Hi everyone,
I am looking for a bit of guidance on a little current mirror circuit. The attached circuit is a 4 transistor wilson mirror.
I am looking to create a current mirror to power 6 LEDs. Due to an input voltage restriction, I need to power the
LEDs in three branches. I want the current to be pretty accurate, 1-2mA difference when drawing 500mA.
If I start off with a two branch configuration with 4 FETs, everything seems to behave. I have 'spiced' the
circuit and it seems to behave correctly. If I short out transistors D4 and D2 in one of the branches, the circuit is pretty well matched.
If I now add in a third branch (schematic attached), the currents seem matched. If I short out one of the LEDs in the third branch (D6).
The currents get mismatched by around 10mA.
1) Does anyone have any idea why this is happening?
2) When I try and do a two transistor configuration current mirror i.e. missing out M3, M4, M5 and M6, the currents were not very well matched if I short out 1 LED. Why might this be happening?
3) I am going to be using discrete FETs to build this circuit. Is it realistic to expect the currents to be matched to
within 1% of the full scale current value?
Your words of wisdom are graciously received
analog_headache
I am looking for a bit of guidance on a little current mirror circuit. The attached circuit is a 4 transistor wilson mirror.
I am looking to create a current mirror to power 6 LEDs. Due to an input voltage restriction, I need to power the
LEDs in three branches. I want the current to be pretty accurate, 1-2mA difference when drawing 500mA.
If I start off with a two branch configuration with 4 FETs, everything seems to behave. I have 'spiced' the
circuit and it seems to behave correctly. If I short out transistors D4 and D2 in one of the branches, the circuit is pretty well matched.
If I now add in a third branch (schematic attached), the currents seem matched. If I short out one of the LEDs in the third branch (D6).
The currents get mismatched by around 10mA.
1) Does anyone have any idea why this is happening?
2) When I try and do a two transistor configuration current mirror i.e. missing out M3, M4, M5 and M6, the currents were not very well matched if I short out 1 LED. Why might this be happening?
3) I am going to be using discrete FETs to build this circuit. Is it realistic to expect the currents to be matched to
within 1% of the full scale current value?
Your words of wisdom are graciously received
analog_headache
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