Principles of Operation and Application Tips

TSM1014

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5

Principles of Operation and Application Tips

5.1 Voltage control

The voltage loop is controlled via a first trans-conductance operational amplifier, the resistor bridge R1,

R2, and the optocoupler which is directly connected to the output.

The relation between the values of R1 and R2 should be chosen as written in Equation 1.

Equation 1

To avoid the discharge of the load, the resistor bridge R1, R2 should be highly resistive. For this type of

application, a total value of 100K

Ω (or more) would be appropriate for the resistors R1 and R2.

As an example, with R2 = 100K

Ω, V

Note that if the low drop diode is inserted between the load and the voltage regulation resistor bridge to

avoid current flowing from the load through the resistor bridge, this drop should be taken into account in

5.2 Current control

The current loop is controlled via the second trans-conductance operational amplifier, the sense resistor

point is tied to the positive input of the current control operational amplifier, and its foot is to be connected

to lower potential point of the sense resistor as shown on the following figure. The resistors of this bridge

are matched to provide the best precision possible.

The control equation verifies:

Equation 2

Equation 3

through it during full load operation.

Equation 4

R

sense

I

lim

×

V

sense

=

V

sense

R

5

V

ref

⋅

R

4

R

5

+

()

-----------------------

=

I

lim

R

5

V

ref

R

sense

⋅⋅

R

4

R

5

+

()

----------------------------------------

=

P

lim

I

lim

V

sense

×

=