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My ready easy PWM 12V 3A transistor

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assassa1221:
Hello

I want to share this easy PWM-plan:

* Power supply: Only 12V !!!(Change resistors if other supply)
* PNP-Transistor: Select according load's current(A) needs(TIP32C=max.3A and so on...)Comments welcome ::) My first electronic project:


http://i1321.photobucket.com/albums/u556/12356562/PWMDC6-12V3Aatleast_zpseda3c5f0.jpg

newInRobotics:
Hi

I already explained it in PM previously that 3A transistor rating is not enough, as 3A Stall Current motor can draw double that when starting or changing direction. Also, 100 Ohm base resistor will not give enough current to the base to fully switch transistor ON, if we consider worst case scenario of hFE = 10 (as in TIP32C Datasheet), meaning that transistor will heat up and possibly burn.

assassa1221:
Sorry but I trust Mads Barnkob. He said it'll work so we'll see. ;) (see link)
"with a 100R base resistor and a 10K pull-up you should have a sturdy driver for your TIP32C." On below blog's comments
http://kaizerpowerelectronics.dk/calculators/transistor-base-resistor-calculator/#comment-14351
Motor 60rpm:
http://dx.com/p/high-torque-60rpm-12v-dc-geared-motor-91625

Hmmm...but I'll buy PNP TIP36C. I=25A +Heatsink. If you think it is a safer option ? (I'll ask Mads precise resistor values later)

* http://www.ebay.de/itm/1-x-TIP36C-TIP36-Power-Transistor-25A-100V-PNP-Free-Shipping-/180856115900?pt=LH_DefaultDomain_0&hash=item2a1bdd52bc
* http://www.futurlec.com/TransPowerTIP.shtml
Phiuuu... Spent 3 months and still stuck in the sandbox even if that won't work :-[

Pogertt:
@ assassa1221

Please read note (6) on page 3 of the data sheet.

http://www.ti.com/lit/ds/symlink/lm555.pdf

Your 555 may have a limited lifespan depending on motor current.

newInRobotics:

--- Quote from: assassa1221 on April 15, 2013, 07:54:39 AM ---Spent 3 months and still stuck in the sandbox even if that won't work :-[
--- End quote ---
That is because You keep asking people whether something will work instead of trying to understand it Yourself. It's not that difficult at all:

* If motor stall current is 3A, go for transistor capable of at least 6A.
* Calculate transistor base resistor:
* Find Min hFE (hFE is gain, it shows how many times base current is amplified and output as Ic (collector current)) value in datasheet
* Divide desired output current (6A) by MinhFE / 2 (In case of TIP36C, Ib (base current) = 6A/(10 / 2)) = 1.2A
* Calculate base resistor using Ohm's Law: R = V/I = 12V / 1.2A = 10 Ohm   
* Check if base current required by transistor matches to what 555 timer can provide:
* Based on 555 timer datasheet Pogertt provided (refer to datasheet of 555 timer You are using), Power Dissipation = 1.18W, hence Max Current @12V can be I = W/V = 1.18W/12V = 0.098A, which is much lower than 1.2A required by transistor, meaning that something will burn (if base resistor is 10 Ohm (to satisfy base current) - 555 timer will burn, if base resistor is 123 Ohm (to satisfy 555 timer parameters) - transistor will burn (or at least get very how reducing its lifespan)).   

--- Quote from: assassa1221 on April 15, 2013, 07:54:39 AM ---Hmmm...but I'll buy PNP TIP36C. I=25A +Heatsink. If you think it is a safer option ? (I'll ask Mads precise resistor values later)
--- End quote ---
This transistor is better suited for 3A stall current motor (although motor that You linked to does not state its stall current), however it still does not solve problem that 555 timer is unable to provide enough current for transistor to switch properly.

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