So anyhow I gave up my old design to work I just cannot get enough drive from the CMOS 555 to drive the transistors very much. So I went to this design:

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and of course R4 and R5 are too big of a load for Q1 and Q2 I will show the oscope results in a bit.

 

1. I want rail to rail.
2. The transistor configuration is inverting. A hysteretic oscillator requires an inverting Schmitt trigger to work. two inverting gates is a buffer.
3. A CMOS 555 at low voltage has a very low drive, I wasn't sure it could handle 1ma at 5V Vcc.The transistors will raise that considerably.

Why don't you just put a discrete CMOS inverter on the output? If the signal inversion bothers you, you can use a small inverter to drive a big one.

That idea was used 4 decades ago to get rail to rail output from opamps like LM358.

 

Sometimes I get so fixed on a design goal that I lose sight of the ultimate goal. Being fixated on a CMOS 555 was probably not the best decision, I will work through this design. Then maybe start from scratch. If I can I want to keep the symmetrical square wave.

 

I'd still recommend a low-side driver such as a MCP1402 as the output driver. Big reduction in component count.

 

Like many of my brain fa..s projects, this is much a learning exercise as anything. I am very against buying specialty chips for this kind of project.

 

Use a CD4049 , it is as far from a specialty device as you can get.

 

Gate driver chips are so common these days, I'd include them in the same category as 4049s.

 

As most gate drivers have hysteresis on the front end, they will oscillate like a 555, so you could eliminate the 555 from your circuit.

 

Like many of my brain fa..s projects, this is much a learning exercise as anything. I am very against buying specialty chips for this kind of project.

Once upon a time everything in your parts collection was a specialty part. As my grandaughter (bless her heart) would say: "OK boomer".

 

At this point I am not worried about parts count, that will come after. I just want to know what the maximum current for the minimum voltage drop I can get from something like this.

 

I just want to know what the maximum current for the minimum voltage drop I can get from something like this.

If you use 2 CMOS inverters, a small one driven by the timer, and a big one driven by the first inverter, the amount of current you can get will be limited by the power supply. Voltage swing should be essentially rail-to-rail if you choose appropriate MOSFETs.

 

At this point I am not worried about parts count, that will come after. I just want to know what the maximum current for the minimum voltage drop I can get from something like this.

Hi Wendy, how can i contact you? There's no button for conversation in your profile.

 

Hi Wendy, how can i contact you? There's no button for conversation in your profile.

You need 10 posts before you can initiate private messages. Then you'll be able to start a conversation with a member by hovering over the member's name under their avatar:

 

So I tried this design next:

and as expected the duty cycle was just about unusable. Fortunately there is away with 555 to control the duty cycles.

555 Out transistors output

Now to relay and try out this schematic:

 

So I tried this design next:
View attachment 270217
and as expected the duty cycle was just about unusable. Fortunately there is away with 555 to control the duty cycles.
View attachment 270218 View attachment 270219
555 Out transistors output

Now to relay and try out this schematic:
View attachment 270220

Aen't D1 and D2 the wrong way round in this circuit?

 

The LEDs appear to have backwards polarities.

 

No question about it! The LED polarities are backward.For an NPN transistor the base current flows in.

 

The unmarked transistors are also backwards if they are European BCxxx type.

 

The unmarked transistors are also backwards if they are European BCxxx type.

you know what assumptions get you don't you? Think the parts list project
PN2222 and PN2904. The thing is about the LEDs if they don't light light they are backwards. Now to see if I could pop the epoxy off of the 555. I have done this in the past.

Project Parts Reference V2.0

 

For this circuit, the transistor and full IC part numbers should be on the schematic, not on another thread that was 1.6 years ago.
Many of us use American, European and Oriental transistors and their three pinouts.