Single-ended active clamp DC/DC converter

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Single-ended active clamp DC/DC converter [Copy link]

Abstract: The performance of single-ended forward and flyback converters is greatly enhanced by the use of active clamping/recovery technology. Its advantages are high efficiency, low external interference and device stress. This paper introduces two active clamping circuit topologies, analyzes the circuit working state, and derives the relationship between magnetizing current and load current. Finally, the advantages of this active clamping DC/DC converter are summarized.

Keywords: power conversion switching power supply

In a switching power supply, a DC voltage can be converted from one level to another, such as a buck circuit, a boost circuit, and a buck-boost circuit. However, when it is required to convert a relatively high DC voltage to a relatively low DC voltage, the efficiency of conventional conversion technology is low, especially when the operating frequency of the converter is above 1MHz, the switching loss becomes particularly large.

The circuit in Figure 1 is a conventional buck (forward) converter. During normal operation of the converter, the switch tube S1 is turned on, and the difference between the input voltage and the output voltage is added to the inductor L1, which increases the current in the inductor L1 and charges the input capacitor CS; this current is then sent to the load RL. When the switch S1 is turned off, the polarity of the inductor L1 is reversed to turn on the diode D1, and then the current flows through D1 and L1, and its amplitude gradually decreases until S1 is turned on again, and the next working cycle begins.

Figure 2 shows a conventional buck-boost converter, which uses a transformer T to isolate the input and output voltages. This converter can make the output voltage amplitude greater or less than the input voltage amplitude. The disadvantage of this circuit is that the switch tube current and the diode current are both larger than the current of the basic buck or boost converter.

The DC/DC power converter with active clamp introduced in this article can work with zero voltage resonant conversion at a switching frequency above 1MHz. In the circuit, only one magnetic core is needed to serve as both an inductor and a transformer. The required voltage can be obtained by changing the turns ratio. The control of its output characteristics is the same as that of ordinary converter topologies. With zero voltage resonant conversion and transformer isolation technology, there is no special requirement for the magnetic core. The control part of this circuit adopts pulse width modulation technology (PWM), which has high operating frequency, high efficiency, and input and output isolation.