MacGyverS2000
Electrical
- Dec 22, 2003
- 8,504
I'm looking for feedback to determine if my driver circuit is as simple as it can be (and also if it will work, as currently designed).
First, some definitions:
1) SINK - irrelevant what's here, other than the fact that they are current sinks, each one sinking the same amount as the others.
2) STRIPE - multiple SINKS in parallel (component value changes are allowed on a STRIPE during construction)
3) controller - separate circuit from a STRIPE (no component value changes are allowed here once a design has been settled on)
The current in each SINK along a STRIPE should be roughly equivalent. The number of SINKS in a STRIPE can vary from project to project, so I expect to change a component value or two during construction to determine the total STRIPE current.
My driver currently looks like this:
1) A digital pot's wiper will vary in voltage from roughly +0.6V to +5.0V. This wiper is connected directly to a voltage follower. This is the "controller".
2) Each STRIPE will have two components on it in addition to the multiple SINKS, a high-power transistor (the current supply for the SINKS) and a resistor tying the transistor base to the controller. The transistor's emitter will be tied to ground.
Since I know the voltage swing of the voltage follower (the same as the digital pot, +0.6V to +5.0V), and the voltage at the base of the power transistor (+0.6V), I can determine the amount of current flowing into the base (and therefore the total current flowing through the STRIPE). I change the base resistor at construction time since I will know how many SINKS are in a particular STRIPE, and the controller stays the same.
To add even more fuel to the fire, STRIPES can be put in parallel, too. The number of STRIPES can also vary, but will probably be no more than 2-3 in parallel.
SO, my question to everyone here is this...is the circuit as simple as it can be while still satisfying all of the criteria I've laid out (feel free to ask questions if anyone needs more detail), and will it even work as described?
My biggest concern was making sure that having several STRIPES in parallel (which means several base resistors in parallel) would not affect the controller/driver, and would the follower be able to provide enough current (my guess would be <50 mA for several STRIPES in parallel)? It looks OK from my viewpoint, but I've learned to get a second opinion for some things
Thanks!
First, some definitions:
1) SINK - irrelevant what's here, other than the fact that they are current sinks, each one sinking the same amount as the others.
2) STRIPE - multiple SINKS in parallel (component value changes are allowed on a STRIPE during construction)
3) controller - separate circuit from a STRIPE (no component value changes are allowed here once a design has been settled on)
The current in each SINK along a STRIPE should be roughly equivalent. The number of SINKS in a STRIPE can vary from project to project, so I expect to change a component value or two during construction to determine the total STRIPE current.
My driver currently looks like this:
1) A digital pot's wiper will vary in voltage from roughly +0.6V to +5.0V. This wiper is connected directly to a voltage follower. This is the "controller".
2) Each STRIPE will have two components on it in addition to the multiple SINKS, a high-power transistor (the current supply for the SINKS) and a resistor tying the transistor base to the controller. The transistor's emitter will be tied to ground.
Since I know the voltage swing of the voltage follower (the same as the digital pot, +0.6V to +5.0V), and the voltage at the base of the power transistor (+0.6V), I can determine the amount of current flowing into the base (and therefore the total current flowing through the STRIPE). I change the base resistor at construction time since I will know how many SINKS are in a particular STRIPE, and the controller stays the same.
To add even more fuel to the fire, STRIPES can be put in parallel, too. The number of STRIPES can also vary, but will probably be no more than 2-3 in parallel.
SO, my question to everyone here is this...is the circuit as simple as it can be while still satisfying all of the criteria I've laid out (feel free to ask questions if anyone needs more detail), and will it even work as described?
My biggest concern was making sure that having several STRIPES in parallel (which means several base resistors in parallel) would not affect the controller/driver, and would the follower be able to provide enough current (my guess would be <50 mA for several STRIPES in parallel)? It looks OK from my viewpoint, but I've learned to get a second opinion for some things
Thanks!
