Discharge of a Capacitor through an Inductance with thyristor  - Page 1
Forum section: electronics / beginners

author: Stan21
author_rank: Contributor
timestamp: June 11, 2024, 05:59:33 am
content: From different sources I see there are two possible component arrangements (see below)What is the functional difference and is there any?(thyristor control circuit skipped; 'TR' - ignition coil primary)

author: MrAl
author_rank: Super Contributor
timestamp: June 11, 2024, 08:15:05 am
content: Quote from: Stan21 on June 11, 2024, 05:59:33 amHi,After a quick look, #2 is easier to turn the SCR on because the cathode is grounded. #1 could be modified with the SCR cathode at ground too though and not change anything. As it stands, #1 needs a 'floating' turn-on driver while #2 does not. If the SCR in #1 is moved to the lower side of the inductor though then it can also use a common ground driver also.#2 would have much less inrush current when the circuit is first connected to Vcc with the SCR 'off'.

author: aliarifat794
author_rank: Regular Contributor
timestamp: June 11, 2024, 11:17:01 am
content: Both circuits are designed to trigger the thyristor and consequently the ignition coil. Their functional difference lies in the charging and discharging paths of the capacitor, which affects the timing and behavior of the thyristor triggering.

author: CaptDon
author_rank: Super Contributor
timestamp: June 11, 2024, 12:58:00 pm
content: Circuit #1 is NOT seen in ignition circuits due to the requirement of a floating gate driver and the fact that the entire SCR would bounce up and down electrically with the ring voltage. Circuit #2 is more common and in addition the same circuit used to trigger the SCR usually mutes the high voltage power oscillator briefly so that the SCR can have enough time to be guaranteed to return to the off state. This very same circuit with a few tiny modifications is used in the pulsing of radar magnetrons.

author: CaptDon
author_rank: Super Contributor
timestamp: June 11, 2024, 01:06:06 pm
content: In circuit #1 the problem is also if the resistor is small and the charge current high the SCR may lock up in the on state. If it does then power must be removed to reset the SCR. This is why when the charging current comes from a power oscillator and rectifier the power oscillator is muted while the SCR is triggered and remains muted for a safety margin of time until the SCR has definately unlatched.

author: MrAl
author_rank: Super Contributor
timestamp: June 12, 2024, 03:44:26 pm
content: Quote from: CaptDon on June 11, 2024, 12:58:00 pmThat was my complaint also.I was trained in Jazz guitar, but played classical as well. Loved the John Williams stuff, played a lot of that.Strange, I was in mostly Rock bands earlier onThey were in more demand.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 13, 2024, 10:05:21 am
content: If you use a pulse transformer it frees up the options on the topolgy.eg Murata 772 or Vishay PT50 series. Rise times are sub mS when properly driven.Its always a good idea to use isolated gate drive, it keeps the control circuit from sudden death.A good investment.You may need an RC damper and/ or freewheel diode to keep the scr safe from back emf.Back emf can put the scr into avalance breakdown and possible destruction.See 9.2 in attached pdf , in this case your L would be their Lstray

author: Stan21
author_rank: Contributor
timestamp: June 17, 2024, 07:14:29 pm
content: Actually I use not a thyristor per se, but FLC10 chip designed for automatic discharge;with VCC 280v, 1k resistor and 1uF capacitor it gives nice 300 Hz spark at ignition coil secondary; I use layout 1 from initial post