hi! actuaaly i'm a diplamo eee student doing a project that is "MICROCONTROLER BASED SCR TRIGGERING CIRCUIT" . IF ANYBODY HAVE THAT IDEA PLEASE INFPRM IT TO ME! I'M IN A HURRY PL REPLY IMMEDIATELY!!!!!!!!!!!!!!
2006-12-11 23:41:27 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Engineering
Zero-crossing detectors are necessary to know when the SCR "resets." When the microprocessor knows the zero-crossing, it can begin a countdown to the trigger point, thus controlling the percentage of the waveform the SCR is ON. A dimmer will have more counts (from internal microprocessor clock) before the port triggers the SCR. A 60 Hz waveform goes from 0 to +169 to 0 volts in 8 1/3 milliseconds, then from 0 to -169 to 0 volts in another 8 1/3 milliseconds. Your microprocessor circuit will store a delay in a memory location. When the 0 crossing detector goes "on", it will run (perhaps by an interrupt) the counter delay routine, then turn the port to the SCR on. Your counter will be counting in the MHz range, so you will have good resolution in a 60Hz waveform. You will need a triggering transformer to interface to the port or an opto-isolator. The gate of the SCR will see the full 169 V, so it could easily fry you and your circuits. BE CAREFUL unless you are using a low voltage AC source under 48V RMS.
2006-12-12 00:57:04 · answer #1 · answered by DellXPSBuyer 5 · 0⤊ 1⤋
A zero crossing detector allows you to trigger the SCR at the point the voltage is zero. This permits the design of circuits which are intrinsically lower in electrical noise.
2006-12-12 08:46:01 · answer #2 · answered by hls 6 · 1⤊ 0⤋
Zero Crossing circuits are used in Solid State Relays (SSR) to detect when the AC is at zero and synchronize when the device is used to turn on (Allways at ZERO). This prevents clipping and noise generation because the AC voltage is as close to zero volts as possible when the device is switched on.
Using a SSR with a zero cross circuit (Built in) will not allow you to controll Phase Angle of Conduction. (Turning on the SSR at some other point in the sine wave to control power i.e. dimming)
Phase Angle of conduction may be accomplised with a UJT with a RC timeconstant on one leg (or a fixed zener reference) and the gate of an SCR on the other.
But that's another topic.....
2006-12-12 09:18:31 · answer #3 · answered by MarkG 7 · 0⤊ 0⤋
Hello, dear sender plz send the question in full format mean to say is modify the question that one can get easily to make reply uuuuu... i am not pointing fingure on u if u find me like that then sorry
2006-12-12 08:43:08 · answer #4 · answered by jack indian 2 · 0⤊ 1⤋
Old and boring.
2006-12-12 15:08:47 · answer #5 · answered by liketoaskq 5 · 0⤊ 1⤋