This Op amp is after a Power supply regulator that is a positive +10 volts

The op amp inverts the +10 volts into a -10 volts to make a negative supply

My question is what does Q7 do? what function does it do in the circuit?

What kind of circuit is this called please, the op amp and Q7 combination to turn a positive voltage into a negative voltage?

 

here is the schematics

 

Q7 is a buffer, it provides more current to whatever is down the line than the op amp could, the op amp would normally only be able to provide a couple mA, a transistor can provide much more

the opamp is in a negative feedback inverting setup
the transistor is a buffer

I would call it a "negative feedback voltage inverter with a current buffer", I don't know if it has an official term

 

Thanks for the help

But the Q7 buffer has no biasing resistors, it's direct to supply voltage on the collect and direct on the emitter to the output

So the Q7 is not biased? any reason why

I thought OP amps outputted more current than a transistor did

Plus the Negative supply rail is not regulated, only the Positive supply
I have seen this type of stuff often when the negative supply is no regulated but the positive supply is, any reason why?

I need supply doesn't source current? only the positive supply sourced current more?

 

So the Q7 is not biased? any reason why

It is biased by the nature of the op amp feedback. The only thing missing is anything to limit current in case of a fault downline.

I thought OP amps outputted more current than a transistor did

Typically it is the other way around.

Plus the Negative supply rail is not regulated, only the Positive supply
I have seen this type of stuff often when the negative supply is no regulated but the positive supply is, any reason why?

Necessity. Cost.

I need supply doesn't source current? only the positive supply sourced current more?

Positive sources, negative sinks. That's typical in most supplies. Offhand I do not know of a positive regulator that sinks or a negative regulator that sources.

 

Q7 is configured as an "emitter follower" or "common collector" circuit. The base current is increased by the current gain of the transistor. The emitter voltage will follow the base voltage (minus the base/emitter voltage drop)

https://www.google.com/search?q=emi...la:en-US:official&client=firefox-a&channel=sb

 

It is biased by the nature of the op amp feedback.

How is the transistor biased by the op amps feedback?

The only thing missing is anything to limit current in case of a fault downline.

How would you limit the current in cause of a fault?

 

How is the transistor biased by the op amps feedback?

transistors have a current gain
Iout=Ibase*β (some multiplication factor, usually in the hundreds)

How would you limit the current in cause of a fault?

usually a resistor or a fuse, depending on the scenario

there are also much more advanced methods

 

Yes they use milliohm resistors in series as a fuse , a series resistor on the output of the p/s. But these aren't current limiting circuits

 

resistors by nature will only allow some certain maximum current for a set voltage range

 

So I was playing with this circuit in multisim because it looked like something I actually needed.

Using an LM148FK, it shows as having a -18V output, with an 18V input.

If I use an LM148J then it only shows as being 157mV.

What gives?

 

This Op amp is after a Power supply regulator that is a positive +10 volts

The op amp inverts the +10 volts into a -10 volts to make a negative supply

My question is what does Q7 do? what function does it do in the circuit?

What kind of circuit is this called please, the op amp and Q7 combination to turn a positive voltage into a negative voltage?

Dexter, is it possible that you post the whole schematic? If you do not like to disclose it, it's OK for me.

 

So I was playing with this circuit in multisim because it looked like something I actually needed.

Using an LM148FK, it shows as having a -18V output, with an 18V input.

If I use an LM148J then it only shows as being 157mV.

What gives?

Spice opamp models have different levels of complexity, and IIRC model 2 doesn't include the supply voltage limits, while level 3 does.

 

Spice opamp models have different levels of complexity, and IIRC model 2 doesn't include the supply voltage limits, while level 3 does.

I don't quite understand.

does that mean if I buy any LM148, the result would be -18V out, with +18V in?

 

With what power supply? Please show your schematic.

 

Why are the diodes in the middle , it's separates the filter caps

Mostly I see the zener diodes at the END of the power supply, not placed in the middle

Why are the zener diodes placed in the middle of the filter caps?

 

Why do you think it matters where they are drawn on the schematic?

 

Because the zener diodes are before 10 filter caps and after 4 filter caps

That must be a reason for this

 

Nope.

You have to learn the purpose of decoupling capacitors and why the designer drew them that way.

 

Yes they are decoupling caps but are drawn like filter caps right?