Powering a TTP223 from 12V - Page 1
Forum section: electronics / beginners

author: ledtester
author_rank: Super Contributor
timestamp: June 13, 2020, 05:39:23 pm
content: The TTP223 capacitive touch sensor only draws microamps but can only be supplied by 5V max.Is there a clever way of powering the TTP223 from a 12V supply (e.g. like a battery pack) and minimizing current draw? Imagine the application is a 12V touch-activated flashlight.Are there other touch-sensors which can be used at 12V?

author: sahko123
author_rank: Frequent Contributor
timestamp: June 13, 2020, 05:40:56 pm
content: if it draws a very small amount of current i cant see anything wrong with using a resistor divider to bring the 12v down to 5v

author: floobydust
author_rank: Super Contributor
timestamp: June 13, 2020, 06:08:21 pm
content: A 12V battery pack is big and the voltage too high for any touch sensor ICs.TTP223 is very sensitive to power supply voltage changes, it needs regulated power 2-5.5VDCYou would add an LDO and waste 10's uA.

author: Ian.M
author_rank: Super Contributor
timestamp: June 13, 2020, 06:12:13 pm
content: Thedatasheetis fairly useless, but like most CMOS logic, I'd expect the supply current to be proportional to the clock frequency. As its internal oscillator jumps from 16KHz low power mode to 512MHz Fast mode (a factor of 32) for up to twelve seconds after a touch is detected, I would expect its current consumption to vary by at least an order of magnitude, depending on what proportion of its standby current is due to the 1MHz sensor oscillator.A low current potential divider is therefore unsuitable to power it - you'd need up to 0.5mA standing current in the divider to get a reasonably stable (+/-10%) output voltage.The best option if no lower voltage is available would be to use a low quiescent current 5V linear regulator, as shown in the datasheet application circuit. Make sure the regulator has an adequate input voltage rating - less than 18V could be problematic due to connection transients, and use an ordinary aluminum electrolytic of x10 the value in parallel with any ceramic input capacitor to damp connection transients.OTOH its quiescent current is low enough that it could be supplied from a tap on the battery pack e.g via the balance connector on a RC LiPO pack, from the bottom cell for a 3.0V to 4.2V supply without significantly unbalancing the pack. If you are using Alkalines, I'd suggest tapping across the bottom three cells of the pack for a 2.4V to 4.7V supply.

author: ledtester
author_rank: Super Contributor
timestamp: June 13, 2020, 08:27:42 pm
content: Does anyone have one of these?GE Enbrighten Battery Operated Touch Activated LED Lighthttps://www.homedepot.com/p/GE-Enbrighten-Battery-Operated-Touch-Activated-LED-Light-27528/205972247It would be interesting to know what design decisions GE went with.

author: kjr18
author_rank: Regular Contributor
timestamp: June 14, 2020, 08:29:44 am
content: Quote from: ledtester on June 13, 2020, 08:27:42 pmIt's not like there is only TTP223 and nothing else, as this one also has sliding dimmer, so another chip is used. As for using TTP223 with 12v supply, just use some LDO and mosfet for switching led's.

author: magic
author_rank: Super Contributor
timestamp: June 14, 2020, 04:15:03 pm
content: I think I have heard of a trick involving n-JFET with its gate tied to ground and drain to Vin, then a few volts appears at the source and small current can be drawn. The voltage is roughly Vgs(off) and minimum load current to avoid overvoltage is Id(off).