> On 08/04/2018 04:23 AM, Piotr Wyderski wrote:
>> I would like to build an off-line switcher based on the TinySwitch4
>> family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
>> V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
>> calculator to get a rough estimate:
>>
>> http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
>>
>> L_PRI=7.36mH. OK, so now use PI Expert Online, provided by the
>> manufacturer:
>>
>> Automatic design mode => TNY285DG, an EE13 core with L_PRI=1276uH,
>> 0.25mm air gap. Almost 6 times lower than the previous value, okaaay...
>>
>> Now, I don't like the proposed IC and replace it with a bit stronger
>> TNY287DG => L_PRI=497uH and a warning that the air gap is too long
>> (0.745mm, yeah, right...).
>>
>> The primary inductances differ just 15 times. What's going on here?
>>
>> Best regards, Piotr
>
> D_limit = 0.5 (current mode controller I believe)
>
> turns ratio = n_2/n_1 = (Vin_min * D_limit)/((V_out + V_diode) * (1 -
> D_limit)) =
> (120*0.5)/(15.2 * 0.5) ~= 8
>
> D_ccm = ((V_out + V_diode) * 8) / ((Vin_min + (V_out + V_diode)) * 8) =
> ~ 10%
>
> Magentizing current referred to the primary = I_m = n_1/n_2 * 1/(1 -
> D_ccm) * I_out = 1/8 * 1/0.1 * 0.5 = 0.07A
Should be 1/8 * 1/0.9 * 0.5 = 0.07A
Reply by bitrex●August 5, 20182018-08-05
On 08/04/2018 04:23 AM, Piotr Wyderski wrote:
> I would like to build an off-line switcher based on the TinySwitch4
> family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
> V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
> calculator to get a rough estimate:
>
> http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
>
> L_PRI=7.36mH. OK, so now use PI Expert Online, provided by the
> manufacturer:
>
> Automatic design mode => TNY285DG, an EE13 core with L_PRI=1276uH,
> 0.25mm air gap. Almost 6 times lower than the previous value, okaaay...
>
> Now, I don't like the proposed IC and replace it with a bit stronger
> TNY287DG => L_PRI=497uH and a warning that the air gap is too long
> (0.745mm, yeah, right...).
>
> The primary inductances differ just 15 times. What's going on here?
>
> Best regards, Piotr
D_limit = 0.5 (current mode controller I believe)
turns ratio = n_2/n_1 = (Vin_min * D_limit)/((V_out + V_diode) * (1 -
D_limit)) =
(120*0.5)/(15.2 * 0.5) ~= 8
D_ccm = ((V_out + V_diode) * 8) / ((Vin_min + (V_out + V_diode)) * 8) =
~ 10%
Magentizing current referred to the primary = I_m = n_1/n_2 * 1/(1 -
D_ccm) * I_out = 1/8 * 1/0.1 * 0.5 = 0.07A
delta_Im = 0.2 * I_m = 0.014A
L_m = (Vin_min * D_ccm * T_s)/(2 * delta_Im) = (120 * 0.1 * 7.57e-6)/(2
* 0.014) = 0.00324
Comes out to about 3.2 mH as an estimate for the required primary side
inductance for CCM, how'd I do
Reply by bitrex●August 5, 20182018-08-05
On 08/05/2018 12:42 AM, Tim Williams wrote:
> "Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
> news:pk3nr1$5up$1@node2.news.atman.pl...
>> I would like to build an off-line switcher based on the TinySwitch4
>> family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
>> V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
>> calculator to get a rough estimate:
>>
>> http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
>>
>> L_PRI=7.36mH.
>
> That sounds too high.� Did you just take its default value?� Did you
> click the Calc button and notice the waveforms?� It recommends CCM.
> Default is based on 20% current ripple, I think.
>
> Nowhere near what a TinySwitch wants: DCM.� Fortunately, you don't need
> to stick with the values given.� You can plug in whatever value you
> like, and see the waveforms you'll get. :-)
>
> Roughly speaking, to get to 100% ripple (BCM), use 5x less inductance.
> Less even than that may be desired, because of the wide input voltage
> range. (Don't forget to check at the voltage extremes and see what
> happens!)
>
> Tim
>
Since it's a flyback it will have to be an air-gapped core of some type,
whether distributed or "real", the saturation curve is more gentle
compared to a ferrite brickwall. AFAIK there's no law that says you
can't run a core a bit into saturation if it helps make the solution
size smaller, for some e.g. powdered irons the curve looks like a
complementary error function u can run four or five times the "cutoff"
of 100% nominal relative mu vs H and only lose about 20% of the mu
Reply by Tim Williams●August 5, 20182018-08-05
"Johann Klammer" <klammerj@NOSPAM.a1.net> wrote in message
news:pk541v$65j$1@gioia.aioe.org...
> inductance is probably chosen to get core loss and wiring loss to equal
> values.
> possibly the switch I^2R loss, aswell.
> The problem with those tools is that you never know what they calculate.
> Of course it might be complete garbage. In the end it is just one
> of those AI conspiracies to lure you onto the website to look at the ads.
>
>
I can't speak for the PI tool, but the Schmidt tool has all the equations
listed in the help box. It's just a calculator, nothing more: garbage in,
garbage out. If your circuit does not conform to the assumptions made, if
you don't get the waveforms seen; that's your problem. :) If you don't fill
in the free variables yourself, it will recommend them, based on whatever
assumption the writer chose to go with -- as it happens, CCM is assumed for
all topologies I think.
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
Reply by Tim Williams●August 5, 20182018-08-05
"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
news:pk3nr1$5up$1@node2.news.atman.pl...
>I would like to build an off-line switcher based on the TinySwitch4 family.
>It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
> V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
> calculator to get a rough estimate:
>
> http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
>
> L_PRI=7.36mH.
That sounds too high. Did you just take its default value? Did you click
the Calc button and notice the waveforms? It recommends CCM. Default is
based on 20% current ripple, I think.
Nowhere near what a TinySwitch wants: DCM. Fortunately, you don't need to
stick with the values given. You can plug in whatever value you like, and
see the waveforms you'll get. :-)
Roughly speaking, to get to 100% ripple (BCM), use 5x less inductance. Less
even than that may be desired, because of the wide input voltage range.
(Don't forget to check at the voltage extremes and see what happens!)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
Reply by bitrex●August 5, 20182018-08-05
On 08/04/2018 04:58 PM, Johann Klammer wrote:
> On 08/04/2018 10:23 AM, Piotr Wyderski wrote:
>> I would like to build an off-line switcher based on the TinySwitch4 family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
>> V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
>> calculator to get a rough estimate:
>>
>> http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
>>
>> L_PRI=7.36mH. OK, so now use PI Expert Online, provided by the manufacturer:
>>
>> Automatic design mode => TNY285DG, an EE13 core with L_PRI=1276uH,
>> 0.25mm air gap. Almost 6 times lower than the previous value, okaaay...
>>
>> Now, I don't like the proposed IC and replace it with a bit stronger
>> TNY287DG => L_PRI=497uH and a warning that the air gap is too long (0.745mm, yeah, right...).
>>
>> The primary inductances differ just 15 times. What's going on here?
>>
>> Best regards, Piotr
> inductance is probably chosen to get core loss and wiring loss to equal values.
> possibly the switch I^2R loss, aswell.
> The problem with those tools is that you never know what they calculate.
> Of course it might be complete garbage. In the end it is just one
> of those AI conspiracies to lure you onto the website to look at the ads.
>
>
> I would like to build an off-line switcher based on the TinySwitch4 family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
> V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
> calculator to get a rough estimate:
>
> http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
>
> L_PRI=7.36mH. OK, so now use PI Expert Online, provided by the manufacturer:
>
> Automatic design mode => TNY285DG, an EE13 core with L_PRI=1276uH,
> 0.25mm air gap. Almost 6 times lower than the previous value, okaaay...
>
> Now, I don't like the proposed IC and replace it with a bit stronger
> TNY287DG => L_PRI=497uH and a warning that the air gap is too long (0.745mm, yeah, right...).
>
> The primary inductances differ just 15 times. What's going on here?
>
> Best regards, Piotr
inductance is probably chosen to get core loss and wiring loss to equal values.
possibly the switch I^2R loss, aswell.
The problem with those tools is that you never know what they calculate.
Of course it might be complete garbage. In the end it is just one
of those AI conspiracies to lure you onto the website to look at the ads.
Reply by Piotr Wyderski●August 4, 20182018-08-04
I would like to build an off-line switcher based on the TinySwitch4
family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V,
V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's
calculator to get a rough estimate:
http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
L_PRI=7.36mH. OK, so now use PI Expert Online, provided by the manufacturer:
Automatic design mode => TNY285DG, an EE13 core with L_PRI=1276uH,
0.25mm air gap. Almost 6 times lower than the previous value, okaaay...
Now, I don't like the proposed IC and replace it with a bit stronger
TNY287DG => L_PRI=497uH and a warning that the air gap is too long
(0.745mm, yeah, right...).
The primary inductances differ just 15 times. What's going on here?
Best regards, Piotr