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35 Threads found on edaboard.com: tl431 Smps
Maybe there is a problem on the feedback line( at the low voltage between optoccupier and tl431
I wonder if there is drawing mistake on the schematic. Something around the opto's cathode return seems strange. I tried to verify with the actual PCB layout, but it is not that easy to follow. Normally, pin 2 will be connected to the cathode of the tl431 as shown below.
Do you agree that equation 35 of page 10 of AN-4137 is incorrect? AN-4137: It surely should say? VFB/Vo1 = - (wi/s) . Do you agree? This is confirmed by equation 3-58 of page 290 of Basso?s book ?switch mode power supplies? (attached)
Hello, Why do the following application notes, both by fairchildsemi, contradict each other about the nearness of the smps crossover frequency to the corner frequency of the output LC filter (?post filter?) The text just above fig22, page 12 of the following document by Choi , suggests that tl431/opto feedback can be undertaken with the cross
Hello, Fig2 ,Page 7 of the attached DER-275 document shows a 3n3 capacitor (C14) across the lower feedback divider resistor of an smps. (Page 9 of this document says that this capacitor is there because of noise getting injected into the tl431 reference pin.) Do you agree that this capacitor should not be there? The way to address that noise
You have no capacitor from opto collector to ground, -there should be. -You have no compensation components from cathode to reference of the tl431 -You have an output LC filter which has too high inductance...also, the most of the output capacitance should be upstream of the output inductor...also, the LC resonant frequency of the output filter i
Use tl431 or similar secondary voltage regulator instead of Z-diode.
Hello, Please could you identify the poles and zeros in this Flyback smps Error amplifier set-up, which uses tl431 and opto.? (schematic of smps, with tl431/Opto Error amplifier shown) Basso book on page 292-295 identifies them for an error amplifier circuit that's almost exactly identical as this one , but there is no (...)
The dominant pole of an opto coupler is associated with the photo transistor, not the LED. (I'm not sure which side you mean with the unusual term "opto diode"). Usual tl431 circuits already achieve a current source characteristic a higher frequencies. A cascode stage can partly improve the frequency characteristic of a resistor loaded poto t
If the feedback loop is tl431 based (tl431 is a 3-pin shunt regulator, aka Variable zener) you can change the resistor values to get 30V on the 12V rail. Formula for tl431 voltage is 2.5*(1+ (HIGH_SIDE_RESISTOR/LOW_SIDE_RESISTOR)) values are in Ohms and 2.5 is the tl431 internal reference voltage. For example: (...)
it depends on the load type, but usually some type of isolation is necessary to prevent electrical shocks. the simplest yet high performance feedback isolation is opto-coupler which consists of a voltage reference (e.g. tl431) and an error amplifier (opamp or tl431 itself). also compensation could be done in the secondary side. BEST
Basically, on the right side of the optocoupler (=LED side) the system has essentially a voltage reference (such as tl431) monitoring the output voltage and controlling the LED current accordingly, You could get the same effect by just using an ordinary transistor instead of optocoupler's output transistor, and regulating the base current of that
what is my fault?is it not the similier circuit to smps feedback output? The missing feedback makes the diference. tl431 can either used as a simpled programmable shunt regulator (as in your second circuit). Then the feedback goes directly from pin3 to to pin 1. Or as a building block of a smps voltage controller. Then the fe
Hello, I wish to make out a feedback loop for a CCM current mode full bridge 250W. It has tl431 /opto feedback but not with the fast lane. Basically the tl431 has been set up like a type 3 opamp. then thers the opto with secondary side led resistor and a pullup resistor on the primary side, in the standard way controller is uc38025.
hii, what would be the circuit and design parameters i need to consider if i have to design a feedback circuit using tl431 for a non isolated smps. Even though i am using a transformer. But the secondary and primary ground are common. 2. In a multiple output flyback smps, reflected voltage is secondary voltage multiplied by turns (...)
Hello, We are doing a 90-265VAC isolated , offline, half-bridge smps which must have a very fast transient response. The load is just going fully on , fully off , very suddenly, all the time. We are using tl431/OPTO regulation and so do you believe that its essential, to get a standing current flowing in the opto-d
hello, Does adding a resistor in parallel with an smps feedback opto diode reduce the gain in the feedback loop? i mean like R33 in the following : ...because if we think about it, when the tl431 trys to pull current through the opto, it ends up pulling it through the resistor not as much
Do you agree with my reasoning? No. tl431 can be used with all kinds of frequency compensations you want to. A first prerequisite is, that you have an idea of the intended loop gain characteristic.
Hi, Please can i confirm that this is a viable method for tl431/opto smps regulation with output voltage of 36V...................................... (The tl431 is only good up to 36V) tl431 DATASHEET:-
Related to the tl431 output, the reference pin is an inverting input.