CN111600473A

CN111600473A - Power chip high-voltage starting circuit

Info

Publication number: CN111600473A
Application number: CN201910451376.7A
Authority: CN
Inventors: 王清金; 秦振; 徐怀海; 洪南
Original assignee: Qingdao Topscomm Communication Co Ltd
Current assignee: Qingdao Topscomm Communication Co Ltd
Priority date: 2019-05-28
Filing date: 2019-05-28
Publication date: 2020-08-28

Abstract

The invention discloses a high-voltage starting circuit of a power chip, which belongs to the field of design of a flyback switching power supply of a PWM (pulse-width modulation) control circuit. The starting circuit adopts a source electrode control strategy, the main circuit is controlled by switching on and off a switch in a chip, a main switch MOS (metal oxide semiconductor) is used as a starting tube to work in a linear region, and the starting tube works in a cut-off region and a saturation region after being started. The mode of charging the capacitor at the VCC end is completed by the matching of the main switch MOS working in a linear region and a switch in the chip. In addition, compared with a power chip internally integrated with a high-voltage starting unit, the chip internally integrated with a common switch has higher price advantage and can better meet the requirements of market customers.

Description

Power chip high-voltage starting circuit

Technical Field

The invention relates to a switching power supply chip, in particular to a novel switching control strategy adopted in a high-voltage starting part of the chip.

Background

Switching power supply products are used in a wide variety of power electronic devices, and different power levels determine the size of the power supply. In the face of power supply products with the same power grade in the market, customers prefer a power supply with light weight, small size, thin height, low noise and strong anti-interference capability. The small-power DC-DC power supply realizes modular production, and more AC-DC power supplies and AC-DC power supply chips are put out on the market. The starting circuit parts designed for the switching power supply ICs of different manufacturers are different, the conventional flyback switching power supply chip is rectified by a sorting bridge and then passes through a high-voltage electrolysis end, low-frequency signals are filtered out to form pulsating direct-current voltage, the pulsating direct-current voltage is directly applied to the power supply end of the chip, and the starting resistance is also required to be connected. The starting resistor generally selects a power resistor, and after the power supply works stably, the starting resistor has power consumption, so that the temperature rise of the whole machine is influenced, and the efficiency of the power supply is reduced. In order to improve the power efficiency, a conventional method is to add a switching tube to the starting circuit, and the starting circuit is turned off after the power is started. This approach increases power efficiency but also increases PCB layout space and cost.

With the rapid development of power electronics, most chip manufacturers develop a power supply IC with a high-voltage starting module, a power bus end is directly connected to a chip high-voltage starting end, and an internal constant current source is activated to charge a capacitor at a VCC end. The starting resistor is omitted, the board distribution space is reduced, the power supply efficiency is improved, and meanwhile, the cost of the chip is correspondingly improved due to the process of starting the module at high voltage inside the chip. With the speed of the power supply chip upgrading, enterprises pursue the cost of the whole switching power supply on the premise of ensuring the reliability of the product. Therefore, the integration of the power supply chip is also higher and higher.

Disclosure of Invention

Compared with the traditional power supply starting circuit, the power supply starting circuit has the design idea that the power supply is started through the logical cooperation of the main switch MOS tube and the built-in switch of the power supply chip. As shown in fig. 1, after the mains supply is switched on, the Cg capacitor is charged at the power supply bus terminal through the R1 resistor, and at this time, the chip internal switch control logic is in an off state. When the voltage at the VG terminal rises to the conducting threshold voltage of the main circuit switch MOS transistor VT1, VT1 conducts linearly. At this time, the current flows through the primary side of the transformer, passes through the drain and the source of the VT1, the switches of the VCC terminal and the DRV terminal inside the chip are turned on, and the capacitor voltage at the VCC terminal gradually rises. Until the voltage at VCC end reaches the start voltage of the chip, the internal logic of the chip is started, as shown in figure 2, the gate voltage stabilizing circuit composed of an operational amplifier and a voltage stabilizing tube makes the VG end always in a high potential state, the source control logic controls the on-off of the internal switch to make the potential difference between the gate and the source of the MOS tube of the main circuit, and when the potential difference is lower than the threshold voltage of the MOS, the main circuit is turned off. When the potential difference is larger than the threshold voltage of the MOS, the main circuit is conducted. In the starting process, the primary side inductor of the transformer and the main circuit MOS are used for working in a linear region, and a starting capacitor charging loop for the VCC end is composed of the primary side inductor of the transformer and the main circuit MOS.

In the conventional power chip starting circuit, as shown in fig. 3, a power bus terminal is connected to a VCC terminal of a power chip through a starting resistor, a VCC potential is continuously raised during starting, until a VCC starting voltage is reached, internal logic of a power supply works to send a driving signal, and a driving current is increased through an internal triode, so that an output drives a main circuit switch MOS. The starting mode is limited by the range of input voltage, because the starting resistor is a fixed value, the starting time under high voltage is short, the power consumption is possibly very large, the starting time under low voltage is long, the power consumption is small, but the problems of short starting time and low power consumption under low voltage and high voltage cannot be simultaneously met. Furthermore, as shown in fig. 4, a high-voltage start control logic unit is integrated inside the start chip, and this chip type does not need a start resistor, which saves board layout space, but the cost of the high-voltage start unit integrated inside the chip is relatively high.

Drawings

For the convenience of understanding how the present invention is implemented and how it differs from conventional schemes, reference will now be made in brief to the implemented schemes in connection with the accompanying drawings, which are merely drawn for comparison of the embodiments of the present invention with conventional schemes and from which other figures may be extended.

FIG. 1 is a diagram of a starting circuit of a flyback power supply with a chip according to the present invention;

FIG. 2 is a diagram of the internal logic control of the chip according to the present invention;

FIG. 3 is a diagram of a conventional power chip start-up circuit;

fig. 4 is a circuit diagram of a flyback power supply with a high-voltage start module unit.

Detailed Description

The technical solution implemented is further described below with reference to the accompanying drawings, wherein the drawings only illustrate the comparison between the embodiment of the present invention and the conventional solution, and mainly specifically illustrate the advantages of the present invention:

as shown in fig. 1, a starting circuit diagram of the chip of the present invention applied to a flyback power supply is shown, and the connection relationship is: the mains supply is connected to the L, N end and is connected to a rectifier bridge through an anti-surge and EMI filter circuit, the rear end of the rectifier bridge is connected with a bus capacitor, and low-frequency signals are filtered to form pulsating direct-current voltage. LP is a primary side inductor, LS is a secondary side inductor which is connected with an output capacitor Cout through a diode D1, RCS is a current detection resistor which is connected to the CS end of a chip, the current of the primary side main circuit is judged by detecting the voltage on the resistor, and then the duty ratio is controlled. LAUX is an auxiliary winding, and after the power supply is started, the chip supplies power and continuously supplies power to the chip through the winding to work. The resistor R1 is a start resistor, and the bus terminal is connected to the capacitor Cg terminal through the resistor R1 and is also connected to the chip VG terminal. After electrification, the Cin bus capacitor charges the Cg capacitor through the R1 resistor, the Cg end voltage slowly rises, the chip does not work at the moment, and when the VG end voltage rises to the conduction threshold voltage of the main circuit switch MOS tube VT1, VT1 is conducted linearly. Current flows through the primary side of the transformer, passes through a drain electrode and a source electrode of VT1, and then charges a capacitor C1 at a VCC end through the switching action of a DRV end and the VCC end which are connected inside a chip. The anode of the capacitor C1 is connected to VCC terminal, and the cathode is connected to the chip ground. As the voltage of the capacitor C1 gradually rises, the internal logic of the chip works after the voltage reaches the starting voltage of the chip. Fig. 2 shows a chip internal logic control diagram of the present invention. The source electrode starts the control logic circuit, a switch is arranged in the control logic circuit, and when the switch is closed, the source electrode end of the MOS of the main circuit is grounded through the RCS resistor and is at a low potential. The MOS grid electrode end potential of the main circuit is determined by the VG end voltage, after the chip is started, a grid voltage stabilizing circuit SW switch formed by the operational amplifier and the switch is switched on, VG is always in a high potential state, one end of a voltage stabilizing tube is connected with the VG end, and the other end of the voltage stabilizing tube is connected with the chip ground, so that the purpose of preventing the main switch MOS grid electrode voltage from being overhigh and playing a role in protection is achieved. At this time, the gate of the main switch MOS is at a high potential, the source is at a low potential, and a voltage difference is greater than a threshold voltage, so that the primary side main circuit of the transformer operates. When the built-in switch is switched off, the MOS grid of the main switch has high potential, the main circuit of the primary side of the transformer is switched off, and the freewheeling diode of the secondary side finishes freewheeling work to charge the Cout capacitor.

As shown in the attached figure 3, Cin is bus-bar terminal high-voltage electrolysis, R2 and R3 are starting resistors, the high-voltage electrolysis is connected to a C2 terminal of a starting capacitor through R2 and R3 resistors and is also connected to a VCC terminal of a chip, and the starting process of the chip is as follows: the DC bus terminal charges a C2 capacitor through resistors R2 and R3, and the C3 is a ceramic capacitor, so that high-frequency signals are filtered to prevent interference on a chip. When the voltage at the C2 end reaches the chip starting voltage, the chip works to send out PWM drive, and in order to directly drive the high-voltage MOS, a triode is connected in the chip to increase the drive capability. R1 is a driving resistor which is used as a damping to prevent the driving waveform from oscillating on one hand and accelerate the charge discharge when the high-voltage MOS is switched off on the other hand. The starting circuit has the disadvantages that R2 and R3 are power resistors, heat is generated when the power supply works, the temperature and the service life of the whole power supply are influenced, and meanwhile, the problem of contradiction between the starting time and the power consumption under low voltage and high voltage cannot be solved.

As shown in FIG. 4, the main circuit of the power supply is the same as that of FIG. 3. The starting circuit is characterized in that a high-voltage starting unit is arranged in a chip, a starting resistor is not needed, a power bus end is directly connected to a high-voltage starting end of the chip, and an internal constant current source is activated to charge a capacitor at a VCC end. The starting resistor is omitted, the board distribution space is reduced, the power supply efficiency is improved, and meanwhile, the cost of the chip is correspondingly improved due to the process of starting the module at high voltage inside the chip.

In summary, the advantages of the invention in the flyback switching power supply starting circuit are shown in the following aspects:

1. the starting circuit adopts a source electrode driving control strategy, the main circuit is controlled by controlling the on and off of a switch in a chip, a main switch MOS (metal oxide semiconductor) is used as a starting tube to work in a linear region, and the starting tube works in a cut-off region and a saturation region after being started.

2. The starting circuit is suitable for wide-range voltage input, and simultaneously solves the problem of contradiction between starting time and power consumption under low voltage and high voltage by means of the characteristic that a main circuit MOS works in a linear region in the starting process.

3. The VCC end capacitor charging mode is completed by the cooperation of the main switch MOS working in a linear region state and the built-in switch.

4. Compared with the internal integrated high-voltage starting module process, the chip has higher price advantage by adopting a common switch mode, and can meet the requirements of market customers.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A power chip high-voltage starting circuit is characterized by comprising: the source electrode drive control module, a grid electrode protection circuit connected with the operational amplifier and the voltage stabilizing tube and a switch control circuit started by a VCC end.

2. The power supply chip high-voltage starting circuit according to claim 1, characterized in that: the source electrode driving control module internally comprises a switch, and the switch of the main circuit is controlled by controlling the on and off of the switch.

3. The power chip high-voltage starting circuit according to claim 2, further characterized in that: the MOS grid of the main circuit is connected to the VG end of the chip through a resistor R1, the source is connected to the DRV end of the chip, a current detection resistor RCS is connected to the CS end of the chip, one end of a chip internal source drive control module is connected to the DRV end of the chip, and the other end of the chip internal source drive control module is connected to the CS end of the chip.

4. The power supply chip high-voltage starting circuit according to claim 1, characterized in that: and the operational amplifier is connected with a grid protection circuit of the voltage stabilizing tube, the anode of the voltage stabilizing tube is grounded, and the cathode of the voltage stabilizing tube is connected with the VG end of the chip.

5. The power supply chip high-voltage starting circuit according to claim 1, characterized in that: when the main switch MOS works in a linear region as a starting tube, the DRV end controls the VCC end to start charging a capacitor through a switch.