Okay, so I have this motor and it is powered by a 24VDC power supply, and I would like to vary the voltage going to this motor. This motor draws 0.4A with 24V. I understand that connecting a pot normally to this motor will burn out the pot rather quickly, so one must use a NPN transistor. I reckon in this fashion:
V+ ---+---------------+ | | P /c O
Use a darlington for the transistor, and a 1K pot.
For 24 VDC it needs to be a 1 watt pot. And a diode across the motor might be needed to absorb back EMF (DC generation) as it slows down.
Paul
Investigate this concept instead:
That will run sorta hot. 5K is reasonable with a darlington.
John
For .4A, a 2.2k pot would probably work fine. You also need a diode in parallel with the motor, pointing up. That will carry any current due to starting and stopping the motor, preventing it from eating your transistor with a voltage transient.
Also, I would probably use another NPN transistor in a darlington configuration (as suggested by Sjouke Burry). If you use the extra transistor, you can use a much smaller pot, like 10k, which will be cooler with a 24V supply:
So, the full circuit would look like this:
24V------o-------o--------. | | | | | | .-. |/ | 10k | | | '-' | | | | |/ | o------| 2N3055 | | |>| | | | | 1k_ | | '--|___|-o | | | .--------o | | | | | .---o----. | - | | | ^ | motor | | 1N4001 | | | | '---o----' | | | | | | GND--------o-------o--------' (created by AACircuit v1.28.6 beta 04/19/05
Here is a simulation using LTSpice for your amusement. Note that the power through the 2N3055 is going to be about 2.4W at the maximum point, so you may need a heat sink.
You can download LTSpice from
It is quite fun to try things out with, but don't believe it too much; always use prototyping as well.
-------- pot-motor.asc -------- Version 4 SHEET 1 880 680 WIRE 144 32 0 32 WIRE 352 32 144 32 WIRE 480 32 352 32 WIRE 144 64 144 32 WIRE 352 64 352 32 WIRE 288 112 192 112 WIRE 480 128 480 32 WIRE 352 176 352 160 WIRE 416 176 352 176 WIRE 352 192 352 176 WIRE 352 208 352 192 WIRE 0 240 0 32 WIRE 480 272 480 224 WIRE 480 272 352 272 WIRE 480 304 480 272 WIRE 352 320 352 272 WIRE 0 400 0 320 WIRE 144 400 144 144 WIRE 144 400 0 400 WIRE 352 400 352 384 WIRE 352 400 144 400 WIRE 480 400 480 384 WIRE 480 400 352 400 FLAG 0 400 0 SYMBOL voltage 0 224 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 24 SYMBOL npn 416 128 R0 SYMATTR InstName Q1 SYMATTR Value 2N3055 SYMBOL res 464 288 R0 SYMATTR InstName R1 SYMATTR Value {24/.4} SYMBOL potentiometer 128 48 R0 WINDOW 3 -72 140 Left 0 SYMATTR Value Rtot=10K wiper={X} SYMATTR InstName U1 SYMBOL npn 288 64 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL diode 368 384 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D1 SYMATTR Value 1N914 SYMBOL res 368 288 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R2 SYMATTR Value 1k TEXT -32 424 Left 0 !.op TEXT -48 472 Left 0 !.step param X .1 .9 .1
------------ end of pot-motor.asc ----------------------
r r r
I think that circuit would be perfect. I think I have all the necessary parts at home. I'll try it out soon and tell you how it goes!
r r r
Now I don't have a 2N3055 handy... But I do have an NPN - PMD16K100 Transistor laying around I could use. Would it be okay if I swapped them? Here are the stats of the PMD16K100:
source:
Absolute Maximum Ratings: (TA =3D +25=B0C unless otherwise specified) Collector-Emitter Voltage, VCEO . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 100Vb Collector-Base Voltage, VCB . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .
100V Emitter-Base Voltage, VEB . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . 5V Collector Current, IC =20 Continuous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . = .. . . . . . . . . . 20A =20 Peak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . = . . .. . . . . . . . . . 40A Base Current, IB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .= . . . . . . 500mA Total Power Dissipation (TC =3D +25=B0C), PD . . . . . . . . . . . . .. . . . . . . . . . 160W Derate Above 25=B0C . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .= . . 0.915W/=B0C Operating Junction Temperature Range, TJ . . . . . . . . . . . . . .. . . . . . . . . -65=B0 to +200=B0C Storage Temperature Range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65=B0 to +200=B0C Thermal Resistance, Junction-to-Case, RthJC . . . . . . . . . . . . . . . . . . . . . 1.09=B0C/WAnd here is the stats for the 2N3055 just for reference:
Source:
Collector-Emitter Voltage VCEO 60 Vdc Collector-Emitter Voltage VCER 70 Vdc Collector-Base Voltage VCB 100 Vdc Emitter-Base Voltage VEB 7 Vdc Collector Current - Continuous IC 15 Adc Base Current IB
7 Adc Total Power Dissipation @ TC =3D 25=B0C PD 115 W Derate Above 25=B0C 0.657 W/=B0C Operating and Storage Junction Temperature Range TJ, Tstg -65 to +200=B0CThanks!
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You can use that. Just add a 4.7K resistor & diode across the motor to your original:
V+ ---+---------------+ | | P /c O|-------+ | | Gnd --+---[Motor]-----+
Ed
..
otor
ler
wer
ou
. . =A0.. . . . . . . . . .
. . . =A0. .. . . . . . . . . .
. . . . . . . .
. . . .
o=A0 =A0 =A0 =A060 =A0 =A0 =A0Vdc
=A0 =A0 =A0 =A070
VCB =A0 =A0 =A0 =A0 100 =A0 =A0 Vdc
=A0 VEB =A0 =A0 =A0 =A0 =A07
=A0 =A0 =A0 15 =A0 =A0 =A0Adc
=A0 =A0 =A0 =A0 =A0 =A0 =A0IB
=A0115 =A0 =A0 W
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A00.657
=A0 =A0 TJ, Tstg =A0 -65 to
I was planning on using a darlington pair for this project...
Your transistor is already a darlington transistor, meaning the two transistors is built into it, so use ehsjr's circuit, and you'll be fine.
Regards, Bob Monsen
oh, perfect! Would a 10k pot still do the trick?
oh, perfect! Would a 10k pot still do the trick?
oh perfect! Will my 10k pot still be fine?
oh perfect! Will my 10k pot still be fine?
=======================================================
10k pot is fine, and really the 4.7 k base resistor is not necessary for an emitter follower.You will only be able to get about 22.5 volts from a 24 VDC supply with a darlington.
You can get a bit more by using a
I set up a programmed voltage source and 5k resistor to simulate the pot, and it shows the inductive kick from the motor when it is turned off quickly. A real motor will also exhibit back EMF due to its action as a generator as it coasts to a stop.
Paul
=======================================================
Version 4 SHEET 1 880 680 WIRE 352 -128 32 -128 WIRE 448 -128 352 -128 WIRE 448 -64 448 -128 WIRE 352 -32 352 -48 WIRE 352 64 352 48 WIRE 448 64 448 0 WIRE 448 64 352 64 WIRE 352 96 352 64 WIRE 352 96 256 96 WIRE 32 128 32 -128 WIRE 192 144 160 144 WIRE 160 176 160 144 WIRE 352 176 352 96 WIRE 256 224 256 192 WIRE 288 224 256 224 WIRE 160 288 160 256 WIRE 32 432 32 208 WIRE 160 432 160 368 WIRE 160 432 32 432 WIRE 352 432 352 272 WIRE 352 432 160 432 WIRE 32 448 32 432 FLAG 32 448 0 SYMBOL voltage 32 112 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 24 SYMBOL pnp 192 192 M180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL npn 288 176 R0 SYMATTR InstName Q2 SYMATTR Value 2N3055 SYMBOL res 336 -144 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL diode 464 0 R180 WINDOW 0 -25 64 Left 0 WINDOW 3 -99 0 Left 0 SYMATTR InstName D1 SYMATTR Value MURS120 SYMBOL ind 336 -48 R0 SYMATTR InstName L1 SYMATTR Value 100m SYMBOL voltage 160 272 R0 WINDOW 3 -95 138 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PWL(0 24 0.1 0 0.9 0 0.901 24) SYMBOL res 144 160 R0 SYMATTR InstName R2 SYMATTR Value 5k TEXT -2 472 Left 0 !.tran 1 startup
.
e.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D
an
r, as in the following LTspice
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D
Actually, a Sziklai pair might be the best for me, because the PMD16K100 I snagged turns out to be a PNP transistor, rather than a NPN, which a assumed it was.
Now would I hook it up like this?
24V------o----------------. | | | |/ | o------| PMD16K100 (PNP) | | |< | | | .-. |/ | 10k | | | '-' | | | | | | '--------o | | | .--------o | | | | | .---o----. | - | | | ^ | motor | | 1N4001 | | | | '---o----' | | | | | | GND--------o-------o--------'
Actually, a Sziklai pair might be the best for me, because the PMD16K100 I snagged turns out to be a PNP transistor, rather than a NPN, which a assumed it was.
Now would I hook it up like this?
24V------o----------------. | | | |/ | o------| PMD16K100 (PNP) | | |< | | | .-. |/ | 10k | | | '-' | | | | | | '--------o | | | .--------o | | | | | .---o----. | - | | | ^ | motor | | 1N4001 | | | | '---o----' | | | | | | GND--------o-------o--------'From my research, your PMD16K100 is an NPN darlington, and its PNP complement is PMD17K100. If it is actually a PNP, then your hook-up is correct. Being a darlington, you lose another 1/2 volt. The data sheet I was directed to was:
Make sure you determine the correct polarity for the transistor. Sometimes an ohmmeter check can give confusing indications.
Paul
as in the following LTspice
A pnp transistor with the colle3ctor to the + side? No way. Stick to one npn darlington instead.
Actually, you can use the PNP, it's just upside down. the emitter needs to go to the (+).
This configuration works well with in a 0.7 V window of regulation.
...
m...
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D
ce
a a=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D
So Jamie, this looks better:
24V------o----------------. | | | |< | o------| PMD16K100 (PNP) | | |\\ | | | .-. |/ | 10k | | | '-' | | | | | | '--------o | | | .--------o | | | | | .---o----. | - | | | ^ | motor | | 1N4001 | | | | '---o----' | | | | | | GND--------o-------o--------'ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.