Electronic Circuits EE359A Bruce McNair B206 bmcnair@stevens.edu 201-216-5549 Lecture 18 488
Class C operation 4 2 h( t) 0 2 4 0 0.2 0.4 0.6 0.8 t 0 ( ) 20 log A j 20 40 60 0 10 20 30 Cconduction_angle j π 3 489
Class C operation 4 2 h( t) 0 2 4 0 0.2 0.4 0.6 0.8 t 0 ( ) 20 log A j 20 40 60 0 10 20 30 Cconduction_angle j π 8 490
Power BJTs Collector currents in the multi-ampere range Multi-watt power dissipation Achieved by: High temperature tolerant designs (T J up to 200 o C) Effective heat dissipation design 491
Thermal resistance model Power dissipation Thermal resistance TJ TA =θjapd 492
Power derating curve Power dissipation at ambient Reduced power rating at increased temperature Maximum allowable junction temperature 493
Achieving efficient heat dissipation TO3 package Maximum heat dissipation surface Mounting holes to allow bolting to heat sink 494
Modeling heat transfer Junction temperature Heat dissipation Case temperature Heat-sink temperature Ambient temperature 495
Modeling heat transfer Junction-case thermal R Heat dissipation Case-heatsink thermal R Heatsink-ambient thermal R 496
Modeling heat transfer Heat dissipation Junction-case thermal R Function of transistor/ case design Case-heatsink thermal R Function of bonding transistor to heatsink Heatsink-ambient thermal R Function of heatsink cooling, e.g., conduction, convection, radiation, etc. 497
Multistage amplifiers - rationale High input Z for minimal loading High power output (differential input for noise immunity) High gain (in multiple stages) Low output Z for minimal impact from load 498
Increasing output power Higher operating voltage High power output stage or Higher collector current 499
Increasing output power High power output stage Higher operating voltage or Higher collector current Limitation of V CC Breakdown voltage Output impedance may be small 500
Increasing output power High power output stage Higher operating voltage or Higher collector current Limitation of V CC Breakdown voltage Output impedance may be small Darlington configuration for increased β 501
NPN Darlington Pair 502
PNP Darlington Pair 503
PNP Darlington Pair NPN used because of limited PNP performance 504
AB Output Stage with Darlington Pair 505
AB Output Stage with Darlington Pair NPN Darlington push stage V BE multiplier PNP Darlington pull stage 506
What if the v O is shorted? 507
What if the v O is shorted? 508
AB amplifier with short circuit protection 509
Thermal overload protection 510
Thermal overload protection Output transistor Normally biased off 511
Thermal overload protection Thermal coupling 512
Thermal overload protection Operation shifts with changing temperature 513
Thermal overload protection Turns on, stealing Q 1 bias current, shutting off Q 1 514
Normal MOSFET 515
Normal MOSFET Thermal conduction path 516
Power MOSFET 517
Power MOSFET Thermal conduction path 518
AB amplifier with power MOSFETs and BJT drivers 519
AB amplifier with power MOSFETs and BJT drivers V BE multiplier 520
AB amplifier with power MOSFETs and BJT drivers Push-pull darlington pairs 521
AB amplifier with power MOSFETs and BJT drivers CMOS power MOSFET output 522
AB amplifier with power MOSFETs and BJT drivers Quiescent point adjustment Temperature compensation adjustment Thermal feedback control 523
AB amplifier with power MOSFETs and BJT drivers Parasitic oscillation suppression 524
AB amplifier with power MOSFETs and BJT drivers 525
Filters and Tuned Amplifiers Ch 17 526
Two-port model of filter General response: Vo () s Ts () = V() s i 527
Two-port model of filter General response: Vo () s Ts () = V() s j ( ) T( jω) = T( jω) e φω i Substituting s = jω and using polar representation: 528
Two-port model of filter General response: Vo () s Ts () = V() s j ( ) T( jω) = T( jω) e φω i Substituting s = jω and using polar representation: ( T jω ) G( ω) = 20log ( ) Gain/Attenuation in db: ( T jω ) A( ω) = 20log ( ) 529
Ideal filter characteristics (Low-pass) 530
Ideal filter characteristics (High-pass) 531
Ideal filter characteristics (Band-pass) 532
Ideal filter characteristics (Band-stop) 533
Practical limitations (Low-pass) 534
Practical limitations (Low-pass) Zero-width transition band Infinite attenuation in stop-band 535
Practical limitations (Low-pass) Zero-width transition band Infinite attenuation in stop-band Infinite complexity Infinite time delay 536
Practical limitations (Low-pass) impulse response input x(t) = δ (t) t output y(t) = sinc(t) = sin(t) t t 537
Practical limitations (Low-pass) impulse response input x(t) = δ (t) t output Response precedes input!! y(t) = sinc(t) = sin(t) t t 538
Example Low-pass specification Pass-band edge Stop-band edge Pass-band variation Minimum stop-band attenuation - 539
Example Band-pass specification Pass-band variation Lower stop-band edge Pass-band edges Upper stop-band edge Minimum stop-band attenuation 540
Typical Low-pass specification Often no constraints on filter curve - 541
Typical Low-pass specification Often no constraints on filter curve Might be monotonic - 542
Typical Low-pass specification Often no constraints on filter curve May have passband ripple - 543
Typical Low-pass specification Often no constraints on filter curve May have stop band ripple - 544
Typical Low-pass specification Often no constraints on filter curve May have both passband and stopband ripple - 545
Typical Low-pass specification Many different approximations to the ideal filter response - 546