A single-phase thyristor-bridge rectifier is fed from a $230 V, 50 Hz$, single-phase $AC$ mains. If it is delivering a constant $DC$ current of $10 A$, at firing angle of $30^\circ$, then value of the power factor at $AC$ mains is
- $0.87$
- $0.9$
- $0.78$
- $0.45$