From 6e0ce9c3a689435d538cf84f36cdc19fb579a5d1 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?King=20K=C3=A9vin?= Date: Fri, 8 Apr 2022 10:58:31 +0200 Subject: [PATCH] add changelog, listing design errors --- CHANGELOG.md | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) create mode 100644 CHANGELOG.md diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 index 0000000..ffcdfbb --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,24 @@ +v0 +-- + +first prototype, with pin header to debug + +the over-voltage protection is based on an design described by Texas Instruments, in Analog Engineer's Circuit: Amplifiers, SNOAA20, Overvoltage protection with comparator circuit. + +this design is not ideal for our case though. +a Zener diode is used as reference voltage. +it requires at least 1 mA to operate. +this is already a lot for my application. +but 1 mA is when VBUS is at it's minimum of 4.75V. +at 35V this would result in 21 mA. +this power is mainly dissipated by the resistor limiting the current going through the diode. +the dissipated ~0.6W exceeds the 0.1W rating of the resistor, also heating up a zone of the board to 100 °C. +the reference voltage is current dependent, thus the cutoff voltage goes above 5.5V. +this is not too much of a problem because VBUS also exceeds this voltage, but it's not ideal. + +design errors: + +- the footprint for the USB-C plug has too small mounting holes +- the LM393 is actually an open-collector comparator, but the circuit uses it as push-pull +- the zener diode needs at least 1 mA to be used as voltage reference, not 10 µA (Ileakage and Ibias/Ikz are mixed) +- the design does not respect the common-mode input-voltage range (up to Vcc-2)