LM358A for high-side current sensing

[Hammy]

I'm using an LM358A for high-side current sensing. I would like to be
able to use the other OP in the so-8 package as a thermal shutdown.
This means that both outputs would be connected to the same point R9&
R8 junction on the schematic. Q1 &Q2 are really a dual prebiased
MUN5311DW1T1-D I'm using as a latch.

Schematic

http://i37.tinypic.com/2z9csja.png

My question is do I have to place blocking diodes on the output of the
OP'S. If one output goes high it will place Vcc-1.5V on the output of
the other OP will this damage the OP?



I don't have any LM358A's on hand but I would like to be able to test
it with maybe a TLC27L2 so the same question for this OPAMP.

Thanks

 

[John Popelish]

Hammy wrote:

I'm using an LM358A for high-side current sensing. I would like to be
able to use the other OP in the so-8 package as a thermal shutdown.
This means that both outputs would be connected to the same point R9&
R8 junction on the schematic. Q1 &Q2 are really a dual prebiased
MUN5311DW1T1-D I'm using as a latch.

Schematic

http://i37.tinypic.com/2z9csja.png

My question is do I have to place blocking diodes on the output of the
OP'S. If one output goes high it will place Vcc-1.5V on the output of
the other OP will this damage the OP?

With that low supply voltage, they probably will not
overheat. But you don't have a very determinate situation,
either. The diodes are a good idea.

I don't have any LM358A's on hand but I would like to be able to test
it with maybe a TLC27L2 so the same question for this OPAMP.

Same answer.

--
Regards,

John Popelish

 

[Jamie]

Hammy wrote:

I'm using an LM358A for high-side current sensing. I would like to be
able to use the other OP in the so-8 package as a thermal shutdown.
This means that both outputs would be connected to the same point R9&
R8 junction on the schematic. Q1 &Q2 are really a dual prebiased
MUN5311DW1T1-D I'm using as a latch.

Schematic

http://i37.tinypic.com/2z9csja.png

My question is do I have to place blocking diodes on the output of the
OP'S. If one output goes high it will place Vcc-1.5V on the output of
the other OP will this damage the OP?



I don't have any LM358A's on hand but I would like to be able to test
it with maybe a TLC27L2 so the same question for this OPAMP.

Thanks
I would feed the R4 Via the extra OP-AMP. Also, I don't think you'll

get a full high side out on this op-amp. This may not be a problem in
your case how ever since the normal operation of your circuit would
require it to hold the output low in which case it looks like it should
do well.
I would how ever, use a hysteresis feed back in the (+) input to make
sure you don't develop a linear region at the critical point, this could
upset the current regulation a bit unless you don't want a latching
effect protect circuit.






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