TW201438384A - Constant current power source apparatus - Google Patents

Abstract

A constant current power source apparatus comprises: a pulse DC power source, an electric switching element, a flyback transformer and a controller, wherein the pulse DC power source is used for receiving an AC power to perform full-wave rectification to output a pulse DC, and the pulse DC source has a positive and negative poles. The electric switching element is electrically connected to the negative pole of the pulse DC power source to conduct or block the outputted pulse DC. The flyback transformer has an excitation coil and an output coil. A one end of the excitation coil is connected to the pulse DC power source while another end is connected to the electric switching element. The controller generates a pulse width modulation signal to the electric switching element to control the time sequence of conducting and blocking the electric switching element to allow the output coil generating DC constant current.

Description

Constant current power supply unit

The invention relates to electrical energy conversion, in particular to a constant current power supply device for driving a light emitting diode (light emitting diode), and the same high power factor can be achieved without setting a power factor improving circuit, and It is also not necessary to provide a feedback circuit from the secondary side to the primary side, and the purpose of stabilizing the current on the secondary side can also be achieved.

In the current situation of paying attention to environmental protection and energy conversion rate, the luminous diode has better electro-optical conversion efficiency than incandescent bulbs and fluorescent lamps. Therefore, in the application of lighting systems, the LED lamp set has gradually replaced the trend of incandescent lamps and fluorescent lamps.

Referring to FIG. 1, which is a conventional analog switching power supply device for a light-emitting diode 300, the power factor correction (PFC) circuit 60 of FIG. 1 is a generally known step-up DC-DC converter. The main function is to convert the DC pulse voltage vi obtained by the commercial AC power supply 400 voltage through the filter 62 and then full-wave rectified by the bridge diode circuit 64 to the DC voltage Vio. In addition, the anode of the DC voltage Vio is connected to the point a of the primary side coil 72 of the transformer 70, the cathode is connected to the source of the field effect transistor 68 through the resistor 66, and the drain of the field effect transistor 68 is connected once. Point b of the side coil 72.

The controller 80 outputs a (a) pulse width modulation (PWM) signal as shown in FIG. 2 to the gate of the field effect transistor 68, thereby controlling the field effect transistor 68 to be turned on (ON) and blocked (OFF). And the voltage of the primary side coil 72 of the transformer 70 is made into the vab waveform shown in (b) of FIG. 2 by the conduction and blocking of the field effect transistor 68, and the secondary measuring coil 74 is generated in the second measuring coil 74. (c) The reverse phase voltage vcd shown. The drain voltage and the source-to-source voltage vd of the field effect transistor 68 are as shown in (d) of FIG. 2, and the drain current and the current ip flowing through the primary side coil 72 of the transformer 70 are as shown in FIG. 2 ( e) shown.

Therefore, when the field effect transistor 68 is turned "ON", it is known from (c) of FIG. 2, The negative point (c) of Vcd is a negative electrode with respect to the point (d). At this time, the light-emitting diode 300 is reverse biased, so that no current flows. When the field effect transistor 68 is turned off (OFF), the positive and negative electrodes of the vcd of (c) in FIG. 2 are reversed, and at this time, the light emitting diode 300 is forward biased, so that as shown in FIG. 2 ( f) The id shown charges the capacitor 76. At the same time, the output current Io flows through the LEDs 300 for discharging, but if the capacity of the capacitor 76 of FIG. 1 is increased, it will not be discharged immediately. Thus, the output voltage Vo is as shown in FIG. (g) is approximately DC and is a fixed value.

In order to make the current Io flowing through the light-emitting diode 300 constant, it is convenient to design a resistor 78 on the current path, and the voltage generated by the resistor 78 is input to the differential amplifier 84 to be compared with the reference value, and the difference is amplified. Then, it is transmitted to the controller 80 through the optical coupler 82. The controller 80 converts the difference received by the optocoupler 82 into a PWM signal to control the field effect transistor 58 to be turned on or off. The Id can be changed as shown in the average value of (f) in Fig. 2, whereby the purpose of stabilization can be achieved.

Further, the voltages Vo applied to the load LEDs 300 can be detected through the resistors 86 and 88, input to the error amplifier 84 for comparison with the reference value, and the difference portion is amplified and transmitted through the optical coupler 82. To controller 80. Then, the controller 80 also converts the difference into a PWM signal to control the field effect transistor 68 to be turned on or off so that Vo (g) in FIG. 2 becomes a predetermined value.

However, if the current Io flowing through the light-emitting diode 300 is controlled in the manner described above, when the current Io and the voltage Vo are measured on the secondary side, the differential amplifier 84 is compared with the target value, and then transmitted through the optical coupler 82. The difference portion is fed back to the controller 80 on the primary side, and then converted to PWM and then input to the gate of the field effect transistor 68. Not only is circuit design and control steps cumbersome, but such conventional power supply designs must be designed with a costly and complex PFC circuit 60 to efficiently convert AC power to the desired DC voltage in order to achieve high power factor.

In view of the above, the first invention of the present invention is directed to the illuminance of the light-emitting diode when the DC Io flowing without change is generated as shown in (a) of FIG. However, in general, if the current of the waveform change of (b), (c), and (d) in Fig. 3 is provided, the average value is also equal to the direct current Io of Fig. 3(a), and the frequency is 500 Hz. Above, it can also be considered to have the same illuminance, and at this time, The secondary side of the transformer eliminates the need for an electrolytic capacitor, which in turn has the advantage of a long service life.

The second object of the present invention aims to reduce the cost by directly observing the voltage and current on the secondary side and then omitting the design of the optical coupler by directly obtaining the appropriate parameters on the primary side measurement.

A third object of the present invention is to provide a power factor correction effect by PWM control, and to achieve cost reduction and miniaturization by omitting a PFC circuit.

The present invention provides a constant current power supply device for outputting a constant current to at least one light emitting diode, and includes a pulsed DC power supply, an electronic switching component, a flyback transformer, and a diode. Body and a controller. Wherein, the pulsed DC power source is configured to receive a pulsed direct current after receiving an alternating current, and the pulsed direct current power source has a positive pole and a negative pole; the electronic switching component is electrically connected to the negative pole of the pulsed DC power source, Turning ON or blocking (OFF) the pulsed direct current output of the pulsed DC power supply; the flyback transformer has an excitation coil on the primary side and an output coil on the secondary side; one end of the excitation coil is connected to the pulse a DC power supply, and the other end is connected to the electronic switching component; one end of the output coil is connected to one end of the at least one light emitting diode; one end of the diode is connected to the other end of the output coil to prevent reverse current Reflowing to the output coil; the other end is connected to the other end of the at least one LED; the controller and the electronic switching component are configured to generate a predetermined pulse width modulation (PWM) signal to the electronic switching component, And controlling, by the pulse width modulation signal, a timing of turning on and blocking the electronic switching component, so that the output coil generates the DC constant current At least one light emitting diode.

According to the above concept, the method for outputting a constant current of a constant current power supply device includes the following steps: A. detecting the pulsed direct current and the voltage and current on the excitation coil; B. according to the detection result of step A, Outputting a corresponding pulse width modulation (PWM) signal; and C. according to the pulse width modulation signal of the step B, turning on or blocking the pulse DC of the pulsed DC power supply to the excitation coil, so that the output coil generates DC Constant current.

Thereby, the manner of controlling the timing of the on and off of the electronic switching element is controlled by the pulse width modulation signal to adjust the pulse of the pulse DC received by the returning transformer. The shape has the effect of power factor correction, and after omitting the PFC circuit, the cost reduction and miniaturization can be achieved.

10‧‧‧ pulsed DC power supply

12‧‧‧ filter

14‧‧‧Bridge rectifier circuit

15~19‧‧‧resistance

20‧‧‧Electronic switching components

S‧‧‧ source

D‧‧‧汲

G‧‧‧ gate

30‧‧‧Return-type transformer

32‧‧‧Exciting coil

L1‧‧‧Inductors

34‧‧‧Output coil

L2‧‧‧Inductors

40‧‧‧ diode

50‧‧‧ Controller

100‧‧‧Lighting diode

200‧‧‧AC power supply

Vi‧‧‧pulse DC

Ip‧‧‧Magnetic current

Vp‧‧‧excitation voltage

Vd‧‧‧汲polar voltage

Vs‧‧‧Second voltage measurement

Is‧‧‧secondary current

Vo‧‧‧ output voltage

Io‧‧‧Average current

60‧‧‧Power factor correction circuit

62‧‧‧ Filter

64‧‧‧Bridge diode circuit

66‧‧‧resistance

68‧‧‧ Field Effect Crystal

70‧‧‧Transformers

72‧‧‧One-side coil

74‧‧‧Second measuring coil

76‧‧‧ capacitor

78‧‧‧resistance

80‧‧‧ controller

82‧‧‧Optocoupler

84‧‧‧Differential Amplifier

86, 88‧‧‧ resistance

Figure 1 is a circuit diagram of a conventional constant current power supply unit.

FIG. 2 is a waveform diagram of the circuit diagram of FIG. 1 when it is activated.

Figure 3 shows a plot of output current versus various average currents.

4 is a circuit diagram of a constant current power supply device in accordance with a preferred embodiment of the present invention.

Figure 5 is a circuit diagram of a flyback transformer of the present invention.

Figure 6 shows a waveform diagram for digitizing an alternating current.

Fig. 7 is a waveform diagram of the circuit diagram of Fig. 4 when it is actuated.

In order that the present invention may be more clearly described, the preferred embodiments are illustrated in the accompanying drawings.

Referring to FIG. 4, the constant current power supply device of the preferred embodiment of the present invention is configured to output a constant current to a plurality of LEDs 100, and includes a pulsed DC power supply 10, an electronic switching component 20, and a flyback type. Transformer 30, a diode 40 and a controller 50. The pulsed DC power supply 10 includes a filter 12 and a bridge rectifier circuit 14 that are electrically connected. The filter 12 is electrically connected to a commercial AC power supply 200, and is filtered and transmitted to the bridge rectifier circuit 14 for full-wave rectification to output a pulsed DC vi, and the pulse DC power supply 10 is pulsed according to the polarity of the vi. It has a positive electrode and a negative electrode.

The electronic switching element 20 is a field effect transistor (FET) in this embodiment, and its source S is connected to the negative electrode of the pulsed DC vi through a resistor 15 for turning ON or blocking (OFF) the source. Pulse DC power supply 10 output pulse DC vi.

The primary side of the flyback transformer 30 has an exciting coil 32, and the secondary side There is an output coil 34. One end of the exciting coil 32 is connected to the positive pole of the pulsed DC power source 10, and the other end is connected to the drain D of the electronic switching element 20. One end of the output coil 34 is connected to the negative ends of the light emitting diodes 100. The flyback transformer 30 is wound in the manner shown in FIG. 5, the excitation coil 32 on the primary side is the inductor L1, and the output coil 34 on the secondary side is the inductor L2, and one or two times The number ratio is n1:n2, and the point a to point b and the point c to point d of the flyback transformer 30 are opposite phases.

The positive terminal of the diode 40 is connected to the other end of the output coil 34, and the negative terminal is connected to the positive terminal of the LEDs 100 to prevent reverse current from flowing back to the output coil 34.

In this embodiment, the controller 50 is connected to a gate G of the electronic switching component 20 for outputting a pulse width modulation signal having a certain frequency (period). The electronic switching element 20 is controlled to control the electronic switching element 20 to be turned ON and OFF repeatedly.

Referring to FIG. 6, the period of the pulsed DC vi after full-wave rectification of the commercial AC power supply 200 is preset to Tac, and the period of the pulse width modulation signal output is preset to be t. At this time, in each period Tac, the pulse width modulation signal controls the period in which the electronic switching element 20 is turned ON (OFF) and OFF (OFF) to repeat Tac/t times, and is applied to the excitation of the flyback transformer 30. The voltage at point a of coil 32 is from 0 to the maximum value vip. In addition, the hatched portion in FIG. 6 indicates that the nth pulse width modulation signal is applied to the gate G from the start point of the period Tac, and at this time, the pulse DC of the point a of the flyback transformer 30 is applied. The instantaneous value is vin.

Referring to FIG. 7, the waveform diagrams of (a), (b), (c), (d), (e), and (f) indicate that when the nth pulse width modulation signal is used, the waveforms are different. The waveform at the location is displayed and enlarged. Fig. 7(a) shows the waveform of the pulsed direct current vi when the nth pulse width modulation signal of Fig. 6 is shown. From the start point 0 to nt of the period Tac, the nth pulse width modulation signal controls the electronic switching element 20 to be turned ON, and the instantaneous value of the pulse DC vi is vin. The next (n+1th) pulse width modulation signal controls the electronic switching element 20 to be turned "ON" to "OFF", and the period t of each pulse width modulation signal is relative to the pulse. The period of the direct current vi, Tac, is very small, and during the period of the nth pulse width modulated signal period t, the pulsed direct current vi can also be considered as a fixed value of vin.

(b) of FIG. 7 shows a timing chart in which the pulse width modulation signal controls the electronic switching element 20 to be turned "ON" and "OFF".

7(c) shows that during the tonn of the nth pulse width modulation signal, the exciting current ip flowing through the exciting coil 32 of the flyback transformer 30 is a triangular wave, and when the nth pulse width is modulated The instantaneous value when the signal will control the electronic switching element 20 from being turned "ON" to "OFF" is ipn. In addition, when the pulse width modulation signal controls the electronic switching element 20 to become OFF, the next (n+1) pulse width modulation signal becomes conductive (ON) when the electronic switching element 20 is controlled. During the toffn before the signal arrives, the instantaneous value ipn of the aforementioned excitation current ip continues to be 0, and the excitation current ip of the triangular wave is the average value Ipn of the period t, which can be expressed by the following formula:

(d) of FIG. 7 shows the waveform of the gate voltage vd between the drain D and the source S of the electronic switching element 20. The drain voltage vd is substantially 0 during the tonn period, but at the instant when the pulse width modulation signal controls the electronic switching element 20 to turn from "ON" to "OFF", the magnitude becomes vdn and continues during tofn. As long as the above period is over, the magnitude of the drain voltage vd becomes the magnitude of vin, and continues to appear as the size of vin before the next (n+1)th pulse width modulation signal arrives.

During the tonn period of the flyback transformer 30, the output coil 34 outputs a secondary measured voltage vs as shown in FIG. 7(f). At this time, since the c point of the output coil 34 is a negative voltage for the d point, the diode 40 and the light emitting diodes 100 are reverse biased at this time, and as shown in FIG. 6 ( e) No secondary current is flowing as shown. Further, at the instant when the pulse width modulation signal controls the onn period during which the electronic switching element 20 is turned "ON", the electronic switching element 20 is turned "ON" to "OFF", and therefore, at this time, in FIG. 7 ( The instantaneous value of the excitation current ip of c) is changed from ipn to zero. At this time, the positive and negative polarities of the voltage generated by the exciting coil 32 of the flyback transformer 30 are reversed. At the same time, the voltage generated by the output coil 34 of the flyback transformer 30 is also reversed in positive and negative polarity, so that the point c of the output coil 34 of the flyback transformer 30 is a positive voltage for the point d, so that the diode 40 and the light-emitting diodes 100 are forward biased, and as shown in (e) of FIG. 7, the secondary side current is started to flow, and the diodes 40 and the light are emitted by the current. Dipole The voltage drop produced by 100 is essentially a constant voltage. In addition, the voltage drop generated by the diode 40 is compared with the voltage drop Vo generated by the diodes. Since it is extremely negligible, the output coil 34 is shown in (f) of FIG. The secondary side voltage vs of the point can be regarded as the output voltage Vo.

In addition, the electromagnetic energy stored in the output coil 34 of the flyback transformer 30 is released to the secondary side by the secondary current is, and the period before the end of the release is preset to the tofn period, and after the power is released, the output voltage is output. Vo is reduced to zero. The excitation coil 32 of the flyback transformer 30 generates a voltage of n1/n2×Vo through the output voltage Vo during the tofn period. Therefore, the vdn of (d) in FIG. 7 can be expressed by the following formula (2):

On the other hand, the instantaneous value isn of the secondary current shown in (e) of FIG. 7 is the average value Isn in the period t, as shown in the following equation (3):

The instantaneous value ipn of the exciting current shown in (c) of FIG. 7 is the average value Ipn in the period t, and can be calculated according to the formula (1) and using the following formula (4). Expression:

If vin=vp.sin(nt) is substituted into the above formula (5) (ip is the excitation voltage of the flyback type pressure accumulator 30 on the primary side), the following formula (6) can be obtained:

It can be seen from the above formula (6) that the average value Ipn of the exciting current is in phase with the sine wave input of the pulse voltage vi, so that the power factor (PF) is 1, which, in other words, can be made through the above design. The inventive circuit has the function of power factor correction.

Then, the average current Io flowing through the light-emitting diodes 100 is summed up in the half-period Tac region by the secondary current average value Isn of (e) in FIG. 6, and the average value thereof can be as follows. Equation (7) is calculated. The formula (8) is developed from the third term in the equation (7), and the equation (9) is developed from the fourth term in the equation (7). In the formula (10), the formula (9) is approximated by using the integral of the continuous function:

Moreover, the above formula can be deformed as shown in the following formula (11):

In this way, in the circuit of FIG. 4 of the present invention, in order to control the electronic switching element 20, the frequency (period t) of the pulse width modulation signal outputted by the controller 50 becomes a constant value, and thus the above (10) It can be seen that if the change in the timing ratio (i.e., tonn/t) can be controlled, the output current Io flowing through the light-emitting diodes 100 can be controlled.

In order to measure the current output current Io, it can be known from the equation (4) that the instantaneous value of the input pulse DC vi must be read in each period t of the pulse width modulation signal signal output of the controller 50. Or, the instantaneous value ipn of the current flowing by the exciting coil 32 of the flyback transformer 30, and the maximum value vip of the pulse DC in its period Tac. The controller 50 detects the voltage value after the voltage division on the resistors 16, 17 to calculate the instantaneous value vin of the pulse DC, and the aforementioned voltage value is an analog signal, and the controller 50 is utilized. The internal AC/DC converter (not shown) is converted into a digital signal for subsequent processing.

In addition, the controller 50 detects the voltage on the resistor 15 and calculates the instantaneous value ipn of the excitation current ip of the excitation coil 32 by using the measured voltage and the resistance value of the resistor 15, and the same is utilized. The AC/DC converter inside the controller 50 converts the analog signal into After the digital signal, the operation is performed inside the controller 50.

The voltage Vo on the light-emitting diodes 100 is calculated by the threshold voltage ratio of the drain voltage vd and the flyback transformer 30, that is, the controller 50 is divided into the detecting resistors 18 and 19. After the instantaneous value vdn of the voltage of the buckling voltage vd, the analog signal is converted into a digital signal by the AC/DC converter inside the controller 50, and is performed inside the controller 50 by the above formula (2). The voltage Vo on the light-emitting diodes 100 can be derived.

In addition, since the controller 50 detects the instantaneous value vin of the pulse DC, the period Tac of the pulse DC vi can be known. Therefore, as shown in FIG. 5, the time interval between two points z1 and z2 at which vin becomes 0 can be calculated inside the controller. In the above manner, in each operation cycle Tac, the instantaneous value vin of the pulse DC vi in each period t of all the pulse width modulation signals, the instantaneous value ipn of the excitation current ip, and the drain voltage vd can be measured. The instantaneous value vdn, the period Tac of the pulse DC vi, and the excitation voltage vp on the primary side. The pulse width modulation signal outputted by the controller 50 controls the electronic switching element 20 to be in a period of tonn, and the period t is constant in the Tac period, and the output voltage is determined by the LEDs 100. Vo, therefore, can also make the output voltage Vo a constant value.

Therefore, the controller simultaneously calculates the current Io output to the light-emitting diodes 100 by the equation (8) at the end of the last pulse width modulation signal in each period Tac. Further, the output current Io can also be calculated by the instantaneous value ipn of the exciting current ip by the equation (11), and the calculated output current Io is compared with the preset current value stored in the controller 50, and then The calculated difference between the output current Io and the preset current value is negatively fed back to the timing ratio of the pulse width modulation signal of the next period Tac, so that the output current Io can be maintained at a predetermined current value to represent the current output.

The equivalent structural changes of the present specification and the scope of the patent application are intended to be included in the scope of the present invention.

10‧‧‧ pulsed DC power supply

12‧‧‧ filter

14‧‧‧Bridge rectifier circuit

15~19‧‧‧resistance

20‧‧‧Electronic switching components

S‧‧‧ source

D‧‧‧汲

G‧‧‧ gate

30‧‧‧Return-type transformer

32‧‧‧Exciting coil

L1‧‧‧Inductors

34‧‧‧Output coil

L2‧‧‧Inductors

40‧‧‧ diode

50‧‧‧ Controller

100‧‧‧Lighting diode

200‧‧‧AC power supply

Vi‧‧‧pulse DC

Ip‧‧‧Magnetic current

Vp‧‧‧excitation voltage

Vd‧‧‧汲polar voltage

Vs‧‧‧Second voltage measurement

Is‧‧‧secondary current

Vo‧‧‧ output voltage

Io‧‧‧Average current

Claims (9)

A constant current power supply device for outputting a constant current to at least one light emitting diode; the constant current power supply device comprises: a pulsed DC power supply for receiving an alternating current, performing full wave rectification to output a pulsed direct current And the pulsed DC power source has a positive pole and a negative pole; an electronic switching component electrically connected to the negative pole of the pulsed DC power source for conducting (ON) or blocking (OFF) the pulsed direct current output of the pulsed DC power source; The flyback transformer has an excitation coil on one side and an output coil on the secondary side; one end of the excitation coil is connected to the pulsed DC power supply, and the other end is connected to the electronic switching element; the output coil is electrically Connecting the at least one light emitting diode; and a controller, and the electronic switching component, for generating a predetermined pulse width modulation (PWM) signal to the electronic switching component, and controlling the pulse width modulation signal The timing of the electronic switching element being turned on and off, so that the output coil generates the DC constant current to the at least one light emitting diode. The constant current power supply device of claim 1, further comprising a diode, one end of which is connected to the output coil, and the other end is connected to the at least one light emitting diode for preventing reverse current from flowing back to the output Coil. The constant current power supply device of claim 1, wherein the controller is further electrically connected to the pulsed DC power source and the excitation coil of the flyback transformer through at least one resistor. The constant current power supply device of claim 3, wherein the controller generates the corresponding pulse width modulation signal control by detecting a pulsed direct current generated by the pulsed direct current power source and a voltage and current on the excitation coil. The timing of the electronic switching element being turned on and off. A method for outputting a constant current of a current source device according to claim 1, comprising the steps of: A. detecting the pulsed direct current, and voltage and current on the excitation coil; B. according to the detection result of step A, Outputting a corresponding pulse width modulation (PWM) signal; and C. according to the pulse width modulation signal of the step B, turning on or blocking the pulse DC of the pulsed DC power supply to the excitation coil, so that the output coil generates DC Constant current. A method for outputting a constant current of a constant current power supply device as claimed in claim 5, wherein Step A is performed in one cycle of the pulsed DC, and steps B and C are performed in the next cycle time. The method for outputting a constant current of a constant current power supply device according to claim 6, the current value of the current of the output coil is calculated in step A, and in step B, the calculated current value and the preset value are used. The difference between the current values of the DC constant currents adjusts the pulse width modulation signal, so that in step C, the current value of the current generated by the output coil is equal to or close to the current value of the preset DC constant current. The method for outputting a constant current of a constant current power supply device according to claim 5, in step B, calculating and outputting a corresponding pulse width modulation signal in a digital proportional-integral-derivative (PID) manner. The method for outputting a constant current of a constant current power supply device according to claim 5, in step A, detecting the instantaneous voltage, the maximum voltage, and the cycle time of the pulsed direct current.