Program launch: "Get Paid to Publish your Project!"

[mixos1]

1. Yes, it's acceptable.
2. After publication you have the rights on the project.. as the project is published with your name and email
3. No there is no restriction

 

[H3LIO]

Hi Hero999,

" found the datasheet for the MCU you're using and noticed that the I/O pins probably won't be abe to supply enough current to ensure a transistor driving a 300mA load will saturate properly so I used two transistors rather than one. Tr2  will deliver between 17mA and 21mA to T1's base but the impedance seen by the MCU's I/O pin will be about 10k so hardly any current will flow out of it."

I try but doesn't work because I need a transistor to be able to drive +/-400mA Load. but this weekend I will do the calculations to see if the values are matching. Using a mosfet driver will increase the price it will be twice more expensive then the LM358. It is useful if you need a faster switching time.

 

[Hero999]

Did you try it or is it what I've said about the fan drawing only 300mA put you off?

I deliberately overrated the design, it should still be fine, the BC338 is rated to 800mA and you're only using it for 400mA which is just half it's rating.

It's specified for an Hfe of at least 60 with a VCE of 1V and a collector current of 300mA.

Assuming 400mA, a base current of 17mA, the forced beta will be 400/17 = 23.5 which is more than enough, even when the fact that the Hfe will be slightly lower at the higher collector current is taken into account.

The maximum power dissipation of the BC338 is 625mW, with a colllctor current of 400mA, VCE = 1V, VBE = 0.8V, IB = 19mA the power dissipation will be around 415mW which is fine.

http://www.datasheetcatalog.org/datasheet/siemens/Q62702-C314-V2.pdf

Do you not have the BC338? Try the BC327 or BC548, which are high gain and rated to 500mA and 800mnA respectively.

It's not too critical but the transistor needs to have enough gain (>25) and low enough VCE (preferably 1V or less) at 400mA. If the transistor gets too hot, it probably means VCE is too high, causing it to dissipate too much power, try reducing R3 to get more base drive.

 

[bogdanfirst]

Are the projects listed under Submitted projects actually approved?

 

[mixos1]

Are the projects listed under Submitted projects actually approved?

Yes, it means they are approved.

 

[bogdanfirst]

Thanks! I'm working on the documentation for mine, will send it soon.

 

[H3LIO]

Hi Hero999,

It works but only with a duty cycle higher than 70%, ib = 12mA. Tomorrow I'm going to change the resistors, let you know.

 

[Hero999]

Does the transistor get hot?

How did you measure Ib?

You need to use a 'scope with either a current probe or to measure the voltage across R3 and working out the current using Ohm's law. If you use a meter, you can only accurately measure it when the duty cycle is 100% because the  meter will only accurately measure DC or 50/60Hz AC.

Here's another idea using a PNP transistor to switch the positive side of the fan's power supply.

View attachment 41170

 

[H3LIO]

"How did you measure Ib?"

I didn

 

[Hero999]

How do did you calculate it?

I reckon IB wil be between 17mA and 21mA, my calculations are shown below:

IB(Q1) = (VDD -  VBE(Q2) - VBE(Q1))/R3


With VBE = 0.7V

IB = (3.3 - 0.7 - 0.7)/100 = 0.019 = 19mA

If VBE is lower IB will be higher and vice versa.

I didn't account for R4 because the current though it will be tiny, 0.6/1000 so won't effect the calculation.

Do you think I've gone wrong somewhere?

 

[H3LIO]

Hi Hero999,

I change R3 for 67 Ohm and I have ib of 24mA and vbe = 1.6V and it works with a min duty cycle of 3.13%.
I will send the file to Mixos.

Thank you for that it will have a faster switching time and it's cheaper to make.

 

[H3LIO]

Your calculations are Roth, I was using a different resistor 160 Ohm as R3 when I was doing I only notice now.

 

[Hero999]

What do you mean by Roth?

I'm glad you got it working but give 68R in the parts list as 67R will be hard if not impossible to get hold of because it's not a standard value.

I don't see why it should limit the minimum duty cycle though, the transistors should be able to turn off continuously, enabling a duty cycle of zero.

Does the fan draw a hight peak current when the duty cycle is low? You'd need a 'scope to measure it but that would make sense.

What transistors are you using?

 

[H3LIO]

I mean Right. I'm using the ones you told me BC338. I was think the same, that the specs in the fan would affect the way it works with dutycycle. It's working nice, but i will try different fans to know why it happens.


Thank you

 

[bogdanfirst]

Has the program been stopped?
I was checking new projects on the website and the add seems to be missing...

 

[mixos1]

The program has ended. Stay tuned for future launch of this program.

 

[mojo_chan]

Any updates? I have a project read to go.