• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

B562 Reduce Gain

Status
Not open for further replies.

Suraj143

Active Member
In my 16x32 led matrix design I use B562 as anode row drivers.

I have two questions,

1) I need to remove R5,R6,R7,R8 anode resistors & reduce current by increasing the base resistors to control brightness in the particular row. Will it work like that?
2) If I increase the supply voltage to 6V will the transistors OFF from a 5V gate signal?

I have added a timing diagram of the base signals.Each transistor will ON for a 1mS time period. My scanning rate is 1/16 duty cycle.
 

Attachments

Nigel Goodwin

Super Moderator
Most Helpful Member
I would say no to everything you suggest, you need the current limiting resistors for the LED's, and the transistor need enough drive to make them switch, not act in a linear fashion.

I also wouldn't be too happy with a 6V supply either.
 

dr pepper

Well-Known Member
Most Helpful Member
Increasing the base resistors would put the tranny's into their linear region, this will increase their power dissipation and slight variances in tranny's might give you variances in led brightness so that not a good idea.
To decrease brightness increase the anode resistors (or cathode resistors).
With such low base resistors theres a good chance a 5v signal will not turn the trannys off with 6v on the collectors, you could either add another tranny as a level shifter, or switch to an npn tranny configured as a emitter follower, doing that though will invert the led, high would be on.
 

Suraj143

Active Member
I need to eliminate base resistor & pull up base resistor (base to Emitter resister- make sure the transistor is fully off). I see a ghost effect in my LED matrix with B562 transistors. Also my PCB gets bigger with these resistors.

I changed my mind & planning to go for a P channel MOSFET APM4953.

*Can I omit the above resistors if I go for a FET?Need to direct drive from a PIC pin.
*Also do these FETs have a saturation voltage?

Thanks
 
Last edited:

ronsimpson

Well-Known Member
Most Helpful Member
You can get transistors with the Base resistors inside. "Pre-Biased transistors"
I have a box of through hole transistors. (some where)
You can get 1,2,4,8 transistors/ IC.
upload_2018-2-22_10-21-47.png
I see a ghost effect in my LED matrix with B562 transistors.
This is often a timing problem. You need to have a small time when all rows and all columns are off. (it takes a small time for the transistors to turn off)
Can I omit the above resistors if I go for a FET?
Yes
If I increase the supply voltage to 6V will the transistors OFF from a 5V gate signal?
With the computer at 5V and the supply at 6v there is 1V of "turn on".


 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top