[sergey23 0]

Hello , I am confused with the components, there is a regulators and there is DC-Dc both can create voltage for my PMA5-83-2W+ sequencer
I can do this l3505 DC-DC and i can do it with regulator like LM7805 or LT1761.

What is the key difference between DC-DC and a regulator with performance?
https://www.sparkfun.com/datasheets/Components/LM7805.pdf
https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf
https://www.analog.com/media/en/technical-documentation/data-sheets/1761sff.pdf
https://www.qorvo.com/products/d/da007774
https://www.analog.com/en/products/lt3505.html

[Yuri7751 24]

1 hour ago, sergey23 said:

What is the key difference between DC-DC and a regulator with performance?

The key difference is the way they control the amount of energy delivered to the load. A linear regulator (like 7805 or LT1761) has a transistor inbuilt which  operates in a linear mode dissipating the excess of energy.

If the input voltage is say 12V, output is 5V and current 0.1A the dissipated power is (12-5)*0.1= 0.7W. And all that power will heat the IC. The efficiency (Pout/Pin) in the case is about 41% only.

In case of what you call DC-DC (step-down converter or switching regulator) the transistor inside the IC operates in the switching mode (on/off). The energy is proportional to the duty cycle. To get the DC at the output a LC filter is essential. The efficiency may exceed 90% even at high load currents. But at the cost of higher noise and more complicated design (calculations, part selection, PCB artwork etc.).

In your case taking into account very low current (4.5mA) needed and your obvious lack of experience (in switching regulators design at least) I'd recommend using a linear regulator.

Maybe 7805 is not the best choice because you should note the following:

To provide such a sequence you may need a regulator with enable/shut-down pin such as LT1761 for example.

[sergey23 0]

Hello, Suppose I have a general bias of +15V gnd -15V.
As you reccomended for  5V  Vg2 i will use LT1761.
What device you reccomend to use for -2V ?

What device you recommend for 12V step?

Thanks.

Изменено Вторник в 19:31 пользователем sergey23

[Yuri7751 24]

6 hours ago, sergey23 said:

What device you reccomend to use for -2V ?

Well you have provided qorvo example of such a circuit yourself. LTC1261 can do the job. You should carefully study the datasheet to understand how to adjust the negative bias to -2V. See Fig.6.

Maybe in will be necessary to adjust the voltage in two steps :  -2V at first and some higher voltage (adjustable?) after the 12V is on.

Btw it is the third variant of step-down regulators - switched capacitor inverter. 

LTC1261-Switched Capacitor Regulated Voltage Inverter (analog.com)

As to the 12V you can use LT3505 as in qorvo example or you can go to Power Designer (ti.com) enter your data (15V input, 12V 0.4A output) and it will propose you more than 300 variants calculated and simulated in Webench 🙂 

Any variant requires your own efforts - you should carefully study datasheets and application examples, PCB artwork requirements, etc. And any basic knowledge books/papers on switching regulators too. Remember that this power amplifier can produce smoke very easily in case you make a mistake in powering it 😉 Good luck.

 

[sergey23 0]

Hello, I have implemented the basic functionality of LT1751-5 datshet shown below. I get perfect 5V when SHDN=Vin pure 15V DC.
.
If i have to use SHDN pin then i need to have Vshdn=Vin as shown in the photo below.
I have tried to put 15V pulse so there will be a time period where Vhsdn=Vin and still i get Vout almost zero.

Where did i go wrong in switching on  the regulator with SHDN and get it 5V?

Thanks.

https://eu.mouser.com/datasheet/2/609/1761sff-3124194.pdf
 

Изменено Среда в 18:59 пользователем sergey23

[Yuri7751 24]

6 hours ago, sergey23 said:

Where did i go wrong in switching on  the regulator with SHDN and get it 5V?

Nothing was wrong except timing 🙂 It is not that fast:

 

[sergey23 0]

Hello Yuri ,I have tried to upgrade the circuit so i could connect INPUT to SHDN when pulse is 3.3V  and to discharge the output when pulse is 0V.
I see the error in the circuit below where whr mosfet discharges when pulse is 3.3V so i tried to reverse the opamp inputs to make the mosfet be closed .

But the bigger problem is that SHDN not equal Vin when i open the M2.there is 2V gap between them.
How do you reccomend to solve this issue?

Thanks.
 

 

opamp_mosfet_switching.asc

[Yuri7751 24]

 

1. If you look at the page 11 charts you will notice that the threshold voltage of SHDN is about 0.7V. So you don't need to apply 15V there to turn it on.

2. I don't understand why you need to discharge anything. After you shut down RF and  Vdd (12V) nothing bad can happen to your amplifier no matter how fast Vg1 and Vg2 decrease naturally. 

Try to make it simple. Avoid unnecessary parts.

There is a mistake in your circuit - you turn the IC on by high S level and M2 and at the same time you short the output by M1.U2 or M1 are heating and smoking 🙂

[sergey23 0]

Hello Yuri , for the -2V i used LTC1261L ,I dont see that an LDO the less noisy version in the datasheet below.
somehow the 5V regulator managed to charge and discharge the output , but in this case i did the schemtics as shown below.
For G1 I need -2V and 4mA according to the datasheet shown below.
But as you can see in the plot i get 400mA peaks of current.

How can i improve this -2V circuit so i will meet the required demands on the datasheet for Vg1?
LTSPICE and relay simbols of the relay compnent are attached.
DC_Dc_relay_m2p4.asc

https://eu.mouser.com/datasheet/2/609/1261lfa-3124642.pdf

Well you have provided qorvo example of such a circuit yourself. LTC1261 can do the job. You should carefully study the datasheet to understand how to adjust the negative bias to -2V. See Fig.6.

Maybe in will be necessary to adjust the voltage in two steps :  -2V at first and some higher voltage (adjustable?) after the 12V is on.

VO14642_CT.asy VO14642_CT_V2.txt