Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Wish to use open drain comparaotr to turn PNP on, so don't need pull up resistor?

Status
Not open for further replies.
T

treez

Guest
Hello,

I wish to use the open drain version of this comparator......(MCP65)

https://ww1.microchip.com/downloads/en/DeviceDoc/22269B.pdf

I do not want to use a pull up resistor at the output though....because all i want to do is get this comparator to turn a PNP transistor on when its output goes low.

Do you think this kind of operation is possible with this comparator?
 

Tahmid

Advanced Member level 5
Joined
Jun 17, 2008
Messages
4,758
Helped
1,793
Reputation
3,578
Reaction score
1,652
Trophy points
1,393
Location
Silicon Valley, California, USA (from Dhaka, Bangl
Activity points
30,535
You should still use a pull up resistor to turn the transistor off and to ensure that it stays off. I have had bad experiences with PNP transistors turning on and staying on with floating base.

Hope this helps.
Tahmid.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
49,919
Helped
14,484
Reputation
29,238
Reaction score
13,396
Trophy points
1,393
Location
Bochum, Germany
Activity points
286,628
You didn't tell how the comparator output is connected to comparator and if you intend e.g. feedback resistors to provide hysteresis. Provided you drive the PNP in common collector configuration, you don't need a base resistor. A pull-up can be omitted only if the comparator's up to 100 nA output leakage isn't an issue.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
T

treez

Guest
thanks, ...i was just worried that it might drive high instead of just pulling high....

i have resistors from B->E and C>B, so that the comparator can switch the PNP on by driving low.

....interesting that i dont need a base resistor for the PNP....there are no hysteresis resistors, ...i believe the internal hysteresis will be enough, and also, this is a comparator that only gets tripped when the customer pulls the battery out without turning off the equipment...which i believe will not happen often....so even if there is some jitter when it trips, i dont think it will be too serious
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
49,919
Helped
14,484
Reputation
29,238
Reaction score
13,396
Trophy points
1,393
Location
Bochum, Germany
Activity points
286,628
To avoid misunderstandings, I would prefer to see a schematic.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top