electronic switches and control circuits · 2020. 8. 6. · with signal and power switching...

NASA SP-5948(01)

TECHNOLOGY UTILIZATION

ELECTRONIC SWITCHESAND

CONTROL CIRCUITS

CASE FILECOPY

A COMPILATION

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

ForewordThe National Aeronautics and Space Adminis t ra t ion and the Atomic Energy

Commission have established a Technology Util ization Program for the dissemina-tion of information on technological developments which have potential utili tyoutside the aerospace and nuclear communities. By encouraging mul t ip le applica-tion of the results of their research and development, NASA and AEC earn forthe public an increased return on the investment in aerospace research anddevelopment programs.

The innovations in this updated series of compilations dealing with electronictechnology represents a carefully selected collection of items on electronic switchesand control circuits. Most of the items are based on well-known circuit designconcepts that have been simplif ied or refined to meet NASA's demanding require-ment for re l iabi l i ty , simplicity, fail-safe characteristics, and the capabili ty ofwithstanding env i ronmenta l extremes. The items included in the sections dealingwith signal and power switching circuits should be of interest to the technicianand electronic hobbyist because of their simplicity and low cost.

Addit ional technical informat ion on individual devices and techniques can berequested by circling the appropriate number on the Reader Service Card in-cluded in this compilation.

Unless otherwise stated, NASA and AEC contemplate no patent action onthe technology described.

We appreciate comment by readers and welcome hearing about the relevanceand u t i l i t y of the in fo rma t ion in this compilation.

Jeff rey T. Hami l ton , DirectorTechnology Utilization OfficeNational Aeronautics anil Space Administration

NOTICt • This document was prepared under the sponsorship of the Nat ional Aeronautics and SpaceAdminis t ra t ion. Neither the United Slates Government nor any person acting on behalf of the UnitedSlates Government assumes any l i ab i l i ty resulting from ihe use of the informat ion contained in ihisdocumenl, or warranls lhal such use wil l be free from privalely owned righls.

For sale by ihe National Technical In formal ion Service. Springfield. Vi rg in ia 2 2 1 5 1 Price $1.00

ContentsSIXTION 1. Signal Switches Page

Solid-Stale Remote-Circuit Selector Switch 1Remotely Actuated Biomedical Switch 2Electronic Bidirectional Valve Circuit El iminates

Crossover Distortion and Threshold Effect 3Bilateral, Zero-Impedance Semiconductor Switch 3Balanced RF Switch Minimizes Switching Transients 4Solid-State Switch Consumes Negligible Power 4Zero-Bias Bilateral Switch Controls RF Signal 5

SI:CTION 2. Solid-State Power SwitchesZener Diode Controls Switching of Large Direct

Currents 5Solid-State Switch Provides High Input - to-Output

Isolation 6Solid-State Circuit Switches AC Loads 6Semiconductor AC Static Power Switch 7Solid-State Switch Controls AC Power 8Magnetically Coupled Power Switch for Power

Conditioning Equipment 8Solid-State Switch Provides 20-Megohm Isolation 9High-Ef f ic iency Switching Regulator 9

SECTION 3. Solenoid Valve Control CircuitsElectronic Position Indicator for Latching Solenoid

Valves 10Variable-Pulse Switching Circuit Accurately Controls

Solenoid Valve Actua t ion 11Redundant Electronic Circuit Provides Fail-Safe Control 11Solenoid Valve Driver Circuit 12Fail-Safe Circuit Controls Solenoid Valve Operations 12Circuit Monitors Poppet Movement of Solenoid Valves 13Switching Ci rcui t with Hysteresis Characteristics

Controls Valve Operation 14Valve Actuator Circuit Minimizes Operating Power

Requirements 14

SI-CTION 4. General Purpose Control CircuitsHeater Control Ci'rcuit Provides Both Fast

and Proportional Control 15Control System Maintains Selected Liquid Level 16Solid-State Switching Used to Speed Up Capacitive

Integrator 17Pressure Transients Reduced During Startup

of Hydraulic Pump 17Solid-State Relay El iminates RF Noise 18Lamp Starting Switch for Low Power Operation 18An Ultrareliable Switch 19

Section 1. Signal Switches

SOLID-STATE REMOTE-CIRCUIT SELECTOR SWITCH

A solid-state remote control circuit uses vol-tage logic to switch on a desired circuit with-out the use of mechanical relays, frequencyresponsive circuits, or capacitors. Impor tan tcircuit design features include: a three-conductor

the control switch applies a potential to theinput of ampl i f ier (A) when any of the controlswitches are depressed. The a m p l i f i e r output isrouted through l ine 3 to the SCR gate "in-hibit" or "fire" circuits.

cn

0 To SwitchCircuits

K1 e.H

Hino-

fL»>

U no

Y lo

U nQ

T

I

1,1 i (

To ControlCircuit

T C

wire connection between the central controlcircuit and the remote switch circuits; a cont inuouscentral-control circui t indicat ion of the remoteswitch c i rcui t that is activated; and a capabil i tyof act ivating any remote c i rcu i t switch in anyorder of desired sequence.

The remote switching action is produced bysilicon controlled rectifiers (Q2, Q4, and Q6)which conduct current through the loads. TheSCR's are latched in the "on" state by theapplication of cur ren t to the gate terminal . Loadcurrent is routed via l ine 1 as a series connectionthrough one section of each of the controlswitches Kl, K.2, K3, etc., and re turns toci rcui t szround via l ine 2. A second section of

The mult i range switch has a 10-circuit switch-ing capacity. Larger switching capacity is l imitedonly by the closeness of the voltage band-width and the voltage breakdown l imi ta t ions ofthe constant-current diodes. The c i rcu i t* canalso be used in a coded remote-circuit activatorwhere a predetermined sequence of remote switch-ing must occur in a defined length of time toprevent false or undesired circuit act ivat ion.

Source: V. S. PetersonLewis Research Center

(LEW-10387)

No further documentation is available.

ELECTRONIC SWITCHES AND CONTROL CIRCUITS

REMOTELY ACTUATED BIOMEDICAL SWITCH

The implantable electronic switch shown in thefigure consumes no power in the off conditionand can be actuated by a single-frequency telem-etry pulse.

capacitor C3 to the gate of SCR2 will in i t i a tea current impulse through its anode-to-cathodecircuit , momentari ly saturating ampl i f i e r switches

i A

Switch

AntennaCoil

Figure 1

The actuator (see Figure 1) for the remotely-actuated biomedical switch generates an rf signalwhen the spring-loaded, momentary-contact switchshorts the capacitor through the inductance ofthe antenna. When returned to its normal posi-tion, the switch reconnects the battery and allowsthe capacitor charge to be established throughthe resistor. The operating distance of the actuatoris determined by the charge stored by thecapacitor. Since the values of the capacitorand the inductance of the an tenna determinethe resonant frequency, the operating frequencycan be readily adjusted wi th in the frequencyrange of the antenna tank circuit of the implantedelectronic switch.

The biomedical ins t rument can be deenergizedon command by recycling the actuator . Theferrite an tenna picks up the rf pulse from the•actuator which saturates amplifier switch Ql,charging capacitors C2 and C3 to the batteryvoltage. Since SCR1 is already in conduct ion,its gate circuit is inact ive and, therefore, thecharging current through capacitor C2 has noeffect. However, the charging current through

Figure 2

Q2 and Q3, thus short-circuiting the anode-to-cathode circuit of SCR1. As a result, SCR1 re-verts to its nonconducting state because its anodecurrent is now at a much lower value withcapacitor C4 f u l l y charged. Consequently, allactive semiconductor devices revert to the i r offconditions, and the biomedical ins t rument isdeactivated.

The sensit ivi ty of the electronic switch to rfimpulses from the actuator drops off as thethird power of the distance. Addi t iona l ly , thereceiving circuit is quite insensitive, but th is lackof sensitivity offers an advantage in that thesystem is not l i ke ly to be triggered by extraneoussignals. Ideal ly , the actuator is used in closeproximity to the implanted electronic switch;other forms of rf activation may provide actua-tion at long distances. A n t e n n a inductance LIis tuned by varying the number of turns on theferrite cylinder core.

Source: Ames Research Center(ARC-10105)

Circle 1 on Reader Service Card.

SIGNAL SWITCHtS

ELECTRONIC BIDIRECTIONAL V A L V E CIRCUIT ELIMINATES CROSSOVERDISTORTION AND THRESHOLD EEEECT

A fou r - t e rmina l network forms a bidirect ional ,thresholdless valve tha t can switch an ac signalwi thout crossover d is tor t ion or threshold e f fec t .The zener voltage is selected at a level su f f i c i en t lylow to protect the emitter-base junct ions ofQl and Q2 f rom reverse voltage breakdown.Terminals 1 and 2 provide the ac signal i npu twhile t e rmina l s 3 and 4 provide the dc controlvoltage.

With the control-signal supply voltage reducedto zero, the electronic valve can block ac inputsignal voltages equal to the breakdown voltage ofDl. When operated from a dc current source,the ac signal current component is alternatedby an amount equal to the product of the gainand dc bias current.

The prime advantage of this network is thatan isolated control signal is suf f ic ien t for circuitturn-on wi thout requi r ing the isolated dc powersupply to carry the ac load current .

Source: A. Kernick ofWestinghouse Electric Corp.

under contract toManned Spacecraft Center

(MSC-00193)


B I L A T E R A L , ZERO-IMPEDANCE SEMICONDUCTOR SWITCH

A static semiconductor switching circui t el im-inates the undesirable features of electrome-chanical relays—slow switching speed, contactbounce, contact p i t t ing , and arcing—and the non-l inear characteristics of convent ional semicon-ductor switching circuits.

The "relay contacts" for this c ircui t are rep-presented by terminals X and Y. The switch isclosed by a positive control signal voltagewhich forward biases transistor Ql and switchesit to the conducting state. With Ql on, the acvoltage is applied to the t ransformer pr imaryth rough the diode bridge circui t Bl. The second-ary voltage of the t ransformer is fu l l -waverect if ied by diode bridge c i rcu i t B2. The outputfrom th is bridge circuit t u r n s on t ransis torQ2 and provides the c u r r e n t ' t o forward biasthe diodes of bridge c i rcui t B3, in the l inearand low resistance region of the i r current-voltagecharacteristic curves. The f i n a l result of th iscurrent f low is to produce a net zero-voltagedrop at te rmina ls X and Y and thus a zero im-pedance for bi la teral cur ren t s at these t e rmina l s .

The switch is tu rned off by removing the con-trol signal voltage from Ql. The bias current IIbecomes zero, and Q2 is open circuited, i.e., theswitch is now opened.

Source: C. L. Doughman ofWestinghouse Electric Corp.

under contract toLewis Research Center

( L E W - I O I 2 9 )


H L K C T R O N I C SWITCHES A N D CONTROL C I R C U I T S

BALANCED RF SWITCH M I N I M I Z E S SWITCHING TRANSIENTS

+ V

+ V

A balanced diode-transformer circuit canswitch rf signals in the 120 MHz range byal ternately d r iv ing a biased diode network atthe rate of 1.5 kHz. The balanced circui t pro-

vides low noise swi tching for rf signals bysuppressing t ransformer voltage spikes and wouldbe useful in high frequency signal switchingapplications that require low noise operation.

The rf switch shown in the f igure is turned onby applying a positive voltage at A and a negativevoltage at B. The diodes Dl, D2, D3, and D4 areturned on and as a result , the flow of cu r ren t 12balances 13, and II balances 14. Consequently, thevoltages induced by the diode currents cancelin the transformers Tl and T2, and the voltagespikes generated by the diode cur rents areminimized. The switch is turned off by reversingthe polarity of the voltages at A and B.

Source: J. R. Pousson ofTRW


(MSC-13241)


SOLID-STATE SWITCH CONSUMES N E G L I G I B L E POWER

Logic Power +VdcSupply

Q3

Load

This solid-state switch is designed for a shortperiod of "on" t ime and consumes very l i t t l epower dur ing the "off" time.

The switch is ideal for dr iv ing small loadssuch as lamps, relays, etc., from logic levels with

very l i t t l e power consumption when the switchis "off.;" The "on" time is short relative to the"off" time.

The c i rcui t consists of three t ransis torsoperated in the switching mode. Ql is a PNPtransistor with its emitter connected to the posi-tive logic power supply. Q2 is an NPN transis torused to drive the ou tpu t switch Q3 tha t connectsthe supply voltage to the load. When the inpu tis at ground potential, Ql, Q2, and Q3 saturateand the switch is "on." When the inpu t is opencircuited or connected to the logic power supply,all the transistors are "off": hence, when theswitch is "off," very l i t t l e power is consumed,only that due to leakage currents of the t ran-sistors.

Source: R. Shigemasa ofNorth American Rockwell Corp.


(MSC-91041)


SIGNAL SWITCHES

ZERO-BIAS B I L A T E R A L SWITCH CONTROLS RF S I G N A L

+ 6 Vdc- Control °

-6 Vdc

Vout

A bilateral transistor switch with a secondtransistor in parallel, cancels the bias effect ofthe switching action. This combination producesa bilateral solid stale switch with a zero bias

in the "on" state. The ci rcui t can switch a ±2.5Vpeak, dc-to-300 kHz input to an operationalamplif ier as controlled by a!-!-6V(on) or -6V (o f f )signal. The novel feature is the use of the bi-lateral transistor Q2 which draws a saturationcurrent of equal ampl i tude and opposite polarityto the saturation current of the bilateraltransistor Ql. This second current cancels thedc bias effect at the i npu t summing point of theoperational ampl i f ier . Since Q2 is switched onwhenever Ql is on, and off when Ql is of f , theoperational ampl i f ie r has a true zero dc bias inboth signal-off and signal-on conditions.

Source: J. M. Husted ofRadio Corp. of America

under contract toGoddard Space Flight Center

(GSC-532)


Section 2. Solid-State Power Switches

ZENER DIODE CONTROLS SWITCHING OF LARGE DIRECT CURRENTS

ZenerRF Filter Diode RF Filter

DC [Input T ^

vu

: R1DC

: Output

RF ControlSignal Zener

Correction Voltage

This simple circui t is designed to control theswitching (gat ing) of large dc signals. A high-current zener diode, connected in series with theposit ive i npu t t e rmina l of the dc supply, blocksthe flow of direct current u n t i l a high-frequency

(rf ) control signal is applied across the zenerdiode.

The application of an rf control signal to thedc blocking capacitors across the zener diodereduces the diode impedance to a very low value,and direct current then flows from the i n p u t tooutput terminals. The rf f i l t e r s and blockingcapacitors isolate the dc lines from the rf lines.Rl is adjusted to compensate for the small dcvoltage drop across the diode dur ing the conduc-tion state.

Source: IBM Corp.under contract to

Manned Spacecraft Center(MSC-00188)


i : i . tCTRONIC SWITCHES AND CONTROL CIRCUITS

SOLID-STATE SWITCH PROVIDES HIGH INPUT-TO-OUTPLT ISOLATION

The solid-state switch can interrupt a 50 kHzsignal (10 mV to 80 V peak range) with i npu t -to-output isolation of 80 db. The high input-out-put isolation is achieved through the use of seriesand shunt-series MOSFET switching.

Signal Input

load reactance to discharge through Q3 andQ2 to ground. Q3 is turned off and disconnectsthe load from the switch. This procedure energizesother switches connected to the same load, allow-

Outputto Data Bus

As shown in the schematic, a P-channelMOSFET (Ql) isolates the input signal voltagefrom the output wi thout introducing an objec-tional level of offset voltage. An N-channeljunct ion FET (Q2) provides a rapid t u r n o f fcapability because of its low "on" resistance. Inorder to prevent a short circuit , (Q3) is used toswitch simultaneously with Ql, thus isolating theoutput from the shunt element. This leaves theoutput voltage at the cutoff level.

The switching voltage waveform is delayed fora few nanoseconds before it is applied to thegate of Q3, allowing the voltage charge on the

—'— Circuit~|~ CapacitanceII

ing measurements to be made of signals fromother sources in rapid succession.

Zener diodes Dl and D2 are connected toeach input l ine to protect the switches from over-voltage due to surges, noise spikes, or excessivepower inputs .

Source: R. L. Magee and L. E. Trowbridge ofGeneral Electric Co.

under contract toNASA Headquarters

(HQN-10488)


SOLID-STATE CIRCUIT SWITCHES AC LOADS

This solid-state circui t is designed to switchac signals which have peak ampl i tudes greaterthan 5 volts.

Applying a dc control voltage of 0.1 to 5.0volts to the base of Q1A, causes it to conductmore heavily than section Q1B. Thus, the

collector of section 1 will be at a lower voltagethan the collector of section 2, and Q3 willconduct to pass the ac signal. Output of thisswitch is f lat wi th in 3 db from 6 Hz to 21.5 kHz,with the use of 1 mfd coupling capacitors.

The circuit consists of a dual NPN transistor,

SOI.ID-STATL POWtR SWITCHES

r + 20 vdc -20 Vdc

01A

AC SignalOut

R2 AC SignalIn

Ql, a current source, Q2, and an ac switch,Q3. Resistors Rl and R2 are initially adjustedto obtain proper switching action and to controlthe ac gain of the switch. With no dc controlvoltage applied, the collectors of Ql are es-sentially at the supply potential of 20 Vdc;Q3 is non-conducting (its impedance is extremelyhigh) and as a result, there is no ac signal output .

Source: C. P. Chapman and D. R. R u p n i k(JPL-798)


SEMICONDUCTOR AC STATIC POWER SWITCH

The desirable characteristics of this staticpower switch include the absence of moving parts(and associated wear), and the high gain betweenthe control power and the power transferred.

O. >A

ControlSignal

signal may or may not be grounded, an oscil-lator-transformer-rectifier circuit provides isola-tion between the control signal and the switch,and permits the use of a single control signal tooperate all three phases of the switch.

The input is 10 Vdc at 10 mA. The switchwill operate with a control signal input as low

o Load

SCR2

Oscillator Circuit Transformer, Recti- Drive Circuitfier and Filter

Power-HandlingCircuit

The static switch is par t icular ly suited in suchapplications as on-off regulation, position con-trols for the orientation of solar panels, radioantennas, and f lashing lights.

M i n i m u m power drain from the controlsignal is achieved by having the control signaltu rn on a small switch that supplies turn-onpower to the main SCR's. Since the control

as 25 mW, over an operating temperaturerange of 233 to 353 K.. The oscillator t ransformerhas three output windings, each feeding a full-wave bridge rectif ier and f i l te r . The rectifiedoutput voltage is applied to the drive t ransistor(Q3) which saturates and supplies power to theSCR's (through D5 to D6, D7 to D8, and R6to R7). The switch w i l l tu rn on, over its operating

i:LI£CTRONIC SWITCHES AND CONTROL CIRCUITS

temperature range, when the l ine voltage is atleast 8 volts. Under normal condit ions, the drivetransis tor dissipates less than 0.1 watt. Theswitch has a design rating of 4 amperes andhas a con t inuous overload capabil i ty of 14amperes for a range of heat-sink temperatures

from 233 to 353 K. The noted voltage is 600peak or 400 rms.

Source: James Vrancik ofLewis Research Center

(LEW-10344)Circle 9 on Reader Service Caret.

SOLID-STATE SWITCH CONTROLS AC POWER

Impor tan t features of the solid-state ac powerswitch shown in the f igure include: (1) no movingparts; (2) explosion proof (no arcing); (3) fastswitching times; and (4) longer operational l i fe .

r

f \

L.

L1 o AC Phase

Saturable < R1 -Reactor *|

• f\ " 1SCR T \SiSU * '

0 .£Ro. pnrv\ ~T I 1

T ' o °k X Y

r

>>SCR

1—

Neutra

"1 11

1

DJ11

J 1

The switching action is initiated with the ap-plication of an external signal to the terminals,X and Y, of the saturable reactor, or (2) bymerely shorting them together. This producesa condition of saturation, i.e., the secondary

winding is in a low impedance state which per-mits the SCR gate circuit to be completed.Depending on the ac polarity at the ins tan t ofsaturation, the appropriate SCR fires andbegins to conduct for the durat ion of thatparticular half cycle, while the other SCR re-mains turned o f f . At the end of the i n i t i a lhalf cycle, the conduct ing SCR tu rns offbecause of the current reversal and the otherSCR conducts for the remaining half of thecycle. The gate voltage for each SCR is developedacross the voltage dividing network (composedof Rl, R2, and R3) and the saturable reactorat the instant that the SCRs are not conducting.The circuit can be commutated at frequenciesranging from 60 to 1600 Hz. Modifications of thiscircuit can be used in 3-4> power control andin motor reversing applications.

Source: G. P. Paul ofNorth American Rockwell Corp.

under contract toMarshall Space Flight Center

(MFS-16092)


MAGNETICALLY COUPLED POWER SWITCH EOR POWER CONDITIONING EQUIPMENT

The transistor power switch shown in thefigure isolates the ac power from the controlcircuitry. The switch has high efficiency andcan accept a wide range of input voltages. Im-mediate applications include its use in voltageregulators and power condi t ioning equipment .

With the manual switch in the A position asshown, t ransformer Tl is short circuited andpresents an extremely low impedance at the ter-minals of windings P1A. The ac source voltage,

minus the voltage drop across ZL, appears acrosswinding P2A of T2. This causes a forwardbase-drive voltage to appear from the base toemitter of Ql and drive current is suppliedthrough Dl, D2, and windings S2 and T2.The drive voltage, VgE , is s u f f i c i e n t l y low sothat the current shunted by the combinat ionof D4, D5, D6, and wind ing SI of Tl is in-s igni f icant .

soun-ST.viT. i'O\vi K SVVITCI

!! D4

T1

D6

D5U

D3-W-

T2

; ;D2

Q Q O O Q O j AC PowerSource

oTT—nnnP1A P2B

( 0 0 1P2A

With the switch in the B position, T2 isshorted and the ac source voltage appearsacross P1A of Tl; this causes D3 to be forwardbiased, thereby holding Ql off and "opening"the switch.

Slight modif ica t ions to the circui t and theaddition of a saturable reactor would increasethe higher power efficiency where variableloads are to be switched.

Source: A. S. Cherdak ofRadio Corp. of America

u n d e r contract toGoddard Space Flight Center

(GSC-10023)


SOLID-STATE SWITCH PROVIDES 20-MEGOHM ISOLATION

The unique feature of this isolation switchis the use of the u l t rahigh input impedanceMOS transistor Ql to achieve ground isolat ion.Ql is selected for low gate-source thresholdvoltage in order to interface with the logicinpu t levels. Isolation between the inpu t andoutput power supplies is greater than 20 MO;

rise and fall times of output pulses are lessthan 2M sec; and the circuit is compatible withthe output levels of standard integrated circui tlogic modules.

R2 is the only connection between in ternaland external power. The input drive developedacross Rl, which enhances the conductionchannel of Ql, provides the drive to Q2 and tothe load. Zero voltage across Rl tu rns Ql offand the output drops to the return voltage.

Source: C. L. Moberly ofMotorola, Inc.


(MSC-11006)

Circle II on Reader Service Card.

HIGH-EFFICIENCY SWITCHING REGULATOR

Switching regulators offer greatly improvedeff ic iency compared to simple series or shuntregulators, but normal ly have very complicatedcircuits. This u n i t requires only 12 componentsand has a regulation efficiency of greater t han85%.

The regulator shown in the block diagramoperates in either the "on" or "off" mode. When

out

10 ELECTRONIC SWITCHES AND CONTROL CIRCUITS

a signal input Vjn is applied to one side of tion of Ql and Q2 is similar to a Schmitt trigger,the series inductor, the current begins to buildup to a predetermined level. The switch is thenturned off and the current flows through theflyback diode, Dl.

The voltage comparator Q2 must have hyster-esis to sustain oscillation, or else the seriesswitch will operate in a l inear mode. The opera-

with Rl and R2 introducing the necessaryhysteresis.

Source: A. G. BirchenoughLewis Research Center

(LEW-11005)


Section 3. Solenoid Valve Control Circuits

ELECTRONIC POSITION INDICATOR FOR LATCHING SOLENOID VALVES

+ 24 Vdc

The circuit shown in the f igure can determinewhether a double latching solenoid valve isopened, closed, or at some in-between position.

The change in impedance of the solenoid valvecoil, caused by the change in position of thesolenoid plunger with respect to the coil, un-balances a bridge network and thus providesa signal for the level detection circuitry. Identicaldetection circuits are connected to the valvecoils so that if the valve is not f u l l y opened orf u l l y closed, neither detection lamp wil l be on.

Transient suppression is provided to e l imina tedamaging voltage spikes. No modification of thevalve is required since the detector is con-

nected directly to the valve coil. The fol lowingdocumentation may be obtained from:

National Technical Information ServiceSpringfield, Vi rg in ia 22151Single document price $3.00(or microfiche $0.95)Reference:

NASA-TM-X-1760 (N69-20874), Elec-tronic Position Indicator for LatchingSolenoid Valves

Source: R. J. Frye, H. L. Wimmer, andR. Fischer

Lewis Research Center(LEW-10926)

SOLtNOID V A L V t CONTROL C I R C U I T S11

VARIABLE-PULSE SWITCHING CIRCUIT ACCURATELY CONTROLSSOLENOID VALVE ACTUATION

o +Vout

+ 28VdcSource

Flip-Flop

The solid state switching circuit shown in thefigure generates variable square wave pulsesof sufficient power to operate a 28 V dcsolenoid valve at precise time intervals.

The circuit includes a pulse-forming branch(Ql, Q2, and Q3) and an amplifier whichpowers the operation of the solenoid valve.Pulse width (on time) can be varied over a rangeof 10 to 40 msec by adjusting potentiometer Rl.Similarly, the interval between pulses (off time)can be varied over a range of 8 to 350 msecby means of R2.

This type of circuit has been used to controla solenoid valve for precise time intervals off lu id flow in combustion experiments. Withan addition of suitable relays, the circuit can beused for sequencing multiple flows in variousprocesses.

Source: J. D.Gil let t , ofNorth American Rockwell Corp.


(MFS-1895)


REDUNDANT ELECTRONIC CIRCUIT PROVIDES FAIL-SAFE CONTROL

Closure of a valve is prevented and valvecontrol is maintained to a close tolerance withthis fail-safe control circuit . The controllercan mainta in the position of the valve ( w i t h i n3% of the intended value) when the supplyvoltages are removed (or shorted) and when eitherou tpu t from the ampl i f iers is shorted.

The circuit is designed to enable the output ofone ampl i f i e r to override a fai lure in the otherampl i f ie r . Addi t ional re l i ab i l i ty is achieved withseparate power supplies for each ampl i f ie r .

The circuit shown in the figure operates inconjunction with a valve that opens upon lossof a signal, thus preventing the valve fromclosing when the control system fails.

The valve position error caused by a fa i lu reis inversely proportional to the gain of the twocontrol amplif iers . Therefore, if the valve gain islow, the gain of the control ampl i f ie rs is in-creased to reduce the error. Conversely, a failed-closed valve system can be made by reversingthe excitation voltage connections to the valve-position potentiometers.

+ 15 Vdc

-15 Vdc

"Valve

Source: J. W. Archer ofAerojet-General Corp.

under contract toA EC-NASA Space Nuclear Systems Office

(NUC-10389)


12 ELECTRONIC SWITCHES AND CONTROL C I R C U I T S

SOLENOID VALVE D R I V E R CIRCUIT

A variable duty-cycle pulser has an exception-al ly high power eff iciency when operatingsolenoid valves. The circui t provides a low-levelholding current once a high-level cur rent has

an emitter follower, to a two-stage current ampli-f ier . The "one shot" pulser consists of a uni junc-tion oscillator which triggers a silicon-controlled

+ V

Variable Pulser One-Shot

actuated the solenoid valves. In i t i a l energizingcurrent is provided by a "one shot" pulser thatcauses f u l l power to flow to the solenoid valvesfor a length of time suf f ic ien t for maximumpull - in . To obtain the solenoid valve holdingcurrent, a variable duty cycle pulser t u r n s thepower switch on and of f . By adjusting the pulseduration and frequency, any desired value ofeffective solenoid valve holding current can beset and maintained. Diode Dl suppresses theinduced-voltage surge when the solenoid valvesare deenergized, and circulates the decaying coilcurrent back through the coil. This effectivelyincreases the decay time constant, making itindependent of other circuit parameters. Thus,the du ty cycle is decreased, which fur therincreases the efficiency of the circuit. Thevariable duty cycle pulser consists of a bistablemult ivibrator which is triggered by a uni-junction relaxation oscillator. The output ofthe multivibrator is capacitively coupled, through

Pulser Current Amplifier

rectifier, which, in turn, operates a transistorswitch. This switch saturates the two-stage cur-rent amplif ier unt i l the silicon-controlled rectifierconducts. The switch on the in i t i a l pulse isdetermined by the time constant, C2 x R4. Thepower switch consists of the two-stage currentamplifier .

The circuit has successfully operated twosolenoid valves simultaneously with an efficiencyof 77 percent. A m i n i m u m holding current of0.3 A is necessary to keep the solenoid valvesheld in. The pulse durat ion is set to 0.53 msec,and time between pulses is set to 2.6 msec, whichyields a holding current of 0.5A.

Source: R. J. Mankovi tzofNorth American Rockwell Corp.


(MSC-254)


FAIL-SAFE CIRCUIT CONTROLS SOLENOID VALVE OPERATIONS

Quite often, in process operations related tothe petrochemical and pharmaceutical indus-tries, control solenoid valves must operate in aspecific sequence. Any deviation could result

in a catastrophic condition. The circuit shown inthe figure prevents out-of-sequence or pre-mature operation of control solenoid valves,dur ing both opening and closing cycles.

SOLIiNOII ) VALVli CONTROL C I R C U I T S 13

Electronic switches (Ql, Q2, and Q3) coupledwith interlocking diodes Dl and D2 are usedto control the operation. The cycle begins with

V j n +28Vdc

valve is lost at any stage, all succeeding stagesclose in rapid succession to provide a fail-safecondition.

+ 28 Vdc

valve #1 opening before valve #2 and closingsoon after #2 opens. Since the resistances ofthe valve coils are low (less than 30£2) thevoltages at points A and B cannot rise suf-ficiently to t u rn on Ql, unless the precedingvalve is energized. If the control signal to a

Source: O. B. Marshall ofNorth American Rockwell Corp.


(MFS-18162)


CIRCUIT MONITORS POPPET MOVEMENT OF SOLENOID VALVES

A large n u m b e r of 28-Vdc solenoid valvescan be s imultaneously and remotely monitoredfor poppet movement for the purposes of

+ 28 Vdc S1 Solenoid ValveCoil

determining the operating times for openingand closing modes. A diode circuit shown inthe f igure monitors the current mode when thesolenoid is energized (opening the valve) andmonitors the voltage mode when the solenoidis deenergized (closing the valve). This circuitrequires only one galvanometer for both modesof operation.

The circuit divides the current to the solenoidthrough Rl, Dl, and the galvanometer. D2blocks the path through R2. On closing, thevoltage across the solenoid reverses polarityas a result of the decreasing magnetic fieldof the solenoid, and the current path now dividesthrough D2, R2, D2, and the galvanometer;Dl blocks the path through Rl. R2 is selectedto give the desired galvanometer deflection.

Source: G. E. Marriner ofNorth American Rockwell Corp.


(MSC-11617)



SWITCHING CIRCUIT WITH HYSTERESIS CHARACTERISTICSCONTROLS VALVE OPERATION

The hysteresis characteristic of the circuitshown in the figure allows two solid stateswitches—one normally closed and the othernormally open—to operate simultaneously. Input

are closed; s imul taneously , Q6 t u r n s off andthe N.C. contacts are opened. The opening andclosing of the contacts in the switch outputs can

voltages ranging from 6 to 12V can be used totrigger the circuit. When the input voltage isbelow the triggering level, very li t t le currentflows in the emitter of Q2; the base and theemitter of Q3 are at the same potential, andQ3 is cut o f f . An i n p u t voltage exceeding thet r igger ing threshold causes Q2 and Q3 to besaturated. The sa tura t ion of Q3 removes basecurrent flow to Q4, t h u s t u r n i n g it off . WhenQ4 is o f f , Q5 t u r n s on and the N.O. contacts

be used to control the current f lowing throughthe solenoid valve coils.

Source: R. E. Melton ofSPACO, Inc.


(MFS-13363)


VALVE ACTUATOR CIRCUIT MINIMIZES OPERATING POWERREQUIREMENTS

The solenoid valve driver circuit reduces thei n p u t electrical power consumption du r ing con-t inuous operation to less than one-tenth thatof conventional circuits. The simplicity of thecircuit and the min ima l power requirements makethis type of valve control attractive in applica-tions where battery power is available.

Circuit operation begins by closing theswitch SW1 to enable a charging current to

flow through Cl and the solenoid coil (seefig. 1). As the current begins to increase, theZener diode (Dl) breaks down (at 60 mA) andcauses Q1B to be turned off . The switch nowbecomes sensitive to a new current level (20 mA)determined by R2 and R3. When the currentthrough the solenoid decays to approximately20 mA, the switch then begins to cycle on andoff in order to main ta in this same current level

SOLLNOID. VALVE CONTROL CIRCUITS 15

Voltage

Time

Current

Time(B)

Figure 1.

through the solenoid. The cycling rate andcurrent f luctuations are controlled by adjustingthe value of the positive feedback resistorR4. Figures 2A and 2B demonstrate the periodicnature of the current-voltage properties andsubsequent power savings of the central circuit.

Figure 2.

Source: W. E. Crawford ofCaltech/JPL

under contract toNASA Pasadena Office

(NPO-10716)


Section 4. General Purpose Control Circuits

HEATER CONTROL CIRCUIT PROVIDES BOTH PASTAND PROPORTIONAL CONTROL

A conventional proportional control c i rcui t ,combined with a fast-heating circuit (R3 andR4), consisting of a voltage divider, providesa voltage at low temperatures which tu rns ontransistor Ql for each dc i n p u t pulse. WithQl "on" the heater operates dur ing the f u l linput pulse durat ion. As the temperature risesabove a preset value, the change in resistance ofR3 (a thermistor) reduces the voltage suppliedby the voltage divider so that heater controlis shifted to the proportional control circuit.The SCR gate output from uni junct ion transistorQl is then delayed on each input dc pulse

Pulsating DCo

From UnfilteredFull-Wave Rectifier

SCR Gateo

4=ci

16ELECTRONIC SWITCHES AND CONTROL CIRCUITS

by the charge time of capacitor Cl. Because ofthis delay, the heater does not t u rn on in theearly portion of each input pulse. DiodeDl is used to isolate the fast heating circuitfrom the proportional control circuit.

When provided with proper sensors, the cir-cuit can be adapted to provide control of otherparameters, such as pressure, volume, f l u id

level, motor speed, voltage, and light intensity.Source: R. W. Baslock of

IBMunder contract to

Marshall Space Flight Center(MFS-906)


CONTROL SYSTEM M A I N T A I N S SELECTED LIQUID LEVEL

A single-sensor control system mainta ins l iquidhydrogen at a desired level, regardless ofboiloff of the hydrogen.

_ R1

uni ts . Potentiometer R5 is adjusted to selectthe desired tank f i l l level, which may range from60 to TOO percent of the tank capacity. A cor-

•

U ,

~1Tarik

t

f

Analog toDigitalEncoder

,

n/ r

PhaseSensitiveAmplifierand Relay

• ControlSignal No. 1

ControlSignal No. 2

This gaging system would have application incontrolling l iquid levels in tank cars where thef l u i d s f requent ly boil or leak away, or for usein indus t r i a l processes where the level offluids must be held constant.

In i t i a l ly , a calibration signal is obtainedfrom empty-adjustment potentiometer Rl andapplied through the tank un i t ( l i qu id level sensor)lo an amplifier-motor combination. Mechanicall inkage from the motor extends to the counterdisplay, an analog-to-digital encoder, and gearing

rection signal, applied through R2 from R5, com-bines with the signal from the tank un i t , andis applied as an input to the amplifier-motorcombination. The motor will operate u n t i l thesignal output from R2 is equal to the tank uni tsignal; this indicates that the fuel level in thetank has reached 100 percent of the setting ofR5. The counter display un i t gives a visualpercentage output indicative of the wiper positionof R2. The analog-to-digital encoder (an optionalcircuit item) accepts the analog signal providedby the gearing and provides a digital output forcomputer use. Potentiometers R3 and R4, inconjunction with R6 and R7, respectively, maybe set" to desired levels to generate controlsignals from phase-sensitive ampl i f i e r and relaycircuits.

GLNHRAL PURPOSE CONTROL CIRCUITS17

Title to this invent ion has been waived underthe provisions of the National Aeronautics andSpace Act [42 U.S.C. 2457 (f)] to Honeywell,Inc., 2600 Ridgeway Rd., Minneapol is , Minnesota55413.

Source: L. Bergeson and J. W. Schuck ofHoneywell , Inc.


(MFS-470)

SOLID-STATE SWITCHING USED TO SPEED UPCAPACITIVE INTEGRATOR

This variable pulse width circuit e l iminatesconventional relays which have limited operatinglifet ime, draw appreciable power, and cannotbe switched in less t han a few msec. The circuithas application in a process control system thatuses a variation in pulse width to indicateparameter changes in the process func t ion .

Referring to the schematic, the circui temploys capacitor integrators to convert the

signal input pulses to an analog voltage propor-t ional to the pulse width. Transistors Ql and Q2are used to steer each inpu t pulse to the propercapacitor in a sequence of charge, discharge,and read. SCR1 and SCR2 are alternatelypulsed "on" by the bistable mul t iv ibra tor com-posed of Q3 and Q4 to discharge the capacitorused in the previous cycle. The resultant outputvoltage is l inearly proportional to the inpu tpulse width. Important circuit design parametersinclude: (1) the abili ty to integrate either highor low duty cycle pulses, with repetit ion ratesranging from 1 to 10,000 pulses per sec, withnegligible ripple factors; and (2) a high i n p u timpedance (500 K.Q) while m a i n t a i n i n g a rela-t ively low ou tpu t impedance.

Source: A. L. Newcomb, Jr.Langley Research Center

(LA R-104)


PRESSURE TRANSIENTS REDUCED D U R I N G STARTUPOE H Y D R A U L I C PUMP

The addi t ion of an RC network to a pumpcontrol circuit reduces the pressure transientsin a hydraul ic system when the pump is started.The RC network electrically retards the pumphanger movement of the servo-controlled, variabledisplacement pump and prevents damage tosystem components caused by the pressuretransients.

A simplif ied electrical schematic of the pumphanger control circui t is shown in the figure.In order to start the pump motor, relay contactK. 1 is closed, thus grounding the inpu t control

Vjn

+ V

GroundK1

+v

RC Network1

I!- I

ServoValveI


signal. Grounding the input signal causesa zero output from the different ia l amplifier,and therefore a m i n i m u m output position ofthe pump hanger. After the motor is started,Kl opens and the increased current flowinto Al generates a voltage output to the pumphanger-positioning servo valve. The pump hangeris then driven towards the maximum output posi-tion by the servo valve. An exponential move-ment of the hanger is achieved as a resultof the current-charging characteristics of Cl. Theeffects of the network to the hanger response,during operation after startup, are eliminated by

maintaining the voltage on Cl and the properlevel.

The pump hanger response can be variedfrom 250 msec to 5.0 sec by changing thevalue of Cl. Actual performance tests indicatea reduction in pressure transients by a factorof 3.

Source: W. L. Flowerday ofThe Boeing Co.


(MFS-15141)No further documentation is available.

SOLID-STATE RELAY ELIMINATES RF NOISE

This solid state circuit replaces an equivalentelectromechanical relay. Power dissipation in the"off" (deenergized) mode is less than 1 mW

Vrout

+ V

and isolation is provided between control andswitching functions. The circuit has the same in-put rf interference noise immuni ty as a relay,and since mechanical contacts are eliminatedthe lifetime is increased.

In operation, the applied inpu t signal chargesCl sufficiently to cause Dl to conduct; Ql

turns on, and C2 couples the signal to pulsetransformer Tl which develops a secondaryvoltage pulse. The use of C2 in series with Tlprovides a relatively high ini t ia l current fora short period of time, since C2 begins tocharge; the current is then reduced to a lowlevel (limited by R2) when C2 is f u l l y charged.When the input signal is removed, Ql tu rns offand C2 now discharges through Tl, causinga secondary voltage pulse of the oppositepolarity. Thus, a secondary pulse in one directionrepresents a relay energized condition, while anopposite pulse represents a relay deenergizedcondition.

Source: J. R. Owen ofIBM Corp.


(MFS-13547)


LAMP STARTING SWITCH FOR LOW POWER OPERATION

Alkal i vapor lamps should be operated atthe lowest possible power level, to increase thelife of the lamp. However, the requirementfor low operating power is in conflict with therequirement for initially striking the lamp sincehigh power and high voltage are required forthe ignit ion.

The circuit shown in the f igure ignites thelamp and then transfers the lamp to a low-power continuous-operation mode. An electronicswitch controlled by the output from a photocelltransfers a high voltage-to-low voltage supplyafter the lamp has been ignited.

The 28 Vdc input starting power can be

G E N E R A L PURPOSE CONTROL CIRCUITS 19

28 Vdci

t

DC-to-DCConverter

pplied directly

\'12 Vd

to tl

ElectronicSwitch

ic lar

LampOscillator -O-

Photc

AtomicReferenceSystem

np oscillator through

x>»

>cel

X

/

DCThresholdDetector

\/?

Vout

the switch. When the lamp ignites, currentis generated in the photocell and is sensed bythe dc threshold detector, which activates theelectronic switch. A 12-Vdc supply is then appliedto the lamp oscillator for continuous runn ingoperation. This switching action minimizes thetotal power required to sustain the lamp inits proper discharge mode.

Source: A. Helgesson ofVarian Associatesunder contract to

Manned Spacecraft Center(MSC-11664)


AN ULTRARELIABLE SWITCH

This circuit (called a cell) switches in thesame manner as a relay and is capable of de-tecting most fai lures wi th in itself. Couplingseveral cells together permits automatic replace-ment of a failed cell with a spare, and therebysignificantly increases the probability ofsuccessful operation. The circuit consumes am i n i m a l amount of power by e l iminat ing powerto the spare cells.

Each cell includes two 2-position latchingrelays of the double-pole double-throw type,and two steering diodes. One cell ( S I ) per-

forms the switching funct ions un t i l i t fails,and is then replaced by another cell (S2). Be-sides funct ional redundancy, component re-dundancy is used within a cell to increase theprobability of automatic cell replacement aftera component fai lure. The relays are double-coiltypes which are capable of switching withoutdeveloping chatter.

Source: J. R. Kinkel(JPL-90831)


NASA-Langley, 1971

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