Circuit module analysis exercise 5 (power supply)

d1,d2,d3 It limits the magnitude and direction of the current ,p and a Is the input power supply ,a-in,vcc Is the output power supply .

The input here is 12v Direct current , adopt r65 and r67 It forms a voltage dividing circuit , Change the current from a-in Output ,r66 It's a current limiting resistor ,c8 It's a filter capacitor .

f1 It is a self-healing fuse , Used to protect circuits

r1 It is used to limit current

  This part is ncv4275 Chip and peripheral circuit of the chip , What it does is it takes 12v Voltage converted to 5v voltage （vcc）.

tvs1 It is a transient voltage suppression diode （Transient voltage suppression diode） Also known as TVS diode , It is an electronic part for protection , It can protect electrical equipment from voltage spikes introduced by conductors .

Here is vcc Direct supply 5vout

The characteristics of the diode are , Conduct when the positive potential is higher than the negative potential , Otherwise, it will be disconnected , Can protect current only from vcc To 5vout, If the current is reversed, it will be disconnected . 

Self recovery fuse , It is an overcurrent electronic protection component , High molecular organic polymers are used under high pressure 、 The high temperature , Under the condition of vulcanization reaction , After adding conductive particle material , It is processed by special technology . Traditional fuse overcurrent protection , Can only protect once , It burns out and needs to be replaced , The self recovery fuse has over-current thermal protection , Automatic recovery dual function .

LDO Linear regulator

LDO Application Summary | Gao Mingfei's blog (gaomf.cn)

NCV4275 - 5.0 V, 450 mA Low-Drop Voltage Regulator (onsemi.com)

Transient voltage suppression diode （Transient voltage suppression diode） Also known as TVS diode , It is an electronic part for protection , It can protect electrical equipment from voltage spikes introduced by conductors .

TVS diode It will be connected in parallel with the circuit to be protected . When the voltage exceeds the sudden collapse level , Direct shunting of excess current .TVS The diode is Clamp , It will suppress excessive voltage exceeding its collapse voltage . When the overvoltage disappears ,TVS Diode will reset automatically , And its absorbed energy is higher than that of similar rated Crowbar circuit It's much bigger. .

TVS Diodes are unidirectional and bidirectional . One way TVS The diode is similar in forward operation Commutator , But its design allows it to withstand a large peak current ,1.5KE The instantaneous power of the series can reach 1500 W.

Bidirectional TVS Diodes can be considered as two of opposite polarity Avalanche diode In series , And then connected in parallel with the circuit to be protected . Although it will be marked as two diodes in the circuit , However, the actual component is to package two diodes in the same package .

TVS Diode over-voltage response will be faster than other over-voltage protection components （ for example Varistor or Gas discharge tube ） Be quick . The actual clamping is only about one picosecond , But because there are wires in the actual circuit inductance , Therefore, the protective element should allow large voltage for a long time . therefore TVS Diodes will be more suitable than other components to protect the circuit from fast , And there are destructive voltage surges . Like many distributed circuits, there are such fast overvoltage surges , It may be caused by internal or external factors , For example, lightning or motor short circuit .

If the transient voltage suppressor is used in an environment exceeding its design conditions , May damage . There are three failure modes for Transient Voltage Suppressors ： A short circuit 、 Open the way 、 Element rating drop .