buck boost

http://en.wikipedia.org/wiki/Buck-boost_converter

Is there a reason why the switch is between the voltage source and the
coil?

What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

Thanks,

Michael

 

[Dan Coby]

mrdarrett@gmail.com wrote:

http://en.wikipedia.org/wiki/Buck-boost_converter

Is there a reason why the switch is between the voltage source and the
coil?

What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

I do not understand exactly what you are asking. I see two possibilities.

1) You want to move both the inductor and the switch as is shown
in the wikipedia article on the boost converter:
http://en.wikipedia.org/wiki/Boost_converter
In this case the circuit will act as described by wikipedia.

2) You simply want to move the switch to being in series with
the inductor. In this case, there will be problems. While the
switch is closed the inductor is storing energy in its magnetic field.
(E = L * I**2 / 2) The inductor will attempt to maintain the current
when the switch is opened. This will result in a voltage spike across
both the inductor and the switch. Most likely the switch contacts
will arc (with a mechanical switch) or the voltage spike will destroy
a semiconductor switch.

 

[Bill]

On Wed, 3 Sep 2008 13:57:25 -0700 (PDT), mrdarrett@gmail.com wrote:

What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

"voltage coil" does not refer to any node. Try rewording your
question, so that we know what you are asking.

Best,

 

[Bill]

On Thu, 4 Sep 2008 17:56:33 -0700 (PDT), mrdarrett@gmail.com wrote:

On Sep 4, 4:43 pm, Bill <z...@z.z> wrote:
On Wed, 3 Sep 2008 13:57:25 -0700 (PDT), mrdarr...@gmail.com wrote:
What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

"voltage coil" does not refer to any node. Try rewording your
question, so that we know what you are asking.

Best,


remove the word "voltage"

Still, the coil is not a node. A coil has two electrical nodes. I
imagine that you are referring to the node that is not ground. You
mean leaving the inductor where it is (you didn't say anything about
moving it) and connecting the switch across it (in parallel with it)?
You shouldn't do that. The switch would short circuit the input
voltage source. That's never good. The input current would be huge if
the voltage source was close to ideal.

Best,

 

On Sep 4, 4:43 pm, Bill <z...@z.z> wrote:

On Wed, 3 Sep 2008 13:57:25 -0700 (PDT), mrdarr...@gmail.com wrote:
What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

"voltage coil" does not refer to any node. Try rewording your
question, so that we know what you are asking.

Best,

remove the word "voltage"

 

On Sep 4, 6:29 pm, Bill <z...@z.z> wrote:

On Thu, 4 Sep 2008 17:56:33 -0700 (PDT), mrdarr...@gmail.com wrote:
On Sep 4, 4:43 pm, Bill <z...@z.z> wrote:
On Wed, 3 Sep 2008 13:57:25 -0700 (PDT), mrdarr...@gmail.com wrote:
What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

"voltage coil" does not refer to any node. Try rewording your
question, so that we know what you are asking.

Best,

remove the word "voltage"

Still, the coil is not a node. A coil has two electrical nodes. I
imagine that you are referring to the node that is not ground. You
mean leaving the inductor where it is (you didn't say anything about
moving it) and connecting the switch across it (in parallel with it)?
You shouldn't do that. The switch would short circuit the input
voltage source. That's never good. The input current would be huge if
the voltage source was close to ideal.

Best,

uh, no. That would be silly.

Ha ha ha.

I'll post a scan, if I find time (and find the correct driver to
install my scanner).

I suppose a picture is worth 1E3 words...

Michael

 

[John Popelish]

mrdarrett@gmail.com wrote:

http://en.wikipedia.org/wiki/Buck-boost_converter

Is there a reason why the switch is between the voltage source and the
coil?

What would happen if the switch were between the voltage coil and
ground (as it is in the Boost converter)?

With the switch between input and coil, the output is
inverted. Positive input supply produces negative output
voltage, since the grounded coil produces reverse voltage
when the switch opens, to try to keep the current going the
same way.

If you put the switch between coil and ground, and connect
the output diode at that same end of the coil, the voltage
across the coil still reverses when the switch opens, but
this reversal adds voltage to the input supply during the
switch off time, so the output is not inverted, but higher
voltage than the input. For instance, when the input is
positive and the switch is on, the switch grounded end of
the coil is negative with respect to the input end. When
the switch opens, the voltage across the coil reverses and
the switched end becomes more positive then the input end,
so the voltage across the coil adds to the input voltage
like two batteries in series.

--
Regards,

John Popelish