Level Shifter 3.3V to 28V

What's wrong with TI's robust 7-line level-shifting IC? The uln2003 7-unit Darlington-transistor IC is rated for 50 volts, and costs as little as 43 cents each, at Mouser and DigiKey.

That would sure be my choice if the pullup and Darlington drop are not concerns. It works fine with 3.3V CMOS levels. Orginally a Sprague product, IIRC. Of course if you have an extra 5V supply that needs a

Best regards, Spehro Pefhany

OK, here's something about _me_: I built a few drivers for "normal clocks" yars ago and used LM358s for the 24V H-bridges. Back then I was stupid and forgot the freewheel diodes for the inductive load, but heck, all these units have been putting out their minute-pulses flawlessly for some 12 years now.

robert

I wonder how someone can use an FPGA but be stumped by the simplest of data sheets. Is this what EE is all about nowadays?

Heck, I wouldn't touch an FPGA with a ten-foot pole but I sure know my basics.

robert

Well, just yesterday I designed-in a 555 (a 7555, actually) for the first time in m,y life. I need an oscillator whose frequency can be changed over a range of at least 200:1 with a 100k 10-turn pot. You need something with some oomph to whack that timing cap around with R < 500 ohms.

Anything better for this than the 555? 100k is the limit for the pot because they get pricey for higher values.

robert

over a

because

Sure. Do it by voltage.

With Ct = 680pF, Fmin = 1Hz, Fmax = 4.5MHz. With Ct = 0 (stray breadboard capacitance only), Fmax = 33MHz(!). That 2N4403 is doing an amazing 10ns square wave edge when the state flips.

Since it's just a diff pair, you can use your imagination to tweak it to, say, variable ON and OFF points. This is essentially a reduced 555 with a CCS tacked onto the capacitor to make a clean triangle.

Tim

-- Deep Fryer: A very philosophical monk. Website @

On a sunny day (29 Nov 2007 08:29:22 GMT) it happened Robert Latest wrote in :

--- As it turns out, nothing. Originally the OP didn't mention that inverting wasn't a problem, but had it been that would have ruled out the TI part unless a set of inverters was placed in front of it.

---

--- Works for me!

-- JF

Yeah, but the f range is way too limited. Tim's circuit is great, but I need dozens of those so I'd prefer an integrated solution.

robert

need

Only dozens I guess? But Jeorg is always complaining about integrated solutions being so expensive! But I guess that's at a thousand dozen, rather than just a dozen. :^)

If you like the 555, you can easily add some parts (like one or two CCS's, which could be as little as a transistor, two resistors and a 10k pot) and, if you want really long run time, a JFET or bifet op-amp follower between the capacitor and pins 2 and 6 to minimize leakage. It's the wide range CCS (from about 5nA -- leakage current -- to 15mA full bias) and JFET follower (pA leakage?) that allow my circuit to cover such a wide range. The "decision" part can just as well be a 555, though it won't run as fast, if that mattered.

Tim (loves discrete)

-- Deep Fryer: A very philosophical monk. Website @

In fact I'm doing this circuit (just the schematic) as a favor for a friend who wants to build it on a breadboard. I'm not going to be able to sell him your design!

Heavens, no!

I noticed. I like 'em, too.

robert

Actually I don't quite understand how your circuit works. As I can see you have a "charge" CCS (the top left Qs) and a "discharge" CCS (the bottom current mirror), and the diodes decide if your cap gets charged (anode of right diode "high") or discharged (anode low, discharge current is difference between charge and discharge CCS).

What I don't get:

1. Why the paralleled Qs?
2. How is I_dis = 2*I_ch ensured?
3. Shouldn't the right diode be connected to the other leg of the comparator? Let's say the voltage on the cap is rising until the left Q of the diff pair starts conducting, tripping the comparator. Then the 4403 conducts, pulling the anode of the right diode up. How is the cap ever going to discharge? Shouldn't it be the other way round?

I wish you'd number your components ;-)

robert

If you program an fpga in vhdl or verilog and treat it as a pure logic engine, you don't have to know much about electricity.

John

That would be an interesting product: a dds synthesizer and stepper motor kit to retrofit old mechanical clocks, like the ones on buildings. Some toothed belts and pulleys could get you into the old hand drive, and the dds would let you match any ratios.

John

LM5112 maybe.

John

I suggested that opamps might be useful as level translators. That's not an argument over details.

Sure, but that's only once, and that voltage may be free anyhow, like from an led pilot light or something. Are you this annoying in real life?

Maybe the loads can short? We don't know. I do know that an opamp can be a lot of stuff in a small, very cheap package.

Quad opamp and no resistors. But don't use an LM324 for this; the sections can interact when used open-loop.

A lot of it is routine, as engineering tends to be. But then, we do a lot of stuff, and some of it is cool. And my life is fairly cool because I designed it to be that way; most anybody can do that if they want to.

So you want me to only talk about electronics in the abstract, things I have no personal connection to, stuff out of peer-reviewed journals? Drop dead.

John

Interact to the point of not giving the correct state? I've seen interaction in the 10's of uV, IIRC, but nothing too crazy.

One Japanese design from the eighties used half a cheap dual op-amp as a very low level amplifier, and the other half as a comparator. They used resistors to feed back the (presumably minus of the measured average value of the) interaction so they could save a few pennies parts cost. Clever.

Best regards, Spehro Pefhany