I hooked up a 3.3V Microchip TC1108 LDO linear reg (300mA) with its 3 pins as follows:
1. Vin (4 NiMH batteries) to bat +
2. GND to picaxe 08M in/out
3. Vout to a parallel string of LEDs (twenty or so to handle the 300mA)
By switching the PICAXE pin from input to output(on) (changes impedance properties of pin, yes?) I got the same effect as if I'd used a Darlington (or other more appropriate interface from the CMOS): The PICAXE switched the LEDs on and off, with enough current to power the whole string.
According to the datasheet, the TC1108 uses about 50uA. I read this as meaning that about 50uA goes from Vin to GND across the TC1108. As such the PICAXE, which can sink or source up to 20mA, can safely switch this LDO on and off in this manner (yes?).
My question is: can anyone tell me if (why) this is a bad idea? For instance, if I decided I want the PICAXE to switch 300mA (the TC1108 claims to output +/- .5% tolerance), is this a viable solution? Are the losses huge? Will I fry the PICAXE (because I am assuming incorrectly about the active amperage or other reason)? Is there a better solution for current regulation?
Last note - before someone chews me all up over this - I have a breadboard and a certain number of parts at my disposal. So I hook them up, see what they do, and then try to discover the meaning of the mistakes I make along the way. Its how I learn. So I had some LEDs, the Reg, and I found out I can switch them with a PICAXE. I may still be an idiot for it, but if anyone wants to know why I did this, the above is why.
Thank you very much.
1. Vin (4 NiMH batteries) to bat +
2. GND to picaxe 08M in/out
3. Vout to a parallel string of LEDs (twenty or so to handle the 300mA)
By switching the PICAXE pin from input to output(on) (changes impedance properties of pin, yes?) I got the same effect as if I'd used a Darlington (or other more appropriate interface from the CMOS): The PICAXE switched the LEDs on and off, with enough current to power the whole string.
According to the datasheet, the TC1108 uses about 50uA. I read this as meaning that about 50uA goes from Vin to GND across the TC1108. As such the PICAXE, which can sink or source up to 20mA, can safely switch this LDO on and off in this manner (yes?).
My question is: can anyone tell me if (why) this is a bad idea? For instance, if I decided I want the PICAXE to switch 300mA (the TC1108 claims to output +/- .5% tolerance), is this a viable solution? Are the losses huge? Will I fry the PICAXE (because I am assuming incorrectly about the active amperage or other reason)? Is there a better solution for current regulation?
Last note - before someone chews me all up over this - I have a breadboard and a certain number of parts at my disposal. So I hook them up, see what they do, and then try to discover the meaning of the mistakes I make along the way. Its how I learn. So I had some LEDs, the Reg, and I found out I can switch them with a PICAXE. I may still be an idiot for it, but if anyone wants to know why I did this, the above is why.
Thank you very much.