Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

In order to prevent switching power supply (switching power supply is a power supply that uses modern power electronics technology to control the turn-on and turn-off time of the switching transistor to maintain a stable output voltage, the switching power supply is generally composed of a pulse width modulation (PWM) control IC and a MOSFET) The distributed inductance and capacitance present in the high-speed switching circuit in the system generate surge voltage and noise under the influence of the accumulated charge of the diode. In this paper, the surge voltage generated by the accumulated charge of the diode by using the RC or LC absorption circuit is magnetically absorbed by the amorphous magnetic core and the rectangular magnetic core, thereby solving the generation and suppression of the surge current of the switching power supply.

0 Introduction The main components of a switching power supply have parasitic inductance and capacitance. The parasitic capacitance Cp is generally connected in parallel with the switching element or diode, and the parasitic inductance L is usually connected in series with it. Due to the effects of these parasitic capacitances and inductances, switching elements often generate large voltage surges and current surges during on-off operation.
Large current surges and voltage surges are generated when the switch is turned on and off and the diode is reversely restored. The most effective way to suppress current surges when the switch is turned on is to use a zero voltage switching circuit. On the other hand, voltage surges that open the switch and voltage surges that reverse the recovery of the diode can damage the semiconductor components and cause noise. For this reason, when the switch is turned off, an absorbing circuit is required. When the diode is reversely restored, the voltage surge generation mechanism is the same as when the switch is turned off. Therefore, this absorption circuit is also applicable to the diode circuit. This paper introduces RC, RCD, LC and other absorption circuits. The basic working principle of these absorption circuits is to bypass the switch when the switch is opened to absorb the energy accumulated in the parasitic inductance and clamp the switching voltage. Suppress inrush current.

1 RC absorption circuit Figure 1 is a circuit diagram of an RC absorption network. It is a circuit in which the resistor Rs is connected in series with the capacitor Cs, and is connected in parallel with the switch. If the switch is turned off, the energy accumulated in the parasitic inductance charges the parasitic capacitance of the switch, and the absorption capacitor is also charged by the absorption resistor. Thus, the impedance will become larger due to the action of the snubber resistor, and the snubber capacitor equivalently increases the capacity of the shunt capacitor of the switch, thereby suppressing the voltage surge of the switch being turned off. When the switch is turned on, the snubber capacitor is discharged through the switch. At this time, its discharge current will be limited by the snubber resistor.

Figure 1 RC absorption network circuit.

2 RCD Absorption Circuit The RCD absorption circuit given in this paper is shown in Figure 2. It consists of a resistor Rs, a capacitor Cs and a diode VDs. The resistor Rs can also be connected in parallel with the diode VDs. If the switch is turned off, the energy accumulated in the parasitic inductance will be charged by the parasitic capacitance of the switch, and the switching voltage will rise. When the voltage rises to the voltage of the snubber capacitor, the snubber diode is turned on, so that the switching voltage is clamped by the absorbing diode (about 1 V), and the energy accumulated in the parasitic inductor also charges the snubber capacitor. During the switch-on period, the snubber capacitor is discharged through the resistor.

Figure 2 RCD absorption network.
The RC and RCD snubber circuits can also be used to demagnetize the transformer without the need for a demagnetization circuit consisting of a transformer winding and a diode. The excitation energy of the transformer is consumed in the absorption resistor. The RC and RCD snubber circuits not only consume the energy accumulated in the leakage inductance of the transformer, but also consume the excitation energy of the transformer. Therefore, this method also reduces the conversion efficiency of the converter.
Since the RCD snubber circuit clamps the switching voltage through the diode, the effect is better than RC. At the same time, it can also use a larger resistor, but the energy loss is also smaller than RC.

3 LC absorption circuit (LC circuit is a circuit composed of capacitors, inductors, resistors and other components and electronic devices capable of generating oscillating current or filtering function. The LC circuit formed by connecting inductor L and capacitor C is the simplest one. Kind of LC circuit)
The LC absorption circuit is shown in Fig. 3, which is composed of Ls, Cs, VDs1 and VDs2. If the switch is turned off, the energy accumulated in the inductance such as magnetic flux leakage or excitation can be discharged through the capacitor Cs through VDs1, so that the voltage of the absorption capacitor Cs is reversed, so that the transformer is demagnetized by the capacitor voltage. During this time, the voltage of the input voltage and the snubber capacitor applied to the switch is reversed again. In general, LC absorption circuits do not consume energy.

Figure 3 LC absorption network.

4 Conclusion To improve the switching frequency and improve the quality of switching power supply products, voltage surges and current surges must be considered. This paper is based on the analysis of the mechanism of interference generation and a lot of practice, and puts forward such effective suppression measures. Therefore, in order to solve the surge problem, it is necessary to analyze the mechanism of the surge in combination with the actual design, and design the surge absorbing circuit in combination with the actual situation to minimize the surge interference of the switching power supply.