You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

I need some help from all you smart circuit / electronics people. This seems like a simple problem, but apparently I don't understand it: I wanted to drop the input voltage a little for a project I'm working on (more about that later) so I made a simple voltage divider. When I looked around at my boxes of resistors, I found some that would let me drop the input voltage of 18 volts to just under 16 volts. I used a 68Kohm for R1 and two 200Kohm resistors in series for 400Kohm total for R2 leg. I measured the voltage before hooking up the circut and it was perfect...just under 16v. The problem is, when I hook it up to the circuit, the input voltage at the board was only 1v! While it was hooked up, I checked the voltage at the R1/R2 junction and it was just under 16v, but at the board it was still 1v. I bypassed the voltage divider altogether and ran the 18v straight to the board and it measured at 18v at the board. Why is my voltage divider showing proper voltage when not attached to the circuit, but only 1V when attached? What am I missing?

<blockquote data-quote="Moleculo" data-source="post: 151777" data-attributes="member: 1"><p>I need some help from all you smart circuit / electronics people. This seems like a simple problem, but apparently I don&#039;t understand it: I wanted to drop the input voltage a little for a project I&#039;m working on (more about that later) so I made a simple voltage divider. When I looked around at my boxes of resistors, I found some that would let me drop the input voltage of 18 volts to just under 16 volts. I used a 68Kohm for R1 and two 200Kohm resistors in series for 400Kohm total for R2 leg. I measured the voltage before hooking up the circut and it was perfect...just under 16v. The problem is, when I hook it up to the circuit, the input voltage at the board was only 1v! While it was hooked up, I checked the voltage at the R1/R2 junction and it was just under 16v, but at the board it was still 1v. I bypassed the voltage divider altogether and ran the 18v straight to the board and it measured at 18v at the board. Why is my voltage divider showing proper voltage when not attached to the circuit, but only 1V when attached? What am I missing?</p></blockquote><p></p>

[QUOTE="Moleculo, post: 151777, member: 1"] I need some help from all you smart circuit / electronics people. This seems like a simple problem, but apparently I don't understand it: I wanted to drop the input voltage a little for a project I'm working on (more about that later) so I made a simple voltage divider. When I looked around at my boxes of resistors, I found some that would let me drop the input voltage of 18 volts to just under 16 volts. I used a 68Kohm for R1 and two 200Kohm resistors in series for 400Kohm total for R2 leg. I measured the voltage before hooking up the circut and it was perfect...just under 16v. The problem is, when I hook it up to the circuit, the input voltage at the board was only 1v! While it was hooked up, I checked the voltage at the R1/R2 junction and it was just under 16v, but at the board it was still 1v. I bypassed the voltage divider altogether and ran the 18v straight to the board and it measured at 18v at the board. Why is my voltage divider showing proper voltage when not attached to the circuit, but only 1V when attached? What am I missing? [/QUOTE]

Top Bottom