Question RE: NE555 pulse generator - Electronic Circuits Projects Diagrams Free

dwhitt · 8th July 2009, 06:42 PM

I have a circuit using the NE555 wired in the typical astable operation. I am using ~6.1V input (Vdd). However my ouptput square wave is measuring 3.2V. I need the ouput square wave to be at least 5V.

What is causing this and what can I do to correct this problem?

FWIW I also tried using ~12V input but I kept burning up chips. It seems to work fine with the lower volate but I am getting the unwanted voltage drop.

Thanks in advance.

BrownOut · 8th July 2009, 06:43 PM

You probably have the output overloaded. Post a schematic of your whole circuit.

dwhitt · 8th July 2009, 06:47 PM

Thanks. I only have a hand drawn one at the moment but will try to come up with something to post before I leave today.

dwhitt · 8th July 2009, 07:33 PM

See if this works. I did this quickly and please keep in mind that drawing electrical schematics are not part of my job so forgive me if I got a symbol wrong.

The switch is actually a double pole double throw switch but the second switch is practically independent with its own power supply. The output of the relay is also on that second schematic.

I'm not sure what information you may need on the counter/timer. If you have specific questions let me know and I can look it up for you. Thanks again.

bailey45 · 8th July 2009, 08:49 PM

The output of a NE555 (Fairchild Version) is rated at 100mA output at 5 volts, however at this output the voltage is down to 3.3 volts. Sounds like you have more than 100mA load on your output. The coil resistance of your relay need to be greater than ~100 ohms for a 5 volt relay.

BrownOut · 8th July 2009, 09:01 PM

Right. You most likely need a transistor to drive the relay.

dwhitt · 8th July 2009, 09:15 PM

Thanks for the inputs Brown and Bailey. Just to clarify... I need to put in a transistor between the output of the NE555 and the relay?

axro · 8th July 2009, 09:21 PM

Quote:

Originally Posted by dwhitt

Thanks for the inputs Brown and Bailey. Just to clarify... I need to put in a transistor between the output of the NE555 and the relay?

Yep, that is correct

BrownOut · 8th July 2009, 10:58 PM

Something like this could get you started, assuming that the relay is small

Hero999 · 8th July 2009, 11:57 PM

The TTL version is rated to 200mA, the CMOS version is rated to 100mA and that depends on the supply voltage.

What's connected to the output of the 555?

dwhitt · 9th July 2009, 06:46 PM

The relay is a Magnecraft W6225DSX-1. I don't see anything from the packaging that tells me the coil resistance? These are the specs they gave me:

Solid State Panel Mount Relay

Control Voltage Type: DC

Load Current RMS Max: 25A

Contacts: SPST-NO

Control Voltage Max: 32V

Control Voltage Min: 3V

Output Current: 25A

Output Device: SCR

Output Type: SCR

Output Voltage: 280VAC

RoHS Compliant: YES

The NE555 I have is (don't laugh) a radio shack brand chip (TLC555 Timer). High output current capacity Sink: 100 mA (typ) and Source: 10mA (Typ).

So this is what I purchased today- two NPN Silicon Transistor: one with an Ic of 3A and the other with 10A.

Please advise which transistor would be best and also please take a look at my updated schematic to see if this *Should* work. TIA.

BrownOut · 9th July 2009, 07:05 PM

I did't realize you were using a SS relay. Accordig to the data sheet, the input resistrance should be 1500 ohms, minimum. You're timer should be capable of driving that directly, unless I'm missing something.

Try disconnecting the relay and measuring the output of the timer. Maybe something else is going on.

dwhitt · 9th July 2009, 07:13 PM

OK. I will try disconnecting the relay, measuring the output.

Then connect doing the same with the timer. I will hold off on the transistor for now and report back.

ericgibbs · 9th July 2009, 07:14 PM

Quote:

Originally Posted by dwhitt

Please advise which transistor would be best and also please take a look at my updated schematic to see if this *Should* work. TIA.

hi,
Your circuit will not work as expected also the freq of the 555 is 75Hz, the relay will buzz.!

dwhitt · 9th July 2009, 07:15 PM

Quote:

Originally Posted by ericgibbs

hi,
Your circuit will not work as expected also the freq of the 555 is 75Hz, the relay will buzz.!

Can you please elaborate on this? I am not sure I am understanding?

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8th July 2009, 06:42 PM	#1
dwhitt	Question RE: NE555 pulse generator added schematic I have a circuit using the NE555 wired in the typical astable operation. I am using ~6.1V input (Vdd). However my ouptput square wave is measuring 3.2V. I need the ouput square wave to be at least 5V. What is causing this and what can I do to correct this problem? FWIW I also tried using ~12V input but I kept burning up chips. It seems to work fine with the lower volate but I am getting the unwanted voltage drop. Thanks in advance. Last edited by dwhitt; 8th July 2009 at 08:04 PM.

8th July 2009, 06:43 PM	#2
BrownOut	You probably have the output overloaded. Post a schematic of your whole circuit. __________________ You don't need a quadraphonic Blaupunkt -- you need a curve ball.

8th July 2009, 06:47 PM	#3
dwhitt	Thanks. I only have a hand drawn one at the moment but will try to come up with something to post before I leave today.

8th July 2009, 07:33 PM	#4
dwhitt	See if this works. I did this quickly and please keep in mind that drawing electrical schematics are not part of my job so forgive me if I got a symbol wrong. The switch is actually a double pole double throw switch but the second switch is practically independent with its own power supply. The output of the relay is also on that second schematic. I'm not sure what information you may need on the counter/timer. If you have specific questions let me know and I can look it up for you. Thanks again. Attached Thumbnails Last edited by dwhitt; 8th July 2009 at 07:36 PM.

8th July 2009, 08:49 PM	#5
bailey45	The output of a NE555 (Fairchild Version) is rated at 100mA output at 5 volts, however at this output the voltage is down to 3.3 volts. Sounds like you have more than 100mA load on your output. The coil resistance of your relay need to be greater than ~100 ohms for a 5 volt relay.

8th July 2009, 09:01 PM	#6
BrownOut	Right. You most likely need a transistor to drive the relay. __________________ You don't need a quadraphonic Blaupunkt -- you need a curve ball.

8th July 2009, 09:15 PM	#7
dwhitt	Thanks for the inputs Brown and Bailey. Just to clarify... I need to put in a transistor between the output of the NE555 and the relay?

8th July 2009, 10:58 PM	#9
BrownOut	Something like this could get you started, assuming that the relay is small Attached Thumbnails __________________ You don't need a quadraphonic Blaupunkt -- you need a curve ball.

8th July 2009, 11:57 PM	#10
Hero999	The TTL version is rated to 200mA, the CMOS version is rated to 100mA and that depends on the supply voltage. What's connected to the output of the 555? __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

9th July 2009, 06:46 PM	#11
dwhitt	The relay is a Magnecraft W6225DSX-1. I don't see anything from the packaging that tells me the coil resistance? These are the specs they gave me: Solid State Panel Mount Relay Control Voltage Type: DC Load Current RMS Max: 25A Contacts: SPST-NO Control Voltage Max: 32V Control Voltage Min: 3V Output Current: 25A Output Device: SCR Output Type: SCR Output Voltage: 280VAC RoHS Compliant: YES The NE555 I have is (don't laugh) a radio shack brand chip (TLC555 Timer). High output current capacity Sink: 100 mA (typ) and Source: 10mA (Typ). So this is what I purchased today- two NPN Silicon Transistor: one with an Ic of 3A and the other with 10A. Please advise which transistor would be best and also please take a look at my updated schematic to see if this Should work. TIA. Attached Thumbnails

9th July 2009, 07:05 PM	#12
BrownOut	I did't realize you were using a SS relay. Accordig to the data sheet, the input resistrance should be 1500 ohms, minimum. You're timer should be capable of driving that directly, unless I'm missing something. Try disconnecting the relay and measuring the output of the timer. Maybe something else is going on. __________________ You don't need a quadraphonic Blaupunkt -- you need a curve ball.

9th July 2009, 07:13 PM	#13
dwhitt	OK. I will try disconnecting the relay, measuring the output. Then connect doing the same with the timer. I will hold off on the transistor for now and report back.