Push-pull 3-state buffer good to 9V? - Page 1
Forum section: electronics / projects

author: 741
author_rank: Frequent Contributor
timestamp: March 15, 2025, 09:43:46 am
content: HiI'm wanting to interface a 5V PIC to a 9V device. (This is a programmable smoke sensor).My existing design uses several MOSFET bi-directional logic level translators (AN10441 NXP/Philips).I'm wanting to use a ready-made logic level translator in the new design. SN74AHCT125-Q1 would be ideal but only runs up to 5.5V.Searching for a suitable device is difficult; I think all the TI 74xxx parts max-out at 5v5.https://www.ti.com/logic-voltage-translation/buffers-drivers-transceivers/products.htmlhttps://www.digikey.co.uk/en/products/filter/logic/buffers-drivers-receivers-transceivers/704?s=N4IgjCBcoCwdIDGUBmBDANgZwKYBoQB7KAbRACYAGcgVgE4B2EAgZjssYgF0CAHAFyggAyvwBOASwB2AcxABfAmEo0ooZJHTZ8RUiBjMQANkMAOQ3RA8QAoQBFCAVwBGGHAoLkYTBBq24CYkgyFnIWI1NVa1tIEXFpOUVwOlNLX1RMAN1gkEoreSTVBF4oMD4SyFokkwQJABMhcgYTPkFY0UlZQ34AT153WLqsZAKgA

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: March 15, 2025, 01:29:10 pm
content: A simple NPN transistor circuit can be used to shift 5V logic to 9V. A pull-up resistor on the collector pulls the signal up to 9V when off.

author: 741
author_rank: Frequent Contributor
timestamp: March 15, 2025, 01:39:58 pm
content: Yeah, I was looking for push-pull. My existing design has pull-ups and the rising edges are not so great. However, I now suspect there will be no level translating buffers able to handle 9V.That was partly due to a weedly switcher I used to boost 5 to 9V, so the pull-ups were a (rather high) 10k.Now thinking I use a DC/DC module with more power, then use 2k2 pull-ups. I was also considering a PNP current source in place of a resistor pull-up.

author: Ian.M
author_rank: Super Contributor
timestamp: March 15, 2025, 01:50:43 pm
content: Consider a SPDT analog switch with enable. Strap one analog NC or NO pin to +9V, the other to ground and take output from analog common. Depending on how you strap the NO/NC pins you can get an inverting or non-inverting buffer function.

author: Peabody
author_rank: Super Contributor
timestamp: March 15, 2025, 01:58:09 pm
content: What about a CD4504?Edit: Or maybe the CD40109 for tristate.

author: Slh
author_rank: Regular Contributor
timestamp: March 15, 2025, 02:11:12 pm
content: How about a gate driver IC? Definitely easy to go from 5V to 9V that way (you might want to be careful that you choose one with a MOSFET output rather than BJT). Something like 2EDN7534B - way over-kill on output current but would probably do the job. I'm guessing that you don't have particularly tight timing requirements?Not sure about the 9V->5V direction but you might find something out there.

author: 741
author_rank: Frequent Contributor
timestamp: March 15, 2025, 05:40:17 pm
content: The SPDT seems like an idea for the unidirectional lines (that's all but one).Also - the CD40109 might be ideal, just looking at the DS now. Most unusual, TI have added selectable text to the old photocopy style.Absolute max is 20V.It is billed as a quad "low to high" level shifter. However the new text adds"there are no restrictions on therelative magnitudes of the supply voltagesor input signals within the device maximumratings, provided that the input signalswings between V SS and at least 0.7 V CC ;VCC may exceed VDD , and input signals mayexceed V CC and V DD . When operated in themode VCC > V DD , the CD40109 will operateas a high-to-low level-shifter."

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 15, 2025, 06:50:03 pm
content: Also check the ICC of any solution.CMOS can draw significant current when not close to the rails.Look at RRIO opamps and comparators if high speed is not vital.

author: 741
author_rank: Frequent Contributor
timestamp: March 15, 2025, 09:10:01 pm
content: Comparators are a thought.[At present] the CD40109 looks easiest, esp with having enable pins.The funny thing is this device did not exactly make its existence obvious when I looked for level shifters on the TI site.