Specialists in electronic kits, components and products. KC5225: 10A DC SPEED CONTROL Silicon Chip Magazine June 1997 (p26 to p30) Rev 2.2 Batch No:

JAYCAR ELECTRONICS PTY LTD (ABN 65 000 087 936), 100 SILVERWATER RD, SILVERWATER, NSW 2128, AUSTRALIA Tel: (02) 9741 8555 Fax (02) 9741 8500 www.jaycar.com.au kits@jaycar.com.au 1 of 1

PLEASE READ BEFORE COMMENCING CONSTRUCTION The guarantee on this kit is limited to the replacement of faulty parts only, as we cannot guarantee the labour content you provide. "For Semiconductor Guarantee, see `Terms and Conditions' In our catalogue. Our Service Department does not do general service on simple kits and it is recommended that if a kit builder does not have enough knowledge to diagnose faults, that the project should not be started unless assistance can be obtained. Unfortunately, one small faulty solder joint or wiring mistake can take many hours to locate and at normal service rates the service charge could well be more than the total cost of the kit. If you believe that you may have difficulty in building this kit (which is simply a complete set of separate parts made up to a list provided by the major electronics magazines) and you cannot get assistance from a friend, we suggest you return the kit to us IN ITS ORIGINAL CONDITION for a refund under our satisfaction guarantee. Unfortunately, kits cannot be replaced under our satisfaction guarantee once construction has been commenced. CONTACTS: For functional or modification queries please contact Silicon Chip Publications who have designed and/or published this project: www.siliconchip.com.au silchip@siliconchip.com.au Silicon Chip Publications, POBox 139, Collaroy Beach, NSW 2097 For quality issues and/or constructive feedback please contact the Production Manager at Jaycar Electronics and provide the following information: • Product Number • Batch No • Details of Quality Issue

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Specialists in electronic kits, components and products. KC5225: 10A DC SPEED CONTROL Silicon Chip Magazine June 1997 (p26 to p30) Rev 2.2

JAYCAR ELECTRONICS PTY LTD (ABN 65 000 087 936), 100 SILVERWATER RD, SILVERWATER, NSW 2128, AUSTRALIA Tel: (02) 9741 8555 Fax (02) 9741 8500 www.jaycar.com.au kits@jaycar.com.au 2 of 2

Notes and Errata (at time of print): It is recommended to check the designers/publishers website for further notes and errata since this document was issued, before starting construction. SC 08/1997 There is a mistake in the text on page 30, third paragraph down. The text states "Make sure that they (the diodes) are connected in the right direction across the motor; ie, anodes to the positive supply line." The diode(s) should be connected with cathode to the positive supply line, as shown in the circuit and wiring diagrams. SC 10/1998 The text on page 30 states that you should be able to measure about +12V at pin 16... of IC1. Pin 16 is grounded - it should refer to pin12.

Jaycar Electronics: The component spacing for the 2 * 100uF/63V(50V) capacitors on the Pcb is insufficient. Jaycar has substituted one of the capacitors with a 100uF/25V to address this issue. Nevertheless the 2 capacitors will not fit flush onto the pcb. Jaycar Electronics has revised the Pcb to address the capacitor fitting issue (see left) and to accommodate both 5 & 10mm VR1 trimpots..

Specialists in electronic kits, components and products. KC5225: 10A DC SPEED CONTROL Silicon Chip Magazine June 1997 (p26 to p30) Rev 2.2

JAYCAR ELECTRONICS PTY LTD (ABN 65 000 087 936), 100 SILVERWATER RD, SILVERWATER, NSW 2128, AUSTRALIA Tel: (02) 9741 8555 Fax (02) 9741 8500 www.jaycar.com.au kits@jaycar.com.au 3 of 3

Possible Substitutions Original Part Original Part Desc Subst Part Subst. Part Desc. EC7839 PCB SC11106971 SPEED CONTR EC7978 PCB (KC5225) SC11106971 REV2

SC06/97 RE6066 10uF 16V Electrolytic RE6070 10uF 25V Electrolytic RT4310 5k horizontal trimpot RT4358 5k horizontal trimpot (piher) and adjust the

pins. Silicon Chip 100uF/50V on the input side of the

12V regulator RE6150 100uF/63V on the input side of the 12V

regulator Silicon Chip 100uF/50V on the output side of the

12V regulator RE6130 100/25V used on the output side of the

12V regulator PARTS LIST Please note that quantities listed refer to the actual number of items required. When purchasing individual items separately, take pack quantities into account. 1 See section about Substitution 2 See section about Notes & Errata RESISTOR(S) Cat.# Qty* Description Component Identification And/Or Location HP1250 4 P.C PIN 0.9MM PKT 50 RR0580 2 2K2 .5W METFILM 1% PKT 8 Red Red Black Brown Brown RR0588 1 4K7 .5W METFILM 1% PKT 8 Yellow Purple Black Brown Brown RR0596 1 10K .5W METFILM 1% PKT 8 Brown Black Black Red Brown RR0602 1 18K .5W METFILM 1% PKT 8 Brown Gray Black Red Brown

Specialists in electronic kits, components and products. KC5225: 10A DC SPEED CONTROL Silicon Chip Magazine June 1997 (p26 to p30) Rev 2.2

JAYCAR ELECTRONICS PTY LTD (ABN 65 000 087 936), 100 SILVERWATER RD, SILVERWATER, NSW 2128, AUSTRALIA Tel: (02) 9741 8555 Fax (02) 9741 8500 www.jaycar.com.au kits@jaycar.com.au 4 of 4

RR0603 1 20K .5W METFILM 1% PKT 8 Red Black Black Red Brown RR0612 2 47K .5W METFILM 1% PKT 8 Yellow Purple Black Red Brown RR0620 1 100K .5W METFILM 1% PKT 8 Brown Black Black Orange Brown RR0644 1 1 M .5W METFILM 1% PKT 8 Brown Black Black Yellow Brown RR1518 2 4R7 5% 1/4W CARB RES PKT 8 Yellow Purple Gold Gold RR3274 1 100 OHM 5W W/W RESISTOR RT4310 1 5K OHM HORZ MIN T-POT 502 CAPACITOR(S) Cat.# Qty* Description Component Identification And/Or Location RE6066 2 10U/16VRB ELECT CAPACITOR 10uF / 16V RE6140 2 1 100U/25VRB ELECT CAPACITOR 100uF / 25V

Output Side of the 12V Regulator, next to the IC

RE6150 1 100U/63VRB ELECT CAPACITOR 100uF / 63V RM7115 1 .068UF 68NF 100V MKT POLY 0.068uF / 68n / 683 RM7125 2 .1UF 100NF 100V MKT POLY 0.1uF / u1 / 100n / 104 RM7145 1 .22UF 220NF 100V MKT POLY 0.22uF / u22 / 220n / 224 SEMICONDUCTOR(S) Cat.# Qty* Description Component Identification And/Or Location PI6502 1 16 PIN IC SOCKET PCB TIN/G ZK8850 1 UA494/ TL494 SWITCHMODE IC UA494/TL494 ZR1014 1 1N5404 3A 400V DIODE 1N5404 ZR1030 2 1 MUR1560/STTA1206D FAST RECOVERY

DIODE D2 MURI 560

ZT2179 1 BC639 NPN 80V 1A SIG TO92 BC639 ZT2180 1 BC640 PNP 80V 1A SIG TO92 BC640 ZT2450 1 STP60NE06 / BUK456-60 N-CH FET *** STP60NE06 / BUK45660 ZV1512 1 7812 +12V 1AMP TO-220 7812 / LM340T12 HARDWARE / WIRE(S) / MISCELLANEOUS Cat.# Qty* Description Component Identification And/Or Location EC7978 2 1 PCB (KC5225) SC11106971 REV2 SC06/97 SEE NOTES AND ERRATA NS3015 50m SOLDER 60/40 1MM 1KG RL

26 SILICON CHIP

These days, car manufacturers arecoming to realise that running pumpsfull bore all the time is wasteful of thebattery/electrical system and alsocauses premature wear of the fuelpump. A prime example of this is thepump use to pressurise the fuel rail infuel injection cars. The pump runs

A high-currentmotor speed controlfor 12V & 24V systemsThis pulse width-modulated 20A speed controlcan be used for controlling 12V DC motors incars. Examples are pumps for fuel injection,water/air intercoolers & water injection onmodified performance cars. It could also beused for headlight dimming in the daytime & forrunning 12V motors & pumps in 24V vehicles.

Design by RICK WALTERS

continuously, regardless of the fueldemand, and the excess fuel is bledoff to the fuel tank to keep the pres-sure constant.

In the future, most cars will havefuel pumps which are variable speedcontrolled according to fuel demand.In the meantime, you can do it now

with this design, using the car�s mapsensor output as a measure of fueldemand. However, the exact methodfor doing this is beyond the scope ofthis article.

The circuit can control 12V loadsup to 20 amps and it uses just twoMosfets to do it.

Other possible applications for thisPWM circuit are for control of 12Vand 24V motors in model locomotivesand cars and in control applicationsin manufacturing. The circuit hasexcellent line and speed regulationand uses just one low-cost IC as wellas the two Mosfets.

Note: this circuit is not suitable foroperating 12V audio equipment in 24Vvehicles since its output is pulsed ataround 2kHz.

As presented, the circuit incorpo-rates a �soft start� feature which isdesirable to reduce inrush currents,particularly if the device is used tocontrol 12V incandescent lamps. How-ever, for some pump applications thesoft start may not be wanted and sowe�ll tell you how to disable it.

We are presenting this project as astandalone PC board. If you want toput it in a case it is a simple matter toinstall it in a suitable plastic box butthat will be up to you. The PC boardhas all components on it except for adiode (D2) and a capacitor which mustbe wired across the motor beingdriven. If the circuit is used to controlincandescent lamps, the diode andcapacitor are not required.

Circuit descriptionThe heart of the circuit shown in

Fig.1 is a TL494 pulse width modula-tion (PWM) controller. It varies theoutput voltage fed to the motor byrapidly turning Mosfets Q3 & Q4 onand off. Because the Mosfets are being

This small PC board will provide speed control of 12V or 24V motors drawingup to 20A. Not shown on this prototype board is the input protection diode D1

JUNE 1997 27

switched fully on or fully off, theydissipate very little power, even whenhandling currents as high as 20 ampstotal. This means that they do not getvery hot and no heatsink or very smallheatsinks (depending on the outputcurrent) are required.

Note that the TL494 is normallyused in switchmode power supplyapplications but it is suitable for vir-tually any PWM application. Its blockdiagram is shown in Fig.2. The chipcontains the following functions:� An oscillator, the frequency ofwhich is determined by a capacitor atpin 5 and a resistor at pin 6.� A stable +5V reference at pin 14.� A �dead time� comparator with oneinput driven from the oscillator.� Two comparators (pins 1, 2, 15 &16) with their outputs ORed togethervia diodes (pin 3).� A PWM comparator with one inputfrom the oscillator and the other fromthe ORed output of the two compara-tors.� A flipflop driven by the dead timeand PWM comparators.� Two 200mA transistors with un-committed emitters (pins 9 & 10) andcollectors (pins 8 & 11), with theirbases driven by the outputs of theflipflop.

In simple terms, the TL494 oper-ates as follows. Its oscillator is set torun at 2kHz and it produces a pulsetrain at its outputs at this frequency.The width of the pulses is varied (ie,pulse width modulated) and the ratioof the �on� time to the �off� timecontrols the amount of power fed tothe load which in this case is themotor.

A fraction of the output voltage isfed to one input of one of the compa-rators, while the other input is con-nected to a reference voltage. If theoutput voltage rises slightly, the com-parator input will sense this changeand will alter the output on-off ratioand consequently the output voltage.This keeps the voltage at the compara-tor input equal to the reference volt-age.

This is done by reducing the driv-ing pulse on time, reducing the timethe switching device is turned on,thereby bringing the output voltageback to the required level. The con-verse applies for falling output volt-ages.

Now if we refer to the circuit ofFig.1 again, we see that the TL494 isfed via a 7812 12V regulator. This isnot strictly essential for the TL494since it can operate with a supply

ranging from +7V to +40V. However,it is important that the gate drive toMosfets Q3 & Q4 does not exceed theirspecifications and so this condition ismet with REG1.

In this circuit, the output duty cy-cle must be able to be controlled overa wide range, from virtually zero up tothe maximum of around 90% and sothe two internal transistors (C1 pin 8and C2 pin 11) have their collectorsconnected to the +12V supply and areused as emitter followers to pull thebases of Q1 & Q2 to +12V. The 2.2kWresistor at pins 9 & 10 is the commonemitter load and it pulls the bases toground. Thus, the emitters of Q1 &Q2, together with the gates of Q3 &Q4, swing from 0V to +12V and so thegate drive signal is limited to this volt-age.

Q1 & Q2 are included for anotherreason and that is to rapidly chargeand discharge the gate capacitances ofthe Mosfets each time they turn onand off. This improves the switchingaction of the Mosfets; ie, it speeds upthe turn-on and turn-off times andthereby reduces the power dissipa-tion in the Mosfets.

Soft startA soft start circuit is incorporated

Fig.1: the heart of the circuit is a TL494 pulse width modulation (PWM) controller. It varies the output voltage fed tothe motor by rapidly turning Mosfets Q3 & Q4 on and off. Note that diode D2 is essential to the circuit operation.

28 SILICON CHIP

to reduce surge current into the motorat turn on. When power is first ap-plied, the REF output, pin 14, rapidlycharges its associated 10mF capacitor,C1. This pulls the INH(hibit), pin 4,high as the 10mF capacitor (C2) be-tween pins 14 and 4 is initially dis-charged. While pin 4 pin is high thereis no output from pins 9 & 10. Ascapacitor C2 charges through the100kW resistor the voltage on pin 4will gradually fall and the output pulsewidth will increase, giving a smoothrise in the output voltage.

In order to control the output volt-age precisely, the TL494 monitors bothsides of the motor; ie, the input volt-age before the 12V regulator (MOTOR+) and the voltage at the Mosfet Drains(MOTOR -).

The MOTOR+ voltage is fed via the20kW and 2.2kW voltage divider resis-tors to comparator 1, pin 1. The MO-TOR- voltage is attenuated by the 18kWand 4.7kW resistors and fed through a47kW resistor to pin 2. The voltagetapped off the +5V reference by thespeed control, VR1, is also fed througha 47kW resistor to pin 2.

When the speed control wiper is atminimum setting (ie, 0V), the voltageat the junction of the 18kW and 47kWresistors will be forced to be twice

that on pin 1 of IC1 (nominally 1.4Vfor +14V input), as the voltage dropacross each 47kW resistor will be 1.4V.The voltage at the MOTOR- terminalwill be about +14V and so the motorwill not run.

As VR1 is advanced, the voltage atthe MOTOR- terminal will decrease,thereby applying a larger voltage tothe motor so it can run.

Normally, the reference voltage onpin 1 of IC1 is fixed and referred to the5V reference at pin 14. In our case thiswould not be desirable as the outputvoltage sensed and regulated by IC1 isbetween the MOTOR- output andground (across the 4.7kW resistor).

This means that as we vary the sup-ply voltage, the voltage between MO-TOR- and ground will be held con-stant but the voltage across the motorwill vary in a direct relation to thevoltage change. By connecting the20kW resistor between the input railand pin 1 of the TL494 we compen-sate for this.

ProtectionReverse polarity protection is pro-

vided by diode D1. It is rated at 3Aaverage but has a one-off surge ratingof 200A and will blow the fuse if theleads to the battery are reversed.

Two essential components to thecircuit are not mounted on the PCboard but are wired directly acrossthe motor itself: D2 and C3. Diode D2is the most important as it preventsthe generation of excessive voltagespikes, each time the Mosfets turn off.D2 must be a fast recovery diode be-cause of the very fast switching of theMosfets.

The importance of diode D2 andthe associated 0.22mF capacitor C3is demonstrated in the oscilloscopewaveforms of Figs.3, 4, 5 & 6. Thewaveform in Fig.3 shows the circuitdriving a resistive load which couldbe a heater element or an incandes-cent lamp. Notice that the waveformis a clean pulse with a duty cycle ofabout 74%. This gives a voltage ofabout 8.8V across the load.

Now have a look at Fig.4. This showsthe circuit set for the same outputwhen driving a motor instead of aresistive load. The scope�s vertical sen-sitivity has been changed to 20V/divinstead of 5V/div. Notice the enor-mous spike voltage amounting to al-most 80V peak-to-peak, each time theMosfets turn off.

This spike voltage is enough to blowthe Mosfets because their Drain-Sourcevoltage rating (VDS) is only 60V.

Fig.2: functional block diagram of the TL494. This chip is intended mainly for switchmode power supplies butwe have adapted it to control motors and resistive loads.

JUNE 1997 29

Fig.5 shows the same circuit condi-tions but with diode D2 connectedacross the motor to clip the voltagespikes. We now see the motor�s back-EMF during the Mosfet �off� period,showing a value about half of thatapplied by the control circuit.

Finally, Fig.6 shows the effect whenboth the diode and 0.22mF capacitorare fitted to the circuit. The capacitorhas a filtering effect, removing most ofthe hash generated by the motor�scommutator.

The reason that diode D2 and the

0.22mF capacitor C3 are fitted directlyacross the motor instead of beingmounted on the PC board is that thismethod stops the motor leads fromradiating commutator hash whichcould otherwise interfere with sensi-tive circuitry elsewhere in the car.

The current rating of diode D2 mustsuit the rating of the motor. It�s notmuch use connecting a 5A diodeacross a motor that pulls 20A; it willjust blow the diode and then blow theMosfets.

Finally, also not mounted on the PC

board is the in-line input fuse F1. Thismust also match the rating of the mo-tor.

PC board assemblyThe PC board for this design is coded

11106971 and measures 68 x 50mm. Itis fairly easy to assemble as it only hasa few components on it. Begin bychecking the copper pattern againstthe PC artwork (Fig.8) and repair anydefects such as undrilled holes, shortsor open tracks. The component over-lay is shown in Fig.7.

Fig.3: this scope capture shows the waveform across aresistive load which could be a heater element or anincandescent lamp. Notice that the waveform is a cleanpulse with a duty cycle of about 74%. This gives avoltage of about 8.8V across the load.

Fig.4: this waveform shows the circuit set for the sameoutput as for Fig.3 but driving a motor instead of aresistive load. The scope�s vertical sensitivity has beenchanged to 20V/div instead of 5V/div. Notice theenormous spike voltage (amounting to almost 80V p-p)each time the Mosfets turn off. This spike voltage isenough to blow the Mosfets because their Drain-Sourcevoltage rating (VDS) is only 60V.

Fig.5: this waveform was produced with the same circuitconditions as for Fig.4 but with D2 connected across themotor to clip the voltage spikes. We now see the motor�sback-EMF during the Mosfet off period, showing a valueabout half of that applied by the control circuit.

Fig.6: this scope waveform shows the effect when bothdiode D2 and the 0.22mF capacitor are fitted to the circuit.Note that the capacitor has a filtering effect which acts toremove most of the hash generated by the motor�scommutator.

30 SILICON CHIP

Fit and solder the resistors, using acut pigtail from one of them for theone link. This done, fit the IC, REG1and trimpot VR1, followed by thetransistors, capacitors and the Mosfets.

If you intend to operate the control-ler from a 12V battery and don�t in-tend to draw more than 6A you canuse one Mosfet. Provided a smallheatsink is fitted you can probablydraw up to 10A with one Mosfet. Forhigher currents, two Mosfets must beused, as shown on the circuit of Fig.1.If you want the full 20A load current,both Mosfets should be fitted withsmall heatsinks.

TestingIf you are careful with the assem-

bly, it should work first up. Turn VR1fully clockwise (minimum speed) andsolder a resistor of around 100W 5Wacross the motor terminals. If you havea variable power supply, feed 14V tothe DC input and ground. If you don�thave a power supply you will have toconnect the controller directly to a+12V battery.

With the negative meter lead con-nected to the 0V line, you should beable to measure about +12V on pin 16and +5V on pin 14 of IC1. The voltageon pin 1 of IC1 should be around+1.4V with 14V input and +1.2V with12V input. If these values are OK pro-ceed with the following tests.

If you now connect the meter leadsacross the 100W resistor it should readzero volts. Rotate trimpot VR1 slowlyanticlockwise and the voltage shouldincrease up to about 12V when fullyrotated.

Because IC1 has an internal �deadtime� of 10%, the output devices can

Fig.8: actual size artwork for the PC board.Fig.7: the component overlay for the PC board.

only be turned on for 90% of the timeand the output voltage will never bethe same as the input. For 14V input,the maximum output will be about12.5V.

Be careful not to burn yourself asthe 100W resistor will become hot atthe maximum setting of VR1.

Using the speed controllerAs noted above, the rating of the in-

line fuse will depend on the load youplan to drive. Obviously a 20A fuse

will not protect a 1A motor.If you don�t want the soft-start facil-

ity, it can be disabled by omitting ca-pacitor C2. We recommend that thesoft-start facility be included for in-candescent loads. However, for mo-tor loads, a better approach would beto connect a 1kW 1W resistor acrossthe output terminals and then place aswitch in series with the motor orwhatever load you wish to drive. Youthen set up the drive voltage you re-quire with trimpot VR1 and use thein-line switch to connect and discon-nect the motor.

If resistive or incandescent loadsare to be driven, D2 and C3 are notnecessary but they must be includedwhen driving any motor, regardless ofits current rating.

D2 must be rated to handle a cur-rent at least equal to that drawn by themotor. A suitable cheap diode is theMUR1515 which is rated at 150V 15Aand should cover most applications.If you want to run a 20A motor, thenuse two MUR1515s in parallel. Makesure that they are connected in theright direction across the motor; ie,anodes to the positive supply line. Ifconnected the other way around, youwill blow the fuse and perhaps theMosfets too.

C2 should be an MKT polycarbonatecapacitor with a rating of at least100VW. The type of FET used de-pends on the current drawn by thecontrolled device. The BUK456-60sspecified are readily available andhave an �on� resistance of .028W.

If you want high currents and 24Voperation, the MTP60N06 is a moresuitable device. It has an �on� resist-ance of .01W. SC

1 PC board, code 11106971, 68x 50mm

1 5kW PC trimpot (VR1)

Semiconductors1 TL494CN switching regulator

(IC1)1 7812 regulator (REG1)11 BC639 NPN transistor (Q1)1 BC640 PNP transistor (Q2)1 or 2 BUK456-60A/B/H

N-channel Mosfets (Q3,Q4)

Capacitors2 100mF 50VW PC electrolytic2 10mF 16VW PC electrolytic

(C1,C2)1 0.22mF 100VW MKT

polycarbonate (C3)2 0.1mF MKT polycarbonate1 .068mF MKT polycarbonate

Resistors (0.25W, 1%)1 1MW 1 10kW1 100kW 1 4.7kW2 47kW 2 2.2kW1 20kW 2 4.7W1 18kW 1 100W 5W (testing)

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1N

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