High-side switch for ±12V supply - Page 1
Forum section: electronics / projects

author: Cs4System
author_rank: Newbie
timestamp: March 29, 2023, 08:39:28 am
content: Hello,I'm designing a board on which clocks for DAC and ADC are derived from an external signal. In case it is missing (which will happen during operation by the user) the circuit is doing unpredictable things. The best would be to go in a kind of standby mode in that scenario. Soft-mute functions of the DAC and ADC are not working, since they require a clockLuckily, I have an error signal which goes high(5V) in case of a missing input.Now I would like to turn off my dual rail (±12V) supply with that error signal.Current draw is about 200mA on each rail in normal operation. Load is mostly Opamps and DCDC Converters.Can anyone point me to a circuit or IC that would do that job? I would like to use standard parts to avoid a shortage.Thanks a lot!I've done some simulations and came up with this circuit for the 12V rail. There is a better solution for sure(pink label are Voltages)

author: dobsonr741
author_rank: Frequent Contributor
timestamp: March 29, 2023, 09:52:14 pm
content: The closest are high side and low side switches, under power management at the various manufacturers. However, they are more “feature rich” and costly than a simple 2 transistor approach you can reduce your example down to. I assumed you can drive it from a GPIO so no need for inverting with one of the 3 transistors. If worried about board space you’ll find dual NPN and dual MOSFETs in sot23-6 packages.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 31, 2023, 01:20:07 am
content: So if you just want to switch two rails from a 5V logic state. See the attched. Can you work out what Q2 is all about?Its not an error.Would it not be better to build a local clock on the board so it won't go strange when it loses conection with the mothership disconected.When mothership clock is present, use it to force the local clock to sync to it or simply over ride local clock.Use a small mico and some eeprom. Read your last good ADC DAC instructions states and store them- Its settings not data?Enable a revmoval and resume routine.

author: Cs4System
author_rank: Newbie
timestamp: April 01, 2023, 09:04:02 am
content: Hi, thanks for the ideas!I would like to avoid any special IC, just to be sure not to be affected be the next upcoming shortage.The schematic looks interesting, I will try and simulate its behavior.EDIT: It works perfectly, but needs ~12mA quiescent current. (that path between 12V and -12V over two 1k resistors is reason, maybe I could make them bigger) That's way too much.I came up with this solution, see attached.The nice extra: I can drive a LED to indicate the standby state or the sync to the external clock with one of the Opamps.Quote from: Terry Bites on March 31, 2023, 01:20:07 amWell...maybe. But how would I do that? I would need a 48Khz or 44.1kHzClock. Low jitter and very temperature stable is a must!I would like to avoid a microcontroller. My project does not need any programming by now, It's all done in hardware.

author: Zero999
author_rank: Super Contributor
timestamp: April 02, 2023, 10:55:13 am
content: It's only a couple of hundred mA, so why not just use BJTs?This circuit hardly uses any power during standby. R1 sets the base current.

author: jwet
author_rank: Frequent Contributor
timestamp: April 04, 2023, 06:04:20 am
content: I don't really think the answer is to kill the analog voltage rails, when that error signal goes away, you're going to have all this powering up finding its, bias etc- not so cool for audio. You don't really care about how much power you're drawing- just mute the signals with cheap FET or an analog swtich in the signal path. That way when the error goes away, you can unmute and come back to your circuit with all its basic bias intact. If your signal swings are really +- 12v, you'll need a decent analog switch maybe a DG4xx type, they can take this. Its likely that you can find a spot in the circuit where you can mute with perphaps some 4000 series CMOS or a little NFET like a VN10K, etc. Don't debias everything- it gets messy.