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Why HP power supplies doesnt have a obvious feedback loop?

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Efe_114:
I cant see the feedback loop even in a single hp power supply anyone can tell me? I am trying to build a power supply like the E3610 and i also looked at the others but cant find the feedback loop. Schematics are attached. (Also this thread will be a nice source for HP power supply schematics.)

Edit: are the attachments empty or is it just me?

Another edit: fixed by removing some of the attachments.

soldar:
You can't see feedback?

tombi:
First the voltage control loop -

So in the first schematic (E3610A)  U1 is the voltage error amplifier. The non-inverting input is connected to either the output or the sense terminal (there is a switch) and the inverting input is connected to a pot fed from the +5 supply. The pot allows a variable voltage to be selected at the inverting input. The opamp will drive the loop to make its inputs equal.

U1 controls the main pass transistors (Q1, Q3, Q6, Q7) via a driver Q2.

So the loop goes Output/Sense -> U1 -> Q2 (driver) -> Pass transistors -> Output.

Current is measured by U4B - the outputs of U1 and U4B are connected via diodes to the driver transistor (Q2) so that whichever one is at a lower voltage controls Q2. This way the voltage control loop is driving the output until the current limit is exceeded and then the voltage control loop governs the output.

Does this help?

Tom

Efe_114:

--- Quote from: soldar on March 13, 2019, 01:49:35 pm ---You can't see feedback?

--- End quote ---
Thank you! I tought S+ Was referanced to ground because the ground was marked S+ somewhere but i dont remember now. But how there is a feedback through the diode(CR8?) there?

--- Quote from: tombi on March 13, 2019, 01:56:59 pm ---First the voltage control loop -

So in the first schematic (E3610A)  U1 is the voltage error amplifier. The non-inverting input is connected to either the output or the sense terminal (there is a switch) and the inverting input is connected to a pot fed from the +5 supply. The pot allows a variable voltage to be selected at the inverting input. The opamp will drive the loop to make its inputs equal.

U1 controls the main pass transistors (Q1, Q3, Q6, Q7) via a driver Q2.

So the loop goes Output/Sense -> U1 -> Q2 (driver) -> Pass transistors -> Output.

Current is measured by U4B - the outputs of U1 and U4B are connected via diodes to the driver transistor (Q2) so that whichever one is at a lower voltage controls Q2. This way the voltage control loop is driving the output until the current limit is exceeded and then the voltage control loop governs the output.

Does this help?

Tom


--- End quote ---
Thanks! This really helped me but why are the back to back diodes(CR6, CR7) there between non inverting and inverting inputs? Wont they limit the voltage between 2 inputs to 0.6V?

If these questions are just so stupid you know who to blame for not making more fundementals friday.

EDIT: As i said S+ is referanced to ground in the display and referance supply

soldar:

--- Quote from: Efe_114 on March 13, 2019, 03:18:55 pm --- Thank you! I tought S+ Was referanced to ground because the ground was marked S+ somewhere but i dont remember now. But how there is a feedback through the diode(CR8?) there?
--- End quote ---
If higher voltage is back-fed into the unit then that diode will conduct and the circuit will raise the voltage to meet the outside voltage and prevent damage to the circuit.

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