Today's medical instrument technology is developing rapidly. New medical devices are emerging all the time But no matter how advanced and complex the functionality of new devices is, there is one thing that is indispensable. That's the power supply. It is the power source of the energy conversion of the entire instrument, although the principle of various devices is different. But the principle of its power supply is much the same. And the failure rate of the power supply is relatively high, because the power supply often works under harsh environments. Especially the switching power supply, it bears the impact of high current and high voltage of the whole machine. Therefore, in the substantial fault of component damage. The failure of the power supply accounts for a large proportion. According to statistics, it accounts for more than 50%. Therefore. As long as you are proficient in power supply. In particular, the maintenance of switching power supply can be carried out well in the maintenance of medical equipment. The following focuses on how to respond to change without changing – from the power supply to manpower. As a breakthrough in the face of faults, the switching power supply to eliminate various complex faults is mainly composed of full-bridge rectifier circuit, start-up circuit, switch excitation circuit, voltage stabilization control circuit, output rectifier filter circuit and various protection circuits. 1 Full-bridge rectifier circuit The full-bridge rectifier circuit input is 220 V AC. The output is 300 V DC high voltage. The consumable part is a full-bridge rectifier diode. As long as there is one damage. The entire bridge pile needs to be replaced. Because the other diodes are definitely overcurrent. The other is an electrolytic capacitor with a withstand voltage of 450 V. This capacitance capacity is not enough. There will be a lot of special failures. Such as computer system crashes repeatedly. 50Hz AC interference appears on the screen, etc. 2 Starting circuit self-excited switching power supply f switch tube plays a switching role. It is also the core element of the gap oscillator of the switching power supply), which is composed of a resistor current limiting method: one end of the resistor is connected to a 300 V DC high voltage. The other end is connected to the base of the switch tube. Due to the large value of the starting resistance (more than 100 kohms), the power is small. Therefore, it is a wearing part. After the resistor is disconnected. The switching power supply does not vibrate. There is no venting circuit, and the 300 V DC high-voltage voltage cannot be vented for a long time. Therefore, it is necessary to pay attention to the discharge of the capacitor during maintenance. It excites the switching power supply (the switch tube of the switching power supply only plays a switching role. does not participate in the formation of the oscillation pulse) There are two main ways: (1) the 300 V voltage is powered to Vee of the integrated circuit after resistor current limiting and step-down: (2) the mains is step-down by the resistor, and the power supply to Vcc after the diode is rectified The consumable parts are the integrated blocks and step-down resistors that participate in the oscillation 3 Switching excitation circuit The self-excited switching power supply is composed of a switching tube, a switching transformer, and a positive feedback loop, and the wearing parts are the capacitors and resistors on the positive feedback loop It excitation switching power supply is composed of an oscillator, a logic processor, and an amplifier. This type of circuit is generally composed of integrated circuits. Even a single thick film manifold is realized, and the wearing part is the switch tube, which is generally composed of N-channel high-power FET. The method of judging the quality should be mastered 4 The voltage regulation control circuit is divided into two types: indirect error sampling and direct error sampling circuit according to the error sampling method, and indirect error sampling refers to setting a sampling winding on the switching transformer. After rectifying the filter, a voltage proportional to the output is obtained. This voltage is used to control the conduction of the switch. So as to play a stabilizing effect when overhauling this switching power supply. It is necessary to pay attention to the false load to be repaired, and the wearing parts are filter capacitors and potentiometers. The direct error sampling circuit refers to the direct sampling of the output voltage of the switching power supply, so the primary and secondary isolation components of the switching power supply should be added. Generally it is a photocoupler. The wearing part is the optocoupler when the component fails. Generally, the output voltage rises significantly. 5 Voltage output circuit refers to the circuit of the switching transformer secondary filtered by high-frequency diodes and capacitors. The wearing parts are various current-limiting resistors and filter capacitors 6 Protection circuits Generally, there are the following types: (1) spike pulse absorption circuits, which are designed to prevent the breakdown of the switch tube; (2) Overvoltage protection circuit. Prevents the output voltage from rising due to the extended on-time of the switch. On the one hand, the load circuit is protected. On the other hand, it also protects the switch tube. It shuts off the switch through the base shunt of the switch. So as to cut off the voltage output of the switching power supply: (3) under-voltage protection circuit and over-current protection circuit The fault of the protection circuit is less. However, this part of the circuit should be understood, and when some faults are repaired, this part of the circuit needs to be disconnected, otherwise the real fault is not easy to be exposed. 7 Troubleshooting and Troubleshooting Introducing 4 Troubleshooting Examples Our maintenance principles are. There are some general-purpose power supplies. In order to increase the speed of maintenance. You can purchase high-quality and low-cost power supply replacement on the market. Except that the voltage should be consistent. Attention should also be paid to the current of the load (e.g., fault 1, fault 2); And some high-power power supplies, such as B-ultrasound power supply, biochemical instrument power supply, and some power supply with feedback function. As well as special voltage power supplies, which are not easy to buy on the market. It needs to be repaired (e.g., fault 3, fault 4).