TW201807943A - High step-down ratio isolated DC-DC converter - Google Patents

Abstract

The present invention relates to a high step-down ratio isolated DC-DC converter, including an input unit, a pre-stage circuit, and a post-stage circuit. The pre-stage circuit is coupled to the input unit and is provided mainly for lowering voltage and reducing input-current ripple. The post-stage circuit is coupled to the pre-stage circuit and is provided mainly for electrical isolation, lowering voltage, and reducing output-current ripple. Thereby, the present invention can achieve high step-down ratio and can be easily controlled by a single switch.

Description

Isolated high step-down ratio DC-DC converter

The invention relates to an isolated high step-down ratio DC-DC converter, which refers to a DC-DC device with electrical isolation function, which can provide high step-down ratio, low input and output current ripple, and requires only one switch. converter.

Today's technological developments, such as integrated circuits and other semiconductor technologies, are developing rapidly. General electronic products are aimed at attracting the general public with the goal of being thin, light, and short. The source of power for general electronic products is a power supply to meet the power requirements of different electronic products , Related power conversion devices have been designed and improved one after another.

For example, the new patent publication No. I462456 (DC / DC conversion circuit) of the Republic of China is a DC / DC conversion circuit, which is coupled between a DC power source and a load, and includes a first charge extraction circuit coupled to The DC power supply; a second charge extraction circuit coupled to the load; a first switch coupled to the first charge extraction circuit; a second switch coupled to the second charge extraction circuit; And a first inductor, one end of the first inductor is coupled to the first charge extraction circuit and the second charge extraction circuit, and the other end is coupled to one of the first switch and one of the second switch A node, wherein the first inductor, the first switch, and the second open relationship are coupled between the first charge extraction circuit and the second charge extraction circuit.

However, there are still some disadvantages such as insufficient step-down ratio, and the non-isolated type has more doubts about safety in use.

Therefore, the inventor has continued to innovate and develop, and then proposes an isolated high step-down ratio DC-DC converter, which includes: an input unit for inputting DC power; a first-stage circuit including an input inductor, a first A diode, a second diode, a third diode, a fourth diode, a first capacitor, a second capacitor, and a switch, wherein one end of the input inductor and the first capacitor The cathode terminal of the quadrupole is electrically connected to one positive terminal of the input unit, and the other end of the input inductor is electrically connected to one terminal of the first capacitor and the cathode terminal of the second diode. The other end of the capacitor is electrically connected to the anode end of the third diode and the cathode end of the first diode, and the anode end of the second diode is electrically connected to the cathode end of the third diode. And one terminal of the second capacitor, the anode terminal of the first diode, the other terminal of the second capacitor, and the first terminal of the switch are all connected to a negative terminal of the input unit; and a rear stage circuit , Including a forward DC-DC converter Road, the forward type DC - DC converter circuit is coupled to the first-half stage circuit, and provides electrical isolation and down.

Further, the forward DC-DC conversion circuit includes a transformer and an output circuit. The transformer is a three-winding transformer, which includes a primary winding, a secondary winding, and a tertiary winding. One end of the winding is electrically connected to the cathode end of the second diode, the other end of the primary winding is electrically connected to one of the second ends of the transfer switch, and one end of the tertiary winding is electrically connected to the changeover switch. At the first end, the other end of the tertiary winding is electrically connected to the anode end of the fourth diode. The secondary winding provides electrical isolation and voltage reduction, and is electrically connected to the output circuit.

Further, the output circuit includes a fifth diode, a sixth diode, an output inductor, an output capacitor, and a load. One end of the secondary winding is electrically connected to the fifth diode. At the extreme, the cathode terminal of the fifth diode is electrically connected to the cathode terminal of the sixth diode and one terminal of the output inductor, and the other end of the output inductor is electrically connected to one terminal of the output capacitor and the load. One end, the anode end of the sixth diode, the other end of the output capacitor, and the other end of the load are all electrically connected to the other end of the secondary winding.

Further, its operation has a mode one and a mode two, the mode one is that the switch is turned on, the first capacitor and the second capacitor are connected in parallel to release energy, the mode two is that the switch is turned off, and the first capacitor And the second capacitor is used to store energy in series.

Further, a pulse width modulation technology is used to control the on and off of the switch.

Further, the switching on relationship is an N-type metal oxide semiconductor field effect transistor.

According to the above technical features, the following effects can be achieved:

1. The voltage gain of the isolated high step-down ratio DC-DC converter of the present invention is , Where n = N ₂ / N ₁ is the turns ratio and D is the duty cycle, which can provide a high step-down ratio.

2. Only using a single switch, the control is simple, and the cost can be reduced.

3. With low input current ripple and low output current ripple, good voltage stability.

4. The system is electrically isolated, which is safer to use.

Based on the above technical features, the main effect of the isolated high step-down ratio DC-DC converter of the present invention will be clearly presented in the following embodiments.

Referring to the first figure, it is a circuit diagram of an isolated high step-down ratio DC-DC converter (1) according to an embodiment of the present invention. The isolated high step-down ratio DC-DC converter (1) includes an input unit ( 11) a first half stage circuit (12) and a second half stage circuit (13), wherein:

The input unit (11) is used to input DC power. The first half-stage circuit (12) includes an input inductor (121), a first diode (122), a second diode (123), a third diode (124), and a fourth diode. The pole body (125), a first capacitor (126), a second capacitor (127), and a switch (128). The first capacitor (126) and the second capacitor (127) have substantially the same capacitance, and one terminal of the input inductor (121) and the cathode terminal of the fourth diode (125) are all electrically charged. One end of the input unit (11) is electrically connected, and the other end of the input inductor (121) is electrically connected to one end of the first capacitor (126) and the cathode end of the second diode (123), the The other end of the first capacitor (126) is electrically connected to the anode terminal of the third diode (124) and the cathode terminal of the first diode (122), and the anode of the second diode (123). The extreme end is electrically connected to the cathode terminal of the third diode (124) and one terminal of the second capacitor (127), the anode terminal of the first diode (122), and the other of the second capacitor (127). One end and a first end of the switch (128) are connected to a negative end of the input unit (11). The switch (128) is, for example, an N-type metal oxide semiconductor field effect transistor. The second-stage circuit (13) includes a forward DC-DC conversion circuit. The forward DC-DC conversion circuit includes a transformer and an output circuit. The transformer includes a primary winding (131), A secondary winding (132) and a tertiary winding (133), the output circuit includes a fifth diode (134), a sixth diode (135), an output inductor (136), a An output capacitor (137) and a load (138). One end of the primary winding (131) is electrically connected to the cathode end of the second diode (123), and the other end of the primary winding (131) is electrically connected to one of the switch (128). Second end, one end of the tertiary winding (133) is electrically connected to the first end of the switch (128), and the other end of the tertiary winding (133) is electrically connected to the fourth diode ( 125) anode terminal, the secondary winding (132) provides electrical isolation and voltage reduction, and is electrically connected to the anode terminal of the fifth diode (134) and the fifth diode (134) with one end. The cathode terminal is electrically connected to the cathode terminal of the sixth diode (135) and one terminal of the output inductor (136), and the other terminal of the output inductor (136) is electrically connected to one terminal of the output capacitor (137). And one end of the load (138), the anode end of the sixth diode (135), the other end of the output capacitor (137), and the other end of the load (138) are all electrically connected to the secondary winding (132) the other end.

Referring to the second figure, it is the equivalent circuit diagram of the aforementioned first figure. The transformer is regarded as an ideal transformer and a magnetizing inductor (139). The ideal transformer includes the primary winding (131), the secondary side The winding (132) and the tertiary winding (133), and the magnetizing inductance (139) is connected in parallel with the primary winding (131).

Refer to the third figure, which is an isolated high step-down ratio DC-DC converter (1) of this embodiment [the isolated high step-down ratio DC-DC converter (1) is shown in the second figure] at The main waveform diagram of a single switching cycle is the use of a pulse width modulation technology to control the on and off of the switch (128) [the switch (128) as shown in the second figure], and includes two modes of operation :

Mode 1: Refer to the third and fourth figures, the operation interval is [t ₀ , t ₁ ]. At t = 0, the changeover switch (128) is turned on, and the current path is as shown by the arrow in the fourth figure. In this interval, the input unit (11) transmits energy to the input inductor (121) and the magnetizing inductance (139) of the transformer. The energy stored in the first capacitor (126) and the second capacitor (127) is sent in parallel to the output inductor (136), the output capacitor (137), and the load (138) through the transformer. Therefore, the current i _{L1 of} the input inductor (121) and the current i _Lo of the output inductor (136) increase linearly (i _L1 and i _Lo as shown in the third figure). In addition, in this interval, the energy stored in the magnetizing inductance (139) of the transformer is small, which is called remanence. When t = t ₁ , the switch (128) is switched off, and mode one ends.

Mode 2: Refer to the third and fifth figures, the operation interval is [t ₁ , t ₂ ]. When t = t ₁ , the switch (128) is turned off, and the current path is shown as the arrow in the fifth figure. In this interval, the input unit (11) and the input inductor (121) release energy in series, and transfer the energy to the first capacitor (126) and the second capacitor (127). At this time, the first capacitor (126) ) And the second capacitor (127) are used to store energy in series. In addition, the residual magnetic energy of the transformer is all returned to the input unit (11) via the third winding (133). The output inductor (136) supplies energy to the output capacitor (137) and the load (138). Therefore, the current i _{L1 of} the input inductor (121) and the current i _Lo of the output inductor (136) decrease linearly (i _L1 and i _Lo shown in the three figures). When t = t ₂ , the changeover switch (128) is switched on again, and the second mode ends.

It can be known from the above analysis that the current of the input inductor (121) and the current of the output inductor (136) can provide a function of low ripple current under continuous conduction mode operation. The voltage gain (M) of the isolated high step-down ratio DC-DC converter (1) in this embodiment is expressed as: , , So the voltage gain , Where n = N ₂ / N ₁ is the turns ratio and D is the duty cycle.

With reference to the sixth figure, when the input voltage V _in is 200 V, the output voltage V _o is 25 V, the full-load output power is 200 W, and the transformer turns ratio is 0.5, the switch (128) The analog waveform diagram of the trigger signal V _GS1 , the current i _{L1 of} the input inductor (121), and the current i _Lo of the output inductor (136), the scale value of the waveform diagram is: i _L1 / i _Lo : 5A / div, Time: 20 μs / div. It can be seen that the input inductor (121) and the output inductor (136) both operate in continuous conduction mode, and the duty cycle is about 0.4.

With reference to the seventh figure, the input unit (11) is operated when the input voltage V _in is 200 V, the output voltage V _o is 25 V, the full-load output power is 200 W, and the transformer turns ratio is 0.5. The analog waveform diagram of the input voltage V _in , the voltage V _{C1 of} the first capacitor (126), the voltage of the second capacitor (V _C2 ), and the output voltage V _o across the load, and the scale of the waveform diagram The values are: V _in / V _c1 / V _c2 / V _o : 100V / div, time: 2ms / div. It can be seen that the isolated high step-down ratio DC-DC converter of this embodiment can achieve a high step-down ratio. Features. And the voltage of the first capacitor (V _C1 ) and the voltage of the second capacitor (V _C2 ) are both 125V, which is consistent with the analysis of the first and second modes.

With reference to the eighth figure, the first diode is operated when the input voltage V _in is 200 V, the output voltage V _o is 25 V, the full load output power is 200 W, and the transformer turns ratio is 0.5. The analog waveform of the current i _{D1 of} (122) and the current (i _D2 ) of the second diode (123). The scale value of the waveform is: i _D1 / i _D2 : 2A / div, time: 20 μs / div.

With reference to the ninth figure, the third diode is operated when the input voltage V _in is 200 V, the output voltage V _o is 25 V, the full-load output power is 200 W, and the transformer turns ratio is 0.5. The current i _{D3 of} (124), and the analog waveform of current i _S1 of the switch (128), the scale value of the waveform is: i _D3 / i _S1 : 2A / div, time: 20 μs / div.

As shown in the tenth figure, when the input voltage V _in is 200 V, the output voltage V _o is 25 V, the full-load output power is 200 W, and the transformer turns ratio is 0.5, the fifth diode ( The analog waveform of the current i _D5 of the 134) and the current i _D6 of the sixth diode (135), the scale value of the waveform is: i _D5 / i _D6 : 5A / div, time: 20 μs / div, Consistent with the analysis of the aforementioned operating modes.

As shown in FIG. 11, it is a voltage gain curve diagram of the isolated high step-down ratio DC-DC converter (1) according to the embodiment of the present invention, and it can be seen that it has a high step-down ratio.

Based on the description of the above embodiments, the operation, use and effects of the present invention can be fully understood, but the above-mentioned embodiments are only preferred embodiments of the present invention, and the implementation of the present invention cannot be limited in this way. The scope, that is, the simple equivalent changes and modifications made according to the scope of the patent application and the description of the invention, are all within the scope of the present invention.

(1) ‧‧‧Isolated high step-down ratio DC-DC converter
(11) ‧‧‧Input unit
(12) ‧‧‧First half circuit
(121) ‧‧‧Input inductance
(122) ‧‧‧First Diode
(123) ‧‧‧Second Diode
(124) ‧‧‧Third Diode
(125) ‧‧‧ Fourth Diode
(126) ‧‧‧First capacitor
(127) ‧‧‧Second capacitor
(128) ‧‧‧Switch
(13) ‧‧‧The second half circuit
(131) ‧‧‧Primary winding
(132) ‧‧‧Secondary winding
(133) ‧‧‧Third side winding
(134) ‧‧‧ Fifth Diode
(135) ‧‧‧Sixth Diode
(136) ‧‧‧Output inductor
(137) ‧‧‧Output capacitor
(138) ‧‧‧Load

[First diagram] is a circuit diagram of an isolated high step-down ratio DC-DC converter according to an embodiment of the present invention.

[Second figure] is an equivalent circuit diagram of an isolated high step-down ratio DC-DC converter according to an embodiment of the present invention.

[Third figure] The main waveform diagram of the isolated high step-down ratio DC-DC converter in a single switching cycle according to the embodiment of the present invention.

[Fourth diagram] is a current path diagram of an isolated high step-down ratio DC-DC converter operating in mode 1 according to an embodiment of the present invention.

[Fifth Figure] A current path diagram of an isolated high step-down ratio DC-DC converter operating in mode two according to an embodiment of the present invention.

[Sixth figure] When the input voltage V _in is 200 V, the output voltage V _o is 25 V, the full-load output power is 200 W, and the transformer turns ratio is 0.5, the trigger signal V _{GS1 of} the switch is operated. The analog waveform of the current i _L1 of the input inductor and the current i _Lo of the output inductor has a scale value of: i _L1 / i _Lo : 5A / div, time: 20 μs / div.

[Seventh figure] The isolated high step-down ratio DC-DC converter according to the embodiment of the present invention operates at an input voltage V _in of 200 V, an output voltage V _o of 25 V, a full load output power of 200 W, and a transformer's turns ratio of At 0.5, the analog waveform of the input voltage V _{in of} the input unit, the voltage V _C1 of the first capacitor, the voltage V _{C2 of} the second capacitor, and the output voltage V _o across the load. The scale value is: V _in / V _c1 / V _c2 / V _o : 100V / div, time: 2ms / div.

[Eighth Figure] The isolated high step-down ratio DC-DC converter according to the embodiment of the present invention operates at an input voltage V _in of 200 V, an output voltage V _o of 25 V, a full load output power of 200 W, and a transformer's turns ratio of At 0.5, the analog waveforms of the current i _D1 of the first diode and the current i _D2 of the second diode, the scale value of the waveform is: i _D1 / i _D2 : 2A / div, time: 20 μs / div.

[Ninth FIG]-based embodiment of the present invention isolated in Example high step-down ratio DC - DC converter is operated in the input voltage V _in is 200V, the output voltage V _o is 25V, and the full output power of 200W is the turns ratio of the transformer At 0.5, the analog waveform of the current i _{D3 of} the third diode and the current i _S1 of the switch, the scale value of the waveform is: i _D3 / i _S1 : 2A / div, time: 20 μs / div.

[Tenth figure] The isolated high step-down ratio DC-DC converter according to the embodiment of the present invention operates at an input voltage V _in of 200 V, an output voltage V _o of 25 V, a full load output power of 200 W, and a transformer's turns ratio of At 0.5, the analog waveform of the current i _D5 of the diode and the current i _D6 of the sixth diode, the scale value of the waveform is: i _D5 / i _D6 : 5A / div, time: 20 μs / div .

[Eleventh figure] is a voltage gain curve diagram of an isolated high step-down ratio DC-DC converter according to an embodiment of the present invention.

(1) ‧‧‧Isolated high step-down ratio DC-DC converter

(11) ‧‧‧Input unit

(12) ‧‧‧First half circuit

(121) ‧‧‧Input inductance

(122) ‧‧‧First Diode

(123) ‧‧‧Second Diode

(124) ‧‧‧Third Diode

(125) ‧‧‧ Fourth Diode

(126) ‧‧‧First capacitor

(127) ‧‧‧Second capacitor

(128) ‧‧‧Switch

(13) ‧‧‧The second half circuit

(131) ‧‧‧Primary winding

(132) ‧‧‧Secondary winding

(133) ‧‧‧Third side winding

(134) ‧‧‧ Fifth Diode

(135) ‧‧‧Sixth Diode

(136) ‧‧‧Output inductor

(137) ‧‧‧Output capacitor

(138) ‧‧‧Load

Claims (6)

An isolated high step-down ratio DC-DC converter includes: an input unit for inputting a direct current; a first half stage circuit including an input inductor, a first diode, a second diode, and a A third diode, a fourth diode, a first capacitor, a second capacitor, and a switch, wherein the first capacitor and the second capacitor have substantially the same capacitance and the input inductance One terminal and the cathode terminal of the fourth diode are electrically connected to a positive terminal of the input unit, and the other terminal of the input inductor is electrically connected to one terminal of the first capacitor and the cathode of the second diode. At the extreme, the other end of the first capacitor is electrically connected to the anode terminal of the third diode and the cathode terminal of the first diode, and the anode terminal of the second diode is electrically connected to the third diode. The cathode terminal of the electrode body and one terminal of the second capacitor, the anode terminal of the first diode body, the other terminal of the second capacitor, and the first terminal of the switch are all connected to a negative terminal of the input unit; One rear stage circuit, including a forward DC-DC Conversion circuit, the forward type DC - DC converter circuit is coupled to the first-half stage circuit, and provides electrical isolation and down. The isolated high step-down ratio DC-DC converter according to item 1 of the patent application scope, wherein the forward DC-DC conversion circuit includes a transformer and an output circuit, and the transformer includes a primary winding, A primary winding and a tertiary winding, one end of the primary winding is electrically connected to the cathode end of the second diode, and the other end of the primary winding is electrically connected to one of the switch One end of the tertiary winding is electrically connected to the first end of the switch, the other end of the tertiary winding is electrically connected to the anode end of the fourth diode, and the secondary winding provides electrical Isolate and step down, and electrically connect the output circuit. The isolated high step-down ratio DC-DC converter according to item 2 of the scope of patent application, wherein the output circuit includes a fifth diode, a sixth diode, an output inductor, an output capacitor, and A load, one end of the secondary winding is electrically connected to the anode end of the fifth diode, and the cathode end of the fifth diode is electrically connected to the cathode end of the sixth diode and the output inductor. One end, the other end of the output inductor is electrically connected to one end of the output capacitor and one end of the load, the anode end of the sixth diode, the other end of the output capacitor, and the other end of the load are all electrical. Connect the other end of the secondary winding. The isolated high step-down ratio DC-DC converter as described in item 3 of the scope of patent application, its operation has a mode one and a mode two, the mode one is that the switch is turned on, the first capacitor and the second The capacitor is used to release energy in parallel. In the second mode, the switch is turned off, and the first capacitor and the second capacitor are used to store energy in series. The isolated high step-down ratio DC-DC converter according to item 1 of the scope of patent application, wherein a pulse width modulation technology is used to control the on and off of the switch. The isolated high step-down ratio DC-DC converter according to item 1 of the scope of patent application, wherein the switching on relationship is an N-type metal oxide semiconductor field effect transistor.