- #1
Controlling 10 mA Relay with Opening/Closing Switches
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Discussion Overview
The discussion centers around the feasibility of controlling a 10 mA relay using opening and closing switches, with a focus on circuit design and component configuration. Participants explore various configurations and components necessary for the relay to function correctly.
Discussion Character
- Technical explanation, Debate/contested, Experimental/applied
Main Points Raised
- Some participants suggest that with additional resistors or a different configuration, along with a diode, it is possible to control the relay using switches.
- There is a claim that the circuit diagram may be misdrawn, with a suggestion that an NPN transistor should be replaced with a PNP transistor for proper functionality.
- One participant expresses that while the circuit may work with the correct PNP transistor, they would not recommend that configuration.
- Another participant notes the importance of including a parallel power diode to protect the transistor from inductive reverse voltage spikes when the relay is turned off.
Areas of Agreement / Disagreement
Participants express differing views on the circuit configuration, with some agreeing on the need for a PNP transistor while others question the initial drawing. The necessity of a diode for protection is also highlighted, indicating some consensus on that point, but overall, multiple competing views remain regarding the best approach.
Contextual Notes
There are unresolved assumptions regarding the circuit design and the specific components needed. The discussion does not clarify the exact configuration or the implications of using different types of transistors.
- #2
berkeman
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Not as drawn, but with a couple more resistors (or just a different configuration) and a diode, it can work. Have you tried using Google Images to find such circuits? Where did you get this one?John1397 said:
- #3
eq1
- 206
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berkeman said:
I think it's just misdrawn. NPN is supposed to be a PNP. I personally wouldn't do it that way but with the correct PNP it should work...
- #4
berkeman
Admin
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Ah, interesting thought! At least it will work once with the PNP (and no diode)...eq1 said:
- #5
Baluncore
Science Advisor
2025 Award
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The relay coil is an inductor so it needs a parallel power diode to prevent the inductive reverse voltage spike that will otherwise destroy the transistor when the switch turns off and the magnetic field collapses.
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