Electronic Circuits EE359A Bruce McNair B206 bmcnair@stevens.edu 201-216-5549 Lecture 20 496
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 497
Thermal resistance model Power dissipation Thermal resistance TJ TA =θjapd 498
Power derating curve Power dissipation at ambient Reduced power rating at increased temperature Maximum allowable junction temperature 499
Achieving efficient heat dissipation TO3 package Maximum heat dissipation surface Mounting holes to allow bolting to heat sink 500
Modeling heat transfer Junction temperature Heat dissipation Case temperature Heat-sink temperature Ambient temperature 501
Modeling heat transfer Junction-case thermal R Heat dissipation Case-heatsink thermal R Heatsink-ambient thermal R 502
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. 503
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 504
Increasing output power Higher operating voltage High power output stage or Higher collector current 505
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 506
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 507
NPN Darlington Pair 508
PNP Darlington Pair 509
PNP Darlington Pair NPN used because of limited PNP performance 510
AB Output Stage with Darlington Pair 511
AB Output Stage with Darlington Pair NPN Darlington push stage V BE multiplier PNP Darlington pull stage 512
What if the v O is shorted? 513
What if the v O is shorted? 514
AB amplifier with short circuit protection 515
Thermal overload protection 516
Thermal overload protection Output transistor Normally biased off 517
Thermal overload protection Thermal coupling 518
Thermal overload protection Operation shifts with changing temperature 519
Thermal overload protection Turns on, stealing Q 1 bias current, shutting off Q 1 520
Normal MOSFET 521
Normal MOSFET Thermal conduction path 522
Power MOSFET 523
Power MOSFET Thermal conduction path 524
AB amplifier with power MOSFETs and BJT drivers 525
AB amplifier with power MOSFETs and BJT drivers V BE multiplier 526
AB amplifier with power MOSFETs and BJT drivers Push-pull darlington pairs 527
AB amplifier with power MOSFETs and BJT drivers CMOS power MOSFET output 528
AB amplifier with power MOSFETs and BJT drivers Quiescent point adjustment Temperature compensation adjustment Thermal feedback control 529
AB amplifier with power MOSFETs and BJT drivers Parasitic oscillation suppression 530
AB amplifier with power MOSFETs and BJT drivers 531
Filters and Tuned Amplifiers Ch 17 532
Two-port model of filter General response: Vo () s Ts () = V() s i 533
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: 534
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 ( ) 535
Ideal filter characteristics (Low-pass) 536
Ideal filter characteristics (High-pass) 537
Ideal filter characteristics (Band-pass) 538
Ideal filter characteristics (Band-stop) 539
Practical limitations (Low-pass) 540
Practical limitations (Low-pass) Zero-width transition band Infinite attenuation in stop-band 541
Practical limitations (Low-pass) Zero-width transition band Infinite attenuation in stop-band Infinite complexity Infinite time delay 542
Practical limitations (Low-pass) impulse response input x(t) = δ (t) t output y(t) = sinc(t) = sin(t) t t 543
Practical limitations (Low-pass) impulse response input x(t) = δ (t) t output Response precedes input!! y(t) = sinc(t) = sin(t) t t 544
Example Low-pass specification Pass-band edge Stop-band edge Pass-band variation Minimum stop-band attenuation - 545
Example Band-pass specification Pass-band variation Lower stop-band edge Pass-band edges Upper stop-band edge Minimum stop-band attenuation 546
Typical Low-pass specification Often no constraints on filter curve - 547
Typical Low-pass specification Often no constraints on filter curve Might be monotonic - 548
Typical Low-pass specification Often no constraints on filter curve May have passband ripple - 549
Typical Low-pass specification Often no constraints on filter curve May have stop band ripple - 550
Typical Low-pass specification Often no constraints on filter curve May have both passband and stopband ripple - 551
Typical Low-pass specification Many different approximations to the ideal filter response - 552