why 7805 ic becom hot?

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i drive a relay by a transistor and base is conected to pt2272.relay drive a dc motor.whenever motor isnot conected to relay,circuite worke well.but when motor conect , ic and 7805 becom hot and circuite dosnot worke.plz hlp me
circute has problem to inductans loads becease when i conecte a resistor instead of motor , it works well

ckshivaram

put the circuit?? what is the current drawn by motor ? did you measure the voltage when it becomes hot.........

points: 2

Member level 1
yes.7805 has not 5 volt.it decreas

ckshivaram

Does it give 5V only when it is hot or always.. please check it... answer my previous post... motor current rating.. the motor is drawing more current so more is drawn from 7805 so it becomes very hot.. do you use any motor driver IC like uln 2803 or l293D?

put your circuit here, so that we can see it.

points: 2

andre_teprom

Super Moderator
Staff member
Also, check if voltage regulator heatsink dimension is properly scaled.

+++

points: 2

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alexxx

Is there any supply for the collectors? I don't see any....

Furthermore you need flyback diodes. This is relay drive basics and concerning of course inductive loads. Take a look at this.

points: 2
V
points: 2

Zanderist

Member level 3
I'm just going to take a shot at this and say, what is the resistance of the motor's windings? Your motor might be improperly sized, also take in consideration the load being placed on the motor.

Also refer to the datasheet of your 7085 to see if this hot temperature you are getting is normal. From the top of my head 7805 can pass maybe about 1 amp if properly heat sinked.

Also see if the 7805 shuts its self off, it has an over heat safety built into it.

points: 2
V
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boldstone

Junior Member level 3
The hot is waste power. see the below formula
W=(Vin-Vout)*I
Vin: inpout voltage of regulator
Vout: output voltage of regulator (in this case =5V)
I: regulator currnt when motor is connected
W: dissipated energy by regulator

if W is greater then absolute maximum rating in the 7805 datasheet you sould change it with another stronger regulator.
to dcrease the heat you can use heatsink (it is recommended) or if possible decrease input voltage. for example if you are using 12v transformer then you can use 6 7 volt transformer.

V
points: 2

points: 2

KerimF

i drive a relay by a transistor and base is conected to pt2272.relay drive a dc motor.whenever motor isnot conected to relay,circuite worke well.but when motor conect , ic and 7805 becom hot and circuite dosnot worke.plz hlp me
circute has problem to inductans loads becease when i conecte a resistor instead of motor , it works well
According to your schematic, the motor current doesn't come from 7805 output, the relay pole is connected to Vcc which is the input of the 5V regulator. Perhaps by mistake, you connected the pole of each relay to 5V instead of Vcc ;-)

Kerim

points: 2

dv_sa559

be sure that reverse and direct voltage produce by motor when you turn on and turn off or changing motor polarity don't effect into source.
maybe if you place zener diode before regulator ,it protect your regulator against over voltage.
so you use free wheeling diode for each transistor (safety).

points: 2

ali1390

points: 2

Member level 1
According to your schematic, the motor current doesn't come from 7805 output, the relay pole is connected to Vcc which is the input of the 5V regulator. Perhaps by mistake, you connected the pole of each relay to 5V instead of Vcc ;-)

Kerim
no.i connected it to vcc.it is right.when motor is disconnect, it worke well.

---------- Post added at 22:07 ---------- Previous post was at 21:59 ----------

be sure that reverse and direct voltage produce by motor when you turn on and turn off or changing motor polarity don't effect into source.
maybe if you place zener diode before regulator ,it protect your regulator against over voltage.
so you use free wheeling diode for each transistor (safety).
it use free wheeling diode and put 2200uf capasitor parallel to it.it becom beter but it dose not becom well compelet

Zanderist

Member level 3
What do you mean by well complete?

That cap you added might be sucking energy away from the motor.

points: 2

KerimF

I try to find out from your schematic a sort of relation between activating the motor and the fact that 7805 gets hot as a consequence.
The supply of the relay coil is missing but this won't make a difference (if Vcc or 5V) since you said that replacing the motor by a resistor you get no problem.

I think what makes your 5V regulator hot (when the motor runs) has something to do with the real circuit layout (PCB, wiring connections) and not its schematic.

If this was happening with me I won't be able to sleep till I found the reason ;-) though to fix it, it may take more work and time later.

Kerim

points: 2

boldstone

Junior Member level 3
Please put an ampermeter series with Motor to measure the actual current pass through the motor.
Another time swap motor with a resistor that you said and measure again.
It will help us to find the root of problem.

points: 2

Member level 1
What do you mean by well complete?

That cap you added might be sucking energy away from the motor.
it meanes that circuite worke well but sometimes occur same problem.

thannara123

is motor work well or have it any problem ?
did you use another motor ?
what is your motor specification ?

points: 2

Zanderist

Member level 3
Do you have a back-up 7805?

Maybe the one you have is damaged.

It might work fine if you have a resistor that's going to make a constant voltage drop, but with a motor the voltage drop would be dependent on the load on the motor.

If that's the case I would say make your Vcc a little larger to compensate for any spike in the load, don't build it to the bare minimum.

Is this a brand new motor? If it's old, maybe the commutator has become dirty. Inspect the motor.
Try with a different motor.

EDIT:
I think I know what it is, It's the relays. The magnetic field in the coil isn't decaying fast enough keeping the contact in place, causing a short from Vcc through the motor to ground. The motor then must be of very small resistance, if this is the case then 7805 along with the motor should be heating up.

Just use the transistor, copy and paste the following configuration in the Circuit Simulator Applet. Just go to file and import.
Code:
\$ 1 5.0E-6 10.20027730826997 50 5.0 50
t 256 272 336 272 0 1 -5.690645832236385 0.0 100.0
w 336 176 416 176 0
w 336 256 416 256 0
w 416 256 480 256 0
w 416 176 480 176 1
d 416 256 416 176 1 0.805904783
l 512 176 512 256 0 1.0 0.016854707487265246
R 336 176 336 96 0 0 40.0 5.0 0.0 0.0 0.5
g 336 336 336 416 0
R 224 272 160 272 1 2 100.0 2.5 2.5 0.0 0.5
r 480 176 512 176 0 100.0
w 512 256 480 256 0
r 336 176 336 256 0 100.0
w 256 272 256 320 0
w 336 288 336 320 0
w 336 320 336 336 0
r 256 320 336 320 0 100000.0
w 224 272 256 272 0
o 6 64 0 35 5.0 0.05 0 -1
Another possible way to do this keeping the relays is to add a resistor to the relay coil.

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points: 2

alexxx

when i conecte a resistor instead of motor , it works well
Motor's physics are much more complicated (non linear actually) than the resistor's. We are missing basic information here.

Imagine the case when motor speens and suddenly you leave its edges floating. Then you would have a spinning conductor inside a magnetic field and so a generator. If at this case you short the edges, then you would short the generators edges, so the voltage tends to go to zero. Generator voltage to zero (and since the magnetic field is still there) means no spinning so this is how you break the motor. If instead of shorting, you move both switches at the same time, then you would supply the motor with a reverse voltage from the generator fuction of the machine, tending to give a very sudden direction reverse. A resistor cannot give you all those, so timing is important.

What is the supply before 7805? According to all the above maybe the supply of the motor is not enough. Maybe. We wouldn't know unless you tell us.

Is there any other circuit on 5V after PT2272?
After how much time is it getting hot?
What is the output of 7805 when it is getting hot?
You use the freewilling diode where? It does not exists in the given schematic...

Hot 7805 means a lot of power consumed on 5V and not on the motor, but you say that when the motor is out, everything works well.
I think that it is better to do some tests first (amperometer, voltometer). Measure the motor current, 7805 current, motor voltage on osciloscop etc, at all conditions. It is a very simple circuit, I'm sure that you will figure it out.
But if you again need further help please give us more information, otherwise we are just assuming...

points: 2

KerimF

Perhaps you may like to supply manually the motor by Vcc (after removing its two terminals from the relays) and while the circuit is running.