As a new type of current protection component, PPTC self recovery fuse has been widely used in the electronics industry, communications equipment, automotive electronics, motor protection, toys and other industries.
In the PPTC self recovery fuse technical indicators, there is a technical indicator is vmaxi, vmaxi said: wh protection in the blocking state of the maximum voltage. That is to say: PPTC self recovery fuse circuit in series, when the circuit current abnormal state, PPTC will be in a certain time range self recovery fuse by low resistance jump into high resistance, thereby preventing abnormal large current flows, protecting the subsequent circuit from high current circuit failure, then the voltage in almost all PPTC self recovery fuse. If at this time on the PPTC self recovery fuse on the voltage over vmaxi, it is easy to cause the damage of the PPTC self recovery fuse, permanent damage, so that the PPTC recovery fuse can not be restored. In the long-term application process, there are some problems that ignore the vmaxi technical requirements.
For example, an engineer in the selection of PPTC self recovery fuse, voltage circuit for 12V, the selection of PPTC self recovery fuse 16V series, self recovery function and fuse in PPTC verification experiments, an external voltage, constant current power supply, in order to get the minimum current PPTC self recovery fuse start protection the load remains unchanged, the output voltage of slowly adjusting power, the load current increases, when the current reaches the minimum current PPTC self recovery fuse start protection, PPTC self recovery fuse into protection state, but at the same time, since the resumption of PPTC fuse burning phenomenon, when the output voltage regulated power supply has been reached 37v.
From the above situation:
1, model selection is correct;
2, the experimental method is not correct;
3, ignored the vmaxi;
Analysis of the reasons: in the course of the experiment, ignoring the technical requirements of the vmaxi, resulting in an applied voltage is much greater than vmaxi, so that PPTC self recovery fuse burned phenomenon. This is because the engineer is to use the load resistance remains unchanged, with the power supply voltage to change the load current.
The correct method: the voltage of the power supply is set to 12V, the PPTC self recovery fuse is connected in series in the circuit, the load of the circuit is changed, and the load current changes. When the current reaches the minimum current PPTC self recovery fuse start protection, within a certain time of PPTC self recovery fuse resistance will jump by low resistance to high resistance, the load current is reduced to about 10mA, to prevent large current flows.
Method for detecting self recovery fuse function by using stabilized voltage and steady current power supply pptc:
1, the voltage regulator, steady current power supply output voltage set to the desired voltage; 2, the voltage regulator, the steady current power supply, the negative output line short;
3, adjust the current output knob, the output current reaches the current required value; 4, PPTC resettable two pins were directly connected to the voltage stabilized power supply, the output line of positive and negative end; 5, open the regulator, when the power supply output from steady flow state transition to the state regulator PPTC, self recovery fuse has entered the state of protection, the end of the experiment.