Hi! This is a follow on from my previous post regarding +- 15 V regulated supply. As per suggestion from this good group - I built a positive supply using a LM 723. Works fine. Now, I have added an inverter follower using an NE5534 op amp. Why NE5534? That is the only opamp I had in my box and besides I want to use a low noise op amp. The op amps power V+ and V- are the 0 and -20.5 output from the filter. The Vin+ is connected to 0 and the Vin - has an input resistor of 33K and a feedback resistor of 33K (Unity gain) with a 2K trimpot in between for adjustment. I have a PNP pass transistor. RESULT: NO OUTPUT - or - rather -0.07 V output If I connect a 3.2K to Pin 1 (Balance) and a 3.2K to Pin 8 (Bal/COMP) - hey presto - everything springs to life! What is going on? Is the Op Amp powered incorrectly? Should I take Pin 7 (VCC+) to the +20.5? If I have to do that - I have to use zeners or something so that the IC does not see more than +- 15V. To +15 Output from the +ve side of the regulator /|\\ | NB: There is a 22pF Comp cap between (5) and (8) _____|____________________________________0 | | 33K 2K | 33K | |__/\\/\\/\\__/\\/\\__|_/\\/\\/\\_ | | | | | | (7)| | | | |\\| | | IN- |_ | \\ (6) /E | (2) | \\____|/ | | / |\\ |_________________ | / \\C IN+ |/|(4) | (3) | |
---------------------------------------- - 20.5
Please can anyone help me understand this? To me it seems that may be the input transistors are not in their active region because the bias current is too low? Maybe I should lower the 33Ks?
Thanks in advance to anyone who even reads this!
Any suggestions will be a bonus!