Texas Penal Code - PENAL § 2.04. Affirmative Defense

(a) An affirmative defense in this code is so labeled by the phrase:  “It is an affirmative defense to prosecution . . . .”

(b) The prosecuting attorney is not required to negate the existence of an affirmative defense in the accusation charging commission of the offense.

(c) The issue of the existence of an affirmative defense is not submitted to the jury unless evidence is admitted supporting the defense.

(d) If the issue of the existence of an affirmative defense is submitted to the jury, the court shall charge that the defendant must prove the affirmative defense by a preponderance of evidence.