Isolated converter and its control circuit and control method
A control method and control circuit technology, applied in control/regulation systems, DC power input conversion to DC power output, instruments, etc., can solve the problems that the control circuit is difficult to sample, cannot be safely shut down, etc., and achieve stable work , The effect of simple circuit structure
Active Publication Date: 2020-03-06
西安矽力杰半导体技术有限公司
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Problems solved by technology
Therefore, when the load changes from light load to heavy load, the switching frequency has an up-frequency action. At this time, it is difficult for the control circuit to sample or predict the turn-on time of the main power switch on the primary side, and it cannot be safely turned off.
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[0027] The present invention is described below based on examples, but the present invention is not limited to these examples. In the following detailed description of the invention, some specific details are set forth in detail. The present invention can be fully understood by those skilled in the art without the description of these detailed parts. In order not to obscure the essence of the present invention, well-known methods, procedures, procedures, components and circuits have not been described in detail.
[0028] Additionally, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
[0029] Meanwhile, it should be understood that in the following description, "circuit" refers to a conductive loop formed by at least one element or sub-circuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "connected to" another eleme...
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Disclosed are an isolated converter, a control circuit and a control method thereof. In the embodiment of the present invention, when the switching frequency needs to be increased, the main power switch is first controlled to work at a lower switching frequency for one or more cycles, and then the frequency-up operation is performed. At the same time, on the secondary side, the switching frequency of the main power switch is detected according to the secondary parameters of the power stage circuit. When it is detected that the switching frequency drops to meet a predetermined condition, the synchronous rectification switch is controlled to keep off in multiple cycles to wait for The upscaling operation on the primary side is complete. After the switching frequency of the main power switch is stable, the synchronous rectification switch is controlled to turn on and off according to the detected switching frequency. Therefore, without relying on the signal communication between the primary and secondary sides, it is still possible to sample the conduction moment of the main power switch on the primary side, and safely turn off the synchronous rectification switch. The circuit structure of the embodiment of the present invention is simple and can work stably.
Description
technical field [0001] The invention relates to power electronics technology, in particular to an isolated converter and its control circuit and control method. Background technique [0002] Synchronous rectification technology is a technology that uses controllable switching devices with low on-state resistance, such as metal oxide semiconductor transistors (MOSFETs), to replace diodes for rectification to reduce rectification losses. MOSFET is a voltage-controlled device, and its volt-ampere characteristics are linear when it is turned on. When using MOSFET for rectification, it is required that the gate voltage must be synchronized with the phase of the rectified voltage. [0003] At the same time, when the isolated converter works in continuous current mode (Continuous Current Mode, CCM), the main power switch on the primary side will be turned on before the synchronous rectification current on the secondary side drops to zero. Therefore, the synchronous rectification s...
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IPC IPC(8): H02M3/335
CPCH02M3/33592Y02B70/10
Inventor 李新磊张俏白永江
Owner 西安矽力杰半导体技术有限公司