Play Meter

TECHNICAL TOPICS CO By Ed Ed Anderson Anderson of of Electronic Electronic Service Service By Power supplies Powe r suppl ies 7 only conducts conducts when wh~n the the cathode cathode is is itit only To get get two two DC DC pulses pulses every every cycle, cycle, To need aa full full wave wave rectifier. rectifier. ItIt is is you need you more efficient efficient and and easier easier to to filter filter and and more always used used in in high high current current isis always common is the full full applications. Most the is common applications. Most wave center centertap tap circuit. circuit. IfIf we we take take the the wave center tap tap transformer transformer in in that that early early center and add add aa half half wave wave rectifier rectifier example and example to each each leg leg and and tie tie the the two two outputs outputs to together, each each diode diode will will contribute contribute together, the positive positive half half cycle cycle of of the the AC AC the voltage to to which which itit isis connected connected (see (see voltage Figure Three). Three) . The The voltage voltage at at one one leg leg Figure positive while while the the other other isis negative. negative . isis positive And the the DC DC pulses pulses out out of of each each And rectifier can't can't happen happen at at the the same same rectifier time; so so we we get get two two pulses pulses out out for for time; full wave wave center center tap tap each cycle. cycle. A A full each circuit isis nearly nearly always always used used in in the the circuit negative with with respect respect to to the the anode. anode. negative The circuit circuitshown shown in in Figure FigureTwo Two isis The called aa half-wave half-wave rectifier. rectifier. Notice Notice called the direction direction of of the the diode diode (In (In circuit, circuit, the the cathode cathode isis always always marked marked by by aa the The dotted dotted wave wave form form band). The band). represents the the AC ACinput input to to the the diode. diode . represents The voltage voltage isis alternating alternating between between The and negative negative but but the the diode diode positive and positive the positive half only conducts during only conducts during the positive half cycle. During During the the negative negative half half cycle, cycle, cycle. the cathode cathode of of the the diode diode isis positive positive the andititisis cut cut off. off. Thus Thus the the output output after after and the rectifier is a positive DC pulse the rectifier is a positive DC pulse the diode diode were were every cycle. cycle. IfIf the every the output would be reversed, reversed, the outputwould be negative. negative. 110 VAL 8 XFMR GNO Ano 8 VAL -0 8 VAL Figure One One Figure ANODE V CATHODE D Half-Wave Rectifier Half -Wave Recti fier Figure Two Figure Two +01 $ Anything that that plugs plugs into into aa wall wall Anything outlet and and does does more more than than just just make make outlet light or or run run aa motor motor probably probably uses uses aa light power supply. supply. Logic Logic boards, boards, T.V. T.V. power monitors , audio amplifiers, and any monitors, audio amplifiers, and any other kind kind of of electronic electronic equipment equipment other will use use at at least least one one filtered filtered DC DC will supply. supply. There are are many many ways ways to to convert convert There the rough rough AC AC lurking lurkingin in the the wall wall to to aa the but usable solid solid state state supply supply voltage voltage but usable there are are only only four four common common building building there blocks: aa transformer transformer to to get get the the right right blocks: to get get DC DC from from the the voltage; aa rectifier rectifierto voltage; AC out out of of the the transformer; transformer; aa filter filter to to AC smooth out out the the DC DC pulses; pulses; and, and, smooth when necessary, necessary, aa regulator regulator to to give give aa when output under under aa constant voltage voltage output constant changing load. load. We'll We'll concern concern ourourchanging power supplies supplies for for now now selves with with power selves and explain explain regulators regulators in in detail detail in in aa and future article. article. future the simplest, simplest, transformer isis the AA transformer safest, and and most most versatile versatile way way to to get get safest, the AC AC voltage voltage needed. needed . The The primary primary the electrically isolated isolated from from the the input isis electrically input secondary output output so so that that innocent innocent secondary people don't don't get get electrocuted electrocuted when when people the line line cord cord isis plugged plugged in in upside upside the down. ItIt isis very very efficient efficient so so itit doesn't doesn't down. waste power power making making heat heat like like aa waste resistor does. does. resistor There can can be be more more than than one one There secondary winding winding for for separate separate secondary supplies or or extra extra taps taps on on aa winding winding supplies more than than one one voltage voltage output. output. for more for For example example (in (in Figure Figure One), One) , aa For 16-volt center center tapped tapped transformer transformer 16-volt tap in in has aa 16-volt 16-volt winding winding with with aa tap has the middle. middle . An An AC AC voltmeter voltmeter will will the read 88 volts volts from from the the center center to to either either read end;but but while while the the voltage voltage at at one one end end end; going positive, positive , the the other other end end is is isis going going negative. negative. going The next next stage stage of of the the power power The supply isis the the rectifier. rectifier. Silicon Silicon diodes diodes supply used in in low low voltage, voltage , high high are always always used are currentapplications applicationsas asfound found in in video video current games. A A diode diode can can be be thought thought of of as as games. one-wav valve valve for for current currPnt because hPr:ri11sP aa one-way