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Published byMicaela Broadhurst Modified about 1 year ago

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1 Transformer Coupling

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2 Introduction Figure shown the transformer coupling to a load resistance such as a Loudspeaker in a radio. With a transformer – the small load resistance can be stepped up to a higher impedance level This improve the voltage gain – also since no signal power is wasted in a collector resistor, all the ac power is delivered to the final load resistor Very popular at audio frequencies (20 Hz - 20 kHz)

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3 AMPLIFIER AMPLIFIER OBJECTIVE PROVIDE V, I, POWER to the LOAD most efficiently C R B1 V out V CC V in(ac) R gen R B2 RCRC RLRL C RERE

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4 AMPLIFIER POWER LOSS C R B1 V out V CC V in(ac) R gen R B2 RCRC RLRL C RERE

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5 TRANSFORMERS V & I transformation n :1 N prim : N sec V prim V sec I prim I sec I & V ONLY ac

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6 TRANSFORMERS Z & R transformation I & V ONLY ac n :1 N prim : N sec V prim V sec I prim I sec Z sec Z prim

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7 TRANSFORMER COUPLED AMPLIFIER C R B1 V out V CC n :1 V in(ac) R gen R B2 RLRL V ou t V CC n :1 V in(ac) RLRL

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8 TRANSFORMER COUPLED AMPLIFIER C R B1 V out V CC n :1 V in(ac) R gen R B2 RLRL V CC R B2 R B1 R primDC DC EQUIVALENT CIRCUIT IDEALLY R prim,DC = 0

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9 TRANSFORMER COUPLED AMPLIFIER C R B1 V out V CC n :1 V in(ac) R gen R B2 RLRL C R B1 V CC V in(ac) R gen R B2 R sec,ac ac EQUIVALENT CIRCUIT R prim,ac = n 2 R L

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10 TRANSFORMER COUPLED AMPLIFIER DC LOAD LINE ‘ideal’ DC load line ‘Q’ point determined by BIAS CIRCUIT V CEQ = V CC Q

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11 TRANSFORMER COUPLED AMPLIFIER ac LOAD LINE ‘ideal’ DC load line ‘Q’ point determined by BIAS CIRCUIT V CEQ = V CC Q ac load line 2V CC OPERATION maximum output voltage

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12 TRANSFORMER COUPLED AMPLIFIERS Advantages: electrical isolation: SAFETY NO XC voltage drop : input higher efficiency : no RC power loss zero or 180 degree phase shift : DOT NOTATION impedance matching : better power transfer voltage / current transformation : can be used as a ‘gain’ stage Disadvantages: COST WEIGHT frequency response SIZE : reduces as frequency increases

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13 EXAMPLE: C RERE R B2 R B1 V out V CC 20 V RLRL k :1 V in(ac) k :1 R gen Determine the amplifier i)Q-point ii)Operating Q-point for the max. o/p iii)i/p impedance, iv)o/p load power

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14 SOLUTION: i)Q-point ii) Operating Q-point for the max. o/p

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15 iii) i/p impedance, C RERE R B2 R B1 k :1 V in(ac) k :1 R gen R in V out RLRL R inb

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16 iii) o/p load power,

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