage controlled oscillator (VCO).
Next, use Fig. 2～Fig. 4, the action when using such LED with power circuit 10 LED14 to be lighted describes.Fig. 2 illustrates and supplies to this LED with alternating voltage Vi (Fig. 2 (a)), the input current Iin (Fig. 2 (b)) of power circuit 10, from the direct voltage Vdc (Fig. 2 (c)) of rectification circuit 16 outputs and the waveform that outputs to the output current Io (Fig. 2 (d)) of LED14.
In addition, Fig. 3 and waveform shown in Figure 4 are the magnitudes of voltage that cut direct voltage Vdc, and (=Vdc1) timing (Fig. 3) or magnitude of voltage are low (to extend the waveform of amplification (in Fig. 2 during down small of=Vdc2) timing (Fig. 4) on transverse axis (time) direction for maximum, 1 cycle is 1/50 second or 1/60 second (frequency 50,60Hz), with respect to this, be 1/ (50 * 10 in Fig. 3, Fig. 4
3) about (frequency 50kHz)), be respectively the current detection voltage Vs (Fig. 3 (c), Fig. 4 (c)) that produces in the voltage VL (Fig. 3 (a), Fig. 4 (a)) that is applied to reactor element 30, the output current Io (Fig. 3 (b), Fig. 4 (b)) that outputs to LED14, the current sense resistor and from the integral voltage Vc (Fig. 3 (d), Fig. 4 (d)) of integrating circuit 34 outputs.
If, connect commercial ac power source 12 at the LED of the 1st embodiment with the primary side (being the primary side of rectification circuit 16) of power circuit 10, and be connected LED14 at secondary side (be direct voltage supply lines 18 with the other end of reactor element 30 between), output 40a from oscillator 40 imports asserts signal to the set terminal S of trigger 38 then, then trigger 38 be set and from the lead-out terminal Q of this trigger 38 to the connection signal input terminal 26c of switch element 26 output connection signal, switch element 26 becomes on-state.
If switch element 26 becomes connection, then direct voltage supply lines 18 and zero volts line 20 conducting by LED14, reactor element 30, switch element 26 and current sense resistor 32, output current Io circulates in proper order according to this.At this moment, the voltage that produces in general switch element 26 and the current sense resistor 32 is small, so shown in Fig. 3 (a), Fig. 4 (a), roughly when trigger 38 is set, to reactor element 30, apply [voltage between direct voltage supply lines 18 and zero volts line 20 (=Vdc)-be applied to LED14 voltage (=Vo)].
In addition, when trigger 38 is set, the electric current (=output current Io) that flows through in direct voltage supply lines 18-LED14-reactor element 30-switch element 26-current sense resistor 32-zero volts line 20 increases linearly gradually with the inclination (reactance of reactor element 30 is big more, and this inclination is slow more) of regulation shown in Fig. 3 (b), Fig. 4 (b).
When having flow through output current Io, the current detection voltage Vs that produces in the current sense resistor 32 is Vs=Io * Rs (Rs is the resistance value of current sense resistor 32), so shown in Fig. 3 (c), Fig. 4 (c), rise linearly, afterwards, the increase gradually with output current Io increases accordingly linearly gradually.
At this moment, from the integral voltage Vc of integrating circuit 34 output that receives this current detection voltage Vs shown in Fig. 3 (d), Fig. 4 (d), not to rise linearly and during the increase gradually corresponding to current detection voltage Vs, increase gradually according to the timeconstant of integrating circuit 34.
, this integral voltage Vc reached reference voltage V ref if increasing gradually, then import reset signal to the reseting terminal R of trigger 38 from the comparison circuit 42 of pwm circuit 36, trigger 38 stops the connection signal input terminal 26c output connection signal at switch element 26, thereby switch element 26 becomes off state.
If switch element 26 becomes off state, then become nonconducting state between direct voltage supply lines 18 and zero volts line 20, form the such loop circuit of direct voltage supply lines 18-LED14-reactor element 30-high speed diode 28-direct voltage supply lines 18, the output current Io that flows through this loop circuit reduces shown in Fig. 3 (b), Fig. 4 (b) linearly.In addition, if switch element 26 becomes off state, be the border then with the switch element 26 that becomes off state, become nonconducting state between direct voltage supply lines 18 and zero volts line 20, so see the current detection voltage Vs vanishing (with reference to Fig. 3 (c), Fig. 4 (c)) that produces the current sense resistor 32 that is in zero volts line 20 sides from switch element 26, the integral voltage Vc from integrating circuit 34 outputs also reduces (with reference to Fig. 3 (d), Fig. 4 (d)) gradually corresponding to the timeconstant of integrating circuit 34 thus.
Afterwards, if vacate the period T (for example, 1/ (50 * 10 of regulation
3) second=50kHz) and once more from oscillator 40 to the set terminal S of trigger 38 output asserts signal, then from this trigger 38 to the connection signal input terminal 26c of switch element 26 input connection signal and switch element 26 becomes on-state, repeat described action.
Use in the comparison circuit 42 of power circuit 10 at this LED, to comparing from the integral voltage Vc and the reference voltage V ref of integrating circuit 34 outputs according to current detection voltage Vs, integral voltage Vc as mentioned above, not to rise linearly and corresponding to the increase part gradually of current detection voltage Vs, increase gradually according to the timeconstant of integrating circuit 34, even so current detection voltage Vs self surpasses reference voltage V ref, himself also can not become the action reason of comparison circuit.In other words, by integral voltage Vc and reference voltage V ref are compared, current detection voltage Vs surpasses reference voltage V ref and is allowed.
Thus, direct voltage Vdc big (promptly, near the central authorities of the waveform in each half period under (=Fig. 3)) situation, even current detection voltage Vs becomes the size above reference voltage V ref, switch element 26 is not also for turn-offing, and flow through corresponding many output current Io, on the contrary direct voltage Vdc little (promptly, near the two ends of the waveform in each half period and under the situation of the direct voltage Vdc part bigger (=Fig. 4)) than the operation voltage of LED, current detection voltage Vs also correspondingly diminishes, so output current Io also tails off.Its result, the waveform of the output current Io of each half period is shown in Fig. 2 (d), and near the waveform (sine wave) of each half period of direct voltage Vdc, meanwhile power factor also improves.
When enumerating concrete numerical value and describe, shown in Fig. 3 (a) and Fig. 4 (a), the voltage V that produces in the reactor element 30
LWith amassing after slave flipflop 38 is set till be reset (promptly of time t, the on-state of switch element 26) with after this trigger 38 is reset till be set once more (promptly, the off state of switch element 26) in, (for example equate mutually, in Fig. 3 (a), become (Vdc1-Vo) * t1=Vo * (T-t1) (Vdc1 means " magnitude of voltage of the direct voltage Vdc in the small time that with dashed lines A represents in Fig. 2 (d) "), in Fig. 4 (a), become (Vdc2-Vo) * t2=Vo * (T-t2) (Vdc2 means " magnitude of voltage of the direct voltage Vdc in the small time that with dashed lines B represents in Fig. 2 (d) ").
Therefore, the time that switch element 26 becomes on-state is not constant all the time in each half period, and direct voltage Vdc become the shortest near maximum (=t1), direct voltage Vdc become the longest near minimum (=t2).
Herein, use peak value Vs1, the Vs2 of current detection voltage Vs and the resistance value Rs of current sense resistor 32, can expression as described below flow to peak value (output current Io (max) 1 under the timing that trigger 38 is reset and the Io (max) 2 of the output current Io of LED14.
Io (max) 1=Vs1/Rs (formula 6)
Io (max) 2=Vs2/Rs (formula 7)
Vc=Vs (1-ε
-(t/Ri * Ci)) (formula 8)
Ri: the resistance value [Ω] of the resistance 34a of integrating circuit 34
Ci: the capacitance [F] of the capacitor 34b of integrating circuit 34
That is the timeconstant of Ri * Ci=integrating circuit 34.
When Vc has reached Vref, during Vc=Vref, switch element is switched into shutoff, so
Vref＝Vsl×(1-ε
-(t1/Ri×Ci))＝Vs2×(1-ε
-(t2/Ri×Ci))
(formula 9).
Herein, as mentioned above, Ri * Ci is that (time constant is meant for the timeconstant of integrating circuit 34, degree for the response speed of the input of integrating circuit, if time constant is little, time integral voltage rise sharp (=response rapidly) then, if time constant is big, time integral voltage rise lentamente (=operating lag) then), by suitably setting this timeconstant, output current Io becomes such waveform shown in Fig. 2 (d), is similar to from the waveform of the direct voltage Vdc of the pulsating current of rectification circuit 16 output.
Carry out some detailed descriptions again with concrete example.For example, used at pwm circuit 36 under the situation of led driver IC " HV9910 " of Supertex company, reference voltage V ref is 250mV (Vref=250mV).So, if the frequency of oscillation f of oscillator 40 is made as 50kHz, T=1/f=20 μ second then.In LED14 was two example, Vo=7V was Vdc1=140V from the maximum of the direct voltage Vdc of the pulsating current of rectification circuit 16 outputs, and minimum value is Vdc2=14V.
As mentioned above, the voltage V that produces in the reactor element 30
LPositive and negative area equate (with reference to Fig. 3 (a), Fig. 4 (a)), so according to (Vdc1-Vo) * t1=Vo * (T-t1), the μ of t1=T * (Vo/Vdc1)=1 second,
According to (Vdc2-Vo) * t2=Vo * (T-t2), become the μ of t2=T * (Vo/Vdc2)=10 second.
In addition, according to (formula 9),
Vs1=Vref/ (1-ε
-(t1/Ri * Ci)) (formula 10)
Vs2=Vref/ (1-ε
-(t2/Ri * Ci)) (formula 11).
As an example, if establish Ri=1k Ω, Ci=3900pF, then timeconstant becomes Ri * ci=3.9 μ second.If they are updated to (formula 10) and (formula 11) respectively, then
Vs1＝Vref/(1-ε
-(t1Ri×Ci))＝1100mV
Vs2＝Vref/(1-ε
-(t2/Ri×Ci))＝270mV。
Herein, if the resistance value Rs of current sense resistor 32 is made as 1.8 Ω, then according to (formula 6) and (formula 7),
Io(max)1＝Vs1/Rs＝1100mV/1.8Ω＝611mA
Io(max)2＝Vs2/Rs＝270mV/1.8Ω＝150mA。
The waveform of output current Io is similar to the waveform of the direct voltage Vdc of pulsating current shown in Fig. 2 (d).In addition, by experiment, under the situation of this waveform, the average current of output current Io is about 400mA.
Result of experiment, input power factor is 55% in example in the past, has been improved to 90% in the present embodiment with respect to this.In addition, for efficient, also from 55% being improved to 65% (LED is two present embodiment) because LED output voltage V o is low to moderate=7V, so absolute value becomes this level.
In addition, the LED that is input to present embodiment from commercial AC power 12 with the waveform of the input current Iin of power circuit 10 shown in Fig. 2 (b), become the waveform of the tendency that descends gradually from initial peak value with half period of commercial frequency, the initial and last bigger peak value that in the past occurred such (Fig. 8 (b)) each half period in the example is suppressed out of imagination ground.Its former because, as mentioned above, the waveform of output current Io be similar to pulsating current direct voltage Vdc waveform and input power factor is improved.
In addition, Fig. 2 (b) (d) and Fig. 8 (b) (d) in, produce current value become zero during the reasons are as follows described.Usually, use in the power supply stabilized power supply that utilization uses the direct voltage Vdc of pulsating current to make in the action of pwm circuit 36.Therefore, near zero volt of the direct voltage Vdc of pulsating current in, brownout and pwm circuit 36 is failure to actuate, its result, drive circuit 22 is failure to actuate, thus produce input current Iin and output current Io become zero during.
In addition, preferably set the timeconstant of integrating circuit 34 for switch element 26 and become the above time of the minimum value of the time of connection (that is the turn-on time when, direct voltage Vdc becomes maximum).It is former because by timeconstant being set for the substantially identical time of minimum value that becomes turn-on time with switch element 26, can be improved to the level of 70% such practicality to major general's input power factor.Therefore and not preferred in addition, if make timeconstant excessive on the contrary, then Io (max) 1 becomes excessive with the difference between current of Io (max) 2, and output current wave is deformed into equilateral triangle, so from the wave form varies of the direct voltage Vdc of pulsating current.So the upper limit of the timeconstant of integrating circuit 34 is preferably about 10 times of minimum value that switch element 26 becomes the time of connection.
The LED of the 2nd embodiment except rectification circuit 16, direct voltage supply lines 18 and zero volts line 20 and drive circuit 22, also possesses voltage detecting circuit 50 with power circuit 10 as shown in Figure 5.In the following description, at quoting the explanation among the 1st embodiment with the common part of the 1st embodiment and omitting its explanation, be primarily aimed at the part different and describe with the 1st embodiment.
Voltage detecting circuit 50 is to be connected in parallel with rectification circuit 16 between rectification circuit 16 and drive circuit 22, magnitude of voltage from the direct voltage Vdc of this rectification circuit 16 outputs is detected and is input to the circuit of oscillator 40, in the present embodiment, comprise two resistance 52a, 52b, detected direct voltage Vdc is input to detection voltage input line road 54 and 1 smoothing capacitor 56 of oscillator 40.
To be one end and rectification circuit 16 be connected with direct voltage supply lines 18 between the drive circuit 22 resistance 52a, the resistive element that the end of the other end and resistance 52b is connected, the resistance 52b resistive element that to be its other end and rectification circuit 16 be connected with zero volts line 20 between the drive circuit 22.
Detecting voltage input line road 54 is that the one end is connected between resistance 52a and the resistance 52b, oscillator 40 wire connecting of the other end and pwm circuit 36.
Smoothing capacitor 56 is that the one end is connected the capacitor that the other end is connected with zero volts line 20 sides of resistance 52b with detection voltage input line road 54.
The oscillator 40 of present embodiment uses voltage controlled oscillators (VCO), and this oscillator 40 comprises as shown in Figure 6: at detection voltage input end 58 of the other end on the detection voltage input line road 54 that has connected voltage detecting circuit 50; And between the asserts signal lead-out terminal 60 of trigger 38 output asserts signal, 3 inverters that are connected in series mutually (near a side who detects voltage input end 58) 62a, 62b, 62c; One end is connected the 1st resistance 64 that the other end is connected with inverter 62a with detection voltage input end 58; One end is connected between the 1st resistance 64 and the inverter 62a, and the other end is connected the 2nd resistance 66 between inverter 62c and the asserts signal lead-out terminal 60; Be installed in the 3rd resistance 68 between inverter 62a and the inverter 62b; One end is connected between the 3rd resistance 68 and the inverter 62b, and the other end is connected the 4th resistance 70 between inverter 62c and the asserts signal lead-out terminal 60; And one end be connected and detect between voltage input end 58 and the inverter 62a, the other end is connected the capacitor 72 between inverter 62a and the 3rd resistance 68.
In addition, oscillator 40 shown in Figure 6 is examples of voltage controlled oscillator (VCO), if carry out the circuit of identical action, also can use the circuit different with described circuit.
If connect commercial ac power source 12 and LED14 with power circuit 10, then from the direct voltage Vdc of rectification circuit 16 output ripple electric currents to the LED of the 2nd embodiment.By resistance 52a and resistance 52b the direct voltage Vdc that is exported is carried out dividing potential drop, on detection voltage input line road 54, detect and detect voltage Vd.Detected like this detection voltage Vd is owing to the power supply voltage variation from the alternating voltage Vi of commercial ac power source 12 changes, but detect mean value in this change of voltage Vd (below, detect voltage Vd and be meant its mean value) to oscillator 40 input by smoothing capacitor 56.Then, imported the oscillator 40 that detects voltage Vd according to the big or small corresponding frequency of oscillation f of this detections voltage Vd, export connection signal to the connection signal input terminal 26c of switch element 26.
Herein, according to the frequency of oscillation f in the oscillator 40 that present embodiment is provided with following formula.
F=[R4/ (4 * C * R2 * R3)] * [1-(2 * R2/R1)
2* (Vd/Vcc-1/2)
2] (formula 12)
R1: the resistance value of the 1st resistance 64, R2: the resistance value of the 2nd resistance 66
R3: the resistance value of the 3rd resistance 68, R4: the resistance value of the 4th resistance 70
C: the capacitance of capacitor 72
Vcc: the supply voltage that supplies to the direct current of inverter 62a, 62b, 62c
According to described (formula 12), frequency of oscillation f is that 1/2 o'clock of Vcc becomes maximum detecting voltage Vd, no matter greater than or less than 1/2 of Vcc, frequency of oscillation f reduces.Therefore, at the maximum Vdc1 of direct voltage Vdc is under the situation of minimum value of change, if set Vd for Vd (min)＞(1/2) * Vcc, then follow the maximum Vdc1 of direct voltage Vdc to increase, and oscillator 40 so that the mode of its frequency of oscillation f step-down move.On the contrary, be under the peaked situation of change at the maximum Vdc1 of direct voltage Vdc, become Vd (max)＜Vcc.That is, the scope of Vd is configured to Vcc＞Vd＞(1/2) * Vcc.
If direct voltage Vdc changes owing to the alternating voltage Vi from commercial ac power source 12 changes (power supply voltage variation), the mean value of the output current Io that then flows through among the LED14 also changes accordingly with it.The output current Io that represents this moment by following (formula 5).
Io (max) 1=Vs/Rs=Vref/ (Rs * (1-ε
-(t1/ τ))) (formula 5)
Herein, because Rs, Vref and τ are constant, thus if the t1 change owing to the change of direct voltage Vdc1, then output current Io (max) 1 would also change accordingly with it.For example, if be made as Vref=250mV, Rs=1.8 Ω, timeconstant=Ri * Ci=3.9 μ second, T=20 μ second and Vo=7V,
Then be t1=T * (Vo/Vdc1), so by Vdc1=140V ± 10%, and t1=1 μ second ± 10%.
Therefore, by described (formula 5), become Io (max) 1=611mA+10%/-7.5%, the change of such output current Io (max) 1 becomes the reason that hinders the LED14 stabilized illumination.
Therefore, use in the power circuit 10 at the LED of the 2nd embodiment, detect the direct voltage Vdc1 that changes corresponding to commercial ac voltage Vi by voltage detecting circuit 50, oscillator 40 makes frequency of oscillation f reduce when the magnitude of voltage of detected direct voltage Vdc has increased, on the contrary, frequency of oscillation f is increased.
Promptly, as described shown in (formula 3), be t1=T * (Vo/Vdc1), so change under+10% the situation at for example Vdc1, make from the period T of oscillator output asserts signal and change+10%, in other words the inverse that makes period T is that frequency of oscillation f changes-10%, thereby can make the value of t1 become constant in the front and back of this variation.In addition, changed under-10% the situation, change+10% owing to same reason makes frequency of oscillation, thereby it has been constant t1 to be become at Vdc1.
Like this, be adjusted into constant by value with t1, the change that can not be subjected to direct voltage Vdc1 (promptly, the vibration that causes from the power supply voltage variation of the alternating voltage Vi of commercial AC power 12 outputs) influence, and can make the mean value of the output current Io that flows through among the LED14 constant, can make LED14 stably luminous.
Claims (3)
1. LED power circuit is characterized in that possessing:
Rectification circuit carries out rectification to the alternating voltage from commercial AC power output, forms the direct voltage of pulsating current;
The zero volts line of extending from the secondary side of described rectification circuit, with and the direct voltage supply lines that is connected with the anode-side of LED of front end; With
Drive circuit receives from the described direct voltage of described rectification circuit output, described LED powered,
Described drive circuit possesses:
Switch element is powered to LED;
Current sense resistor detects the electric current that flows through LED, and it is exported as current detection voltage;
Integrating circuit receives from the current detection voltage of described current sense resistor output the output integral voltage; With
Pwm circuit, after described switch element has been exported connection signal, reception compares described integral voltage and reference voltage from described integrating circuit output from the output of described integrating circuit, when described integral voltage has reached described reference voltage, stop described connection signal, thereby described switch element is connected/turn-offed.
2. LED power circuit is characterized in that having:
Rectification circuit carries out rectification to the alternating voltage from commercial AC power output, forms the direct voltage of pulsating current;
The zero volts line of extending from the secondary side of described rectification circuit, with and the direct voltage supply lines that is connected with the anode-side of LED of front end; With
Drive circuit receives from the described direct voltage of described rectification circuit output via described direct voltage supply lines, described LED powered,
Described drive circuit possesses:
Switch element has the 1st terminal, the 2nd terminal and connection signal input terminal, during described connection signal input terminal input connection signal, and described the 1st terminal and described the 2nd terminal mutual conduction;
High speed diode, cathode side is connected with described direct voltage supply lines, and anode-side is connected with described the 1st terminal of described switch element;
Reactor element, an end are connected between the anode-side and described switch element of described high speed diode, and the other end is connected with the cathode side of described LED;
Current sense resistor, an end is connected with described the 2nd terminal of described switch element, and the other end is connected with described zero volts line;
Integrating circuit receives the current detection voltage that produces in the described current sense resistor, the output integral voltage; With
Pwm circuit receives the output from described integrating circuit, imports described connection signal to the described connection signal input terminal of described switch element with predetermined timing,
Described pwm circuit has:
Oscillator, cycle output asserts signal according to the rules;
Comparison circuit compares described integral voltage and reference voltage from described integrating circuit output, when described integral voltage has reached described reference voltage, and the output reset signal; With
Trigger, have set terminal, reseting terminal and lead-out terminal, if imported described asserts signal from described oscillator to described set terminal, then begin to export described connection signal to the described connection signal input terminal of described switch element from described lead-out terminal, if imported described reset signal to described reseting terminal, then stopped exporting described connection signal from described lead-out terminal from described comparison circuit.
3. LED power circuit according to claim 2, it is characterized in that, also possess between described rectification circuit and described drive circuit and be connected in parallel with described rectification circuit, magnitude of voltage from the direct voltage of described rectification circuit output is detected, be input to the voltage detecting circuit of described oscillator
The described oscillator of described pwm circuit makes frequency of oscillation reduce when the magnitude of voltage of the direct voltage of importing from described voltage detecting circuit increases owing to power supply voltage variation, and frequency of oscillation is increased.
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|---|---|---|---|
| JP2009263294A JP2011108529A (en) | 2009-11-18 | 2009-11-18 | Power supply circuit for led |
| JP2009-263294 | 2009-11-18 |
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|---|---|
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| TWI657327B (en) * | 2014-03-10 | 2019-04-21 | 韓商美格納半導體有限公司 | Switch control circuit, switch control method and converter using the same |
| CN104917357A (en) * | 2014-03-10 | 2015-09-16 | 美格纳半导体有限公司 | Switch control circuit, switch control method and converter using the same |
| CN111342640A (en) * | 2014-03-10 | 2020-06-26 | 美格纳半导体有限公司 | Switch control circuit, switch control method and converter using the same |
| CN111342640B9 (en) * | 2014-03-10 | 2023-10-17 | 美格纳半导体有限公司 | Switch control circuit, switch control method and converter using the same |
| CN104917357B (en) * | 2014-03-10 | 2020-09-01 | 美格纳半导体有限公司 | Switch control circuit, switch control method and converter using the same |
| CN111342640B (en) * | 2014-03-10 | 2023-06-20 | 美格纳半导体有限公司 | Switch control circuit, switch control method and converter using the same |
| US11626797B2 (en) | 2014-04-23 | 2023-04-11 | Guangzhou On-Bright Electronics Co., Ltd. | Systems and methods for output current regulation in power conversion systems |
| US10757778B2 (en) | 2014-04-23 | 2020-08-25 | Guangzhou On-Bright Electronics Co., Ltd. | Systems and methods for output current regulation in power conversion systems |
| US9986605B2 (en) | 2014-04-23 | 2018-05-29 | Guangzhou On-Bright Electronics Co., Ltd. | Systems and methods for output current regulation in power conversion systems |
| US11996773B2 (en) | 2014-04-23 | 2024-05-28 | Guangzhou On-Bright Electronics Co., Ltd. | Systems and methods for output current regulation in power conversion systems |
| CN105281557A (en) * | 2014-07-21 | 2016-01-27 | 三星电机株式会社 | Signal generator and PFC converter using the same |
| CN104703343A (en) * | 2015-02-05 | 2015-06-10 | 成都赛昂电子科技有限公司 | Intelligent PWM (pulse width modulation) drive circuit |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2011108529A (en) | 2011-06-02 |
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Application publication date: 20110518 |