I am in the middle of a High Power SMPS design, and need a 15VDC non isolated supply, to feed my onboard PFC circuit.
The PFC is build around the UCC28019 from TI, that needs this auxilary supply of approx 15VDC drawing max 10mA.
I could use a small power transformer, but it does not seem that elegant.
As far as I remember, I saw some integrated swithing regulators, that only need a few external components to do this, like an inductor and some capacitors. But I cannot remember where
Please help.
The PFC is build around the UCC28019 from TI, that needs this auxilary supply of approx 15VDC drawing max 10mA.
I could use a small power transformer, but it does not seem that elegant.
As far as I remember, I saw some integrated swithing regulators, that only need a few external components to do this, like an inductor and some capacitors. But I cannot remember where
Please help.
@ Luka:
I am aware of the zener version, directly from the mains voltage. But since the PSU is designed for a wide input voltage range, 85-265 VAC, the DC voltage after the rectifier will be between 120-375 volt.
At 120 VDC, I need a resistor of 5,25kohms to get 20mA. Power dissipation in the resistor will be 20mA*105V = 2,1watt.
At 275 VDC, the current will be 50mA, and the power dissipated will be almost 13 watt.
I could go for a CCS to feed the zener, and keeping the current at 20mA. This wil need a few "no cost" components, but will still give a power dissipation of min 5 watt.
The PSU will be rated at 300 watt. And 5 watt dissipated will lower the efficiency by 1,66% at full load. At lower loads, the efficiency is even worse.
Therefor I will not go for the zener version, even though it is very easy.
@ Star882:
I could use an auxiliary winding. But I need the 15VDC supply to be always ON, even when the PFC/PSU is in power down mode. And that will not be possible with the auxiliary winding.
So what I need, is a simple switcher, that can run directly on the mains voltage, and give me 15 VDC. As mentioned, I do not need it to be isolated.
I am aware of the zener version, directly from the mains voltage. But since the PSU is designed for a wide input voltage range, 85-265 VAC, the DC voltage after the rectifier will be between 120-375 volt.
At 120 VDC, I need a resistor of 5,25kohms to get 20mA. Power dissipation in the resistor will be 20mA*105V = 2,1watt.
At 275 VDC, the current will be 50mA, and the power dissipated will be almost 13 watt.
I could go for a CCS to feed the zener, and keeping the current at 20mA. This wil need a few "no cost" components, but will still give a power dissipation of min 5 watt.
The PSU will be rated at 300 watt. And 5 watt dissipated will lower the efficiency by 1,66% at full load. At lower loads, the efficiency is even worse.
Therefor I will not go for the zener version, even though it is very easy.
@ Star882:
I could use an auxiliary winding. But I need the 15VDC supply to be always ON, even when the PFC/PSU is in power down mode. And that will not be possible with the auxiliary winding.
So what I need, is a simple switcher, that can run directly on the mains voltage, and give me 15 VDC. As mentioned, I do not need it to be isolated.
It doesn't matter what is your input voltage, it works from say few volts above set voltage and up to voltage of transistor rating
I have missed at first read, that this is PFC, so you have no trouble starting ic(right?), you need supply for it, and as it was said, put winding on inductor, and that will power IC
You can check my PFC too, also on my page... All I can say, number of turns will depend on:
When minimal input voltage, you still need voltage that will IC need to function, and at high input voltage, you'll need to check that voltage will be below max IC rating, or somehow limit it to some value below that
I have missed at first read, that this is PFC, so you have no trouble starting ic(right?), you need supply for it, and as it was said, put winding on inductor, and that will power IC
You can check my PFC too, also on my page... All I can say, number of turns will depend on:
When minimal input voltage, you still need voltage that will IC need to function, and at high input voltage, you'll need to check that voltage will be below max IC rating, or somehow limit it to some value below that
@ Luka:
I still need this 15VDC when the PFC and DC-DC is in power down. Therefor I can not use an extra winding for the 15VDC.
That's why I'm looking for a simple switcher, that can give the 15VDC directly from the mains.
I have seen such an switcher a few years ago, but can't remember where
I did some "googling" but did not find it.
I still need this 15VDC when the PFC and DC-DC is in power down. Therefor I can not use an extra winding for the 15VDC.
That's why I'm looking for a simple switcher, that can give the 15VDC directly from the mains.
I have seen such an switcher a few years ago, but can't remember where
I did some "googling" but did not find it.
I found out that my friend is designing a direct DC UPS for a workstation, and he needs something similar. (140-380v input, 13.8-14.4v output with 1-3A current limit, no isolation needed.) So I'll look into how to design a simple power supply for that use. Then just downsize it for your application.
There are several ICs from Power Integrations that can work as high voltage buck converters with just an off-the-shelf inductor.
LNK3xx are the ones intended for that purpose, but others like LNK36x or even TNY2xx may be used too for higher output.
An optocoupler with high dv/dt immunity, like HCPL4504, may be required for sending output voltage feedback signal to these ICs when used as floating switchers.
LNK3xx are the ones intended for that purpose, but others like LNK36x or even TNY2xx may be used too for higher output.
An optocoupler with high dv/dt immunity, like HCPL4504, may be required for sending output voltage feedback signal to these ICs when used as floating switchers.
Yes, but the most powerful ICs, the ones not intended for buck operation (but useable), have the wrong polarity on the feedback input (intended for opto feedback), and the opto does the level shifting and the polarity inversion at once.
btw: In a boost PFC I would fed such a switching regulator from the output capacitor (maybe with a 0.5A fuse to reduce damage in case of failure).
btw: In a boost PFC I would fed such a switching regulator from the output capacitor (maybe with a 0.5A fuse to reduce damage in case of failure).
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