[EE] 3V - 400V royer converter

[Van Horn, David]

I'm having some trouble with an exercise in LTSpice, for a DC-DC converter from 3V (Lithium cell nominal) to 400V
Basically, no matter how I set up the transformer I don't seem to get past 40V.
It's been a while since I built a Royer converter, and I think I'm missing something in the transformer design.

Taking a WAG at the inductor design, I have a center tapped primary of two 10uH inductors.
I defined the relationship as Pin = Pout = (Vin * Iin) = (Vout * Iout), more or less.
Vout / Vin = turns ratio 400/3 = 133/1 turns ratio

Since inductance is kN^2, I defined the output inductor to be the inductance of one half of the primary winding (10uH) multiplied by (133^2)
Coupling between all inductors in the transformer is 0.95, another WAG.

I added 1uH leakage inductance (not coupled ) to both legs of the primary, but not to the centertap leg.

Ancillary problem, whenever I define the output inductor with a param statement like .param L2=L1*(133^2) I get the dreaded "Time step too small" message pointing to my mosfets.
I have to work it outside of spice, and then use something like .param L2 = 178mH.



--
David VanHorn
Lead Hardware Engineer

Backcountry Access, Inc.
2820 Wilderness Pl, Unit H
Boulder, CO 80301 USA
phone: [phone] x110
email: ***@backcountryaccess.com<mailto:***@backcountryaccess.com>

[Sean Breheny]

I am not familiar with Royer converters but a quick Google search leads me
to understand that they rely on inductor saturation for their operation.
LTSpice can model saturation but doesn't do so by default - you need to
define some additional parameters.

On Thu, Jul 5, 2018 at 1:12 PM, Van Horn, David <

Post by Van Horn, David
I'm having some trouble with an exercise in LTSpice, for a DC-DC converter
from 3V (Lithium cell nominal) to 400V
Basically, no matter how I set up the transformer I don't seem to get past 40V.
It's been a while since I built a Royer converter, and I think I'm missing
something in the transformer design.
Taking a WAG at the inductor design, I have a center tapped primary of two 10uH inductors.
I defined the relationship as Pin = Pout = (Vin * Iin) = (Vout * Iout), more or less.
Vout / Vin = turns ratio 400/3 = 133/1 turns ratio
Since inductance is kN^2, I defined the output inductor to be the
inductance of one half of the primary winding (10uH) multiplied by (133^2)
Coupling between all inductors in the transformer is 0.95, another WAG.
I added 1uH leakage inductance (not coupled ) to both legs of the primary,
but not to the centertap leg.
Ancillary problem, whenever I define the output inductor with a param
statement like .param L2=L1*(133^2) I get the dreaded "Time step too small"
message pointing to my mosfets.
I have to work it outside of spice, and then use something like .param L2 = 178mH.
--
David VanHorn
Lead Hardware Engineer
Backcountry Access, Inc.
2820 Wilderness Pl, Unit H
Boulder, CO 80301 USA
phone: [phone] x110
backcountryaccess.com>
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[Jason White]

Before I read Sean's email: Post the LTSPICE file, I recall facing a
similar issue recently in a power supply design class I took. I think the
issue was something simple like a 1milliohm series resistance in the
default LTSPICE inductor & switch models. Changing it to 1 nanoohm fixed
that.

After I read Sean's email: if you need to model saturation you can do it
but I think you'll have to define your own model/subcircuit.

On Thu, Jul 5, 2018 at 1:12 PM, Van Horn, David <

Post by Van Horn, David
I'm having some trouble with an exercise in LTSpice, for a DC-DC converter
from 3V (Lithium cell nominal) to 400V
Basically, no matter how I set up the transformer I don't seem to get past 40V.
It's been a while since I built a Royer converter, and I think I'm missing
something in the transformer design.
Taking a WAG at the inductor design, I have a center tapped primary of two 10uH inductors.
I defined the relationship as Pin = Pout = (Vin * Iin) = (Vout * Iout), more or less.
Vout / Vin = turns ratio 400/3 = 133/1 turns ratio
Since inductance is kN^2, I defined the output inductor to be the
inductance of one half of the primary winding (10uH) multiplied by (133^2)
Coupling between all inductors in the transformer is 0.95, another WAG.
I added 1uH leakage inductance (not coupled ) to both legs of the primary,
but not to the centertap leg.
Ancillary problem, whenever I define the output inductor with a param
statement like .param L2=L1*(133^2) I get the dreaded "Time step too small"
message pointing to my mosfets.
I have to work it outside of spice, and then use something like .param L2 = 178mH.
--
David VanHorn
Lead Hardware Engineer
Backcountry Access, Inc.
2820 Wilderness Pl, Unit H
Boulder, CO 80301 USA
phone: [phone] x110
backcountryaccess.com>
--
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View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Van Horn, David]

Sorry, this is a resonant royer, without the second winding for driving the transistors.

Similar to the first schematic here:
https://www.eevblog.com/forum/projects/efficient-magnetics-design-for-offline-resonant-push-pull-(royer)-converter/
Just add a bridge rectifier on the output and a feedback path to a comparator that drives the power control fet (Q3) in this circuit.

I'm nowhere near regulation, but if I alter the circuit to regulate at 40V instead of 400V it actually works in spice, turning "Q3" on and off appropriately.


-----Original Message-----
From: piclist-***@mit.edu <piclist-***@mit.edu> On Behalf Of Jason White
Sent: Thursday, July 5, 2018 12:31 PM
To: Microcontroller discussion list - Public. <***@mit.edu>
Subject: Re: [EE] 3V - 400V royer converter

Before I read Sean's email: Post the LTSPICE file, I recall facing a similar issue recently in a power supply design class I took. I think the issue was something simple like a 1milliohm series resistance in the default LTSPICE inductor & switch models. Changing it to 1 nanoohm fixed that.

After I read Sean's email: if you need to model saturation you can do it but I think you'll have to define your own model/subcircuit.

Post by Van Horn, David
I'm having some trouble with an exercise in LTSpice, for a DC-DC
converter from 3V (Lithium cell nominal) to 400V Basically, no matter
how I set up the transformer I don't seem to get past 40V.
It's been a while since I built a Royer converter, and I think I'm
missing something in the transformer design.
Taking a WAG at the inductor design, I have a center tapped primary of two 10uH inductors.
I defined the relationship as Pin = Pout = (Vin * Iin) = (Vout * Iout), more or less.
Vout / Vin = turns ratio 400/3 = 133/1 turns ratio
Since inductance is kN^2, I defined the output inductor to be the
inductance of one half of the primary winding (10uH) multiplied by
(133^2) Coupling between all inductors in the transformer is 0.95, another WAG.
I added 1uH leakage inductance (not coupled ) to both legs of the
primary, but not to the centertap leg.
Ancillary problem, whenever I define the output inductor with a param
statement like .param L2=L1*(133^2) I get the dreaded "Time step too small"
message pointing to my mosfets.
I have to work it outside of spice, and then use something like .param L2 = 178mH.
--
David VanHorn
Lead Hardware Engineer
Backcountry Access, Inc.
2820 Wilderness Pl, Unit H
Boulder, CO 80301 USA
phone: [phone] x110
backcountryaccess.com>
--
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--
Jason White
--
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[Jason White]

I'd suggest posting a file that recreates your issue.

On Friday, July 6, 2018, Van Horn, David <

Post by Van Horn, David
Sorry, this is a resonant royer, without the second winding for driving the transistors.
https://www.eevblog.com/forum/projects/efficient-magnetics-
design-for-offline-resonant-push-pull-(royer)-converter/
Just add a bridge rectifier on the output and a feedback path to a
comparator that drives the power control fet (Q3) in this circuit.
I'm nowhere near regulation, but if I alter the circuit to regulate at 40V
instead of 400V it actually works in spice, turning "Q3" on and off
appropriately.
-----Original Message-----
Sent: Thursday, July 5, 2018 12:31 PM
Subject: Re: [EE] 3V - 400V royer converter
Before I read Sean's email: Post the LTSPICE file, I recall facing a
similar issue recently in a power supply design class I took. I think the
issue was something simple like a 1milliohm series resistance in the
default LTSPICE inductor & switch models. Changing it to 1 nanoohm fixed
that.
After I read Sean's email: if you need to model saturation you can do it
but I think you'll have to define your own model/subcircuit.
On Thu, Jul 5, 2018 at 1:12 PM, Van Horn, David <

Post by Van Horn, David
I'm having some trouble with an exercise in LTSpice, for a DC-DC
converter from 3V (Lithium cell nominal) to 400V Basically, no matter
how I set up the transformer I don't seem to get past 40V.
It's been a while since I built a Royer converter, and I think I'm
missing something in the transformer design.
Taking a WAG at the inductor design, I have a center tapped primary of
two 10uH inductors.
I defined the relationship as Pin = Pout = (Vin * Iin) = (Vout * Iout), more or less.
Vout / Vin = turns ratio 400/3 = 133/1 turns ratio
Since inductance is kN^2, I defined the output inductor to be the
inductance of one half of the primary winding (10uH) multiplied by
(133^2) Coupling between all inductors in the transformer is 0.95,

another WAG.

Post by Van Horn, David
I added 1uH leakage inductance (not coupled ) to both legs of the
primary, but not to the centertap leg.
Ancillary problem, whenever I define the output inductor with a param
statement like .param L2=L1*(133^2) I get the dreaded "Time step too

small"

Post by Van Horn, David
message pointing to my mosfets.
I have to work it outside of spice, and then use something like .param L2 = 178mH.
--
David VanHorn
Lead Hardware Engineer
Backcountry Access, Inc.
2820 Wilderness Pl, Unit H
Boulder, CO 80301 USA
phone: [phone] x110
backcountryaccess.com>
--
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View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

--
Jason White
--
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mailman/listinfo/piclist
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