Continue to Site

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.

Register Log in

Current mirror for parallel led current matching

Status
Not open for further replies.
T

treez

Guest
Newbie level 1
In figure 3 of the following, the LHS transistor has its Base and Collector shorted.

**broken link removed**

....the LHS led string also has less current in it, due to the vf's of its leds being higher.

What if the base and collector of the RHS transistor had been shorted instead...would the current mirror still have worked?
 

The base-emitter voltage is a range of voltages so the actual amount of current in the current sink is a wide range.
The transistors probably do not match (but it is better since they are thermally joined) so the currents probably will not match as well as the example.

The base currents are on the left side so I think the LED current is higher in the left side.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
treez said:
What if the base and collector of the RHS transistor had been shorted instead...would the current mirror still have worked?
Click to expand...

I dont see why not

I also agree with audioguru that currents on the LHS should be higher
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
It is the power supply that is limiting the currents, not the current mirror that on the left is simply some LEDs in series with a diode.
Since there are two LED strings then the 700mA from the power supply is simply divided roughly in half.
 
  • 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

Back
Top