* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Power Supply Decoupling
Standby power wikipedia , lookup
Power inverter wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Wireless power transfer wikipedia , lookup
Power factor wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Earthing system wikipedia , lookup
Power over Ethernet wikipedia , lookup
Buck converter wikipedia , lookup
Three-phase electric power wikipedia , lookup
Audio power wikipedia , lookup
Electrical substation wikipedia , lookup
Electric power system wikipedia , lookup
Voltage optimisation wikipedia , lookup
Electrification wikipedia , lookup
History of electric power transmission wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Alternating current wikipedia , lookup
Power engineering wikipedia , lookup
Electromagnetic compatibility wikipedia , lookup
Power supply wikipedia , lookup
Power Supply Decoupling The objective of a power distribution system is: 1. 2. Supply a nearly constant dc voltage to all loads under conditions of varying load currents. Any ac noise signals generated by the load should not generate an ac voltage across the dc power bus. A typical power distribution system as it might appear on a schematic Fuse A local decoupling capacitor JHLin, EMC; Balacing & Filtering 1 Power Supply Decoupling The actual circuit for a dc power distribution system, including parasitics JHLin, EMC; Balacing & Filtering 2 Power Supply Decoupling Circuit of Fig. 4-15, less the decoupling capacitor and noise pickup voltage The performance of the power distribution system: 1. The static or dc performance of the system. 2. The transient or noise performance of the system. JHLin, EMC; Balacing & Filtering 3 Power Supply Decoupling The minimum dc voltage is VL (min) Vdc (min) I L (max) ( RS RF RT ) max . Transient noise voltages on the power distribution circuit are produced by sudden changes in the current demand of the load. VL I L Z 0 where Z 0 LT . CT For best noise performance, a power distribution system transmission line with as low as a Z 0 as possible is desired --typically 1 or less. JHLin, EMC; Balacing & Filtering 4 5 Power Supply Decoupling 6 Power Supply Decoupling The optimum power distribution line would be one with parallel flat conductors, as wide as possible, placed one on top of the other, and as close together as possible. JHLin, EMC; Balacing & Filtering 7 Power Supply Decoupling Demonstration of the difficulty in providing power distribution systems with very low Z 0 . D d 1.5 Teflon dielectric t 0.0027 in w 0.02 in h 0.04 in epoxy glass PCB w 0.25 in h 0.005 in of Mylar JHLin, EMC; Balacing & Filtering 8 Power Supply Decoupling To achieve the desired low impedance, decoupling capacitors can be placed across the power bus at the load end. Although this is a good approach, a discrete capacitor will not maintain its low impedance at high frequencies, because of series inductance. Low-Frequency Analog Circuit Decoupling 9 10 Power Supply Decoupling 1. 2. 3. The inductor used must also be able to pass the direct current required by the circuit without saturation. A second capacitor, such as those shown dashed in Fig. 4-18, can be added to each section to increasing filtering to noise being fed back to the power supply from the circuit. This turns the filter into a network.. When considering noise, a dissipative filter such as the R-C circuit is preferred to a reactive filter, such as the L-C circuit. Amplifier Decoupling 1. Even if only a single amplifier is connected to a power supply, consideration of the impedance of the power supply is usually required. JHLin, EMC; Balacing & Filtering 11 Power Supply Decoupling 2. The capacitor should serve as a short circuit across the frequency range over which the amplifier is capable of producing gain. JHLin, EMC; Balacing & Filtering 12 Driving Capacitive Loads An emitter follower, which feeds a capacitive load such as a transmission line, is especially susceptible to high-frequency oscillation caused by inadequate power-supply decoupling. Voltage gain Zc Ze 13 Driving Capacitive Loads Emitter follower decoupled from power supply JHLin, EMC; Balacing & Filtering 14 Driving Capacitive Loads The feedback can be decreased even more by adding an R-C filter in the power supply to the first stage. 15 Driving Capacitive Loads An op-amp is driving a heavy capacitive load. The Ro and CL from a low-pass filter that adds phase shift to the output signal. Break frequency f B One solution: 1 2 Ro CL Ro Another solution 16 System Bandwidth One simple but often overlooked method of minimizing noise in a system is to limit the system bandwidth to only that required by the intended signal. High-speed logic (fast rise time) is much more likely to generate and be susceptible to high-frequency noise than its lower speed counterpart. JHLin, EMC; Balacing & Filtering 17 Modulation and Coding The susceptibility of a system to interference is a function not only of the shielding, grounding, cabling, and so on, but also of the coding or modulating scheme used for the signal. JHLin, EMC; Balacing & Filtering 18