DinizApp/Electronics Center

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  The DIAC, or "diode for alternating current", is a diode that conducts electrical current only after its breakover voltage has been reached momentarily. When breakdown occurs, the diode enters a region of negative dynamic resistance, leading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode. The diode remains in conduction until the current through it drops below a value characteristic for the device, called the holding current. Below this value, the diode switches back to its high-resistance, non-conducting state. This behavior is bidirectional, meaning typically the same for both directions of current. Most DIACs have a three-layer structure with breakover voltage of approximately 30 V. Their behavior is similar to that of a neon lamp, but it can be more precisely controlled and takes place at a lower voltage. DIACs have no gate electrode, unlike some other thyristors that they are commonly used to trigger, such as TRIACs and SCRs. DIACs are also called "symmetrical trigger diodes" due to the symmetry of their characteristic curve. Because DIACs are bidirectional devices, their terminals are not labeled as anode and cathode but as A1 and A2 or main terminal MT1 and MT2. (It is similar to two Zener diodes connected in series. It is possible to produce an equivalent DIAC of 9V, for example, connecting two Zener diodes of 9V in (anti)series, cathode with cathode and anode with anode). The circuit above shows how to test a DIAC, notice that it conducts when reaches 30V and the voltage drops to 0, behaving like a short-circuit or a closed switch.

   
  The DIAC, or "diode for alternating current", is a diode that conducts electrical current only after its breakover voltage has been reached momentarily.  
  When breakdown occurs, the diode enters a region of negative dynamic resistance, leading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode. The diode remains in conduction until the current through it drops below a value characteristic for the device, called the holding current. Below this value, the diode switches back to its high-resistance, non-conducting state. This behavior is bidirectional, meaning typically the same for both directions of current. 
  Most DIACs have a three-layer structure with breakover voltage of approximately 30 V. Their behavior is similar to that of a neon lamp, but it can be more precisely controlled and takes place at a lower voltage. 
  DIACs have no gate electrode, unlike some other thyristors that they are commonly used to trigger, such as TRIACs and SCRs.  
  DIACs are also called "symmetrical trigger diodes" due to the symmetry of their characteristic curve. Because DIACs are bidirectional devices, their terminals are not labeled as anode and cathode but as A1 and A2 or main terminal MT1 and MT2. 
   
  (It is similar to two Zener diodes connected in series. It is possible to produce an equivalent DIAC of 9V, for example, connecting two Zener diodes of 9V in (anti)series, cathode with cathode and anode with anode). 
  The circuit above shows how to test a DIAC, notice that it conducts when reaches 30V and the voltage drops to 0, behaving like a short-circuit or a closed switch.

   
  O DIAC, ou Diode for Alternating Current, é um gatilho bidirecional, ou diodo que conduz corrente apenas após a tensão de disparo ser atingida, e para de conduzir quando a corrente elétrica cai abaixo de um valor característico, chamada de corrente de corte. Este comportamento é o mesmo nas duas direções de condução de corrente. A tensão de disparo é por volta dos 30 volts para a maioria destes dispositivos. Este comportamento é de certa forma similar, porém mais precisamente controlado e ocorrendo em menor valor, ao comportamento de uma lâmpada de neon. 
   
  O DIAC é normalmente usado para disparar TRIACs e SCRs. 
   
  Como um DIAC é um gatilho bidirecional, seus terminais não são marcados como anodo ou catodo mas a maioria é marcada como A1 ou MT1 e A2 ou MT2. 
   
  (Funciona da mesma maneira que dois diodos zener em Série. Pode-se produzir um DIAC equivalente de 9V, por exemplo, ligando dois diodos zener de 9v em (anti)série, cátodo com cátodo e ânodo com ânodo). 
  O circuito acima mostra como devemos testar um Diac, observe que quando atinge os 30v ele entra em condução e a tensão vai a zero, se comportando como um curto circuito ou uma chave fechada.

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