R
Ramendra S Roy
- Jan 1, 1970
- 0
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!
Regards
Ramendra
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!
Regards
Ramendra