I want to know if it is possible to use a shunt regulator in series with a load. I need to make a 5mA 3.3v supply from a 12v rail, however it needs to be efficient and extremely cheap.
The average load at the 3.3v rail will only be about 200 uA, but the burst current could be 5-10 mA for a second or two at a time. A series regulator such as an LM317 would work just fine, but it is expensive. It's about 7 cents in quantity. A 431 on the other hand can be had for less than 5 cents.
Essentially, during sleep periods there is just enough current coming from the divider and a trickle through the 431 to power to the MCU. Once a burst starts, it will start draining the capacitor. That will cause the 3v3 rail to drop, and the reference voltage to rise above 2.5v, which should open the shunt regulator and increase the current. It will turn off when it has recharged the cap back up to 3.3v.
I can tolerate +10/-20% ripple on the 3.3v rail, but I don't have a feeling for how fast the 431 will respond or if I will have any problems with oscillations. Has anyone ever tried to do this before? Will it even work?
2 cents really makes a difference here. We could be making over a million of these. I don't want to use the more expensive part unless I absolutely have to.
Thoughts?
The average load at the 3.3v rail will only be about 200 uA, but the burst current could be 5-10 mA for a second or two at a time. A series regulator such as an LM317 would work just fine, but it is expensive. It's about 7 cents in quantity. A 431 on the other hand can be had for less than 5 cents.
Essentially, during sleep periods there is just enough current coming from the divider and a trickle through the 431 to power to the MCU. Once a burst starts, it will start draining the capacitor. That will cause the 3v3 rail to drop, and the reference voltage to rise above 2.5v, which should open the shunt regulator and increase the current. It will turn off when it has recharged the cap back up to 3.3v.
I can tolerate +10/-20% ripple on the 3.3v rail, but I don't have a feeling for how fast the 431 will respond or if I will have any problems with oscillations. Has anyone ever tried to do this before? Will it even work?
2 cents really makes a difference here. We could be making over a million of these. I don't want to use the more expensive part unless I absolutely have to.
Thoughts?
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