I have a professional audio amplifier schematic and I am trying to describe what the blocks do, since these schematics are very difficult to get because the companies dont let them leak, I only managed to get the diagram, can someone help me describe what the blocks do? Since I am not so certain myself.

 

Sorry I forgot to upload the circuit at the first post. I upload it here.

 

A - Control block for enable/disable of the amplifier.
B - Current to Voltage converter from the DAC ( I/V converter).
C - The "switch" section to change the block D gain.
D - Gain stage ( the amplifier)
E - Mute control and mute BJT's

 

Thank you very much, its a bit difficult for me to read a large circuit when I see it like this, it looks too complicated and I loose myself.

Can you help me to understand how exactly the blocks work, I will try also.

Since its for control, BLOCK A should be a 20KHz switch, with the bipolar transistor to provide enough current for the MOS, the MOS is in key mode switching at 20KHz in order to decrease the temperature over the elements?
Pin "9" of operational amplifier 1632 is for enabling or disabling the amplifier (chip select)?

 

Since its for control, BLOCK A should be a 20KHz switch, with the bipolar transistor to provide enough current for the MOS, the MOS is in key mode switching at 20KHz in order to decrease the temperature over the elements?

No, wrong.
Why 20kHz ? Why do you want ON and OFF the amplifier at 20kHz?

Q1 is probably driven from the μC, supply from +5V, but the opamp enable function is referenced to the negative supply ( - 15V) of the opamp. So this is why you need a Q1 and Q2 to "convert" logic levels.

Pin "9" of operational amplifier 1632 is for enabling or disabling the amplifier (chip select)?

No, Pin 7 is for enabling or disabling the amplifier.

 

So the control block is only for converting the logic levels? Since we have from "+5" to "-15V", that means the maxium we can get is 20V from the output of the MOS divided by the 10k resistor?

I thought that a PWM would drive the transistor base at 20KHz since its outside of the human hearing range, but now that I hear it myself I understand that this isnt a motor and even if driven by impulses it will be at maximum 14KHz.

Why do we need a voltage divider of 47k and 1k to drive the transistor base? I am guessing that since this is an PNP transistor, the divider is inverted and the voltage on the transistor base would be the voltage over the 47k resistor (this doesnt seem right, I am risking a lot here)?
Whats the point of the voltage divider for the GATE of the MOS, it will decrease the voltage since we have 2 by 10k resistors and the voltage drop over the transistor (collector-emitter) will be 1-2V also, leaving about 5V for the base of the MOS? Whats the point in this?

Edit: I did not see it properly, yes its pin 7 thats "chip select", sorry for that!

 

So the control block is only for converting the logic levels?

Yes

that means the maxium we can get is 20V from the output of the MOS divided by the 10k resistor?

No wrong again. When the MOS is OFF (cut-off) the opamp is working. But when Q1 and Q2 are Turn ON the MOS drain is at -15V the opamp disables the output.

thought that a PWM would drive the transistor base at 20KHz since its outside of the human hearing range, but now that I hear it myself I understand that this isnt a motor and even if driven by impulses it will be at maximum 14KHz.

No PWN is needed here. This is just a simple "level control" ON/OFF type.

Why do we need a voltage divider of 47k and 1k to drive the transistor base?

47kΩ is a pull-up resistor. It will ensure that the BJT is OFF when control pin is at High state.

More detailed explanation
https://electronics.stackexchange.c...a-pnp-transistor-pull-up-itself/311336#311336

Whats the point of the voltage divider for the GATE of the MOS

R4 serves as a pull-down resistor. And the voltage divider limits the Vgs voltage to make sure the max Vgs voltage is not reached.

 

Why do they put 1 pull up resistor first and then 1 pull down, dont they do the same thing?
Plus why is it that they use a PNP transistor and -15V?

 

Why do they put 1 pull up resistor first and then 1 pull down, dont they do the same thing?

Have you read this?
https://electronics.stackexchange.c...a-pnp-transistor-pull-up-itself/311336#311336

In short. R2 (pull-up resistor) was add to ensure that BJT will be turn-off when the signal from microcontroller is at high state.
This voltage ( from microcontroller output) maybe too low ( lower then 4.7V) to ensure proper Q1 cut-off.
See a similar example:
https://forum.allaboutcircuits.com/attachments/as1-png.55973/

Also this resistor helps turn-off the BJT during power-up ( or while the μC is in reset).

R4 serves the similarly function., but this time he ensures Q2 turn-off, when Q1 is off without R4 the Q2 gate voltage is undetermined. The gate is floating. Aslo any leakage current from Q1 may also Turn-ON the Q2 and R4 prevent this from happening.

Plus why is it that they use a PNP transistor and -15V?

Do you know any better way? With NPN or without it?

As for -15V. Well the amplifier is supplied from -15V also the "enable" pin voltage must be referenced to -15V. So, this is why we need this Logic Level Converter.

 

I will read it as soon as I can. I have a lot to read.

 

So the pull-up resistor is to stabilize the voltage only, and the pull-down is to ensure faster route to ground and leakage current to be neglected?

 

Pull-up resistor also ensures "faster route" but not to ground but to Vcc. Because you have PNP transistor.

 

OK, thanks for your help! I wanted to know when to use them if I make a design by myself.

 

You must add some "pull up/down" if you are driven the transistor directly from μC, or as in this case (Q1 and Q2) from " open collector/drain" output.
https://learn.sparkfun.com/tutorials/pull-up-resistors/what-is-a-pull-up-resistor
https://electronics.stackexchange.c...tter-for-pulling-down-an-npn-transistors-base

 

With the risk of sounding stupid, I ask until I know every detail.
This brings me back to why should I prefer PNP instead of NPN?

 

This brings me back to why should I prefer PNP instead of NPN?

Ther is no simple answer for this type of a question. It all depends on the situation we have and what we want to achieve in the circuit.

 

Ok, so in this case why is it better to use a PNP instead of NPN?

 

Ok, so in this case why is it better to use a PNP instead of NPN?

In this case you cannot use NPN transistor. At least I don't see how. Notice that the MOSFET source termina is at -15V and the control circuit μC is at ground reference. So clearly we are need a "high side switch" to ON/OFF the mosfet. And the PNP is a "high side switch" (in saturation PNP transistor shorts the collector to the Vcc the emitter). And NPN is a "low side switch".

 

Thanks, I need to read a lot about transistors, I have started with 180 pages, but we will see when I will finish them.

 

You can try this
https://forum.allaboutcircuits.com/...r-amp-doubts-and-questions.91084/#post-663195
https://forum.allaboutcircuits.com/threads/simple-shunt-regulator.26675/page-2#post-165135