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 serious cases. In the process of power supply design, overheat protection function is necessary and very important. Especially more than 100W high-power power supply and outdoor LED lights, LED screen power supply, because of their own  heating or high working environment temperature, more need to set overheating protection. Inaddition, in the heat dissipation environment is not good mining lamp power supply also need to  add overheating protection.

2. Protection principle

Temperature switch is a mechanical passive component, mainly set in the control loop,through the internal heat sensitive element bimetallic sheet to sense the external temperature,  deformation, disconnect contact, resistance from 50mΩ changes to infinity, thus giving the control loop signal, IC or MCU after receiving the signal, Through the MOS tube or other executive components and then turnoff the main circuit current, so as to play a role in the protection of the whole machine.

When the ambient temperature is reduced, the heat sensitive element returns to the initial state, the contact is closed again, and the resistance value signal is given to the control loop within 50mΩ. The actuator then operates according to the program setting.

3. Installation position

• Near the power tube: Among all the components of the switching power supply, the power tube has the highest heating temperature, usually the working temperature cannot exceed 130℃, you can choose a temperature switch below 130℃, and stick the temperature switch to the power tube through the heat shrink 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 change.

• On the PCB board: Select a temperature switch with a PIN foot and insert it into the hole of the PCB through wave soldering, so that the temperature switch can feel the ambient temperature inside the power supply.

• Heat sink: stick to the surface of the heat sink, can be glued by thermal silicone or directly inserted into the heat sinkslot (pay attention to whether the temperature switch can be closely fitted to the inner wall of the slot).

• Inner wall of the chassis: secure it with a metal mounting bracket.

4. Type Selection

• Volume: Considering the installation space problem, there are two shell sizes of the product, the larger model is BW-BCP, and the size is 15*7*3.5mm. The smaller model is BW-ECP size 12*5.5*2.4mm. In ultra-thin power supplies, BW-ECP is generally used due to limited installation space.

• current: Because the temperature switch is used to control the loop, the current through   the temperature switch is the signal current of the MA level, the rated current of BW-BCP is 5A, and the rated current of BW-ECP is 2A, both of which are greater than the MA level current, so both models can be applied.

• Protection temperature: usually 85 ~ 130℃, every 5 degrees of gear, according to the design and installation position selection of different temperatures, such as close to the power tube generally choose the higher 125℃, 120℃ and 115℃, installed on the shellselection of lower temperature, 85℃ or 90℃ and soon.

• contact switch form: divided into normally closed, normally open two, normally closed for the initial state of contact closure, to the protection temperature contact disconnect.

            Normally open is just the opposite. Choose different switch forms according to the design. 

            Normally closed models are BW-BCP and BW-ECP, and normally open models are BW-BOP and BW-EOP