Interesting 7555 circuit. - Electronic Circuits Projects Diagrams Free

Hero999 · 6th August 2007, 10:35 PM

Can anyone guess what it does?

ljcox · 6th August 2007, 11:30 PM

It's an oscillator.

When the output goes high, the voltage at pins 2 & 6 rises at the rate set by the L/R time constant. When it reaches the upper threshold, the output goes low so the voltage at 2 & 6 decays. When it reaches the lower threshold the output goes high again.

Hero999 · 7th August 2007, 06:16 PM

I was bord and started plaing around with components.

I am aware that RC oscillators exist but I've never seen any LR oscillators so I decided to design one. However, I don't see how this is any use, other than for determining the value of a large value inductor using a frequency counter.

ljcox · 8th August 2007, 02:32 AM

Yes, capacitors are cheaper than inductors.

Yes, it could be used as a crude inductance measuring set.

adash · 22nd February 2009, 05:39 PM

Sorry for posting on a tread that low, but did you try this circuit?
I am asking this because I am at the start of various SMPS experiments
and I need to know how an inductor behaves when loaded with large currents.
Any idea if output frequency/period will be linearly proportional to inductor value?
Regards

Hero999 · 22nd February 2009, 08:23 PM

It works, there are much better ways to build an oscillator though.

adash · 22nd February 2009, 09:35 PM

Did you take a look at the voltage waveforms?
I tried simulating it in LTSPICE but voltage on 2+6 pin node swings from gnd to supply voltage, while in a normal 555 circuit it should swing from 33% to 66% of Vcc.
I was thinking about measuring an inductance, not about constructing a generic oscillator with it.
Regards:
Dimitar

Hero999 · 22nd February 2009, 10:25 PM

I would have thought pin 6 would swing from 33% to 66%.

Going from the 7555's datasheet the frequency should be approximately equal to the following formula:

$F=\frac{1.1R}{L}$

kinarfi · 20th July 2009, 07:18 PM

Quote:

Originally Posted by Hero999

Can anyone guess what it does?

Did you ever try this with a Programmable Unijuction?
Kinarfi

Hero999 · 20th July 2009, 07:32 PM

No but I'm sure it's possible with a programmable unijunction.

You can build an LR oscillator using a comparator or just transistors. There's little point in building an RL oscillator, apart from determining the value of an unknown inductor.

kinarfi · 21st July 2009, 12:49 AM

Quote:

Originally Posted by Hero999

No but I'm sure it's possible with a programmable unijunction.

You can build an LR oscillator using a comparator or just transistors. There's little point in building an RL oscillator, apart from determining the value of an unknown inductor.

I'm sure you're right, but every experiment teaches you something, and of course, so does every failure, if you can figure out what you learned

I guess I just gotta see if I can do it.

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6th August 2007, 10:35 PM	#1
Hero999	Interesting 7555 circuit. Can anyone guess what it does? Attached Thumbnails __________________ 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.

6th August 2007, 11:30 PM	#2
ljcox	It's an oscillator. When the output goes high, the voltage at pins 2 & 6 rises at the rate set by the L/R time constant. When it reaches the upper threshold, the output goes low so the voltage at 2 & 6 decays. When it reaches the lower threshold the output goes high again. __________________ Len

7th August 2007, 06:16 PM	#3
Hero999	I was bord and started plaing around with components. I am aware that RC oscillators exist but I've never seen any LR oscillators so I decided to design one. However, I don't see how this is any use, other than for determining the value of a large value inductor using a frequency counter. __________________ 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.

8th August 2007, 02:32 AM	#4
ljcox	Yes, capacitors are cheaper than inductors. Yes, it could be used as a crude inductance measuring set. __________________ Len

22nd February 2009, 05:39 PM	#5
adash	Sorry for posting on a tread that low, but did you try this circuit? I am asking this because I am at the start of various SMPS experiments and I need to know how an inductor behaves when loaded with large currents. Any idea if output frequency/period will be linearly proportional to inductor value? Regards

22nd February 2009, 08:23 PM	#6
Hero999	It works, there are much better ways to build an oscillator though. __________________ 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.

22nd February 2009, 09:35 PM	#7
adash	Did you take a look at the voltage waveforms? I tried simulating it in LTSPICE but voltage on 2+6 pin node swings from gnd to supply voltage, while in a normal 555 circuit it should swing from 33% to 66% of Vcc. I was thinking about measuring an inductance, not about constructing a generic oscillator with it. Regards: Dimitar

22nd February 2009, 10:25 PM	#8
Hero999	I would have thought pin 6 would swing from 33% to 66%. Going from the 7555's datasheet the frequency should be approximately equal to the following formula: $F=\frac{1.1R}{L}$ __________________ 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.

20th July 2009, 07:32 PM	#10
Hero999	No but I'm sure it's possible with a programmable unijunction. You can build an LR oscillator using a comparator or just transistors. There's little point in building an RL oscillator, apart from determining the value of an unknown inductor. __________________ 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.