vne147
Member
Hello everyone. I'm working on a project and have run into to some trouble. I'm hoping someone here can help me resolve it.
I'm building a prototype of a small, battery powered, motion sensor. I've made the PCB and have started soldering components onto it. I've gotten as far as the power supply portion of the circuit but it's not working correctly.
The power supply is a DC-DC boost converter based on the MC34063EDB IC. I'm powering it with 3V and need about 5.7V at the output. I've attached a schematic showing the portion of the circuit I've built so far and also, here is a datasheet for the MC34063EDB.
Ultimately, I want to power the circuit from 2 AAA batteries but when I tried that, it didn't output 5.7V; it output closer to 28V. After seeing this, I supplied the board with 3V from my bench power supply just to see what would happen and when I did, the circuit seemed to work fine. I measured 5.68V at the output.
Next, with the circuit still powered from my bench power supply I measured the current being drawn by the circuit and was surprised to see about 285 mA. I didn't look at it through an oscilloscope and my multimeter is not of the best quality so I'm not sure how close to reality the number is but it still seems surprisingly high to me. I mean there isn't even a load hooked up to it yet.
What I think is happening is when the circuit is hooked up to the AAA batteries, it is drawing more current than they can supply. As a result, their combined voltage drops to around 1.5V (which I've measured) and that undervolts the IC. The IC stops working, the battery voltage rebounds, the IC turns on again, the battery voltage drops, and so on. I think this astable operation is causing the higher than intended output voltage. Conversely, when I power the circuit from my bench supply, it has no problem giving 285 mA at 3V and the IC works normally.
So my question is this; why is the circuit drawing that much current? Shouldn't it be much much less especially since there is no load connected to the output yet? 285 mA seems like a ridiculously high quiescent current consumption. What can I do to reduce the current? Can I use a larger inductor? A different diode? Does anyone have any ideas?
Thanks in advance for your help.
I'm building a prototype of a small, battery powered, motion sensor. I've made the PCB and have started soldering components onto it. I've gotten as far as the power supply portion of the circuit but it's not working correctly.
The power supply is a DC-DC boost converter based on the MC34063EDB IC. I'm powering it with 3V and need about 5.7V at the output. I've attached a schematic showing the portion of the circuit I've built so far and also, here is a datasheet for the MC34063EDB.
Ultimately, I want to power the circuit from 2 AAA batteries but when I tried that, it didn't output 5.7V; it output closer to 28V. After seeing this, I supplied the board with 3V from my bench power supply just to see what would happen and when I did, the circuit seemed to work fine. I measured 5.68V at the output.
Next, with the circuit still powered from my bench power supply I measured the current being drawn by the circuit and was surprised to see about 285 mA. I didn't look at it through an oscilloscope and my multimeter is not of the best quality so I'm not sure how close to reality the number is but it still seems surprisingly high to me. I mean there isn't even a load hooked up to it yet.
What I think is happening is when the circuit is hooked up to the AAA batteries, it is drawing more current than they can supply. As a result, their combined voltage drops to around 1.5V (which I've measured) and that undervolts the IC. The IC stops working, the battery voltage rebounds, the IC turns on again, the battery voltage drops, and so on. I think this astable operation is causing the higher than intended output voltage. Conversely, when I power the circuit from my bench supply, it has no problem giving 285 mA at 3V and the IC works normally.
So my question is this; why is the circuit drawing that much current? Shouldn't it be much much less especially since there is no load connected to the output yet? 285 mA seems like a ridiculously high quiescent current consumption. What can I do to reduce the current? Can I use a larger inductor? A different diode? Does anyone have any ideas?
Thanks in advance for your help.