What is the duty of a trial court to instruct a jury on an affirmative defense?

"In a criminal case, a trial court has a duty to instruct the jury on ' " ' "the general principles of law relevant to the issues raised by the evidence." ' " ' [Citation.] The 'general principles of law governing the case' are those principles connected with the evidence and which are necessary for the jury's understanding of the case. [Citations.] As to pertinent matters falling outside the definition of a 'general principle of law governing the case,' it is 'defendant's obligation to request any clarifying or amplifying instruction.' [Citation.]" (People v. Estrada (1995) 11 Cal.4th 568, 574.)

A trial court has a duty to instruct sua sponte on an affirmative defense "only if it appears that the defendant was relying on the defense, or that there was substantial evidence supportive of the defense, and the defense was not inconsistent with the defendant's theory of the case. [Citations.]" (People v. Michaels (2002) 28 Cal.4th 486, 529.) "A jury instruction need not be given whenever any evidence is presented, no matter how weak. [Citation.] Rather, the accused must present 'evidence sufficient to deserve consideration by the jury, i.e., evidence from which a jury composed of reasonable men [and women] could have concluded that the particular facts underlying the instruction did exist. [Citation.] [] This does not requireor permitthe trial court to determine the credibility of witnesses. It simply frees the court from any obligation to present theories to the jury which the jury could not reasonably find to exist.' " (People v. Strozier (1993) 20 Cal.App.4th 55, 63.)