LM9036: Architecture/Functional Block diagram

Hi Murali,

LM9036 and LM2936 are both bipolar linear regulators with PNP pass transistors.

See the following app note for general block diagram for a PNP LDO regulator:
www.ti.com/.../snva167a.pdf

Most linear regulators use a resistor divider to compare a reference voltage against the divided output voltage at the error amplifier. LM9036 likely has this configuration of resistor divider connected to the output for voltage feedback.

Hi Eric,

For example consider the application as below. Because of the internal resistor divider, the LDO output is no longer regulated to fixed voltage in case of LM9036 and LM2936. However, LM78L05 regulates to fixed voltage in the same application. I am looking for a high voltage part (40V min) to replace LM78L05. Is the feedback is actual output in LM78L05 instead of resistor divider?

Regards

Murali

Hi Murali,

No, your circuit diagram is incorrect. All three of these linear regulators: LM78L, LM9036, and LM2936 have internal feedback resistor dividers. This means the resistors are internal to the linear regulator IC. They are not external resistors.

The part numbers for 5.0 V fixed output version:
LM9036-5.0
LM2936-5.0

The LM78L datasheet includes a functional block diagram in section 7.2. The LM78L fixed linear regulator has internal feedback divider resistors shown as R12 and R13 in the block diagram.

See figure 1 of this application note for the internal resistor divider connection:
www.ti.com/.../snva167a.pdf
The internal feedback divider resistors are R1 and R2 in the figure.

Hi Eric,

R1 & R2 in my circuit are not feedback resistors. I am testing with fixed output version of regulators. V1 is a variable voltage representing some parameter in my application. By varying V1 and at fixed regulator output voltage VLDO(In this case 5V), Vx varies linearly.

Vx = f(V1, VLDO, R1, R2). *VLDO = LDO output

Ideally all the three regulators LM78L05, LM9036-5.0 & LM2936-5.0 should performance similarly.

Practically VLDO output is at 5V with LM78L05 when V1 is varied from 0 to 10V.

But with LM9036-5.0 VLDO output is not regulated to 5V. VLDO is increasing by increasing with V1.

I also understand these are positive output current regulators which means these cannot sink current at the output. But the question is what is the different between these three LDO for behaving differently.

Thanks & Regards
Murali

Hi Murali,

What are the resistor values for R1 and R2? What is the value of V2?

These are positive voltage regulators. They are not current regulators.

There are conditions where a voltage regulator sinks current at the output:
Vout - Vin reverse voltage drop. When the reverse voltage is sufficiently large, there can be junction breakdown and current flow into the output.

Hi Eric,

V2 = 30V
V1 = 0 t0 10V
R1 = R2 = 4.99K

Regards
Murali

Hi Murali,

I haven’t heard back from you. I’m assuming you were able to resolve your issue. If not, just post a reply below or create a new thread if the thread has locked due to time-out.