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19 Threads found on edaboard.com: Scr Turn Off
Hi Guys, Im having a bit of trouble with a circuit. Please see schematic below. the top portion is a Capacitor Discharge Ignition circuit using a scr, this is triggered by a microcontroller (not in schematic), the second portion is a 150-250V DC generator using a Step-Up DC-DC Controller (using the
The block diagram seems flawed, don't know if also the real circuit. What's the purpose of a controlled scr rectifier after a bridge rectifier with filter capacitor? How can the scr ever turn off? Would you mind to sketch a real schematic? I'm aware that the circuit needs a transformer and output coil but I would (...)
Electric Fields are inherently high impedance and impulse EMF are exceptional wide bandwidth. What range of levels and frequency are you hoping to detect in uV and Hz? A cheap FET gives the impedance required but further signal amplification is required to trigger a latch such as a small signal scr to turn off an LED driver, thus at (...)
SSR =Solid State Relay, which is what you asked for. However, as you have found, most SSR are used in AC applications where they inherently turn off when the control voltage is removed. In a DC application, an AC circuit using a triac or scr will not work unless you have a method of disrupting the current to turn them (...)
Here is an old presentation on an scr upgrade to IGBT's FWIW
Well the device you called a scr, but a scr only conducts when its anode is positive, so it is only used for DC unless there is a diode across it to conduct when the supply goes negative. A triac is like a like a pair of back- to-back scrs, so it conducts when the supply is positive or negative, so its used for AC. Frank
ADC reads the voltage on the battery (VRLA 12V / LC-R127R2NA Panasonic). If the battery voltage is below 11V then the microcontroller turn on the scr. if the battery voltage is greater then 14.4V the microcontroller turn off the scr. Need Help: *)Is there a better way to charge VRLA baterrey ? *)Is (...)
Thyristors and triacs have been used for 3 phase motor speed control. The method is different. The AC is not rectified, snubbers and inductances are used to turn off the scr once it started conduction. You can search for cycloconverter to see how it works. Some schemes uses GTOs that are basically thyristors that you can (...)
You have to pass current through the LED side of the opto-coupler for it to work. When it conducts, the first transistor turns off, this turns the second transistor on and fires the scr to make the light turn on. scrs stay conducting until the current through them is removed so once (...)
In your original post, you have written "turn on and off High Voltage", which means DC voltage as clarified. A scr can't be (or at least not easily) switched off. For a capacitor discharge circuit this isn't necessary a problem if the capacitor is discharged completely because the scr (...)
As the most serious problem, a scr can't be turned off without an additional "extinguishing" circuit. If turn-off fails, the input voltage will be shorted and can be only interrupted by a fuse. In addition, a scr has a on-state voltage above 1 V, which is quite a lot with 10 V input.
he said that to overcome this problem, an IGBT should be used instead of an scr The suggestion doesn't seem to solve a problem (if any exist) but creates new instead. Unlike a scr, a basic iGBT has no reverse blocking capabiliities, it can be even damaged by applying a reverse voltage. The basic difference is it's turn-off (...)
the 470 ohm resitance discharge the capacitor when the scr is off, and the scr charge the capacitor when swiched on, but the scr cannot stay on because when the capacitor is charged, the scr current will be to low (below holding). so the scr goto off state...
The scr will be the rectifier. The top two transistors are actually powered at DC by the battery itself. If the battery voltage is below the threshold set by the pot (it's discharged), then the top right transistor will be off. The left transistor will then be on and it can turn on the scr through the LED and diode. (...)
Traic and scr are also used at optocoupler, because they are cheep and faster.
Once scr begins to conduct, it is latched on and it cannot be turn off by the gate, only when reversing polarized. GTO can turned off aplying a negative gate-cathode voltage. There are three significant differences between a GTO and a scr. First the gate and cathode structures are (...)
Yes, this is exactly my scheme... Except voltage - I have +5V not +12V Could it be cause that scr doesn't turning on? It will turn on once you've supplied the gate of the scr. But it will turn off when you remove the gate supply if your current flowing in the scr is not (...)
Why do you want to use a scr to control LED's. You can use a microcontroller to check the no of switch On states and switch on ur led's. You can also use a decoder, if you want to use few switches and more outputs scr's are mostly used where you need to leave ckt ON once it is triggered. Also you need another switch to turn (...)
one thing that i did not understand was the way to turn off a scr! you simply "wait" for to turn off? when a gate current it given, the scr turns on, then i still behaves like an open circuit for how long? it's until the sine wave reaches a certain value of voltage (...)