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1 Transformer Coupling. 2 Introduction  Figure shown the transformer coupling to a load resistance such as a Loudspeaker in a radio.  With a transformer.

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Presentation on theme: "1 Transformer Coupling. 2 Introduction  Figure shown the transformer coupling to a load resistance such as a Loudspeaker in a radio.  With a transformer."— Presentation transcript:

1 1 Transformer Coupling

2 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)

3 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

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

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

6 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

7 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

8 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

9 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

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

11 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

12 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

13 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

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

15 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

16 16 iii) o/p load power,


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