In this paper, an AC chopper circuit, using a power transistor, is described which chops the AC voltage with a commercial frequency. The circuit is composed of a diode bridge and a power transistor in series with a load and capable of adjusting the switching frequency, fc, and the time ratio, T=ton/(ton+toff). The switching frequency and the time ratio of the AC chopper circuit depend on switching-times, that is, delay time, rise time, carrier storage time and fall time, especially in the high frequency. The upper limit of the switching frequency (about 150kHz) and the output characteristics of the circuit are investigated

Funabiki, Shigeyuki

Himei, Toyoji

Nakanishi, Senichiro

English

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Behavior of Transistor Switching in AC Chopper Circuit

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Memoirs of the School of Engineering Okayama University Vol. 12, February 1978Behavior of Transistor Switching In A C Chopper CircuitToyoji HIMEI*, Senichiro NAKANISHI*and Shigeyuki FUNABIKI*(Received December 14, 1977)SynopsisIn this paper, an AC chopper circuit, using a powertransistor, is described which chops the AC voltagewith a commercial frequency. The circuit is composed ofa diode bridge and a power transistor in series witha load and capable of adjusting the switching frequency,f c , and the time ratio, T=ton/(ton+toff). The switchingfrequency and the time ratio of the AC chopper circuitdepend on switching-times, that is, delay time, risetime, carrier storage time and fall time, especiallyin the high frequency. The upper limit of the switchingfrequency (about 150kHz) and the output characteristicsof the circuit are investigated.1. IntroductionRecently for significant advances in the electronics, transistorshave been developed in their power handling capability. Therefore, insome industrial applications, for example, inductive motor loads,. .t' . h b d' d l ) 2) 3) .c~rcu~ s us~ng power trans~stors ave een stu ~e • By us~ng powertransistors the power control circuits are expected to be smaller sizeand lighter weight, furthermore improvements in controllability andreliability also expected.Because of transistor's unidirectional switching property,the circuitis composed of a diode bridge and a power transistor. The circuit has* Department of Electrical Engineering.4546 Toyoji HIMEl, Senichichiro NAKANISHI c;nd Shigcyuki FUNABIKIabilities to adjust the switching frequency, fe, and the time ratio,T=ton/(ton+toff). The switching frequency and the time ratio dependon switching-times (delay time, rise time, carrier storage time andfall time)4), especially in the high frequency.In this paper, the upper limit of the switching frequency and theoutput characteristics of the AC chopper circuit with a resistiveload are described.2. AC Chopper CircuitFig.l shows an AC chopper circuit using a power transistor.A main circuit with a resistive load is composed of a diode bridge anda power transistor, since a transistor is an unidirectional switchingelement. A driving circuit consists of an astable multivibrator, adifferentiation circuit and a monostable multivibrator. By means ofthese circuits, the AC voltage with a commercial frequency is chopped.rv e=EmSinwt(a)R(b)Fig.l. AC chopper circuit.(a) Main circuit.(b) Driving circuit.3. Behavior of Switch3.1 Behavior of'TransistorFig.2 shows the behavior of a transistor. In this figure, eachBehavior of Transistor Switching in AC Chopper Circuit 47Fig.2.. Behavior of transistor.is defined as follows:td(delay time):the period oftime required for the currentto reach 10 per cent of itscurrent saturation.tr(rise time):the period oftime required for the currentto reach from 10 per cent to90 per cent of its currentsaturation.ts(carrier storage time) :theperiod of time for the currentto reach 90 per cent of itscurrent saturation after thebase current is removed.tf(fall time):the period oftime required for the currentto decay from 90 per cent to10 per cent of its current90%I B1o1---+,_..L--I---r---..._tIIII IIoE-To~I ,I IILIII, 10%o'------i---.,.---.--~-tIBIeIe~saturation.Using a transistor as a switch, it is necessary to supply a large basecurrent enough for a transistor to be saturated, namely lc<hFElBl.. h h " ft' t 4)Each perlod depends on lBl, lB2 and t e c aracterlstlcs 0 ranS1S ors •3.2 Behavior of AC Switch.. toI--L.---+__• t18RBehavior of AC switch,experimental result.Fig.3.current is set, switching-timesof the transistor are effectedby the external circuit, whichdetermines the collector currentin the collector current satura-tion. It is necessary for thetime ton to be shorter than theswitching period so that theswitch perfectly turns on andFig.3 shows the behavior of the AC switch using a diode bridgeand a power transistor. The ratings of a transistor and a diode in thiscircuit are given in Table 1 and 2, respectively. The behavior of thisswitch is similar to that of the transistor, because its behaviordepends prominently on thetransistor. When the base48 Toyoji HIMEl, Senichichiro NAKANISHI and Shig-c:,uki FUNABIKITable.l. Rating of transistor (2SD641).Term Symbol Rating unitCollector to base voltage, dc, VCBO 600 Vemitter openCollector to emitter voltage, dc,VCEO 400 Vbase openEmitter to base voltage, dc, VEBO 5 Vcollector openCollector current, dc I C 15 AEmi tter current, dc IE -15 ABase current, dc IB 5 ACollector power dissipation Pc 150 WJunction temperature T" 150 DCJ. storage temperature Tstg -65"'150 DCTable.2. Rating of diode (SR30C-IO).Term Symbol Rating UnitRepetitive peak reverse voltage VRRM 500 VNon-repetitive peak reverse voltage VRSIvI 600 VReverse voltage, dc VR{DC) 400 VRMS forward current Ip{RMS) 47 AAverage forwa,rd current Ip{AV) 30 ASurge forward current IpSM 500 AJunction temperature T" -40"'125 DCJStorage temperature Tstg -40-150 DCBehavior of Transistor Switching in AC Chopper Circuitoff. In the AC chopper circuit, the perfect switching function isprevented in the neighborhood of a zero of the sinusoidal supplyvoltage. When IBl=lOOmA and IB2=67mA, each time, Tl(=td+tr) and tf,is shorter than 1.Ovs.49R=160nR=100flR= 40flR= 20fl1210842- - -...:..:.==-::-=..----=-": ==::=.-,;,'::';;=------ ------~ ~~,~/,/',''/:il,I.",~,'t,0~--'-:- .L-----L_--l..----1_---l...-_L-_o 10 20 30 40 50 60 70TO (1-1 5)Fig.4. Carrier Storage time t s vs. TO,experimental result, Vcc=lOV.Fig.4 shows the storage time t s vs. TO, where Vcc=lOV. In f c =50kHzand R=lOOn, TO must be shorter than lOvs in order that this switchoperates perfectly. The time TO is longer than Tl in order for thisswitch to turn on, that is, the time TO must be longer than 2.0vs.On that occasion, since ts=3.5vs and tf=l.Ovs, the upper limit of theswitching frequency is about 150kHz.It will be necessary to take notice of characteristics of a drivingcircuit in the higher frequency.4. Characteristics of AC Chopper CircuitFig.5 shows oscillograms of voltage waveforms. If diodes and atransistor are assumed to be ideal elements, RMS load voltage, RMScurrent, power, power factor and distortion factor are represented50 Toyoji mMEI, Senichichiro NAKANISm and Shigeyuki. FUNABIKI(a)(c)(b)Fig.s. Oscillograms of voltage and current waveforms,E=40V, fc=lOkHz, R=40n, timebase: 2ms/div.(a) Supply voltage waveform, sOV/div.(b) Load voltage waveform, 20V/div.(c) Transistor voltage waveform, sOV/div.as follows:RMS load voltage VL=EIT.RMS current I=VL/R=EIT/R.Power p=E 2 i/R.Power factor P.F.=IT.Distortion factor D.F.=jl~T x 100.Fig.6 shows RMS load voltage and RMS current calculated and measured,respectively. Due to the switching characteristics of transistors asdescribed in the previous section and the switching loss, errorsbetween the calculated and the measured are large in the high frequencyThe load voltage waveform is expanded in a Fourier series as follow:TEmsinwt + E ~ sin nTIT;[sin { (nwc+w) t-nTIT }-sin{ (nwc-w) t-mn}]n=l TInBehavior. of Transistor Switching in AC Chopper Circuit- CALCULATEDlC : fc =4800MEASillEDo : fc =96001.0><{::: 0.5o 01--_-'--_--'--_---'--_---'-_---'o 0.2 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 1.0TIME RATIO T TIME RATIO T(a) (b)Fig.6. RMS load voltage and RMS current, E=lOOV and R=lOOn.(a) RMS load voltage.(b) RMS current.51where wc=2nfc ' w=2nf.Hence, a fundamental power factor is always 1.0 and it is found thatlower components of higher harmonics don't appear.5. ConclusionsIn this paper~ the AC chopper circuit using a power transistor isdescribed. The switching characteristics of the AC switch depend onswitching-times of a transistor~ especially in the high frequency.Also switching-times are effected by the external circuit. WhenIB1=100mA and IB2=67mA, the upper limit of the switching frequency isabout 150kHz.It will be necessary to take account of characteristics of a drivingcircuit in the higher frequency.References1) A.Mozder and B.K.Bose, IEEE Trans. Ind. AppZi, vol.IA-12, No.5,pp.499-505, 1976.2) T.Himei, S.Nakanishi and S.Funabiki, 1977 Nat'Z Conv. Inst. EZec. Engrs.~52 Toyoji HIMEl, Senichichiro NAKANISHI and Shigeyuki FUNABIKIJapan, No. 954.3) T.Himei, S.Nakanishi and S.Funabiki, 1977 Chugoku Branah Joint ConvFour Insts. EZea. Engrs., Japan, No.8070l.4) J.L.Mo11, Proa. I.R.E., vol.42, No.12, pp.1773-1784, 1954.

Behavior of Transistor Switching in AC Chopper Circuit

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