I cant figure out how does this circuit work - Page 1
Forum section: electronics / beginners

author: DarkZero
author_rank: Regular Contributor
timestamp: August 07, 2015, 07:27:49 pm
content: Hello!lately i have been messing around with thyristors and high voltage stuff and i found this schematic that i just cant wrap my head around how does it work i build it and it works i just cant figure out how i guess that L and C2 are used to somehow shut down thyristor. but from my experiments the only ways i know to shut down thyristor is to bring gate directly to ground or to short anode and cathode once there is no trigger on the gate.

author: Fank1
author_rank: Regular Contributor
timestamp: August 07, 2015, 08:11:14 pm
content: T2 is an SCR, the ONLY way to turn it off once it is on is to remove the supply voltage or reverse the polarity across it which is what the coil and capacitor do.Grounding the gate does nothing once it is on.

author: piranha32
author_rank: Unknown
timestamp: August 08, 2015, 04:32:44 am
content: Quote from: DarkZero on August 07, 2015, 07:27:49 pmThis looks like a classic AC dimer circuit with resistors and diac determining firing angle. Are you sure the 700V DC is not a typo?

author: DarkZero
author_rank: Regular Contributor
timestamp: August 08, 2015, 08:56:14 am
content: Hello !yes i'm sure its DC on the output i connected 3x150W 220V buld and the circuit strobes device i found it in has transformer > bridge rectifier > High voltage High capacitance bank > this circuit, i don't like whats this circuit being used for i'm strongly against it but hey if i learn something from it great.on my "gate to gnd" i basically shorted my PS that's why it turned off stupid me ...but i still cant get it how it works how does that C2 get its negative charge?

author: SeanB
author_rank: Super Contributor
timestamp: August 08, 2015, 10:57:24 am
content: I will guess and say this is driving a DC series wound or permanent magnet motor, where the commutator will provide the voltage pulses to commutate the SCR, and the capacitor bank is small enough that the ripple voltage across it is very large, so that it basically will deliver full power into the load till the motor is running, then the ripple across the capacitor allows the voltage across the SCR anode to drop below the cathode ( held up by the motor back EMF) so it turns off for the rest of the cycle, then it will turn on again on the next cycle ( happens at twice the mains frequency because of the full wave bridge) to add power to the motor.Speed control will provide a basic rough constant speed providing there is enough load on the motor, but it will hunt at no load as the motor speeds up. Driving a fan or a machine spindle is the likely applications, where you want speed control but precision is not too critical, and there is always something absorbing energy.

author: DarkZero
author_rank: Regular Contributor
timestamp: August 08, 2015, 05:41:57 pm
content: i redrawn this circuit from a home made fish stunner and like i said when i connect light bulbs they pulse its not like dimmer circuit. i have no use of the device since i don't support this way of fishing im just interested how does C2 gets its negative charge and how it dumps it i understand the "dimmer" part of the circuit also i don't understand why convert it to DC ... wouldn't it be much simpler to bridge rectify it without capacitors