Recent content by bogdan2011

Yes that is true, the chip is limited to 50% duty cycle with this topology so without regulation that's the maximum voltage I can get out of it.

So out of curiosity I built a single switch forward (with reset winding). All works fine but the output can't sustain even a small load (few hundred miliamps) without dropping (for example 500mA drops from 25V to about 10). The transistor doesn't heat up, the output diodes don't, I tried...

I'm revisiting this since I've come across the need to use GDTs again. It seems that the BC546/BC556 isn't really enough to drive a GDT. I've built a similar SMPS for another project and while the drive is good enough for the main transistors, the poor totem pole pair driving the GDT blows up...

I have built a half bridge SMPS that outputs 110V at around 5A amps to power a CNC motor. It's based on SG3525 with a GDT. The power supply works fine under resistive loads (some light bulbs), there's no abnormal heating up of the components even after a long time under load, but when connecting...

In fig. 5 the whole core of the transformer is used since the voltage swings from +1/2 VCC to -1/2 VCC. Is that still the case in fig. 3?

Forgot to mention, this is the GDT

Well, it makes sense since peak currents are basically double that of a half bridge where transistors are driven one at a time. But I was thinking, a BC546/BC556 totem pole can only sink 100mA continuously, and a UC3845 can do 500mA. Even a TL494 can do 200mA. So how is it helping?

Q1 is 2N7000. I did remove it along with D2 and placed a cap between pins 1 and 3 of Q1 and the waveform looks better. But nothing changed, and eventually one of the mosfets blew up along with some tracks. I'll re-do the PCB.

It is a circuit posted on the TI blog: https://e2e.ti.com/blogs_/b/powerhouse/posts/power-tips-a-simple-circuit-for-driving-gate-drive-transformers

This was tested using a separate power supply for the chip. The slow rise time comes from the drive circuitry around Q1. I can maybe try driving the GDT directly through a series cap, see if that helps.

I haven't yet built the power supply I posted, but I built a similar one. The problem I'm having is that the transistors are getting really hot even under the minimum load. There's also a ringing noise on the transformer. First waveform is with no input, second with input. I suspect the...

Yes, I will be adding an auxiliary power supply. From what I've read, the SG is not really capable of starting up like a UC3843 does (it maybe can but the resistor has to handle the whole supply current).

I connected the feedback circuit at about 51V and this is what happens with the transformer: This is probing at the auxiliary winding, the secondary winding looks the same (only with a different ratio). The rectified DC also seems to be lower than expected, at least with this auxiliary winding...

I rewinded the transformer and I now get around 58V unloaded at the output. I rated the windings for 7A, although I don't know if the core can handle it (I had enough space for thicker wires). For now, it's unregulated. Loaded at 4A the voltage drops to 55V. That's the maximum current I could...

Ah so there's my mistake. I assumed (I'm taking your example) that the entire winding needs to have 20V, so I wound 2+2 turns, not 4+4. That's why I was getting half the expected voltage at the output.