CN1972096A - Switching power supply and its zero-voltage switching (ZVS) control method - Google Patents

Abstract

The invention relates to a switching power supply and a control method of Zero Voltage Switching (ZVS) thereof, the switching power supply at least comprises a transformer, a main switch and an auxiliary switch which are coupled with a primary side of the transformer, the control method fixes the turn-on time of the auxiliary switch each time, and generates the effect that the turn-off time of the main switch each time is fixed, thereby achieving the purpose of zero voltage switching the main switch.

Description

Switching power supply and its zero-voltage switching (ZVS) control method

【Technical field】

The present invention refers to a switching power supply and its control method, in particular to a forward or feedback switching power supply and its control method.

【Background technique】

Generally speaking, a power supply (Power Supply) uses an AC/DC converter to receive input commercial AC power, and converts the AC power into DC power with a high voltage level, and then uses a DC/DC converter to have The high-voltage direct current is converted into a low-voltage direct current for operating an electronic device; for example, as a power source for a desktop computer or a notebook computer.

Power supplies can be divided into two types: linear power supplies and switching power supplies. At present, the mainstream system in the power supply market is switching power supplies.

A switching power supply is generally composed of an input stage circuit, a power factor adjustment stage (PFC stage) circuit, a power stage (power stage) circuit, and a feedback stage circuit. The core of the switching power supply Mainly in the power stage circuit.

Please refer to FIG. 1 , which is a schematic diagram of a power stage circuit of a conventional switching power supply, wherein the switching power supply 10 is a forward structure switching power supply.

In FIG. 1, the switching power supply 10 is composed of an auxiliary capacitor Ca, a main switch Q1, an auxiliary switch Q2, a transformer T, a driver transformer (driver transformer) T1, a zero voltage switching (ZVS) detection integrated circuit (IC) 11, The first rectifier switch S1, the second rectifier switch S2, the filter inductor L and the filter capacitor Cb are formed.

The operation of the switch mode power supply 10 in FIG. 1 is as follows: when the main switch Q1 is turned on, the input voltage from the previous stage (power factor adjustment stage circuit) will be supplied to the primary side of the transformer T, and the secondary side of the transformer T After the energy is sensed, the voltage is converted to DC through the first rectifier switch S1 that is turned on, and the ripple component is filtered by the filter inductor L to output a DC voltage; when the main switch Q1 is turned off, the auxiliary switch Q2 is turned on, and the transformer T The polarity of the voltage on the winding will be reversed, so that the first rectifier switch S1 is not turned on, and the second rectifier switch S2 is turned on. At this time, the energy stored in the filter inductor L and filter capacitor Cb is transferred by the second rectifier switch S2 Supply to output Vo.

In the conventional switching power supply 10 shown in FIG. 1, in order to achieve zero-voltage switching of the main switch Q1, the method adopted is to detect the main switch Q1 through the ZVS detection IC11, and then cooperate with the driving transformer T1 to switch the auxiliary switch Q2. , to achieve the aforementioned purpose of turning on and off the main switch Q1 and the auxiliary switch Q2 in turn.

However, in Fig. 1, the input voltage Vin is generally a high voltage of about 400V, and the circuit design of the ZVS detection IC11 is extremely complicated when the purpose of using the ZVS detection IC11 to start and drive the transformer T1 is to be achieved under such a high voltage; Furthermore, since the ZVS detection IC 11 designed to withstand 500V and 600V voltages has a high voltage process, the production cost is extremely high, which is not conducive to the cost control of the manufacturing unit (cost down).

For this reason, the applicant, in view of the deficiencies in the conventional technology, carefully tested and researched, and with a persistent spirit, finally conceived the project "Switching Power Supply and Its Zero-Voltage Switching (ZVS)" Control method”, the following is a brief description of this case.

【Content of invention】

The idea of this case is to propose a switching power supply and its zero-voltage switching control method, which is not only applicable to switching power supplies with forward and flyback structures, but also the control method and manufacturing cost are also lower than the conventional ones mentioned above. Switching power supplies are inexpensive.

According to the idea of this case, a switching power supply and its zero-voltage switching (ZVS) control method are proposed. The switching power supply includes at least a transformer, a main switch and a primary switch coupled to the primary side of the transformer. The auxiliary switch, the control method is to fix the opening time of the auxiliary switch each time, so as to produce the effect that the closing time of the main switch is fixed each time, so as to achieve the purpose of switching the main switch with zero voltage. .

This case can be understood more deeply through the following diagrams and detailed descriptions:

【Description of drawings】

Figure 1: A schematic diagram of a power stage circuit of a conventional switching power supply;

Figure 2(a) and (b): respectively, the schematic diagram of the power stage circuit of the forward switching power supply in this case and the timing diagram of the voltage and current of each functional switch; and

Figure 3(a) and (b): respectively, the schematic diagram of the power stage circuit of the flyback switching power supply in this case and the timing diagram of the voltage and current of each functional switch.

【Detailed ways】

Please refer to Fig. 2 (a) and (b), which are respectively the schematic diagram of the power stage circuit of the forward type switching power supply and the timing diagram of the voltage and current of each functional switch, wherein the switching power supply 20 is A switching power supply with forward structure.

In FIG. 2(a), the switching power supply 20 is an auxiliary circuit composed of an auxiliary capacitor Ca and an auxiliary switch Q2, a main switch Q1, a transformer T, a first rectifier switch S1, a second rectifier switch S2, and a filter inductor. The filter circuit composed of L and the filter capacitor Cb, the auxiliary switch control circuit 21 and the zero voltage switching detector 22 are composed.

In Fig. 2(a), the auxiliary capacitor Ca and the auxiliary switch Q2 are connected in series with each other, and then connected in parallel to the primary side of the transformer T, one end of the main switch Q1 is connected to the primary side of the transformer T and the zero voltage switching detector 22, and the other One end is connected to the ground and the input terminal Vin. The auxiliary switch control circuit 21 is connected to the control end of the auxiliary switch Q2 and the primary side of the transformer T. The auxiliary switch control circuit 21 is composed of a driver 211 and a timer 212. It is worth noting Yes, in the second figure, the primary side coil of the transformer T is used as the embodiment of the driver 211. In addition to the primary side coil of the transformer T, for those skilled in the art, the driver 211 used to control the auxiliary switch Q2 Of course there are other configuration methods.

In addition, the first rectifier switch S1 and the second rectifier switch S2 are coupled to the secondary side of the transformer T, and the filter inductor L and the filter capacitor Cb are coupled to both ends of the second rectifier switch S2.

In order to achieve the purpose of zero-voltage switching of the main switch Q1, the control method proposed in this case is (please refer to Figure 2(b)), using the auxiliary switch control circuit 21 to fix the opening time of the auxiliary switch Q2 each time, so as to achieve a fixed The effect of each turn-off time of the main switch Q1; that is, the driver 211 of the auxiliary switch control circuit 21 is used to control the auxiliary switch Q2, and the timer 212 is used to count the time, so that the turn-on time of the auxiliary switch Q2 is fixed each time. As shown in the timing diagram of Figure 2(b), when the auxiliary switch Q2 is turned on, the primary side coil Lm and the auxiliary capacitor Ca resonate at point a, and when the auxiliary switch Q2 is turned off, the zero voltage switching detector 22 can detect Go to the zero-voltage switching point on the first terminal node of the main switch Q1, and turn on the main switch Q1, as shown in point b. The effect reflected on the main switch Q1 is that the off time Toff of the main switch Q1 is fixed each time, so that the purpose of zero-voltage switching on the first terminal node of the main switch Q1 can be achieved.

Please refer to Fig. 3 (a) and (b), which are respectively the schematic diagram of the power stage circuit of the flyback type switching power supply in this case and the timing diagram of the voltage and current of each functional switch, wherein the switching power supply 30 is A switching power supply with feedback structure.

Most of the components in the switching power supply 30 that are the same as those in the second figure have the same symbols; however, the second rectifier switch S2 and the filter inductor 1 are removed in the third figure.

Similar to the second figure, the control method proposed in this case is (please refer to Figure 3(b)), use the auxiliary switch control circuit 31 to fix the opening time of the auxiliary switch Q2 each time, so as to achieve the fixed closing time of the main switch Q1 each time That is to say, the driver 311 of the auxiliary switch control circuit 31 is used to control the auxiliary switch Q2, and the timer 312 is used to count the time, so that the opening time of the auxiliary switch Q2 is fixed each time. The difference is that, as shown in the timing diagram of Figure 3(b), when the auxiliary switch Q2 is turned on, the primary side coil Lk and the auxiliary capacitor Ca resonate in region d, and then when the auxiliary switch Q2 is turned off, the primary side coil Lk and the capacitor Coss resonate in the e region to achieve zero voltage. At this time, when the zero voltage switching detector 32 can detect the zero voltage switching point on the first terminal node of the main switch Q1, and turn on the main switch Q1, as Shown at point c. The effect reflected on the main switch Q1 is that the off time Toff of the main switch Q1 is fixed each time, so that the purpose of zero-voltage switching on the first terminal node of the main switch Q1 can be achieved.

In summary, this case achieves the purpose of zero-voltage switching of the main switch by fixing the opening time of the auxiliary switch on the primary side of the transformer in the switching power supply to produce the effect of fixing the closing time of the main switch each time. It is applicable to switching power supplies with both forward and flyback structures, and does not require complex circuits and expensive drive transformers. Its control method is simpler than the conventional switching power supplies mentioned above, and its manufacturing cost is also lower than that of the conventional switching power supplies mentioned above. Inexpensive power supplies.

This case can be modified in various ways by a person who is familiar with this technology, but it does not deviate from the desired protection of the appended patent scope.

Claims (14)

1. A switching power supply, comprising: An auxiliary circuit, including an auxiliary capacitor and an auxiliary switch, the auxiliary capacitor is connected in series with the auxiliary switch; a transformer, the auxiliary circuit is connected in parallel to the primary side of the transformer; An auxiliary switch control circuit, connected to the auxiliary switch and the primary side of the transformer, for fixing the opening time of the auxiliary switch each time; a main switch having a first terminal, a second terminal and a control terminal, the first terminal is connected to the primary side of the transformer; a zero-voltage switching (ZVS) controller connected to the first terminal and the control terminal of the main switch; a first and a second rectifier switch coupled to the secondary side of the transformer; and a filter circuit connected in parallel to both ends of the second rectifier switch; Wherein, the auxiliary switch control circuit fixes the turn-on time of the auxiliary switch each time, which produces the effect that the turn-off time of the main switch is fixed each time, so as to achieve the purpose of zero-voltage switching of the main switch. 2. The switching power supply according to claim 1, wherein the auxiliary switch control circuit comprises a driver and a timer. 3. The switching power supply according to claim 2, wherein the driver is a primary side coil of the transformer. 4. The switching power supply according to claim 1, wherein the zero voltage switching detector is used to detect zero voltage on the first terminal of the main switch. 5 . The switching power supply according to claim 1 , wherein the auxiliary switch, the main switch, the first and the second rectifier switches are semiconductor switching elements. 6. The switching power supply according to claim 1, wherein the filter circuit comprises a filter inductor and a filter capacitor. 7. A switching power supply, comprising: An auxiliary circuit, including an auxiliary capacitor and an auxiliary switch, the auxiliary capacitor is connected in series with the auxiliary switch; a transformer, the auxiliary circuit is connected in parallel to the primary side of the transformer; An auxiliary switch control circuit, connected to the auxiliary switch and the primary side of the transformer, for fixing the opening time of the auxiliary switch each time; a main switch having a first terminal, a second terminal and a control terminal, the first terminal is connected to the primary side of the transformer; a zero-voltage switching (ZVS) controller connected to the first terminal and the control terminal of the main switch; a first rectifier switch, one end of which is coupled to the secondary side of the transformer; and a filter circuit, one end is connected to the other end of the first rectifier switch, and the other end is connected to the secondary side of the transformer; Wherein, the auxiliary switch control circuit fixes the turn-on time of the auxiliary switch each time, which produces the effect that the turn-off time of the main switch is fixed each time, so as to achieve the purpose of zero-voltage switching of the main switch. 8. The switching power supply according to claim 7, wherein the auxiliary switch control circuit comprises a driver and a timer. 9. The switching power supply according to claim 8, wherein the driver is a primary side coil of the transformer. 10. The switching power supply according to claim 7, wherein the zero voltage switching detector is used to detect zero voltage on the first terminal of the main switch. 11. The switching power supply according to claim 7, wherein the auxiliary switch, the main switch and the first rectifier switch are semiconductor switching elements. 12. The switching power supply according to claim 7, wherein the filter circuit comprises a filter capacitor. 13. A control method for zero-voltage switching (ZVS) of a switching power supply, the switching power supply at least includes a transformer and a main switch and an auxiliary switch coupled to a primary side of the transformer, the control The method includes the following steps: Fixing the turn-on time of the auxiliary switch each time produces the effect that the turn-off time of the main switch is fixed each time, so as to achieve the purpose of switching the main switch with zero voltage. 14. The control method according to claim 13, wherein the switching power supply is selected from a forward switching power supply and a feedback switching power supply one of them.

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