simulate this circuit – Schematic created using CircuitLab
Hello everyone, I want the current to flow from A to B if the switch is pressed. What can I do here?
Total newbie here.
Thank you.
EDIT 1: Can't move the switch.
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- \$\begingroup\$ Do you have a power source that can drive a relay? \$\endgroup\$user16324– user163242020-04-29 19:44:16 +00:00Commented Apr 29, 2020 at 19:44
- \$\begingroup\$ Yes. But something quiet would be really nice. @BrianDrummond \$\endgroup\$SMNK– SMNK2020-04-29 19:45:21 +00:00Commented Apr 29, 2020 at 19:45
- 2\$\begingroup\$ A transistor with pull-up to the gate? \$\endgroup\$winny– winny2020-04-29 19:47:54 +00:00Commented Apr 29, 2020 at 19:47
- \$\begingroup\$ @winny Could you give a schematic? \$\endgroup\$SMNK– SMNK2020-04-29 19:49:23 +00:00Commented Apr 29, 2020 at 19:49
- 2\$\begingroup\$ It is frustrating for us to play guessing games like this and tease details out from you one detail at a time. It would have been better if you drew the WHOLE CIRCUIT from the beginning, including the UA741 AND the things attached to the UA741. Anyway, your best bet appears to be a high-side PMOS switch between A and B. \$\endgroup\$user57037– user570372020-04-29 20:21:11 +00:00Commented Apr 29, 2020 at 20:21
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2 Answers
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simulate this circuit – Schematic created using CircuitLab
Figure 1. Rewire the switch as shown.
I assume that there is some reason you don't want to do this but you haven't explained it in your question.
Figure 2. (a) The simplest - unlikely to go wrong - solution. (b) A simple, no-component solution.
This is really hard to beat. Automotive relays come in insulated enclosures, take standard crimp terminals and are very robust.
- \$\begingroup\$ Sorry for the inconvenience. But cant access the switch. @Transistor \$\endgroup\$SMNK– SMNK2020-04-29 19:42:48 +00:00Commented Apr 29, 2020 at 19:42
- \$\begingroup\$ So what is on B? How much current? What is the application? \$\endgroup\$Transistor– Transistor2020-04-29 19:52:46 +00:00Commented Apr 29, 2020 at 19:52
- \$\begingroup\$ A UA741 IC. @Transistor \$\endgroup\$SMNK– SMNK2020-04-29 20:17:43 +00:00Commented Apr 29, 2020 at 20:17
- 2\$\begingroup\$ @SMNK? But why? It’s one of the worst op-amps. \$\endgroup\$winny– winny2020-04-29 20:21:48 +00:00Commented Apr 29, 2020 at 20:21
- \$\begingroup\$ See the update. \$\endgroup\$Transistor– Transistor2020-04-29 20:25:49 +00:00Commented Apr 29, 2020 at 20:25
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8 This should solve it.
Feel free to substitute the transistor to any suitable P-MOSFET.
simulate this circuit – Schematic created using CircuitLab
- \$\begingroup\$ You beat me to it. \$\endgroup\$user57037– user570372020-04-29 20:29:47 +00:00Commented Apr 29, 2020 at 20:29
- 1\$\begingroup\$ Comment for the OP: generally bad things can happen if you apply voltage to any of the inputs or outputs of the 741 when its 12V supply is de-energized. Since you haven't shown what is connected to the 741, I am not sure whether this is an issue for your circuit or not. \$\endgroup\$user57037– user570372020-04-29 20:32:03 +00:00Commented Apr 29, 2020 at 20:32
- \$\begingroup\$ @mkeith I've never found another site, save for Amibay perhaps, where you need to be reeeealy trigger happy to get anything done than this one. \$\endgroup\$winny– winny2020-04-29 20:32:37 +00:00Commented Apr 29, 2020 at 20:32
- \$\begingroup\$ @mkeith 741 is junk by most standards, but your comment is valid for many op-amps. \$\endgroup\$winny– winny2020-04-29 20:33:33 +00:00Commented Apr 29, 2020 at 20:33
- \$\begingroup\$ I didn't intend for my comment to apply to the 741 only. It was supposed to be a general concept for all IC's. Applying voltage to inputs of IC's when the supply rail is at 0V usually violates the abs max ratings. Of course, there may be input diodes so applying voltage to an input may power up the rail through the input diodes. All this business is best avoided by design. \$\endgroup\$user57037– user570372020-04-29 20:50:57 +00:00Commented Apr 29, 2020 at 20:50