Show Posts
Pages: 1 [2] 3
16  Using Arduino / General Electronics / Help reading current gain from BJT datasheet on: February 03, 2011, 04:58:59 pm
The bjt I'm working with is the 2N4401: http://www.onsemi.com/pub_link/Collateral/2N4401-D.PDF

On page 5 of the datasheet they have current gain vs Ic graph as seen below



If the top 2 curves are unit 1 and unit 2, then what are the bottom 2 curves for? Which curve should I use?
17  Using Arduino / Motors, Mechanics, and Power / Re: How do flyback diodes work in H-bridge configuration? on: February 03, 2011, 04:51:55 pm
Ah, I see it now. Thank you for your help.
18  Using Arduino / Motors, Mechanics, and Power / Re: How do flyback diodes work in H-bridge configuration? on: February 03, 2011, 02:26:37 pm
I still cannot visualize this, can you someone draw a current path in diagram above showing this? I would appreciate it.
19  Using Arduino / Motors, Mechanics, and Power / Re: How do flyback diodes work in H-bridge configuration? on: February 03, 2011, 03:01:13 am
I still don't understand especially about the part where he talks about the motor voltage being below gnd.
20  Using Arduino / Motors, Mechanics, and Power / How do flyback diodes work in H-bridge configuration? on: February 03, 2011, 01:49:45 am
In a single direction configuration such as below I can see how placing the diode in parallel will cause a short with the motor.


But in an H-bridge configuration below, how does the diode configuration allow current to flow from one end to the other end of the motor? The polarity of the back emf is shown on the picture below



21  Forum 2005-2010 (read only) / Interfacing / Re: driving 8x8 LED using 2 74HC595 on: August 01, 2010, 02:16:37 pm
If you want to turn on one row, do you turn on a darlington pair, and switch all the top 595 output to high?

Would that cause the uln2803 to sink 20 * 8 = 160 mA? Wouldn't that current have to flow through the 595 which can only take 35 mA and damage it?
22  Forum 2005-2010 (read only) / Interfacing / Re: driving 8x8 LED using 2 74HC595 on: August 01, 2010, 01:05:46 pm
Quote
... make sure that 2803 is the one that you put only one zero on at a time and put the data for that row on the top 595.

What do mean by that? Do mean that 1 led can only be turned on at a time?

Or do you mean that each pin on the 595 can only handle 20mA on each pin, and that I can only turn on 1 darlington pair at a time?
23  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 04:59:06 pm
Okay, I get everything now! Thank you for your patience and expertise RuggedCircuits!
24  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 04:34:27 pm
What do you mean by double the 595s? I thought p MOSFETs were to replace the top 595 so that it can source enough current for the column?
25  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 04:04:55 pm
My leds have a Max Peak Forward Current of 75 mA. 80% of that is 60 mA. So does that mean that when multiplexing, the maximum possible brightness of the leds would be equivalent to an led with a constant current of 7.5 mA?
26  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 03:27:28 pm
Is Max Peak Forward Current the same as instantaneous current?
27  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 03:16:30 pm
So if the regular on brightness is drawing 20 mA, I would have to draw 160 mA per led to get the same brightness. Wouldn't that burn out the LED?
28  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 03:06:45 pm
Quote
This multiplexing method only has each LED on 1/8 of the time meaning it has to be 8x brighter than usual for the same average brightness as if it were just "on" all the time (hence the need for high instantaneous current).

I am not sure what you mean by that...1/8 of what time? Wouldn't the brightness depend on how fast you switch each column?
29  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 02:42:27 pm
So if I want to light all leds in a row, I have to turn them on really fast one at a time? If that is so, then what is the point of using a ULN2803?
30  Forum 2005-2010 (read only) / Interfacing / Re: Help Hooking Up ULN2803 and 595s to 8x8 Led Matrix on: August 03, 2010, 02:27:32 pm
I don't follow you Osgeld...
Pages: 1 [2] 3