Solution
Solutions for global temperature control systems
Switching power supply
subcategory： Solution
2024-09-12
1. application background
The switching power supply will overheat under abnormal working conditions, which will burn the power supply and even cause a fire. In the process of power supply design, overheat protection function is necessary and very important. In particular, high-power power supplies above 100W and outdoor LED lights and LED screen power supplies need to be set up for overheat protection because of their own severe heat or high working environment temperature. In addition, the miner's lamp power supply with poor heat dissipation environment also needs to be protected from overheating.
2. protection principle
The temperature switch is a mechanical passive component, which is mainly arranged in the control loop. After sensing the external temperature through the internal thermal sensitive element bimetallic strip, it will deform, disconnect the contact, and the resistance will change from within 50 milliohms to infinity, thus giving the control loop signal. After receiving the signal, the IC or MCU will turn off the main loop current through the MOS tube or other actuators, thus playing the role of protecting the whole machine. When the ambient temperature decreases, the heat sensitive element returns to the initial state, the contact is closed again, and the resistance signal within 50 milliohms is given to the control circuit, and the actuator operates according to the program setting.
3. installation position
Near the power tube: Among all components of the switching power supply, the power tube has the highest heating temperature, usually the working temperature cannot exceed 130 degrees. A temperature switch below 130 degrees can be selected, and the temperature switch is attached to the power tube through a heat shrinkable sleeve, so that it can better transfer heat;
· Transformer: the temperature switch close to the transformer coil, so that it fully feel the coil temperature changes
On PCB board: a temperature switch with PIN pin is selected and inserted into the hole of PCB through wave soldering, so that the temperature switch can feel the ambient temperature inside the power supply.
Radiator: close to the surface of the radiator, it can be glued by thermal conductive silicon adhesive or directly inserted into the radiator groove (pay attention to whether the temperature switch can be closely attached to the inner wall of the groove)
· Inner wall of casing: fixed by metal mounting bracket
4. selection
Volume: Considering the installation space, there are two shell sizes of the product, the larger model is TB05-BB5D, the size is 15X7X3.5mm. The smaller model has a TB02-BB8D size of 12x 5.4x 2.4mm. In the ultra-thin power supply, due to the limited installation space, the general use of TB02-BB8D;
Current: Since the temperature switch is used in the control loop, the current through the temperature switch is a signal current of milliampere level, the TB05-BB5D rated current is 5A, and the TB02-BB8D rated current is 2A, which is greater than the milliampere level current, so both models can be applied;
· Protection temperature: usually 30~155 degrees, every 5 degrees, according to the design and installation position to choose different temperatures, such as close to the power tube generally choose a higher 125 degrees, 120 degrees and 115 degrees, installed on the shell choose a lower temperature, 85 degrees or 90 degrees and so on
· Contact switch form: it is divided into two types: normally closed and normally open. Normally closed is the initial state of contact closure, and the temperature protection contact is disconnected. It is always the opposite. Different switch forms are selected according to the design.
· Normally closed models for TB05-BB5D and TB02-BB8D
· Normally open models for TB05-KA5D and TB02-KA8D
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