Can a 555 Timer Serve as a Level Translator? Let's Find Out!

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

scottiebabe — Sun, 02 Oct 2022 16:25:15 GMT

[deleted]

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

jc2048 — Sat, 01 Oct 2022 22:24:24 GMT

I couldn't resist - I tried an experiment with a couple of the 555s I've got here. This is with a 50mR thick-film resistor between the part GND pin and the board ground. The yellow trace is the voltage across the resistor, the blue trace the output of the timer. I've done this on a piece of pcb material, so NOT a plug-in breadboard, but the part is in a socket and I'm probing with a 10M probe (might have been better with a piece of 50R co-ax).

This is a Fairchild bipolar part which might be from 1986. It's brutal. As the output rises, it gets to 30A for a few nanoseconds before limiting and falling. (The local decoupling is two 10uF tants and a 1uF ceramic - possibly not a very good combination.) It's a poor test, though, because the ground has lifted to 1.5V. I haven't shown the other end of the waveform, but, curiously, there's no shoot-through when the output drops.

This next is the TLC555 part. Here the shoot-through is worse at the end when the output comes down again, though it's nothing like as bad as the bipolar part. Something that's interesting is that there's a very short period before the output goes up when the chip is taking a little under an amp (perhaps that's a more limited shoot-through when the driver stage for the output MFETs starts transitioning) - by starting a fair current moving, it looks like it improves the situation when the output actually starts to move.

I think all that I'm showing here is that the shoot-through current will depend very much on what the decoupling is and how it's arranged. It's all very messy to interpret - the decoupling caps will be interacting, there's enough inductance to play a part, and my probing isn't going to truly reflect what's there. I think I've ended up with more questions than answers, but it's looking fairly certain that there IS a shoot-through current there.

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

scottiebabe — Sat, 01 Oct 2022 19:34:19 GMT

[deleted]

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

jc2048 — Fri, 30 Sep 2022 20:42:42 GMT

This is what a CMOS 555 (TLC555) manages, translating from 5V to 12V. The input (blue) is from an Arduino UNO, the
output (yellow) is the unloaded output from the 555 with a 12V supply.

For some reason, I imagined that the CMOS part might be faster than your bipolar part, but it isn't.

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

DAB — Thu, 29 Sep 2022 18:52:55 GMT

I am always amazed at the versatility of the 555.

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

dang74 — Thu, 29 Sep 2022 16:38:49 GMT

No doubt there's been a number of 555 timer cook-books written over the years, so it's very admirable that you came up with something original.

RE: Can a 555 Timer Serve as a Level Translator? Let's Find Out!

robogary — Thu, 29 Sep 2022 01:12:23 GMT

Scottiebabe - Tinkerbelle really cracked me up, very appropriate description in this context ! 555 as a level shifter is a truely unique idea, nice. I also have a ton of them on hand and no they weren't from the original manufacturing batch :-) I use the level shifters alot since my stash of sensors and such were purchased for 5V Arduino projects and now I'm using the Raspberry Pi Pico in half the projects. Good job on selecting a relevant project