Bipolar transistor anti-saturation clamp using auxiliary bipolar stage, and method

An output stage (1-2) includes a gain circuit (Q1,Q2) for driving a base of a main transistor (Q3) having a collector coupled to an output (18) in response to an input signal V11) which also controls a base of an auxiliary transistor (Q7) having a collector coupled to the output. A clamping transistor (Q6) has a control electrode coupled to the base of the auxiliary transistor, a first electrode coupled to the output, and a second electrode coupled to provide feedback from the output via the gain circuit to the base of the main transistor and to provide feedback from the output to the base of the auxiliary transistor. When the auxiliary transistor goes into deep saturation it causes the clamping transistor to provide negative feedback from the output to the main output stage so as to prevent the main transistor from going into deep saturation.