Agreed, but I'm not sure if the TS picked up on the relevance of the two different modes and why their transistors are burning out.Thanks for the mention, but that suggestion was first made in post #2.
Agreed, but I'm not sure if the TS picked up on the relevance of the two different modes and why their transistors are burning out.Thanks for the mention, but that suggestion was first made in post #2.
Your design is deficient and rewiring or starting over isn't an option??sadly I have built a board already with everything wired together on a vero board so the current layout will only work for a 3 pin throughhole type hence my earlier statement of using a mosfet but I have no knowledge of the type of mosfet to use
Thank you for that. I just double checked my built circuit and that is exactly how I have it wired up except my R2 value is 10K not 430. The GPIO's can supply 6mA no problem. If I did it exactly as the above drawing then why do I blow transistors? Could it be that I cycle the power too often and the transistor can not handle that?You should be switching the load low side. If the load is inductive, you need a snubber diode.
View attachment 228456
For a 60mA load, base current needs to be 6mA. Can the GPIO's provide that?
I am switching low side. My schematics are not perfect and I am still learning on how to correctly draw them however when building the board I did have it low side switching because from what I have learnt that is the correct way of using a NPN transistor. I admit I made a mistake but I would like to fix the current design because it was a lot of work to build the first board using Vero board(would have had it printed but way to costly in the country I live in) so would prefer not to redo the entire board from scratch but if it is the only option then I will need to do it.Your design is deficient and rewiring or starting over isn't an option??
If you want to switch high side, you should use a P type device. The voltage difference between the load supply and the GPIO's will require the use of an inverter or other level shifting method so you can turn the switches off.
The easiest option for you is to switch the load low side. Just admit you made a mistake, learn from it, and redo your board.
What do you mean by "exactly as above"? With a diode, a 10k resistor, or a 430 ohm resistor?I just double checked my built circuit and that is exactly how I have it wired up except my R2 value is 10K not 430. The GPIO's can supply 6mA no problem. If I did it exactly as the above drawing then why do I blow transistors? Could it be that I cycle the power too often and the transistor can not handle that?
Drawing a schematic willy-nilly and using incorrect symbols is one thing, but there's no excuse for not being able to accurately show how things are connected.My schematics are not perfect and I am still learning on how to correctly draw them however when building the board I did have it low side switching because from what I have learnt that is the correct way of using a NPN transistor.
You need to post an actual accurate schematic of what you have on the actual board for people to analyze. My suggestion of using Darlington drivers still stands.I am switching low side. My schematics are not perfect and I am still learning on how to correctly draw them however when building the board I did have it low side switching because from what I have learnt that is the correct way of using a NPN transistor. I admit I made a mistake but I would like to fix the current design because it was a lot of work to build the first board using Vero board(would have had it printed but way to costly in the country I live in) so would prefer not to redo the entire board from scratch but if it is the only option then I will need to do it.
I can’t read Fritzing diagrams without too much work. But you have confused the 24V power connections.Good day all,
So I have attached two drawings to better explain what my original drawing does. Please see attached. I used fritzing to draw the schematic and also attached a breadboard image
Would switching out the 2N2222A for a MOSFET work better?60mA x 24V = 1.44 Watts of heat from the 2n2222 ... the 2n2222 has a maximum rating of 1.5 Watts at ambient temperatures of 25C . Anything above 25C is derated. It also says that the heat dissipation is 12mW per degree .... This means that at 1.44 Watts you would have an increase above ambient temperature of 120 Deg (1440 mW / 12 mW = 120) ... 120 +25 yields 145 Deg wich is very close to the 150 Deg max.
Simply put ... you need a bigger transistor
View attachment 230543
View attachment 230544
reference datasheet:
https://www.onsemi.com/pub/Collateral/P2N2222A-D.PDF
If the transistors are fully saturated with only a fraction of a volt across them when on they won't be dissipating anything like 1.44W!Would switching out the 2N2222A for a MOSFET work better?
How I measured the current draw of the load is using a lab bench power supply set to 24V. At idle the device uses 0.034A and under load about 0.050A so for safety I have adjusted it to 60mA. I have also updated the schematic again doing my best to follow convention and insuring no errors. The CBE of the transistor could be connected incorrectly so I have decided on getting a schematic with values that will work in theory and rebuilding the entire board from scratch following the schematic as I build." If the transistors are fully saturated with only a fraction of a volt across them when on they won't be dissipating anything like 1.44W! " - Agreed ... my mistake. However it would be worst case scenario.
SILENT001 - How did you measure 60mA and what is the LOAD you are driving? And your absolutely positive you have the CBE of the transistor connected properly?
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