Re: When I remove GND from AVR µP TINY15, become very hot.
- From: Pooh Bear <rabbitsfriendsandrelations@xxxxxxxxxxx>
- Date: Mon, 15 May 2006 16:44:08 +0100
Mats Myhrman wrote:
Hi!
First, Thanks for all your help.
Second, I will try to include some schematics in here, I have not the the
picture in my head but will try to make it tomorrow.
The LED is an IR-LED, and I thought that if I calculate the hfe-value on the
Transistor (round 300) and if the PIN from TINY can give ~4.8 volt the
current over 2k2 resistor will be 2.2mA.
Actually you also need to subtract the transistor's Vbe = ~ 0.6V. So the
voltage across the resistor is 4.8V - 0.6V = 4.2V.
Ib = V/R = 1.9 mA.
Times 300 = 65 mA.
Actually =~ 650mA ! Which exceed your transistor's spec IIRC.
It's bad practice to use hfe like this. It's highly variable from device to
device. It likely varies from 100-300.
It's better to define the cuurent with a series resistor in the collector load.
What current do you actually need for the led ?
You also need to use an NPN transistor here !
Graham
.
- Follow-Ups:
- Re: When I remove GND from AVR µP TINY15, become very hot.
- From: Spehro Pefhany
- Re: When I remove GND from AVR µP TINY15, become very hot.
- References:
- When I remove GND from AVR µP TINY15, become very hot.
- From: Mats Myhrman
- Re: When I remove GND from AVR µP TINY15, become very hot.
- From: Pooh Bear
- Re: When I remove GND from AVR µP TINY15, become very hot.
- From: Mats Myhrman
- When I remove GND from AVR µP TINY15, become very hot.
- Prev by Date: Re: OT: In case your Minolta camera quit
- Next by Date: Re: fuse for Craftsman digi multimeter
- Previous by thread: Re: When I remove GND from AVR µP TINY15, become very hot.
- Next by thread: Re: When I remove GND from AVR µP TINY15, become very hot.
- Index(es):
Relevant Pages
|
