The structure and principle of SCR Rectifier
SCR Rectifier is a new non-contact switching device, its components are solid-state electronic components. It uses the electronic components (such as switching transistor, triac and other semiconductor devices) switching characteristics, can be achieved without contact without spark to open and disconnect the circuit, and therefore known as "non-contact switch" It came out in the 1970s, because of its non-contact work characteristics, so that in many areas of electronic control and computer control has been increasingly widely used.
SCR Rectifier according to the use of occasions can be divided into two types of AC and DC, they are in the AC or DC power supply load switch, can not mix below the AC type SCR Rectifier as an example to illustrate its working principle, Figure 1 is (A and B) and two output terminals (C and D), the rectifier has only two input terminals (A and B) and two output terminals (C and D), which are the main body of the AC rectifier. A four-terminal device. Work as long as the A, B with a certain control signal, you can control the C, D between the ends of the "pass" and "off" to achieve "switch" function, in which the coupling circuit function is A, The B-side input control signal provides a channel between the input and output terminals but electrically disconnects the (electrical) connection between the input and output terminals of the SCR Rectifier to prevent the output from affecting the input, coupling The circuit component is "optocoupler", it is sensitive, responsive, high input / output insulation (voltage) level; because the input load is light-emitting diodes, which makes the SCR Rectifier input is easy Do match with the input signal level, in use can be directly connected with the computer output interface, that is, "1" and "0" logic level control. Trigger circuit function is to produce the desired trigger signal, drive switch circuit ④ work, but because the switch circuit without special control circuit, will produce radio frequency interference and high harmonics or spikes pollute the grid, this special "Zero-crossing control circuit". The "zero crossing" means that when the control signal is added and the AC voltage is zero, the SCR Rectifier is on; and when the control signal is turned off, the SCR Rectifier waits for the intersection of the positive half and negative half of the alternating current (zero Potential), the SCR Rectifier is in the off state. This design can prevent high-order harmonic interference and pollution of the grid. The absorption circuit is designed to prevent the occurrence of spikes and surges (voltages) from the power supply on the impact and interference (or even malfunction) of the triacs of the switching devices. Generally, the "RC" series absorber circuit Linear resistance (varistor).
DC-type SCR Rectifier compared with the AC-type SCR Rectifier, no zero-crossing control circuit, do not have to set the absorption circuit, switching devices generally use high-power switching transistor, the other works the same. However, the DC SCR Rectifier should be used in the note: ① load for the inductive load, such as DC solenoid valve or electromagnet, should be connected in parallel at both ends of a diode, polarity shown in Figure 3, the diode current should be equal to Working current, voltage should be greater than 4 times the operating voltage. ② SCR Rectifier should try to work close to the load, the output lead should meet the load current needs. ③ the use of power is by AC buck rectified income, the filter electrolytic capacitor should be large enough.
Before selecting SCR Rectifier for the appliance, we must first determine the electronic components to be dissipated, clear its working parameters, working conditions, size, installation, select the size of the bottom of the electronic SCR Rectifier than the component mounting surface slightly larger , Due to the limitations of the installation space, SCR Rectifier mainly rely on air convection to heat, beyond the interface with the components of the SCR Rectifier, the cooling effect with the increase in the distance between the components and decreased. For single-rib SCR Rectifiers, if the width of the required SCR Rectifier is missing in the table, select a double or triple width of the SCR Rectifier cut off.