# Thyristor as a switch

#### Momentory

Joined Sep 4, 2022
67
Assuming i have a circuit like this

Batteries 220v - Capacitor 300v 1000uf - thyristor 1200v- 50A - load

Connected AAA battery with required thyristor gate voltage and current to switch the thyristor on

(It is assuming circuit not i won't to make, just want understanding how thyristor and capacitor work in same circuit)

My question
Will the thyristor turn off when the cap discharged?

Note the cap will be charged immediately after discharging

#### Ian0

Joined Aug 7, 2020
6,287
Assuming i have a circuit like this

Batteries 220v - Capacitor 300v 1000uf - thyristor 1200v- 50A - load

Connected AAA battery with required thyristor gate voltage and current to switch the thyristor on

(It is assuming circuit not i won't to make, just want understanding how thyristor and capacitor work in same circuit)

View attachment 275619

My question
Will the thyristor turn off when the cap discharged?

Note the cap will be charged immediately after discharging
Yes, it would, but you have a 220V voltage source that is keeping it charged.
(Your thyristor is the wrong way round, and the main circuit has no earth reference, so it would never switch on)

#### MrChips

Joined Oct 2, 2009
27,115
Thyristors do not turn off DC voltages.

#### Momentory

Joined Sep 4, 2022
67
Yes, it would, but you have a 220V voltage source that is keeping it charged.
(Your thyristor is the wrong way round, and the main circuit has no earth reference, so it would never switch on)
Sorry i am not sure i understand you

Regardless the thyristor direction and the ground of main circuit
I mad this circuit fast just as assuming

i just want to know will the thyristor turn off after cap discharged and there is a power supply will charge the cap

#### Momentory

Joined Sep 4, 2022
67
Thyristors do not turn off DC voltages.
Actually it dc with the Dc you need to make the current low than holding current or completely cut the circuit

#### Ian0

Joined Aug 7, 2020
6,287
The thyristor turns off when the anode current falls below the holding current.
However, the datasheet will only specify a maximum holding current. The minimum holding current, below which the device is guaranteed to switch off is unlikely to be specified.

#### Momentory

Joined Sep 4, 2022
67
The thyristor turns off when the anode current falls below the holding current.
However, the datasheet will only specify a maximum holding current. The minimum holding current, below which the device is guaranteed to switch off is unlikely to be specified.
After capacitor discharged the current should be zero, right?
Or as the cap will immediately charging the current will not be zero?

#### Ian0

Joined Aug 7, 2020
6,287
After capacitor discharged the current should be zero, right?
Or as the cap will immediately charging the current will not be zero?
If the capacitor remains connected to the power supply, it won't discharge.

#### Momentory

Joined Sep 4, 2022
67
If the capacitor remains connected to the power supply, it won't discharge.
So is there any solution to make the capacitor discharge without switch between cap and P. supply

#### Ian0

Joined Aug 7, 2020
6,287
So is there any solution to make the capacitor discharge without switch between cap and P. supply
No.

#### Momentory

Joined Sep 4, 2022
67
If we set Power supply max output 0.2A and thyristor holding current 500mh
will face same problem?

#### Ian0

Joined Aug 7, 2020
6,287
That would hypothetically work, but the holding current of a 50A thyrsitor would probably be less than 100mA

#### Momentory

Joined Sep 4, 2022
67
That would hypothetically work, but the holding current of a 50A thyrsitor would probably be less than 100mA
The whole circuit is hypothetically , i am just trying to understand the relation between power supply, cap and thyristor in one circuit

Thanks for really usefull info
I really appreciate

#### Ramussons

Joined May 3, 2013
1,316
Assuming i have a circuit like this

Batteries 220v - Capacitor 300v 1000uf - thyristor 1200v- 50A - load

Connected AAA battery with required thyristor gate voltage and current to switch the thyristor on

(It is assuming circuit not i won't to make, just want understanding how thyristor and capacitor work in same circuit)

View attachment 275619

My question
Will the thyristor turn off when the cap discharged?

Note the cap will be charged immediately after discharging
V1 is reversed. The SCR will never conduct. Correct the polarity of V1.

The Thyristor requires a Gate current to turn ON. The way the schematic is drawn, there is no way to turn on the Thyristor.
The -ve of V2 will need to be connected to the -ve of V1 (after correcting the polarity). You will also need to put a current limiting resistor in series with the SCR gate.

R1 is the load through which the Capacitor will discharge. If you put a resistor R2 in series with V1 +ve (after polarity correction), then when the SCR fires, the capacitor will discharge and if the current flow through R2 ( ~ V1/ (R1 + R2) is less than the minimum holding current of the SCR, yes , it will turn OFF.