I'm working on a project where I need a 3.3V reference for a PIC A/D. I tried using a BZX55B3V3 which is a 3.3V Zener using a circuit like below:
**broken link removed**
Initially I tried it with R=10K and Uin = 4.5-5V. In theory, Uout should be 3.3V under no/minimal load, right? I got closer to 2.2V. I tried reducing R to 1K and that got me somewhere in the 2.8-3 volt range. When I used a 9V battery for Uin and R=470Ω I got around 3.5V, with about 10 mA draw.
So what gives? Why would a 3.3V zener conduct at 2.2V at low current levels? The only thing connected at the output was my DVM, so it isn't an output impedance issue loading the circuit. Since this is a battery-operated circuit, Uin can vary depending on battery strength, and I don't want my reference to be drawing several mA of current to get the correct voltage, but I need my reference voltage to be reasonably stable. I couldn't find a precision shunt reference @ 3.3V that was in stock, which is why I went with the zener.
**broken link removed**
Initially I tried it with R=10K and Uin = 4.5-5V. In theory, Uout should be 3.3V under no/minimal load, right? I got closer to 2.2V. I tried reducing R to 1K and that got me somewhere in the 2.8-3 volt range. When I used a 9V battery for Uin and R=470Ω I got around 3.5V, with about 10 mA draw.
So what gives? Why would a 3.3V zener conduct at 2.2V at low current levels? The only thing connected at the output was my DVM, so it isn't an output impedance issue loading the circuit. Since this is a battery-operated circuit, Uin can vary depending on battery strength, and I don't want my reference to be drawing several mA of current to get the correct voltage, but I need my reference voltage to be reasonably stable. I couldn't find a precision shunt reference @ 3.3V that was in stock, which is why I went with the zener.